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Space time coding for a multiple input, multiple output (MIMO) system with finite-bit feedback and maximum-likehood (ML)-decoding is considered. Based on the analysis of union bound of error probability of the system, it is shown that designing the system with good performance can be divided into the following three steps: (1) efficiently packing finite points into a dynamic ellipsoid in a finite dimensional real Euclidean space; (2) effectively quantizing a Stiefel manifold; (3) optimally quantizing a cone in a real Euclidean space. Furthermore, criteria and methods to implement the above steps are given. A design example for a system, which has 2 transmit and 2 receive antennas, 2 time slot delay and 4 bits transmission rate, shows that 5 bits feedback can derive 1.8 dB gain over the system without feedback. | We derive performance limits for two closely related communication scenarios involving a wireless system with multiple-element transmitter antenna arrays: a point-to-point system with partial side information at the transmitter, and a broadcast system with multiple receivers. In both cases, ideal beamforming is impossible, leading to an inherently lower achievable performance as the quality of the side information degrades or as the number of receivers increases. Expected signal-to-noise ratio (SNR) and mutual information are both considered as performance measures. In the point-to-point case, we determine when the transmission strategy should use some form of beamforming and when it should not. We also show that, when properly chosen, even a small amount of side information can be quite valuable. For the broadcast scenario with an SNR criterion, we find the efficient frontier of operating points and show that even when the number of receivers is larger than the number of antenna array elements, significant performance improvements can be obtained by tailoring the transmission strategy to the realized channel. | The research on formative assessment and feedback is reinterpreted to show how these processes can help students take control of their own learning, i.e. become self-regulated learners. This reformulation is used to identify seven principles of good feedback practice that support self-regulation. A key argument is that students are already assessing their own work and generating their own feedback, and that higher education should build on this ability. The research underpinning each feedback principle is presented, and some examples of easy-to-implement feedback strategies are briefly described. This shift in focus, whereby students are seen as having a proactive rather than a reactive role in generating and using feedback, has profound implications for the way in which teachers organise assessments and support learning. | eng_Latn | 5,300 |
Impulsive noise (IN) is the most dominant factor degrading the performance of communication systems over powerlines. Many IN mitigation techniques have been introduced in the literature such as the application of a blanker at the front-end of the receiver which sets the incoming signal to zero when it exceeds a certain threshold. Determining this threshold is the key for achieving best performance in this technique. Most studies dealing with threshold optimization require prior knowledge about the IN characteristics. However, if the peak to average power ratio (PAPR) of the OFDM symbols can be determined at the receiver, this will allow optimal blanking of IN without requiring any knowledge about the noise parameters. In this paper we propose a look-up table (LUT) based algorithm with uniform quantization to estimate the peak of OFDM symbols. We also investigate the impact of quantization bits on the system performance in terms of the signal-to-noise-ratio (SNR) at the output of the blanking device, in two different scenarios, weakly and heavily disturbed IN environments. Simulation results reveal that a 5 bit LUT is sufficient for reliable performance. | In this paper, we study the performance of an orthogonal frequency division multiplexing (OFDM) receiver with blanking nonlinearity in the presence of impulsive noise. Closed-form analytical expressions for the signal-to-noise ratio at the output of the blanking nonlinearity and the optimal blanking threshold are derived. Simulation results are provided that show good agreement with theory, if the number of OFDM subcarriers is sufficiently large. | Distillation at an infinite reflux ratio in combination with an infinite number of trays has been investigated. | eng_Latn | 5,301 |
An extended quadratic residue (QR)-decomposition (QRD)-based RLS-algorithm is introduced, applicable for equalization, allowing an estimate of the transmitted symbol, when it is a-priori unknown. To achieve low-cost implementations strength reduction and square-root free Givens-rotations are applied. Several QRD-based RLS-algorithms are compared in terms of the number of mathematical operations. The QR-RLS-algorithm indicates lowest complexity and is always a good candidate, when a huge training overhead has to be avoided, resulting in an equalizer of less than 15 taps. Finally, the hardware complexity of a 13 MBaud-DFE for wireless ATM is estimated. | Carefully designed PMP RLL systems at RF frequencies greater than 10 GHz are characterized by radio cells with a great number of network terminations with very small multipath propagation and only a few radio channels, if ever, with bad conditions. The proposed algorithm allows to equalise all radio channels with the average effort, which may be much less than the usual necessary effort for the worst case channel. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,302 |
The authors investigate the relationship between the nonuniform sampling theorem and the fundamental theorem of information theory. This analysis leads to an alternative method of error correction. They propose not to correct for the lost samples but rather to reconstruct the original signal from the rest of the samples using nonuniform sampling reconstruction techniques. This idea can be generalized to additive noise where the binary digits are in error but there is no erasure. > | Communication Systems and Information Theory. A Measure of Information. Coding for Discrete Sources. Discrete Memoryless Channels and Capacity. The Noisy-Channel Coding Theorem. Techniques for Coding and Decoding. Memoryless Channels with Discrete Time. Waveform Channels. Source Coding with a Fidelity Criterion. Index. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,303 |
This paper addresses the problem of tracking of time-varying mobile radio channels with time-varying parameters, and the channels are modeled as auto-regressive (AR) models. A polynomial H-infinity channel filter in Krein space is designed for the tracking problem. With the help of an ARMA innovation model, the solution to the tracking problem can be obtained. The H-infinity channel estimators are calculated by performing one J-spectral factorization. | We consider the estimation of channel parameters for code-division multiple access (CDMA) communication systems operating over channels with either single or multiple propagation paths. The multiuser channel estimation problem is decomposed into a series of single user problems through a subspace-based approach. By exploiting the eigenstructure of the received signal's sample correlation matrix, the observation space can be partitioned into a signal subspace and a noise subspace without prior knowledge of the unknown parameters. The channel estimate is formed by projecting a given user's spreading waveform into the estimated noise subspace and then either minimizing the likelihood or minimizing the Euclidean norm of this projection. Both of these approaches yield algorithms which are near-far resistant and do not require a preamble. | This note presents an elementary proof of the familiar Routh-Hurwitz test. The proof is basically one continuity argument, it does not rely on Sturm chains, Cauchy index and the principle of the argument and it is fully self-contained. In the same style an extended Routh-Hurwitz test is derived, which finds the inertia of polynomials. | eng_Latn | 5,304 |
DENSITY-DEPENDENT LESLIE MATRIX MODELING FOR LOGISTIC POPULATIONS WITH STEADY-STATE DISTRIBUTION CONTROL | Equilibrium and local stability in a logistic matrix model for age-structured populations | Completely Stale Transmitter Channel State Information is Still Very Useful | yue_Hant | 5,305 |
Precoding Method Interference Management for Quasi-EVD Channel | A novel signaling for communication on MIMO Y channel: Signal space alignment for network coding | An instrumental variable approach finds no associated harm or benefit from early dialysis initiation in the United States | eng_Latn | 5,306 |
Cooperative Coding Schemes: Design and Performance Evaluation | Design Criteria and Genetic Algorithm Aided Optimization of Three-Stage-Concatenated Space-Time Shift Keying Systems | On the Very Idea of a Conceptual Scheme | eng_Latn | 5,307 |
Closed-Form Sum-MSE Minimization for the Two-User Gaussian MIMO Broadcast Channel | A Game Theoretic Approach to Uplink Pilot and Data Power Control in Multi-Cell Multi-User MIMO Systems | A Multiple Mass-Flux Parameterization for the Surface-Generated Convection. Part I: Dry Plumes | eng_Latn | 5,308 |
A coherent amplify-and-forward relaying demonstrator without global phase reference | Distributed beamforming for information transfer in sensor networks | Amplify-and-forward with partial relay selection | eng_Latn | 5,309 |
Outage Capacity of MIMO Poisson Fading Channels | Service outage based power and rate allocation for parallel fading channels | Completely Stale Transmitter Channel State Information is Still Very Useful | eng_Latn | 5,310 |
Trellis coded double differentially coherent (TCD/sup 2/C) MPSK with carrier phase noise | The phase of a vector perturbed by Gaussian' noise and differentially coherent receivers | Completely Stale Transmitter Channel State Information is Still Very Useful | eng_Latn | 5,311 |
Separating distributed source coding from network coding | Efficient distributed source coding for multiple receivers via matrix sparsification | Network Coding for Correlated Sources | eng_Latn | 5,312 |
Blind channel estimation in synchronous MC-CDMA system with consideration of carrier offset compensation | Subspace based blind channel estimation for OFDM by exploiting virtual carrier | Completely Stale Transmitter Channel State Information is Still Very Useful | eng_Latn | 5,313 |
On an approximate eigenvector associated with a modulation code | The approximate eigenvector associated with a modulation code | The approximate eigenvector associated with a modulation code | eng_Latn | 5,314 |
Turbo Receivers for Single User MIMO LTE-A Uplink | Link adaptation in LTE-A uplink with Turbo SIC receivers and imperfect channel estimation | Microtubule capture by CENP-E silences BubR1-dependent mitotic checkpoint signaling | kor_Hang | 5,315 |
Full-rate and Low Complexity Space-time Coding Scheme Concatenated with LDPC Codes | Design of provably good low-density parity check codes | The Development of Turbo and LDPC Codes for Deep-Space Applications | eng_Latn | 5,316 |
From the STFT to the Wigner Distribution | On the ISAR Image Analysis and Recovery with Unavailable or Heavily Corrupted Data | Completely Stale Transmitter Channel State Information is Still Very Useful | eng_Latn | 5,317 |
On the Maximum Achievable Partial Decode-and-Forward Rate for the Gaussian MIMO Relay Channel | A zero-forcing partial decode-and-forward scheme for the Gaussian MIMO relay channel | A zero-forcing partial decode-and-forward scheme for the Gaussian MIMO relay channel | eng_Latn | 5,318 |
Broadband beamforming with alpha-stable distributions | Spectral density estimation for stationary stable processes | Completely Stale Transmitter Channel State Information is Still Very Useful | eng_Latn | 5,319 |
Series expansion of the MIMO spatial covariance | From antenna spacings to theoretical capacities - guidelines for simulating MIMO systems | A fine-grained solution to the mutual exclusion problem | eng_Latn | 5,320 |
Quasi-3D tool to analyse of the radio propagation channel | Radio channel investigations for mobile systems | Completely Stale Transmitter Channel State Information is Still Very Useful | eng_Latn | 5,321 |
Frequency-Domain Turbo Equalization with Soft Successive Interference Cancellation for Single Carrier MIMO Underwater Acoustic Communications | Joint equalization and phase drift estimation for underwater acoustic communications | Mounting evidence against the role of ICC in neurotransmission to smooth muscle in the gut | eng_Latn | 5,322 |
This paper provides an analysis of the performance of conventional preamble-based time synchronization techniques, which have been proposed for Orthogonal Frequency Division Multiplexing (OFDM) radio transmissions, in the context of optical Intensity Modulated and Direct Detected (IMDD) OFDM transmissions over single-mode fiber. A novel preamble structure along with a two-stage synchronization algorithm is proposed. Thanks to the particular structure of the preamble, a first coarse synchronization metric does not present minor peaks. In addition, without the knowledge of the preamble waveform the receiver can perform both coarse and fine synchronization steps. As maximal delay in arrival time between different frequency components of a signal depends on chromatic dispersion and the signal bandwidth, it is also observed that a slowly time-varying preamble is more robust than a fast time-varying one. By means of numerical simulations, the proposed method is shown to provide better performance when compared to other conventional methods in terms of timing offset variance with reduced receiver complexity. In unamplified transmissions the proposed technique guarantees a quasi-optimal transmission capacity even with a short cyclic prefix. | 5G wireless systems are envisioned to provide ultra-high data rates, increased robustness and low latency for new applications such as machine-to-machine (M2M) and car-to-car (C2C) communications. This paper considers high-speed visible light communication (VLC) as a candidate serving technology to fulfill this set of requirements. Synchronization as the first step towards reliable data detection is studied here thoroughly aiming at high robustness and low complexity. Three schemes are reviewed, namely Schmidl-Cox and Park autocorrelation as well as a cross-correlation based approach, all using a predefined preamble. All schemes are examined concerning their robustness against multipath propagation and their precision in time estimation versus the preamble length. It is found that the simple Schmidl-Cox scheme, originally designed for complex-valued radio waveforms, can be applied also for real-valued optical wireless waveforms. Based on these investigations, an optimized preamble structure is finally proposed. Preamble boosting and fine synchronization can also be applied to reach a similar performance like optimal cross-correlation at reduced complexity. We study the fundamental trade-off between the preamble duration and the minimum signal-to-noise ratio (SNR) required for reliable synchronization and observe that ultra-low latency needs sufficient SNR. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,323 |
We study two different parallel concatenated coding schemes by way of EXIT chart prediction. One scheme is the famous turbo code, while the other is a concatenation of regular LDPC codes. Both schemes can be decoded by soft-in/soft-out decoders in an iterative fashion, which makes them attractive for usage in modern communication systems. In these iterations extrinsic information is exchanged between decoder stages, enabling us to use the EXIT chart theory based on extrinsic information transfer. We use a simplified simulation setup to obtain the EXIT characteristics for the constituent encoders and apply the results to the parallel concatenated codes. The performance of these coding schemes is evaluated by predicting Cliff E/sub b//N/sub o/, residual bit error rate, and decoder complexity beyond the Cliff E/sub b//N/sub o/. | The authors report the empirical performance of Gallager's low density parity check codes on Gaussian channels. They show that performance substantially better than that of standard convolutional and concatenated codes can be achieved; indeed the performance is almost as close to the Shannon limit as that of turbo codes. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,324 |
We experimentally examine the maximum achievable transmission performance of a 7 channel Nyquist-WDM system with 10GBd per carrier. Back-to-back, a maximum of 11.9 bit/sym and 13.8 bit/sym can be transmitted for DP-64QAM and DP-256QAM respectively, while after 2 spans of transmission, a maximum of 12.4 bit/sym and 11.6 bit/sym can be achieved. | Quantum mechanics allows measurements that surpass the fundamental sensitivity limits of classical methods. To benefit from the quantum advantage in a practical setting, the receiver should use communication channels resources optimally; this can be done employing large communication alphabets. Here we show the fundamental sensitivity potential of a quantum receiver for coherent communication with frequency shift keying. We introduce an adaptive quantum protocol for this receiver, show that its sensitivity outperforms other receivers for alphabet sizes above 4 and scales favorably, whereas quantum receivers explored to date suffer from degraded sensitivity with the alphabet size. In addition, we show that the quantum measurement advantage allows the much better use of the frequency space in comparison to classical frequency keying protocols and orthogonal frequency division multiplexing. | We review currently discussed solutions for 80 km DWDM transmission targeting inter data-center connections at 100G and 400G line rates. PDM-64QAM, PAM4 and DMT are investigated, while the focus lies on directly detected solutions. | eng_Latn | 5,325 |
The fragment molecular-orbital (FMO) method was combined with the single-reference coupled-cluster (CC) theory. The developed method (FMO-CC) was applied at the CCSD and CCSD(T) levels of theory, for the cc-pVnZ family of basis sets (n=D,T,Q) to water clusters and glycine oligomers (up to 32 molecules/residues using as large basis sets as possible for the given system). The two- and three-body FMO-CC results are discussed at length, with emphasis on the basis-set dependence and three-body effects. Two- and three-body approximations based on interfragment distances were developed and the values appropriate for their accurate application carefully determined. The error in recovering the correlation energy was several millihartree for the two-body FMO-CC method and in the submillihartree range for the three-body FMO-CC method. In the largest calculations, we were able to perform the CCSD(T) calculations of (H2O)32 with the cc-pVQZ basis set (3680 basis functions) and (GLY)32 with the cc-VDZ basis set (712 co... | An electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method is developed for efficient linear-scaling quantum mechanical (QM) calculation of protein energy. This approach is based on our previously proposed GMFCC/MM method (He; et al. J. Chem. Phys. 2006, 124, 184703), In this EE-GMFCC scheme, the total energy of protein is calculated by taking a linear combination of the QM energy of the neighboring residues and the two-body QM interaction energy between non-neighboring residues that are spatially in close contact. All the fragment calculations are embedded in a field of point charges representing the remaining protein environment, which is the major improvement over our previous GMFCC/MM approach. Numerical studies are carried out to calculate the total energies of 18 real three-dimensional proteins of up to 1142 atoms using the EE-GMFCC approach at the HF/6-31G* level. The overall mean unsigned error of EE-GMFCC for the 18 proteins is 2.39 kcal/mol with reference to the full system HF/6-31G* energies. The EE-GMFCC approach is also applied for proteins at the levels of the density functional theory (DFT) and second-order many-body perturbation theory (MP2), also showing only a few kcal/mol deviation from the corresponding full system result. The EE-GMFCC method is linear-scaling with a low prefactor, trivially parallel, and can be readily applied to routinely perform structural optimization of proteins and molecular dynamics simulation with high level ab initio electronic structure theories. | Wireless transmission over 15Gb/s data rate is reported using space diversity MIMO. Multi-diversity planar antennas are designed and fabricated to transmit and receive the radio frequency signal simultaneously in 2 radiation diversities. Reliable 15Gb/s indoor data transmission over 5m distance is demonstrated in the super high frequency band (SHF) of 11.6GHz to 20.4GHz. Low BER is achieved with 2×2 MIMO space time block coded OFDM modulation. | eng_Latn | 5,326 |
Combining coding, modulation, transmit and receive diversity, and validly increases the anti-noise performance in fading channels, OSTBC (orthogonal space-time block codes) is a new channel coding technology accompanying with the extensive application of wireless communication. Based on typical channel model of the OSTBC in MIMO (multiple-in, multiple-out) wireless communication channels, a general expression of instant output SNR(signal-to-noise ratio ) and anti-noise performance for OSTBC over qusi-static flat Rayleigh fading channel is deduced, and the simulation and the comparison and analysis of the BER(bit-error rate) results are implemented on several OSTBC systems, based on different modulations using Simulink. | A method of producing a panel heater element by the steps of mixing carbon fiber with natural or synthetic fibers, forming the mixture into a base sheet, heat-treating the base sheet to expel volatile matter therefrom, fitting electrodes to the sheet, placing an insulative thermoplastic resin film against both surfaces of the base sheet and hot-rolling the base sheet, and finally cold-rolling the resin-coated sheet. | ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system... | eng_Latn | 5,327 |
We consider a simple conceptual model of random accessing to a receiver deploying multiuser detection techniques. The model is a simple extension of Massey and Mathys' collision channel without feedback in which a certain probability of recovery from collision is introduced. As the main result, we derive the slot-synchronized capacity region of this recovery channel and show that for sufficiently powerful multiuser detectors, maximal performance is achieved without any sophisticated transmission protocols. We also explore the effect of a simple fading model. | We study and compare the Shannon capacity region and the stable throughput region for a random access system in which source nodes multicast their messages to multiple destination nodes. Under an erasure channel model which accounts for interference and allows for multipacket reception, we first characterize the Shannon capacity region. We then consider a queueing-theoretic formulation and characterize the stable throughput region for two different transmission policies: a retransmission policy and random linear coding. Our results indicate that for large blocklengths, the random linear coding policy provides a higher stable throughput than the retransmission policy. Furthermore, our results provide an example of a transmission policy for which the Shannon capacity region strictly outer bounds the stable throughput region, which contradicts an unproven conjecture that the Shannon capacity and stable throughput coincide for random access systems. | E-commerce provides manufacturing enterprise with a direct access to market besides traditional sale channels, thus causing changes in the supply chain structure. A mixed-integer programming model based on optimal control theory for the new pattern supply chain of dual-channel market of manufacturing enterprise is developed. The simulation computing on the model's key parameters of the pricing of manufacturer and retailer with Monte Carlo optimal method is made, and the result of simulation shows that the profits of the supply chain can be improved radically when some conditions are met. | eng_Latn | 5,328 |
In this paper, we investigate the robustness of the Unique Word Orthogonal Frequency Division Multiplexing (UW-OFDM) technique for channel estimation issue. We consider the UW-OFDM technique instead of Zero-Padding (ZP) OFDM one to construct the OFDM symbols for MultiBand Orthogonal Frequency Division Multiplexing Ultra WideBand (MB-OFDM UWB) systems. Then, we propose a two-step LMMSE channel estimator. In the first step, by using the knowledge of UW sequence in the receiver side, the Channel Frequency Response (CFR) is estimated. In the second step, the Linear Minimum Mean-Squared Error (LMMSE) channel estimation is performed using the estimated CFR of the first step and the Channel Estimation Sequence (CES) included in the frame preamble. We evaluate the performance of the proposals in terms of Bit Error Rate (BER) by computer simulations. We show that the consideration of UW-OFDM technique provides, not only reduction of complexity, but also improvement in BER performance. Moreover, we show that the two-step LMMSE channel estimation does not affect the system performance mainly for low Signal-to-Noise Ratio (SNR). | This paper proposes low-complexity channel estimator for Unique Word (UW) MultiBand Orthogonal Frequency Division Multiplexing (MB-OFDM) based Ultra WideBand (UWB) communication systems. The proposed channel estimator is performed in two stages. The pre-FFT stage employs the Least Square (LS) estimation and smoothing technique to estimate the Channel Frequency Response (CFR). The post-FFT stage employs this CFR estimate to extract the UW influence and then refines the CFR estimate using a decision feedback technique. Via simulation results, we show that the proposed estimator provides higher performance gain over the conventional LS channel estimator and performs closely to the Linear Minimum Mean-Squared Error (LMMSE) one. Additionally, the computational complexity of our proposal is comparable with the LS approach and significantly lower than that of LMMSE one. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,329 |
In MIMO space division multiplexing (SDM) systems, the peak power of the transmit signal at each antenna element is increased by the precoder and hence it causes the power efficiency degradation and/or nonlinear distortion at the power amplifier. To solve this problem, this paper present a peak power aware precoding scheme for MIMO-SDM systems, where the precoder is designed to mitigate the peak output power at each antenna element so that peak amplitude of the transmit signal at each antenna is reduced while minimizing the performance degradation caused by the peak power restriction. The proposed system employs an alternative iterative optimization algorithm that determines the precoding matrix so that the precoding and virtual post-coding matrices are alternatively optimized under the constraint of peak output at each antenna element. Simulation results show that the proposed method is effective in restricting the peak transmission power at each antenna within a permissible level while mitigating performance degradation in bit error rate (BER) performance of the precoded SDM systems. | The use of space-division multiple access (SDMA) in the downlink of a multiuser multiple-input, multiple-output (MIMO) wireless communications network can provide a substantial gain in system throughput. The challenge in such multiuser systems is designing transmit vectors while considering the co-channel interference of other users. Typical optimization problems of interest include the capacity problem - maximizing the sum information rate subject to a power constraint-or the power control problem-minimizing transmitted power such that a certain quality-of-service metric for each user is met. Neither of these problems possess closed-form solutions for the general multiuser MIMO channel, but the imposition of certain constraints can lead to closed-form solutions. This paper presents two such constrained solutions. The first, referred to as "block-diagonalization," is a generalization of channel inversion when there are multiple antennas at each receiver. It is easily adapted to optimize for either maximum transmission rate or minimum power and approaches the optimal solution at high SNR. The second, known as "successive optimization," is an alternative method for solving the power minimization problem one user at a time, and it yields superior results in some (e.g., low SNR) situations. Both of these algorithms are limited to cases where the transmitter has more antennas than all receive antennas combined. In order to accommodate more general scenarios, we also propose a framework for coordinated transmitter-receiver processing that generalizes the two algorithms to cases involving more receive than transmit antennas. While the proposed algorithms are suboptimal, they lead to simpler transmitter and receiver structures and allow for a reasonable tradeoff between performance and complexity. | By using a superluminescent diode as the light source and a depolariser inside the fibre coil, a constant scale factor is achieved without using polarisation control elements. For long-term behaviour an RMS-bias drift of 10 degrees/h is obtained. | eng_Latn | 5,330 |
Wireless channels operate through the transmission of electromagnetic signals from the transmitter to the receiver. In a fixed wireless network, the transmission medium is often distorted or disrupted by inherent natural phenomenon which in turn corrupt, obstruct or cause most of the data transmitted over the channel to generally get garbled. In a vehicular network, greater complexity is added as a result of the fast mobility of the nodes within the network. It therefore becomes very difficult for the receiver to decode the data transmitted efficiently. Based on the IEEE standard, communication between two mobile can only be possible if a minimum required threshold has been met. In this paper, a Direct Development Method (DDM) strategy is presented that seeks to combat the effect of Doppler Shift (DS) in a vehicular network. The proposed approach is developed based on the principle of basic communication theory and validated through simulations. It is demonstrated that it is possible to achieve a good communication link between two mobiles moving at the relative speed of up to 250 km/h taking into account the prescribed threshold. | A new and effective Doppler effects compensation scheme for orthogonal frequency division multiplex (OFDM) systems based on constellation estimation is presented with analytical descriptions that quantitatively clarify the mechanism of inter-carrier interference. The proposed compensation techniques, applicable in both frequency and time domain with remarkable accuracy, are crucial to the future OFDM system operating on ultra-high-speed mobile vehicles. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,331 |
We study the asymptotic behavior of space-time codes when the number of transmit and receive antennas grows to infinity. Specifically, we determine the behavior of pairwise error probabilities with maximum-likelihood (ML) decoding and with three types of receiver interfaces: the ML interface, the linear zero-forcing (ZF) interface, and the linear minimum-mean-square-error (MMSE) interface. Two situations are studied: when the number of receiving antennas grows to infinity while the number of transmitting antennas is finite, and when both numbers grow to infinity but their ratio remains constant. We show that with ML or linear interfaces the asymptotic performance of space-time codes is determined by the Euclidean distances between codewords. Moreover, with the two linear interfaces examined here the number r of receive antennas must be much larger than the number t of transmit antennas to avoid a sizeable loss of performance; on the other hand, when r /spl Gt/ t, the performance of these linear interfaces comes close to that of ML. The dependence of error probabilities on Euclidean distance is valid for intermediate signal-to-noise ratios (SNRs) even when the number of antennas is small. Simulations validate our theoretical findings, and show how asymptotic results may be substantially valid even in a nonasymptotic regime: thus, even for few antennas, off-the-shelf codes may outperform space-time codes designed ad hoc. | It is shown that while the mutual information curves for coded modulation (CM) and bit interleaved coded modulation (BICM) overlap in the case of a single input single output channel, the same is not true in multiple input multiple output (MIMO) channels. A method for mitigating fading in the presence of multiple transmit antennas, named coordinate interleaving (CI), is presented as a generalization of component interleaving for a single transmit antenna. The extent of any advantages of CI over BICM, relative to CM, is analyzed from a mutual information perspective; the analysis is based on an equivalent parallel channel model for CI. Several expressions for mutual information in the presence of CI and multiple transmit and receive antennas are derived. Results show that CI gives higher mutual information compared to that of BICM if proper signal mappings are used. Effects like constellation rotation in the presence of CI are also considered and illustrated; it is shown that constellation rotation can increase the constrained capacity. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,332 |
In this paper, the applicability of the subspace-based blind adaptive algorithm in multiple access ultra-wideband systems is investigated. However, in the multiuser transmission environment, multiple access interference becomes a serious issue and results in the degradation of system performance. In order to overcome this shortcoming, we propose a novel and low complexity decision mechanism, termed the decision timing instant (DTI). A major advantage of the DTI algorithm is that it admits an adaptive implementation with low computational complexity instead of singular value decomposition. In the present paper, we exploit the joint blind multiuser detection in UWB systems, a combined scheme is proposed, which couples the minimum-mean-square-error and the DTI subspace tracking algorithm under UWB time-variant channels. Simulation results show that DTI is able to fast and precisely trace the variation of the channel environment and to improve the performance of the blind adaptive multiuser detection with a subspace approach over time-varying channels. | The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,333 |
A computationally efficient expression is presented for evaluating the average bit error rate (BER) of an intensity-modulation and direct-detection free-space optical system with on-off keying signaling technique operating in turbulent atmosphere described by the exponentiated Weibull distribution. The presented numerical results show the effects of aperture averaging on the average BER under weak and moderate turbulence conditions, and are confirmed by Monte Carlo simulations. | The performances of the decode-and-forward (DF) multihop free-space optical communication system with exponentiated Weibull distribution considering the fading induced by pointing error have been studied. With Meijer's G-function, the probability density function (PDF) of the aggregated channel model and the closed-form expression for the average bit error rate (ABER) of binary pulse position modulation are derived. The average bit-error-rate performance is then investigated with different hop numbers $H$ , turbulence strength values, receiver aperture sizes, beamwidths, and jitter variances. Compared with the case without pointing error, the mitigation effect of aperture averaging for fading is more significant over the aggregated channel, regardless of the selected $H$ , and it is less effective for the degradation induced by the increase in $H$ , which can be restrained by larger beamwidth and lower jitter. The outage probability is also investigated, and the results show that aperture averaging has less of an effect on the outage probability under moderate turbulence than that under the weak turbulence condition at a given value of $H$ , which is different from the scenario without pointing error. After this, the end-to-end average capacity is analyzed. Monte Carlo simulation is provided to confirm the validity of the proposed ABER expression. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,334 |
In recent years, communications systems through mains, known as PLC (Powerline Communication), have received a lot of interest as part of intelligent networks or smart grids, as well as for multimedia applications at homes. In broadband PLC, systems using multicarrier modulations allow the mitigation of selective frequency fading in the channel. Nevertheless, these modulations require accurate time synchronization for correct operation. This paper proposes a robust temporal synchronization algorithm based on multilevel complementary sequences for broadband PLC channel with selective frequency fading, providing improvements around 80% in RMSE (Root Mean Squared Error) with respect to the common metrics used in OFDM (Orthogonal Frequency Division Multiplexing), where multipath effect is not considered. | The characteristics of the power line communication (PLC) channel are difficult to model due to the heterogeneity of the networks and the lack of common wiring practices. To get the full variability of the PLC channel, random channel generators are of great importance for the design and testing of communication algorithms. In this respect, we propose a random channel generator that is based on the top-down approach. Basically, we describe the multipath propagation and the coupling effects with an analytical model. We introduce the variability into a restricted set of parameters, and, finally, we fit the model to a set of measured channels. The proposed model enables a closed-form description of both the mean path loss profile and the statistical correla tion function of the channel frequency response. As an example of application, we apply the procedure to a set of in-home measured channels in the band 2-100 MHz whose statistics is available in the literature. The measured cha nnels are divided into nine classes according to their channel capacity. We provide the parameters for the random generation of channels for all nine classes, and we show that the results are consistent with the experimental ones. Finally, we merge the classes to capture the whole hetero- geneity of in-home PLC channels. In detail, we introduce the class occurrence probability, and we present a random channel generator that targets the ensemble of all nine classes. The statistics of the composite set of channels is also studied, and it is compared to the results of experimental measurement campaigns in the literature. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,335 |
This paper outlines that when decoding an arbitrary analog block codes, i.e., a block codes over the complex or real numbers, in an iterative fashion by splitting the H-Matrix in two, leads to a least-squares estimate. Such a Turbo-like algorithm represents iterative projections in Euclidean space. A step size controls the convergence speed. The paper generalized an earlier result based on array codes (product codes) with analog parity-check component codes. The results in here are considered to be an important step towards an intuitive understanding of iterative decoding schemes of conventional Turbo and LDPC codes. | The relationship between the discrete Fourier transform and error-control codes is examined. Under certain conditions we show that discrete-time sequences carry redundant information which then allow for the detection and correction of errors. An application of this technique to impulse noise cancellation for pulse amplitude modulation transmission is described. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,336 |
In this paper, we propose a cooperative diversity scheme to improve the end-to-end outage performance via Alamouti space-time block coding with two transmit antennas at a source node in a backward link and a best-relay selection scheme in a forward link. We derive an exact closed-form expression of the outage probability for the proposed scheme over a Rayleigh fading channel and analyze end-to-end outage probabilities. Keywords-cooperative communication; decode-and-forward; selective relaying; space-time block coding; outage probability. | Cooperative diversity improves the performance of wireless networks by having several nodes transmit the same information. We present an outage probability analysis for a decode-and-forward system, valid at all signal to noise ratios (SNR). A closed form solution is obtained for independent and identically distributed (i.i.d.) channels, and two tight lower bounds are presented for correlated channels. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,337 |
Three prominent features of massive MIMO are studied using channel measurements. Those features are extensively exploited in signal processing methods for massive MIMO and have been only partially, or not at all, validated. First, channel hardening is characterized as a function of the number of antennas. Second, user decorrelation is evaluated as a function of the distance between users. At last, the channel angular spread, proposed as a basis for pilot contamination and frequency division duplexing operation, is assessed. The whole study is based on two measurement campaigns involving a base station with 64 antennas and 128 antennas. | In this paper, we consider the uplink of massive MIMO systems where the channel capacity is almost deterministic and varies slowly over time. We exploit this fact, by appropriately choosing the length of the codeword only once based on an initial estimate of the uplink channel capacity fed back by the base station (BS). The user terminal (UT) then transmits the codeword over consecutive coherence time intervals without waiting for any acknowledgement (ACK/NACK) from the BS. The BS sends only a single ACK/NACK after it completes decoding. Therefore, the proposed method has significantly less latency and signaling overhead when compared with stop-and-wait type hybrid automatic repeat request (HARQ) methods (as in LTE uplink) where a lot of delay is introduced as the UT needs to wait for the BS to signal the ACK/NACK for every retransmission. Analysis reveals that for sufficiently large number of antennas at the BS, the average codeword length of the proposed method (in number of coherence intervals) is the same as the average number of retransmissions (in number of coherence intervals) required by incremental redundancy (IR)-based HARQ and also that the energy efficiency of the proposed method and IR-HARQ is the same. | We report enhancement of the mechanical stability of graphene through a one-step method to disperse gold nanoparticles on the pristine graphene without any added agent. | eng_Latn | 5,338 |
This paper presents a simple yet effective decoding for general quasi-cyclic low-density parity-check (QC-LDPC) codes, which not only achieves high hardware utility efficiency (HUE), but also brings about great memory block reduction without any performance degradation. The main idea is to split the check matrix into several row blocks, then to perform the improved message passing computations sequentially block by block. As the decoding algorithm improves, the sequential tie between the two-phase computations is broken, so that the two-phase computations can be overlapped which bring in high HUE. Two overlapping schemes are also presented, each of which suits a different situation. In addition, an efficient memory arrangement scheme is proposed to reduce the great memory block requirement of the LDPC decoder. As an example, for the 0.4 rate LDPC code selected from Chinese Digital TV Terrestrial Broadcasting (DTTB), our decoding saves over 80% memory blocks compared with the conventional decoding, and the decoder achieves 0.97 HUE. Finally, the 0.4 rate LDPC decoder is implemented on an FPGA device EP2S30 (speed grade −5). Using 8 row processing units, the decoder can achieve a maximum net throughput of 28.5 Mbps at 20 iterations. | High-throughput design approaches for quasi-cyclic (QC) low-density parity-check (LDPC) decoders are presented in this paper. Three novel schemes for the horizontal process in min-sum algorithm and its revisions are derived to reduce design and implementation complexity. The schemes can be directly applied for variant QC codes and easily pipelined to increase the operating frequency of the decoder. Some improvements of the semi-parallel architecture are proposed to enhance throughput performance and hardware efficiency. Employing the proposed approaches, QC-LDPC decoders for Chinese Digital Television Terrestrial Broadcasting (DTTB) standard are implemented using field programmable gate array (FPGA). As shown in the results, the proposed approaches can substantially improve the throughput performance, as well as the throughput-and-hardware tradeoff, of decoders with semi-parallel architecture. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,339 |
This paper presents a novel parallel architecture for decoding LDPC codes. The proposed architecture has low memory and interconnection requirements, becoming attractive for high speed applications such as fiber optic communications and high density magnetic recording. As an example, the implementation on an FPGA of a TPC/SPC code using the proposed architecture will also be described. | We propose a novel class of provably good codes which are a serial concatenation of a single-parity-check (SPC)-based product code, an interleaver, and a rate-1 recursive convolutional code. The proposed codes, termed product accumulate (PA) codes, are linear time encodable and linear time decodable. We show that the product code by itself does not have a positive threshold, but a PA code can provide arbitrarily low bit-error rate (BER) under both maximum-likelihood (ML) decoding and iterative decoding. Two message-passing decoding algorithms are proposed and it is shown that a particular update schedule for these message-passing algorithms is equivalent to conventional turbo decoding of the serial concatenated code, but with significantly lower complexity. Tight upper bounds on the ML performance using Divsalar's (1999) simple bound and thresholds under density evolution (DE) show that these codes are capable of performance within a few tenths of a decibel away from the Shannon limit. Simulation results confirm these claims and show that these codes provide performance similar to turbo codes but with significantly less decoding complexity and with a lower error floor. Hence, we propose PA codes as a class of prospective codes with good performance, low decoding complexity, regular structure, and flexible rate adaptivity for all rates above 1/2. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,340 |
Massive multiple-input multiple-output technology has been considered a breakthrough in wireless communication systems. It consists of equipping a base station with a large number of antennas to serve many active users in the same time-frequency block. Among its underlying advantages is the possibility to focus transmitted signal energy into very short-range areas, which will provide huge improvements in terms of system capacity. However, while this new concept renders many interesting benefits, it brings up new challenges that have called the attention of both industry and academia: channel state information acquisition, channel feedback, instantaneous reciprocity, statistical reciprocity, architectures, and hardware impairments, just to mention a few. This paper presents an overview of the basic concepts of massive multiple-input multiple-output, with a focus on the challenges and opportunities, based on contemporary research. | We consider the uplink (UL) and downlink (DL) of non-cooperative multi-cellular time-division duplexing (TDD) systems, assuming that the number N of antennas per base station (BS) and the number K of user terminals (UTs) per cell are large. Our system model accounts for channel estimation, pilot contamination, and an arbitrary path loss and antenna correlation for each link. We derive approximations of achievable rates with several linear precoders and detectors which are proven to be asymptotically tight, but accurate for realistic system dimensions, as shown by simulations. It is known from previous work assuming uncorrelated channels, that as N→∞ while K is fixed, the system performance is limited by pilot contamination, the simplest precoders/detectors, i.e., eigenbeamforming (BF) and matched filter (MF), are optimal, and the transmit power can be made arbitrarily small. We analyze to which extent these conclusions hold in the more realistic setting where N is not extremely large compared to K. In particular, we derive how many antennas per UT are needed to achieve η% of the ultimate performance limit with infinitely many antennas and how many more antennas are needed with MF and BF to achieve the performance of minimum mean-square error (MMSE) detection and regularized zero-forcing (RZF), respectively. | Adenomyoepithelioma is thought to be a low-grade malignancy, and cases showing malignant behavior are rare. | eng_Latn | 5,341 |
In this paper we propose a computationally effi- cient subcarrier allocation algorithm for a multiuser OFDM system suited for downlink and uplink transmission. The al- gorithm considers user-individual bitrate and power con- straints and allocates to each user the most appropriate subcarriers in a way that the total transmit power is mini- mized. The bit and power allocation for each user is done by a single-user bitloading algorithm on the base of this subcar- rier allocation. The performance of the proposed algorithm is compared to a near-optimum algorithm which is based on Lagrange optimization. It is found that the proposed algo- rithm is computationally much more efficient while is has very little performance degradation, in some situations it even achieves better performance. The execution time for the pro- posed algorithm is compared for different numbers of users and OFDM sizes with the near-optimum algorithm and is found to offer advantages of various orders of magnitudes. | In this paper, we propose sub-carrier allocation algorithms for a multiple access scheme in downlink OFDM transmission. Knowing the channel characteristics of all the users at the base station, the sub-carrier allocation algorithm assigns sub-carriers to the users in a way that the total transmit power is minimized. An optimal algorithm is presented to provide the best sub-carrier assignment. The complexity of the optimal solution renders it impractical for real-time application. To deal with the frequently changing channel characteristic of a fast time-varying multipath fading channel, a heuristic algorithm based on constructive assignment and iterative improvement is proposed which can give out a valid solution in real time. Experimental results show that the performance of this real-time algorithm is close to that of the optimal allocation. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,342 |
A new numerical method based on numerical homogenization and model order reduction is introduced for the solution of multiscale inverse problems. We consider a class of elliptic problems with highl... | Certain projection post-processing techniques have been proposed for computing the boundary flux for two-dimensional problems (e.g., see Carey, et al. [5]). In a series of numerical experiments on elliptic problems they observed that these post-processing formulas for approximate fluxes were almost (O(h 2)-accurate for linear triangular elements. In this paper we prove that the computed boundary flux isO(h 2 ln 1/h)-accurate in the maximum norm for the partial method of [5]. If the solutionu?H 3(Ω) then the boundary flux error isO(h 3/2) in theL 2-norm. | The use of space-division multiple access (SDMA) in the downlink of a multiuser multiple-input, multiple-output (MIMO) wireless communications network can provide a substantial gain in system throughput. The challenge in such multiuser systems is designing transmit vectors while considering the co-channel interference of other users. Typical optimization problems of interest include the capacity problem - maximizing the sum information rate subject to a power constraint-or the power control problem-minimizing transmitted power such that a certain quality-of-service metric for each user is met. Neither of these problems possess closed-form solutions for the general multiuser MIMO channel, but the imposition of certain constraints can lead to closed-form solutions. This paper presents two such constrained solutions. The first, referred to as "block-diagonalization," is a generalization of channel inversion when there are multiple antennas at each receiver. It is easily adapted to optimize for either maximum transmission rate or minimum power and approaches the optimal solution at high SNR. The second, known as "successive optimization," is an alternative method for solving the power minimization problem one user at a time, and it yields superior results in some (e.g., low SNR) situations. Both of these algorithms are limited to cases where the transmitter has more antennas than all receive antennas combined. In order to accommodate more general scenarios, we also propose a framework for coordinated transmitter-receiver processing that generalizes the two algorithms to cases involving more receive than transmit antennas. While the proposed algorithms are suboptimal, they lead to simpler transmitter and receiver structures and allow for a reasonable tradeoff between performance and complexity. | eng_Latn | 5,343 |
The six-port receiver concept offers new possibilities on the way toward multi-band/multi-mode low cost receiver frontends for high frequencies up to the nun-wave range. The expense for the reduced effort on the analog side is claimed as higher complexity on digital side. Especially, the synchronization of the receiver by considering the necessary calibration leads to a significantly higher computational load. This paper presents a new way to reduce the calibration to a linear equalization, which allows applying standard well known baseband architectures, used in conventional receiver designs. Herein, the six-port effects are processed in conjunction with the channel equalization. | Estimation of time-varying dispersive radio channels is one of the most important tasks of receiver synchronisation. State-of-the-art adaptive estimators employing decision feedback suffer from error propagation and limited robustness against faster fading. In this paper, the optimal feedforward channel estimator using only known training symbols is systematically derived. Statistical channel information is assumed to be available. For moderately rapid fading channels (snapshot assumption), the optimal estimator is shown to be divided into the two subtasks of maximum-likelihood acquisition and subsequent Wiener filtering of the acquired quantities. If perfect training sequences resulting in optimal performance are used, the Wiener filtering operation collapses into independent filtering of the individual acquired tap estimates, and the resulting channel estimator becomes efficient and flexible. The performance of the optimal estimator is evaluated for important cases. A design example of a near-optimal HF channel estimator/receiver is discussed. Linear interpolation is used to reduce the computational complexity of receiver coefficient adjustment. Simulation results confirm the superiority and robustness of feedforward synchronization having near-optimal performance at reduced complexity. > | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,344 |
We consider degenerate elliptic equations of the form where X i, j are defined with the Heisenberg vector fields, and the matrix coefficient is uniformly elliptic. We obtain an invariant Harnack's inequality on metric balls for nonnegative solutions under the additional assumption that the ratio between the maximum and minimum eigenvalues of the coefficient matrix is sufficiently close to one. In the paper we prove critical density and double ball estimates. Once this is established, Harnack follows directly from the results from [4]. | We consider second order linear degenerate-elliptic operators which are elliptic with respect to horizontal directions generating a stratified algebra of H-type. Extending a result by Guti\'errez and Tournier for the Heisenberg group, we prove a critical density estimate by assuming a condition of Cordes-Landis type. We then deduce an invariant Harnack inequality for the non-negative solutions from a result by Di Fazio, Guti\'errez, and Lanconelli. | In this work, we propose and investigate a new coding strategy devised to increase the throughput of hybrid ARQ (HARQ) transmission over block fading channel. In our proposition, the transmitter jointly encodes a variable number of bits for each round of HARQ. The parameters (rates) of this joint coding can vary and may be based on the negative acknowledgment (NACK) signals provided by the receiver or, on the past (outdated) information about the channel states. The results indicate that significant gains can be obtained using the proposed coding strategy especially where the conventional HARQ fails to offer throughput improvement even if the number of transmission rounds is increased. | eng_Latn | 5,345 |
This paper analyzes the effect of the insuffi- cient synchronization (carrier frequency offset, timing off- set) on hexagonal multicarrier transmission (HMT) systems for doubly dispersive channel. Exact SINR and demodu- lated symbol expressions for HMT systems in the presence of insufficient synchronization transmission conditions over doubly dispersive channel with exponential delay power profile and U-shape Doppler power spectrum and uniform delay power profile and uniform Doppler power spectrum are derived, respectively. Theoretical analysis shows that similar degradations on symbol amplitude and phase caused by insufficient synchronization are incurred as in traditional cyclic-prefix orthogonal frequency division multiplexing (CP-OFDM) transmission. HMT systems outperform tradi- tional OFDM systems with respect to signal to interference- plus-noise-ratio (SINR) against inter-symbol interference (ISI) and inter-carrier interference (ICI) caused by insuffi- cient synchronization and doubly dispersive(DD) channel. The BER performance of the HMT systems using Monte Carlo simulation match with the conclusion given by the proposed exact SINR expression. | This paper is concerned with various aspects of the characterization of randomly time-variant linear channels. At the outset it is demonstrated that time-varying linear channels (or filters) may be characterized in an interesting symmetrical manner in time and frequency variables by arranging system functions in (timefrequency) dual pairs. Following this a statistical characterization of randomly time-variant linear channels is carried out in terms of correlation functions for the various system functions. These results are specialized by considering three classes of practically interesting channels. These are the wide-sense stationary (WSS) channel, the uncorrelated scattering (US) channel, and the wide-sense stationary uncorrelated scattering (WSSUS) channel. The WSS and US channels are shown to be (time-frequency) duals. Previous discussions of channel correlation functions and their relationships have dealt exclusively with the WSSUS channel. The point of view presented here of dealing with the dually related system functions and starting with the unrestricted linear channels is considerably more general and places in proper perspective previous results on the WSSUS channel. Some attention is given to the problem of characterizing radio channels. A model called the Quasi-WSSUS channel is presented to model the behavior of such channels. All real-life channels and signals have an essentially finite number of degrees of freedom due to restrictions on time duration and bandwidth. This fact may be used to derive useful canonical channel models with the aid of sampling theorems and power series expansions. Several new canonical channel models are derived in this paper, some of which are dual to those of Kailath. | It is common practice to convert patients with acute respiratory insufficiency (ARI) from controlled mechanical ventilation to some form of assisted spontaneous breathing as early as possible. A widely used mode of assisted spontaneous breathing is patient-triggered inspiratory pressure support (IPS). We investigated 11 patients with ARI during weaning from mechanical ventilation using IPS and found that in 9 of these patients, desynchronization between patient and ventilator occurred, ie, that the ventilator did not detect and support all the patients' breathing efforts. Five of these 9 patients displayed severe desynchronization lasting at least 5 min and with less than half of all breathing efforts being supported by the ventilator. We present the analysis of gas flow, volume, esophageal pressure, airway pressure, and tracheal pressure of 1 patient with ARI displaying desynchronization under IPS. Our results imply that desynchronization can occur due to the following: (1) inspiratory response delays caused by the inspiratory triggering mechanisms and the demand flow characteristics of the ventilator; (2) a mismatch between the patient's completion of the inspiration effort and the ventilator's criterion for terminating pressure support; and (3) restriction of expiration due to resistance from patient's airways, endotracheal tube, and expiratory valve. From our analysis, we have made proposals for reducing desynchronization in clinical practice. | eng_Latn | 5,346 |
In wireless scenarios an effective protocol to increase the reliability for time-varying channels is the hybrid automatic repeat request (H-ARQ). The H-ARQ scheme with cross-packet channel coding (CPC) is a recently published extension of H-ARQ with several advantages. No full-diversity low-density parity-check (LDPC) code design for the whole range of coding rates yielding full-diversity has been published. In this paper the authors provide a new outage behavior analysis and a new structured LDPC code ensemble achieving full-diversity for H-ARQ with CPC by exploiting the rootcheck principle. Simulation results show that the new code design outperforms the previous approaches, providing full-diversity and good coding gain, also at high coding rates. | In this work, we propose and investigate a new coding strategy devised to increase the throughput of hybrid ARQ (HARQ) transmission over block fading channel. In our proposition, the transmitter jointly encodes a variable number of bits for each round of HARQ. The parameters (rates) of this joint coding can vary and may be based on the negative acknowledgment (NACK) signals provided by the receiver or, on the past (outdated) information about the channel states. The results indicate that significant gains can be obtained using the proposed coding strategy especially where the conventional HARQ fails to offer throughput improvement even if the number of transmission rounds is increased. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,347 |
In this paper, a novel fast CMA employing fast convolution in the DFT domain is proposed. It is similar to the FBLMS (frequency domain block LMS) which is used for the conventional linear adaptive filtering. However, the FBLMS can not be applied to the CMA, since the CMA has no reference signal and it should minimize the nonlinear cost function. Thus, in this paper, a new nonlinear adaptation rule minimizing the CMA cost function in the DFT domain is proposed. The computer simulation results reveal that the proposed algorithm shows comparable performance to the conventional CMA, while requiring much less computation. The multiplications required for the conventional CMA and the proposed algorithm are in the order of O(N/sup 2/) and O(NlogN), respectively. | Conventional equalization and carrier recovery algorithms for minimizing mean-square error in digital communication systems generally require an initial training period during which a known data sequence is transmitted and properly synchronized at the receiver. This paper solves the general problem of adaptive channel equalization without resorting to a known training sequence or to conditions of limited distortion. The criterion for equalizer adaptation is the minimization of a new class of nonconvex cost functions which are shown to characterize intersymbol interference independently of carrier phase and of the data symbol constellation used in the transmission system. Equalizer convergence does not require carrier recovery, so that carrier phase tracking can be carried out at the equalizer output in a decision-directed mode. The convergence properties of the self-recovering algorithms are analyzed mathematically and confirmed by computer simulation. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,348 |
Ever-increasing intra-datacenter traffic will spur the introduction of high-baud rates and high-order modulation formats. Increasing symbol rates and modulation levels decreases tolerance against transmission impairment that includes chromatic dispersion. Transmission distance in warehouse-scale datacenters can be several kilometers, and then management of chromatic dispersion is necessary. Dispersion-compensating fibers are widely deployed in backbone networks, however, applying them in datacenters is not cost-effective since wavelength channels are coarsely multiplexed. In digital coherent systems, signal distortion due to chromatic dispersion can be resolved in digital domain; however, it will take long time before coherent systems can be introduced in datacenter networks because of their high cost. In this paper, we propose a novel impairment mitigation method employing machine learning. The proposed method is effective even after non-coherent detection and hence it can be applied to cost-sensitive intra-datacenter networks. The machine learns optimum symbol-decision criteria from a sequence of dispersed training signals, and it discriminates payload signals in accordance with the established decision criteria. With the scheme, the received signals can be demodulated in the presence of large chromatic dispersion. The transmission distance thus can be extended without relying on costly optical dispersion compensation. Since information of transmission links is not a priori required, the proposed scheme can easily be applied to any datacenter network. We conduct transmission experiments using 400-Gbps channels each of which comprises 8-subcarrier 28-Gbaud 4-ary pulse-amplitude-modulation (PAM-4) signals, and confirm the effectiveness of the proposed scheme. | We demonstrated a support vector machine (SVM) based machine learning method to mitigate modulation nonlinearity distortion for PAM-4 and PAM-8 vertical cavity surface emitter laser multi-mode fiber (VCSEL-MMF) optical link. Simulations at 100 Gb/s data rate and experimental work at 60 Gb/s data rate were carried out. We achieved a significant improvement in bit error rate (BER) when complete binary tree SVMs (CBT-SVMs) are applied for both PAM-4 and PAM-8 signals. Quantitative analysis of the sensitivity gain versus modulation nonlinearity distortion is presented with experimentally verification. The results indicate that CBT-SVMs have better performance for PAM-8 compared to PAM-4. The sensitivity gain increases almost linearly with the increase of eye-linearity (increase of modulation nonlinearity distortion). Up to 2.5-dB sensitivity improvement is achieved by the proposed CBT-SVMs at eye-linearity of 1.72 for PAM-4. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,349 |
Matrix multiplication operations are heavily used in communication systems, video, signal and image processing applications such as echo cancellation, adaptive beamforming, and Multiple-Input Multiple-Output (MIMO) systems, and are also used in matrix factorizations such as Cholesky, LU, QR and DCT. However, it is challenging to implement a high speed matrix multiplication operator for large matrices due to the fact that the number of multiplication operations grows rapidly with functions of n3. This paper presents the implementation of a reconfigurable pipelined high speed and high precision matrix multiplication module designer for large matrices on Xilinx Virtex-5 and Spartan 3E FPGAs using high speed memory interface for data transfers. | We introduce a 64-bit ANSI/IEEE Std 754-1985 floating point design of a hardware matrix multiplier optimized for FPGA implementations. A general block matrix multiplication algorithm, applicable for an arbitrary matrix size is proposed. The algorithm potentially enables optimum performance by exploiting the data locality and reusability incurred by the general matrix multiplication scheme and considering the limitations of the I/O bandwidth and the local storage volume. We implement a scalable linear array of processing elements (PE) supporting the proposed algorithm in the Xilinx Virtex II Pro technology. Synthesis results confirm a superior performance-area ratio compared to related recent works. Assuming the same FPGA chip, the same amount of local memory, and the same I/O bandwidth, our design outperforms related proposals by at least 1.7X and up to 18X consuming the least reconfigurable resources. A total of 39 PEs can be integrated into the xc2vp125-7 FPGA, reaching performance of, e.g., 15.6 GFLOPS with 1600 KB local memory and 400 MB/s external memory bandwidth. | Massive multiple-input multiple-output (MIMO) wireless communications refers to the idea equipping cellular base stations (BSs) with a very large number of antennas, and has been shown to potentially allow for orders of magnitude improvement in spectral and energy efficiency using relatively simple (linear) processing. In this paper, we present a comprehensive overview of state-of-the-art research on the topic, which has recently attracted considerable attention. We begin with an information theoretic analysis to illustrate the conjectured advantages of massive MIMO, and then we address implementation issues related to channel estimation, detection and precoding schemes. We particularly focus on the potential impact of pilot contamination caused by the use of non-orthogonal pilot sequences by users in adjacent cells. We also analyze the energy efficiency achieved by massive MIMO systems, and demonstrate how the degrees of freedom provided by massive MIMO systems enable efficient single-carrier transmission. Finally, the challenges and opportunities associated with implementing massive MIMO in future wireless communications systems are discussed. | eng_Latn | 5,350 |
In this paper, we propose a method for the reconstruction of a complex discrete-valued vector from its linear measurements. In particular, we mainly focus on the underdetermined cases, where the number of measurements is less than that of the unknown complex discrete variables, and propose a reconstruction approach of solving an optimization problem called sum of complex sparse regularizers (SCSR) optimization. The sum of sparse regularizers in the objective function can directly utilize the discrete nature of the unknown vector in the complex domain. We also propose an algorithm for the SCSR optimization problem on the basis of alternating direction method of multipliers. For the proposed convex regularizers, we analytically prove that the sequence obtained by the proposed algorithm converges to the optimal solution of the problem. To obtain better reconstruction performance, we further propose an iterative approach named iterative weighted SCSR (IW-SCSR), where we update the parameters in the objective function in each iteration by using the tentative estimate in the previous iteration. Simulation results show that IW-SCSR can reconstruct the complex discrete-valued vector from its underdetermined linear measurements and achieve good performance in the applications of overloaded multiple-input multiple-output signal detection and channel equalization. | Massive multiple-input multiple-output (MIMO) wireless communications refers to the idea equipping cellular base stations (BSs) with a very large number of antennas, and has been shown to potentially allow for orders of magnitude improvement in spectral and energy efficiency using relatively simple (linear) processing. In this paper, we present a comprehensive overview of state-of-the-art research on the topic, which has recently attracted considerable attention. We begin with an information theoretic analysis to illustrate the conjectured advantages of massive MIMO, and then we address implementation issues related to channel estimation, detection and precoding schemes. We particularly focus on the potential impact of pilot contamination caused by the use of non-orthogonal pilot sequences by users in adjacent cells. We also analyze the energy efficiency achieved by massive MIMO systems, and demonstrate how the degrees of freedom provided by massive MIMO systems enable efficient single-carrier transmission. Finally, the challenges and opportunities associated with implementing massive MIMO in future wireless communications systems are discussed. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,351 |
Interferences of various kinds are of a major concern in communication system design and operation, since they could cause serious system performance deterioration. As the demand on communication resources, such as frequency spectrum, increases steadily, the desire for a more effective signal processing techniques for interference suppression resulting in efficient usage of resources becomes more important. This paper presents the results of a survey conducted on signal processing techniques and adaptive antenna arrays used for interference suppression applications. The interference types considered in this paper are jamming, adjacent channel interference (ACI), co-channel interference (CCI) and multi-access interference (MAI), and inter-symbol interference (ISI). A preliminary assessment of the impact of signal processing trends on the power spectral density, bandwidth, and spectrum packing efficiency is also presented in the paper. | Use of multiple antennas at the transmitter and the receiver to increase the information capacity has received considerable attention. To exploit the capability of such systems in a practical way, it is of interest to ask if there are good codes with reasonable decoding complexity. Another question of interest is the simplicity of design. This issue is particularly important in the case where the number of antennas in transmitter and receiver are large and a space-time code may be to complex to design and decode. We illustrate a class of codes which are simpler to design and the interference across antennas is suppressed by linear processing at the receiver. The performance of such codes is excellent and much better than the group interference suppression techniques employed in conjunction with the space-time codes. Use of error detection schemes is shown to further improve the performance without much change in the design of codes and decoding complexity. | It is beyond controversy that in bimanual coordination tasks, parameter planning related to the movements of one hand influences the planning and execution of movements simultaneously performed with the other hand. A well-researched example of such bimanual interference is the finding that reaction times tend to be longer when preparing bimanual pointing movements with different amplitudes than for equal amplitude movements. Interestingly, these reaction time costs were found to increase when movement targets were cued symbolically (e.g., using letters) as compared to spatially. Therefore, it was suggested that interference may be primarily related to cue translation and response selection processes rather than resulting from cross-talk at the motor programming level. Here, we argue that spatial interference effects do not necessarily depend on the type of cues used but instead depend on the general task demands (difficulty). In two experiments we show that bimanual interference effects can (1) be abolished in symbolic cueing conditions when highly compatible cues placing minimal demands on response selection processes are used and (2) occur in direct/spatial cueing conditions when a secondary cognitively demanding, but movement-unrelated task is performed. Thus, our findings suggest that whether or not interference effects emerge during movement planning depends on the overall task difficulty and hence the resources available during movement preparation. | eng_Latn | 5,352 |
A model suitable for analyzing the nonlinear interaction between signal and noise, mediated by the Kerr effect in optical communication systems, is presented. This model treats separately signal and noise and permits analysis of the symbols' central time position and frequency evolution. It is shown that this nonlinear interaction between signal and noise leads to symbols' random frequency shifts, which induce timing jitter in all types of systems. We also discuss the problem of estimating timing jitter for a signal embedded in noise. | Using a recirculating loop, we measured nonlinearly induced timing jitter in a terrestrial wavelength-division-multiplexed system at different transmission distances with different amounts of precompensation. Within each 600-GHz subband, we achieved error-free transmission using the same amount of precompensation for all channels at all distances up to 5000 km. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,353 |
This paper analyzes cross-polarization cancellation in dual-polarization digital radio links transmitting M-ary quadrature amplitude-modulation (M-QAM) signals. We consider the use of three options in the receiver: (1) no cancellation; (2) ideal (i.e., total) cancellation; and (3) optimal nondispersive cancellation. For every option, we assume the canceler to be followed, in each polarization branch, by an ideal minimum mean-square error equalizer. By postulating a statistical model for the co-polarization and cross-polarization responses of a digital radio channel, and then simulating thousands of sets of these responses, we obtain curves that relate outage probability to the number of modulation levels. We show graphically that the no-canceler case is unthinkable; that total cancellation permits results close to those for single-polarization transmission; and that optimal nondispersive cancellation can have a limited range of application. We also examine the effects of key system parameters and the various modeling assumptions. | Recent analysis/simulation studies have quantified the multipath outage statistics of digital radio systems using ideal adaptive equalization. In this paper, we consider the use of finite-tap delay line equalizers, with the aim of determining how many taps are needed to approximate ideal performance. To this end, we assume an M -level QAM system using cosine rolloff spectral shaping and an adaptive equalizer with either fractionally spaced or synchronously spaced taps. We invoke a widely used statistical model for the fading channel and computer-simulate thousands of responses from its ensemble. For each trial, we compute a detection signal-to-distortion measure, suitably maximized with respect to the tap gains. We can thereby obtain probability distributions of this measure for specified combinations of system parameters. These distributions, in turn, can be interpreted as outage probabilities (or outage seconds) versus the number of modulation levels. A major finding of this study is that, for the assumed multipath fading model, very few taps (the order of five) are needed to approximate the performance of an ideal infinite-tap equalizer. We also find that a simple, suboptimal form of timing recovery is generally quite adequate, and that fractionally spaced equalizers are more advantageous than synchronously spaced equalizers with the same number of taps. This advantage is minor for rolloff factors of 0.5 and larger but increases dramatically as the rolloff factor approaches zero. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,354 |
With the rapid development of communication technology, the demand of rate of communication network is higher and higher, and the problem of energy consumption is becoming more and more serious. Data and Energy Integrated communication Networks (DEINs) can simultaneously transmit information and energy for the terminal, which greatly improves the convenience of the terminal and makes devices without batteries possible in future. This paper studies the joint design of transceivers in a full-duplex cloud access number-integrated network. The system model considers both upstream and downstream users. Considering the need for joint resource allocation for system uplink and downlink, full-duplex technology and self-interference caused by full-duplex technology are considered into the system. The optimization goal of this problem is to minimize the total power consumption under the uplink and downlink SINR and EH constraints. For this non-convex optimization problem, An algorithm combining ZF beamforming and MRT beamforming is proposed. In the hybrid beamforming algorithm, the zero-forcing (ZF) beamformer and MRT beamformer are linearly combined, which simplifies the optimization of the downlink beam vector to the optimization of the combination ratio. The proposed algorithm is simulated. Simulation results show that the power consumed in the half-duplex scenario is higher than that in the full duplex scenario. The time spent in the hybrid beamforming algorithm does not change with the increase in the number of RRH antennas. | In this paper, we propose a power-efficient approach for information and energy transfer in multiple-input single-output downlink systems. By means of data-aided precoding, we exploit the constructive part of interference for both information decoding and wireless power transfer. Rather than suppressing interference as in conventional schemes, we take advantage of constructive interference among users, inherent in the downlink, as a source of both useful information signal energy and electrical wireless energy . Specifically, we propose a new precoding design that minimizes the transmit power while guaranteeing the quality of service (QoS) and energy harvesting constraints for generic phase shift keying modulated signals. The QoS constraints are modified to accommodate constructive interference, based on the constructive regions in the signal constellation. Although the resulting problem is nonconvex, several methods are developed for its solution. First, we derive necessary and sufficient conditions for the feasibility of the considered problem. Then we propose second-order cone programming and semi-definite programming algorithms with polynomial complexity that provide upper and lower bounds to the optimal solution and establish the asymptotic optimality of these algorithms when the modulation order and SINR threshold tend to infinity. A practical iterative algorithm is also proposed based on successive linear approximation of the nonconvex terms yielding excellent results. More complex algorithms are also proposed to provide tight upper and lower bounds for benchmarking purposes. Simulation results show significant power savings with the proposed data-aided precoding approach compared to the conventional precoding scheme. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,355 |
The nonlinear behavior of power amplifier (PA) in orthogonal frequency-division multiplexing (OFDM)-based cogni- tive radio (CR) system introduces in-band and adjacent channel interferences. The power in the adjacent channels is an important issue in the CR because it can act as interference to primary users. In this paper, we derive a closed-form expression for the leakage power at adjacent channels when CR devices use OFDM modulation. Moreover, the PA nonlinearity creates in-band dis- tortion that produces intercarrier interference and reduces the secondary system capacity. To control this effect, we derive the optimum power scaling factor for the input signal that maximizes the secondary user rate. The optimization process is executed by considering nonlinear effects on signal-to-interference-and-noise ratio under the constraints of the powers in the adjacent channels. The power in the adjacent channels should not exceed the inter- ference temperature limit. The analytical results are verified by simulation studies. | In this paper, we investigate an optimal power loading algorithm for an OFDM-based cognitive radio (CR) system. The downlink transmission capacity of the CR user is thereby maximized, while the interference introduced to the primary user (PU) remains within a tolerable range. We also propose two suboptimal loading algorithms that are less complex. We also study the effect of a subcarrier nulling mechanism on the performance of the different algorithms under consideration. The performance of the optimal and suboptimal schemes is compared with the performance of the classical power loading algorithms, e.g., water-filling and uniform power but variable rate loading schemes that are used for conventional OFDM-based systems. Presented numerical results show that for a given interference threshold, the proposed optimal scheme allows CR base station (BS) to transmit more power in order to achieve a higher transmission rate than the classical loading algorithms. These results also show that although the proposed suboptimal schemes have certain degradation in performance compared to the optimal scheme, they outperform the classical loading algorithms. We also present numerical results for nulling mechanism. Finally, we investigate the effect of imperfect channel gain information at the transmitter. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,356 |
Channel noise in modern perpendicular channels is well approximated by a linear jitter model. In this paper, we propose a new type of Viterbi detector matched to such a channel model. The differentiating feature of this detector is recursive evaluation of whitened noise strengths for survivor paths using the on-the-fly Cholesky factorization of path-dependent correlation matrices. We study the performance of the detector using the simplest example of low-density channels with intersymbol interference length equal to three. We find that at BER = 10-4, the new detector outperforms the data-dependent AR-detector of the comparable complexity by about 0.9 dB. | The authors delayed-decision-feedback sequence estimation (DDFSE) for uncoded PAM signals is considered. Estimates on the performance of the algorithm are given, and simulation results are provided for several examples. A more general form of DDFSE applicable to coded modulation systems is also presented. As an example, detection of trellis-coded QPSK (quadrature phase-shift keyed) signals over intersymbol interference channels is discussed. > | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,357 |
In this work we consider the uplink of an OFDMA system and present a novel receiver that performs joint frequency offset acquisition, channel estimation and data detection for each active user. The proposed receiver can be used with any subcarrier assignment scheme, and it operates in an iterative fashion. Users' separation is accomplished at the base station through space-alternating generalized-expectation (SAGE) techniques. Each separated user's signal is then passed to an expectation-conditional maximization (ECM)-based processor that jointly performs frequency acquisition, channel estimation and data detection at each iteration. Compared to conventional OFDMA systems, the proposed receiver allows significant reduction of the synchronization overhead as it dispenses from the need of returning estimated frequency offsets back to active users for frequency adjustment. Simulations indicate that the proposed scheme provides accurate data detection for unsynchronized OFDMA uplink transmissions over doubly-selective fading channels | Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,358 |
This paper provides an overview on the rationales in incorporating massive multiple-input multiple-output (MIMO), non-orthogonal multiple access (NOMA), and interleave division multiple access (IDMA) in a unified framework. Our emphasis is on multi-user gain that refers to the advantage of allowing multi-user transmission in massive MIMO. Such a gain can potentially offer tens or even hundreds of times of rate increase. The main difficulty in achieving multi-user gain is the reliance on accurate channel state information (CSI) in the existing schemes. With accurate CSI, both OMA and NOMA can deliver performance not far away from capacity. Without accurate CSI, however, most of the existing schemes do not work well. We outline a solution to this difficulty based on IDMA and iterative data-aided channel estimation (DACE). This scheme can offer very high throughput and is robust against the pilot contamination problem. The receiver cost is low, since only maximum ratio combining (MRC) is involved and there is no matrix inversion or decomposition. Under time division duplex, accurate CSI acquired in the up-link can be used to support low-cost down-link solutions, such as zero forcing. These findings offer useful design considerations for future systems. | This paper considers uplink massive multiple-input multiple-output (MIMO) systems with lowresolution analog-to-digital converters (ADCs) over Rician fading channels. Maximum-ratio-combining (MRC) and zero-forcing (ZF) receivers are considered under the assumption of perfect and imperfect channel state information (CSI). Low-resolution ADCs are considered for both data detection and channel estimation, and the resulting performance is analyzed. Asymptotic approximations of the spectrum efficiency (SE) for large systems are derived based on random matrix theory. With these results, we can provide insights into the trade-offs between the SE and the ADC resolution and study the influence of the Rician K-factors on the performance. It is shown that a large value of K-factors may lead to better performance and alleviate the influence of quantization noise on channel estimation. Moreover, we investigate the power scaling laws for both receivers under imperfect CSI and it shows that when the number of base station (BS) antennas is very large, without loss of SE performance, the transmission power can be scaled by the number of BS antennas for both receivers while the overall performance is limited by the resolution of ADCs. The asymptotic analysis is validated by numerical results. Besides, it is also shown that the SE gap between the two receivers is narrowed down when the K-factor is increased. We also show that ADCs with moderate resolutions lead to better energy efficiency (EE) than that with high-resolution or extremely low-resolution ADCs and using ZF receivers achieve higher EE as compared with the MRC receivers. | Impaired gastric motility ascribable to a defective nitric oxide (NO) production has been reported in dystrophic (mdx) mice. Since relaxin upregulates NO biosynthesis, its effects on the motor resp... | eng_Latn | 5,359 |
Large array size real time direction finding systems like phased array radars require very fast processing of signals. With subspace based array signal processing like MUltipleSIgnalClassification (MUSIC) algorithm high accuracy and resolution can be achieved if the data collection time is sufficiently large or the Signal to Noise Ratio (SNR) is adequately high. However high computational complexity of search based MUSIC algorithm prohibits its use for large arrays. Root MUSIC was proposed to reduce the computational complexity of search based MUSIC algorithm. It avoids the search in MUSIC by polynomial rooting to estimate Direction of Arrival (DOA). However the computational complexity of polynomial roots finding is still high for large array size real time systems. For large arrays, we propose to use Discrete Fourier Transform (DFT) based MUSIC algorithm where the polynomial rooting in root MUSIC is replaced with DFT, which can be computed efficiently with Fast Fourier Transforms (FFT). The Hierarchical Pruned FFT (HPFFT) based method in this paper, further reduces the computational complexity for large array size. Adaptive techniques are chosen for subspace estimation which require much lesser computations compared to Eigen Value Decomposition (EVD) based methods. It is proposed that low complexity hierarchical pruned FFT based MUSIC algorithm combined with adaptive subspace estimation, can be used for large array based DOA estimation. Simulation results for rectangular array are presented to compare the complexity and performance of root MUSIC, DFT MUSIC and HPFFT MUSIC. | The number of digits it takes to write down an observed sequence x"1, ..., x"N of a time series depends on the model with its parameters that one assumes to have generated the observed data. Accordingly, by finding the model which minimizes the description length one obtains estimates of both the integer-valued structure parameters and the real-valued system parameters. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,360 |
In this paper, an efficient implementation of the Chase II soft-input/soft-output (SISO) decoder using the distance-based decoding algorithm is proposed, where a piece-wise-linear based method is proposed to simplify the calculation of the extrinsic values. As a demonstration, a (64; 51; 6)2 block turbo decoder is implemented. Compared to the DBD-based decoder presented in the previous literature, the proposed decoder achieves a higher throughput and a higher efficiency. | This article presents an innovative turbo product code (TPC) decoder architecture without any interleaving resource. This architecture includes a full-parallel SISO decoder able to process n symbols in one clock period. Syntheses show the better efficiency of such an architecture compared with existing previous solutions. Considering a 6-iteration turbo decoder of a (32,26)2 BCH product code, synthetized in a 90 nm CMOS technology, the resulting information throughput is 2.5 Gb/s with an area of 233 Kgates. Finally a second architecture enhancing parallelism rate is described. The information throughput is 33.7 Gb/s while an area estimation gives A=10 mum2. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,361 |
"Detection" in the title of this paper is used in the sense of decision-making, rather than demodulation. The ideal communication rate for a physical channel is provided by Shannon's formula C \leq W \log(1 + P/N) , and for a binary symmetric channel the theoretical amount of information per digit is I = 1 + p log p + q log q , where p is probability of error per digit and p + q = 1 . Various error-correcting codes are compared with the second formula. It is shown that correlation-detection is equivalent to minimum-distance detection provided all code groups are of equal mean power, and that a binary-coded signal can always be adjusted to the constant-power state. Experimental results are reported on error reduction in a two-out-of-five code by the use of correlation detection. It is noted that square-law detection would be inferior to linear detection in such a system. | In this paper, we propose and discuss the challenges of a novel method for securing the readings of smart electricity meters against tampering or malfunctioning. We apply the idea of linear error-correcting block codes, which has originally been used in detecting and correcting errors in data transmission, to detect and correct customer attacks aimed at changing the readings of smart electricity meters. We propose to use these codes, with some modifications, in order to detect and correct deceptive readings of a group of electricity meters measuring the energy delivered by cables\feeders fed from the same node\bus. We start by considering a single meter attack, and we show that the detection and correction of a single attack in the readings of ${ 2}^{ M}{ -}{ M}{ -}{ 1}$ meters, connected to cables fed from the same node, requires only using ${M}$ current transformers in addition to knowing the voltage at the common node. We demonstrate the theoretical implementation of this coding scheme, and then we discuss some practical challenges and their proposed solutions. Furthermore, extension to multi-error correcting codes, which are capable of detecting and correcting several simultaneous deceptive readings of a group of meters, is also discussed. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,362 |
We describe a parallel algorithm for finding the eigenvalues and eigenvectors of a dense symmetric matrix. We follow the traditional three step process: we reduce the dense matrix to tridiagonal form, solve the tridiagonal problem then backtransform the result. Since the different steps have different algorithmic characteristics, this problem serves as an perfect vehicle for exploring some issues associated with parallel linear algebra calculations, In particular we examine the effects of matrix distribution and blocking on the computational performance of tridiagonalization and backtransformation. Through experiments on an Intel Paragon, we demonstrate that block storage of the matrix is not necessary for a highly efficient block algorithm. We compare the performance of our implementations to that of the corresponding ScaLapack routines. | Dense linear systems of equations are quite common in science and engineering, arising in boundary element methods, least squares problems, and other settings. Massively parallel computers will be necessary to solve the large systems required by scientists and engineers, and scalable parallel algorithms for the linear algebra applications must be devised for these machines. A critical step in these algorithms is the mapping of matrix elements to processors. In this paper, the use of the torus-wrap mapping in general dense matrix algorithms is studied from both theoretical and practical viewpoints. Under reasonable assumptions, it is proved that this assignment scheme leads to dense matrix algorithms that achieve (to within a constant factor) the lower bound on interprocessor communication. It is also shown that the torus-wrap mapping allows algorithms to exhibit less idle time, better load balancing, and less memory overhead than the more common row and column mappings. Finally, practical implementation i... | Information-theoretic security guarantees that a message is kept secret from potential eavesdroppers regardless of their current or future computational abilities. But current information-theoretic security approaches generally rely on an advantage of the channel of the desired recipient over the adversary, and such an advantage can be difficult to guarantee in a wireless network where an eavesdropper might be very near the transmitter. This paper initiates an approach to everlasting security for wireless communication links by exploiting a fundamental concept from systems theory: that nonlinear systems are not (necessarily) commutative. This property is exploited by employing a short-term cryptographic key to force the eavesdropper's signal to be subjected to nonlinear operations in the reverse order of that of the signal at the desired recipient. After introducing the idea and providing analysis for the general case, we next consider a simple (and practical) instantiation where the transmitter uses the ephemeral cryptographic key to rapidly power modulate the transmitted signal. Secrecy rates with this rapid power modulation under various assumptions establish the promise of the approach, even in the case of an eavesdropper with uniformly better conditions (channel and receiver quality) than the intended recipient. | eng_Latn | 5,363 |
Cooperative diversity using distributed space-time codes has been recently proposed to form virtual antennas in order to achieve diversity gain. In this paper, we propose a distributed space-time coding with amplify-and-forward relaying. Motivated by protocol (III) presented in [1], we propose a distributed space-time code for an arbitrary number of relay nodes. The pairwise error probability is derived and the theory analysis demonstrates that our protocol achieves a diversity of order where is the number of relay nodes. Quasi-orthogonal space-time codes are used as they give much better performance than random linear-dispersion codes. As the transmission power of the source node is a critical parameter in this protocol because it transmits in both phases, the optimal power allocation is derived using numerical and theoretical analysis. Simulation results demonstrate an improvement over the existing orthogonal protocols for different source-destination channel conditions. | We propose the use of simple full inter-relay self interference cancellation (FSIC) at the relay nodes within a four relay network. The four single antenna relay nodes are arranged as two spatially well separated groups of two relays with offset transmission scheduling. This approach can achieve the full available distributed diversity order and its end-to-end transmission rate can asymptotically approach one when the number of samples is large. Pairwise error probability analysis is used to confirm the available diversity and simulation studies are employed to verify the end-to-end bit error rate (BER) as a function of the level of inter-relay interference. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,364 |
A new algorithm for adapting the coefficients of an equalizer for continuous phase modulated data signals in a flat-fading environment is presented. The cost function to optimize is based on the maximum likelihood sequence estimation index for such signals and channel conditions. It is shown that this equalizer algorithm, called the maximum likelihood equalizer, involves the iterative computation of one of the eigenvectors of a matrix. An implementation is proposed, which combines iterative estimation procedures for QR decomposition, matrix eigenvalue tracking and channel prediction error. Simulation results are presented that demonstrate the ability of the algorithm to equalize the channel filtering effects in a fast fading environment, without requiring phase coherent carrier recovery. > | An optimization criterion for inverse filtering (equalization) of signals transmitted over a Rayleigh flat-fading channel is presented. This criterion is based on the maximization of the ratio of the equalizer output power to the combined power of the intersymbol interference and the noise present at this output. A method to isolate and compute the power of a function of the joint interference signals is presented. This algorithm makes use of the signal innovations concept, in decorrelating a version of the received faded signal to produce the interference estimate. It does not require carrier phase recovery, as do conventional equalization algorithms, and it is relatively insensitive to a multiplicative process imposed on the transmitted signal. This fact allows the algorithm to be very effective in fast flat-fading or severe phase noise conditions. Simulations results are presented to show the performance of this approach. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,365 |
In this paper, we propose an method which is optimizing length of the equalizer taps using genetic algorithm (GA). The equalizer is a decision feedback equalizer (DFE). Feed-forward filter length and feed-back filter length are regarded as genetic information in GA. The GA uses different random cross-over methods. It finds out the optimized DFE tap length for low bit error rate BER. There are two methods for BER calculation in the object function of GA; first, it is to use all data of preamble and payload in order to calculating BER; second, it is merely to use preamble data for communication. | As real world communication channels are stressed with higher data rates, intersymbol interference (ISI) becomes a dominant limiting factor. One way to combat this effect that has recently received considerable attention is the use of a decision feedback equalizer (DFE) in the receiver. The action of the DFE is to feed back a weighted sum of past decision to cancel the ISI they cause in the present signaling interval. This paper summarizes the work in this area beginning with the linear equalizer. Three performance criteria have been used to derive optimum systems; 1) minimize the noise variance under a "zero forcing" (ZF) constraint i.e., insist that all intersymbol interference is cancelled, 2) minimize the mean-square error (MMSE) between the true sample and the observed signal just prior to the decision threshold, and 3) minimize the probability of error (Min P e ). The transmitter can be fixed and the receiver optimized or one can obtain the joint optimum transmitter and receiver. The number of past decisions used in the feedback equalization can be finite or infinite. The infinite case is easier to handle analytically. In addition to reviewing the work done in the area, we show that the linear equalizer is in fact a portion of the DFE receiver and that the processing done by the DFE is exactly equivalent to the general problem of linear prediction. Other similarities in the various system structures are also shown. The effect of error propagation due to incorrect decisions is discussed, and the coaxial cable channel is used as an example to demonstrate the improvement available using DFE. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,366 |
The concept of solitons has been successfully utilized in optical communications to handle signal distortion. In this light, the present work explores modulation using soliton carriers and subsequently, prototype wireless communication system based on Orthogonal Frequency Division Mutiplexing (OFDM) and Code Division Multiplexing (CDMA) at 11GHz involving Additive White Gaussian Noise Channel is implemented using LabVIEW. The performance of Soliton carriers are compared with sinusoidal counterparts using eye diagrams. The low distortion values observed for solitons form the novelty of the present work. ( | (NOTE: Most chapters begin with an Introduction and conclude with Summary, References, and Problems.) 1. Introduction to Digital Data Transmission. Components of a Digital Communication System. Communications Channel Modeling. Communication Link Power Calculations. Driving Forces in Communications. Computer Use in Communication System Analysis and Design. Preview of the Book. 2. Signals, Systems, Modulation, and Noise: Overview. Review of Signal and Linear System Theory. Basic Analog Modulation Techniques. Complex Envelope Representation of Bandpass Signals and Systems. Signal Distortion and Filtering. Practical Filter Types and Characteristics. Sampling Theory. Random Processes. Computer Generation of Random Variables. 3. Basic Digital Communication Systems. The Binary Digital Communications Problem. Signaling through Bandlimited Channels. Equalization in Digital Data Transmission. A Digital Communication System Simulation Example. Noise Effects in Pulse Code Modulation. 4. Signal-Space Methods in Digital Data Transmission. Optimum Receiver Principals in Terms of Vector Spaces. Performance Analysis of Coherent Digital Signaling Schemes. Signaling Schemes Not Requiring Coherent References at the Receiver. Comparison of Digital Modulation Systems. Comparison of M-ary Digital Modulation Schemes on Power and Bandwidth-Equivalent Bases. Some Commonly Used Modulation Schemes. Design Examples and System Tradeoffs. Multi-h Continuous Phase Modulation. Orthogonal Frequency Division Multiplexing. 5. Channel Degradations in Digital Communications. Synchronization in Communication Systems. The Effects of Slow Signal Fading in Communicative Systems. Diagnostic Tools for Communication System Design. 6. Fundamentals of Information Theory and Block Coding. Basic Concepts of Information Theory. Fundamentals of Block Coding. Coding Performance in Slow Fading Channels. 7. Fundamentals of Convolutional Coding. Basic Concepts. The Viterbi Algorithm. Good Convolutional Codes and Their Performance. Other Topics. 8. Fundamentals of Repeat Request Systems. General Considerations. Three ARQ Strategies. Codes for Error Detection. 9. Spread-Spectrum Systems. Two Communication Problems. Types of Spread-Spectrum Systems. Complex-Envelope Representation of Spread Spectrum. Generation and Properties of Pseudorandom Sequences. Synchronization of Spread-Spectrum Systems. Performance of Spread-Spectrum Systems in Jamming Environments. Performance in Multiple User Environments. Multiuser Detection. Examples of Spread-Spectrum Systems. 10. Introduction to Cellular Radio Communications. Frequency Reuse. Channel Models. Mitigation Techniques for the Multipath Fading Channel. System Design and Performance Prediction. Advanced Mobile Phone Service. Global System for Mobile Communications. Code Division Multiple Access. Recommended Further Reading. 11. Satellite Communications. Allocation of a Satellite Transmission Resource. Link Power Budget Analysis. Examples of Link Power Budget Calculations. Low- and Medium-Earth Orbit Voice Messaging Satellite Systems. Appendix A. Probability and Random Variables, Probability Theory. Random Variables, Probability Density Functions, and Averages. Characteristic Function and Probability Generating Function. Transformations of Random Variables. Central Limit Theorem. Appendix B. Characterization of Internally Generated Noise. Appendix C. Attenuation of Radio-Wave Propagation by Atmospheric Gases and Rain. Appendix D. Generation of Coherent References. Description of Phase Noise and Its Properties. Phase-Lock Loop Models and Characteristics of Operation. Frequency Synthesis. Appendix E. Gaussian Probability Function. Appendix F. Mathematical Tables. The Sinc Function. Trigonometric Identities. Indefinite Integrals. Definite Integrals. Series Expansions. Fourier Transform Theorems. Fourier Transform Pairs. Index. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,367 |
We propose an estimator for the Ricean K-factor which has applications in mobile communication systems. The estimator is based on the statistics of the instantaneous frequency (IF) of the received signal. Using simulations, we show that the proposed estimator is robust to shadowing and its mean-square error (MSE) is significantly lower than that of the envelope-based estimators. | In this paper, we investigate a downlink transmission algorithm for single-cell multiuser systems with two-dimensional (2-D) large-scale antenna array at the base station (BS) over Rician fading channels. We first derive some properties of the channel’s line-of-sight (LOS) component in the large-scale antenna array scenario. Next, based on these properties and under the assumption of only statistical channel state information (CSI), i.e., the LOS component and Rician $K$ -factor, at the BS, we derive the optimal beamforming vector for each user in maximizing an approximation of the ergodic sum rate. The main guidelines for user scheduling are also presented. Then, a three-dimensional (3-D) beamforming downlink transmission algorithm exploiting only the statistical CSI of each user is proposed. For this algorithm, we derive an exact analytical closed-form expression for the achievable ergodic rate and present tractable approximations. Based on our analysis, we gain some valuable insights. The proposed algorithm is shown to perform well in achieving considerable sum rate while requiring much less CSI at the BS. It requires three scalar values at the BS for each user, and can achieve an ergodic sum rate closer to the ergodic sum rate achieved by the matched-filter precoding with perfect CSI at the BS. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,368 |
One of the key advantages for the time-division duplex (TDD) system is the capability to deliver asymmetric traffic services by allocating different numbers of uplink and downlink time slots. However, in a TDD/code-division multiple-access (CDMA) system, asymmetric traffic may result in severe opposite-direction interference because downlink transmitted signals from neighboring base stations may interfere with the uplink received signals of the home cell. In this paper, we investigate the effect of four-antenna beamforming schemes from the perspective of suppressing the opposite-direction interference. We compare the uplink bit energy-to-interference density ratio of a traditional beam-steering technique (Scheme I) with that of the minimum-variance distortionless-response (MVDR) beamformer (Scheme II). Furthermore, Scheme III applies the conventional beam-steering technique for both downlink transmissions and the uplink reception. In Scheme IV, we implement beam-steering for downlink transmissions, while adopting the MVDR beamformer to process the uplink signals received at base stations. Our numerical results indicate that Scheme IV outperforms all the other three schemes, which can effectively suppress the strong opposite-direction interference in TDD/CDMA systems. While keeping low implementation costs in mind, employing the simpler Scheme III in a sectorized cellular system can also allow every cell to provide different rates of asymmetric traffic services. | This second edition is an extensive modernization of the bestselling introduction to the subject of adaptive array sensor systems. With the number of applications of adaptive array sensor systems growing each year, this look at the principles and fundamental techniques that are critical to these systems is more important than ever before. Introduction to Adaptive Arrays, 2nd Edition is organized as a tutorial, taking the reader by the hand and leading them through the maze of jargon that often surrounds this highly technical subject. It is easy to read and easy to follow, as fundamental concepts are introduced with examples before more current developments and techniques are introduced. Problems at the end of each chapter serve both instructors and professional readers by illustrating and extending the material presented in the text. Both students and practicing engineers will easily gain familiarity with the modern contribution that adaptive arrays have to offer practical signal reception systems. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,369 |
Modern automobiles comprise more and more radio systems and sensors, e.g. communication systems for LTE, systems based on the IEEE 802.11p standard, or radar sensors. Vehicle-to-vehicle and vehicle-to-infrastructure (vehicle-to-X) communications will play an important role to reduce accidents and also to improve traffic flow. Mobile ad-hoc as well as cellular communications via base stations might be established in order to connect traffic participants. Due to the tremendous amount of coexisting radio systems and users, vehicle-to-X systems need to be tested extensively for reliability and interoperability in various traffic situations and for different radio channel conditions. In order to minimize expensive and time-consuming test drives, current research focuses on testing automotive wireless systems under reproducible laboratory conditions, by emulating realistic propagation channels in virtual electromagnetic environments over-the-air. This paper proposes an experimental approach to emulate spatial channel properties for a MIMO setup with two LTE receive antennas for cellular vehicle-to-X applications. In view of the multipath propagation, the spatial correlation of received signals is the figure-of-merit, especially for MIMO transmission schemes. A concept for the measurement of spatial correlation is proposed, based on the transmission parameters between any pair of transmit and receive antennas. Measurements are performed in the virtual road simulation and test area of the Thuringian Center of Innovation in Mobility in the frequency range from 1700 MHz to 2700 MHz. The measured data are compared to numerical computations and partially good agreement is found. | Multiple-input multiple-output (MIMO) over-the-air (OTA) testing is a standardized procedure to evaluate the performance of MIMO-capable devices such as mobile phones and laptops. With the growth of the vehicle-to-everything (V2X) service, the need for vehicular communication testing is expected to increase significantly. The so-called multi-probe anechoic chamber (MPAC) setup is standardized for MIMO OTA testing. Typically, a test zone of 0.85 wavelength in diameter can be achieved with an 8-probe MPAC setup, which can encompass device-under-test (DUT) of small form factors. However, a test zone of this size may not be large enough to encompass DUTs such as cars. In this article, the sufficient number of OTA probes for the MPAC setup for car testing is investigated with respect to the emulation accuracy. Our investigation shows that the effective antenna distance of the DUT is more critical than its physical dimensions to determine the required number of OTA probes. In addition, throughput measurements are performed under the standard SCME UMa and UMi channel models with the 8-probe MPAC setup and the wireless cable setup, i.e. another standardized testing setup. The results show reasonably good agreement between the two setups for MIMO OTA testing with cars under the standard channel models. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,370 |
In this paper, we study the performance of blind adaptive beamforming algorithms for smart antennas in realistic environments. A constrained constant modulus (CCM) design criterion is described and used for deriving a recursive least squares (RLS) type optimization algorithm. Furthermore, two kinds of scenarios are considered in the paper for analyzing its performance. Simulations are performed to compare the performance of the proposed method to other well-known methods for blind adaptive beamforming. Results indicate that the proposed method has a significant faster convergence rate, better robustness to changeable environments and better tracking capability. | The use of adaptive antenna techniques to increase the channel capacity is discussed. Directional sensitivity is obtained by using an antenna array at the base station, possibly both in receiving and transmitting mode. A scheme for separating several signals at the same frequency is proposed. The method is based on high-resolution direction-finding followed by optimal combination of the antenna outputs. Comparison with a method based on reference signals is made. Computer simulations are carried out to test the applicability of the technique to scattering scenarios that typically arise in urban areas. The proposed scheme is found to have great potential in rejecting cochannel interference, albeit at the expense of high computational requirements. > | Perfect Quantum Cloning Machines (QCM) would allow to use quantum nonlocality for arbitrary fast signaling. However perfect QCM cannot exist. We derive a bound on the fidelity of QCM compatible with the no-signaling constraint. This bound equals the fidelity of the Bu\v{z}ek-Hillery QCM. | eng_Latn | 5,371 |
Maximum-likelihood (ML) receivers have been investigated for the fast frequency-hopped binary frequency-shift-keying (FFH/BFSK) spread-spectrum communications system with the worst case of the band multitone jamming and the additive white Gaussian noise over frequency-selective Rayleigh-fading channels. A suboptimal ML diversity-combining receiver has been theoretically analyzed based upon an approximation of the natural logarithm of the modified Bessel function under a correlated two-path frequency-selective channel model. The performance of the receiver compared with that of other diversity-combining receivers, in terms of the bit error rate, has been scrutinized. Computer simulations confirm that our numerical analysis is valid, and the proposed suboptimal ML receiver outperforms other receivers. | Based on the likelihood ratio, we derive the maximum-likelihood (ML) receiver for a synchronous fast frequency-hopped multiple-access system employing M-ary frequency-shift-keying (MFSK) modulation over frequency-selective Rayleigh-fading channels. The derived ML receiver is proposed and analyzed to obtain bit-error rate (BER) expressions. Analytical results are then validated by computer simulations. All system users are assumed to experience independent frequency-selective Rayleigh fading. Performance comparison among several commonly-used receivers shows that the proposed ML receiver gives the best BER performance for different combinations of parameters of the analyzed system under various fading conditions. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,372 |
The satellite system is one of the most efficient means for broadcasting due to its wide service coverage as well as the fact that it can provide high data rate services by using high frequency bands. However, there are a number of problems in the satellite system, such as a long round trip delay (RTD) and heterogeneity of the channel conditions of the earth stations. Even though utilizing adaptive coding and modulation (ACM) is almost mandatory for the satellite systems using high frequency bands due to the serious rain fading, the long RTD makes it difficult to quickly respond to channel quality information, resulting in a decrease in the efficiency of ACM. A high heterogeneity of earth stations caused by a wide service coverage also makes it difficult to apply a uniform transmission mode, and thus satellite systems require receiver-dependent transmission modes. A rateless code can be an effective means to compensate for these disadvantages of satellite systems compared to terrestrial wireless systems. This paper presents soft iterative decoding algorithms for efficient application of rateless codes in satellite systems and demonstrates that rateless codes can be effectively used for hybrid automatic repeat request schemes. | The Luby transform (LT) code is the first practical implementation of the digital fountain code, and its utilisation over a noisy channel invokes iterative decoding with soft information. For a good decoding performance, the role of the encoder degree distribution is vital. Especially, when utilising the soft iterative decoder, the bit error rate (BER) performance of the LT code can be improved by increasing the number of the degree-1 encoding nodes and reducing the number of lower-degree variable nodes. This study proposes an efficient LT-code encoding algorithm that satisfies the conditions for improving the BER performance. The proposed scheme applies different priorities for selecting the neighbouring source nodes for given degrees of the encoding nodes. The simulation results demonstrate that the proposed scheme outperforms the existing schemes. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,373 |
A quantizer that must accommodate a wide range of signal powers would ordinarily require a large number of output levels compared to a quantizer of signals with known power. In this paper a quantizlng scheme is described for situations in which the signal power is unknown a priori but remains constant for the duration of a communication. The required number of levels is reduced because the quantizer amplitude range is adjusted during an initial training period to the value appropriate to the current signal power. At each sample time during the training period, the amplitude range is adjusted by a multiplicative quantity that depends on the most recent quantized output and upon the time elapsed since the onset of training. Assuming independent identically distributed inputs, it is shown that the quantizer range converges to a fixed multiple of the rms value of the input. The ratio of final range to rms input is a unique function of the multipliers, and a formula is presented that allows a designer to choose multipliers that result in any desired range-to-signal ratio. For each final ratio, there are many sets of multipliers, and formulas are derived that indicate, for a limited training period, the tradeoff between the accuracy of the quantizer range and the size of the set of signal powers to which the quantizer can adapt. Computer simulations illustrate the effects of particular multiplier sequences. | We combine backward adaptive quantization with the scalar-vector quantizer (SVQ) and the trellis coded quantizer (TCQ) both of which have an underlying scalar quantizer (USQ) in their structure. The resulting adaptive scalar-vector quantizer (ASVQ) and adaptive trellis coded quantizer (ATCQ) redesign the USQ based on the past quantized outputs. The adaptive quantizers require no side information and also outperform the SVQ and the TCQ, respectively, when the input signal is non-stationary. For an input sequence from a bimodal source switching infrequently between two Gaussian distributions with the same mean and different variances, both adaptive quantizers achieve performance gains of more than 1.3 dB over the non-adaptive quantizers designed on the training set from the same bimodal source. Also the adaptive quantizers demonstrate minimal performance degradation due to adaptation when stationary inputs are considered. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,374 |
This work focuses on the impact of residual transmit impairments on the performance of Multiple-Input Multiple-Output (MIMO) systems with linear and non-linear receivers and precoders. We show that transmit noise significantly affects the performance of systems using precoding. Also, we show that non-linear MIMO receivers and precoders are more sensitive to transmit noise than their respective linear counterpart. Nevertheless, performance degradation can be noticeably alleviated if transmit noise is considered into filter optimization. | This study analyzes the impact of transmitter noise on the performance of multiple-input multiple-output (MIMO) systems with linear and nonlinear receivers and precoders. We show that the performance of MIMO linear and decision-feedback receivers is not significantly influenced by the presence of transmitter noise, which does not hold true in the case of MIMO systems with precoding. Nevertheless, we also show that this degradation can be greatly alleviated when the transmitter noise is considered in the MIMO precoder design. A MIMO testbed developed at the University of A Coruna has been employed for experimentally evaluating how much the transmitter noise impacts the system performance. Both the transmitter noise and the receiver noise covariance matrices have been estimated from a set of 260 indoor MIMO channel realizations. The impact of transmitter noise has been assessed in this realistic scenario. | This study analyzes the impact of transmitter noise on the performance of multiple-input multiple-output (MIMO) systems with linear and nonlinear receivers and precoders. We show that the performance of MIMO linear and decision-feedback receivers is not significantly influenced by the presence of transmitter noise, which does not hold true in the case of MIMO systems with precoding. Nevertheless, we also show that this degradation can be greatly alleviated when the transmitter noise is considered in the MIMO precoder design. A MIMO testbed developed at the University of A Coruna has been employed for experimentally evaluating how much the transmitter noise impacts the system performance. Both the transmitter noise and the receiver noise covariance matrices have been estimated from a set of 260 indoor MIMO channel realizations. The impact of transmitter noise has been assessed in this realistic scenario. | eng_Latn | 5,375 |
It has been established that the appropriate criteria for space-time trellis coded modulation (STTCM) design on slow Rayleigh fading channels are maximisation of the minimum rank and the minimum determinant of the distance matrices. It is demonstrated that when STTCM is used in systems with a large product (>3) of the numbers of transmit and receive antennas, the design of codes with maximum coding gain is governed by the minimum trace of the distance matrices. A number of new codes based on the proposed design criterion have been constructed and shown to be superior to other known codes. | Optimum space-time convolution code, which provides maximum diversity and coding gain, are produced for cases with PSK modulation and various numbers of states and antennas. In this paper, we modify the conventional Viterbi algorithm used in space-time encoder under the MIMO system, and give the recursive metric equation. The modified Viterbi algorithm can be used in the receiver when the MIMO channel information is known a prior. The new approach provides an efficient method that allows a search for optimum path. Compared with the conventional decoding algorithm, the improved algorithm can be used in the every receiver respectively. It is shown that the improved algorithm is also an optimal algorithm, however, its metric convergence speed is faster than the standard Viterbi algorithm. | MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity. | eng_Latn | 5,376 |
In this paper, we consider the performance of downlink multiuser relay networks (MRN) equipped with a single amplify-and-forward (AaF) relay. We present exact analysis in closed-form for the outage probability of MRN with channel state information (CSI)-based gain relaying in Nakagami-m fading channels. In doing so, we derived a new expression for the cumulative distribution function (CDF) of the highest end-to- end signal-to-noise ratio (SNR) associated with the strongest destination terminal. We demonstrate the impact of the fading severity m and the number of destination terminals on the system performance in unbalanced fading conditions. Numerical results substantiate the validity of our analysis. I. INTRODUCTION | The end-to-end performance of dual-hop cooperative diversity systems equipped with nonregenerative relays and a selection combining receiver at the destination terminal over independent and nonidentical Nakagami-m fading channels is studied. Closed-form expressions for the cumulative distribution function and the probability density function of the end-to-end signal-to-noise ratio (SNR) are presented, while analytical formulae are derived for the moments and the moment generating function. Using these statistical results, closed-form expressions for the outage probability are presented for both channel state information and fixed gain relays. Furthermore, for the case of fixed gain relay, the average end-to-end SNR, the amount of fading, and the average bit error rate can be numerically evaluated. The proposed mathematical analysis is complemented by numerical examples, including the effects on the overall performance of the SNRs unbalancing as well as the fading severity. | Distillation at an infinite reflux ratio in combination with an infinite number of trays has been investigated. | eng_Latn | 5,377 |
In this paper, we are concerned with low-complexity detection in large multiple-input multiple-output (MIMO) systems with tens of transmit/receive antennas. Our new contributions in this paper are two-fold. First, we propose a low-complexity algorithm for large-MIMO detection based on a {\em layered low-complexity local neighborhood search}. Second, we obtain a lower bound on the maximum-likelihood (ML) bit error performance using the local neighborhood search. The advantages of the proposed ML lower bound are i) it is easily obtained for MIMO systems with large number of antennas because of the inherent low complexity of the search algorithm, ii) it is tight at moderate-to-high SNRs, and iii) it can be tightened at low SNRs by increasing the number of symbols in the neighborhood definition. Interestingly, the proposed detection algorithm based on the layered local search achieves bit error performances which are quite close to this lower bound {\em for large number of antennas and higher-order QAM}. For e.g., in a $32\times 32$ V-BLAST MIMO system, the proposed detection algorithm performs close to within 1.7 dB of the proposed ML lower bound at $10^{-3}$ BER for 16-QAM (128 bps/Hz), and close to within 4.5 dB of the bound for 64-QAM (192 bps/Hz). | Low-complexity near-optimal signal detection in large dimensional communication systems is a challenge. In this paper, we present a reactive tabu search (RTS) algorithm, a heuristic based combinatorial optimization technique, to achieve low-complexity near-maximum likelihood (ML) signal detection in linear vector channels with large dimensions. Two practically important large-dimension linear vector channels are considered: i) multiple-input multiple-output (MIMO) channels with large number (tens) of transmit and receive antennas, and ii) severely delay-spread MIMO inter-symbol interference (ISI) channels with large number (tens to hundreds) of multipath components. These channels are of interest because the former offers the benefit of increased spectral efficiency (several tens of bps /Hz) and the latter offers the benefit of high time-diversity orde rs. Our simulation results show that, while algorithms including variants of sphere decoding do not scale well for large dimensions, the proposed RTS algorithm scales well for signal detection in large dimensions while achieving increasingly closer to ML performance for increasing number of dimensions. Index Terms—Linear vector channels, large dimensions, low- complexity detection, near-ML performance, V-BLAST, non- orthogonal STBCs, MIMO-ISI channels, UWB, severe delay spread, tabu search. | Perfect Quantum Cloning Machines (QCM) would allow to use quantum nonlocality for arbitrary fast signaling. However perfect QCM cannot exist. We derive a bound on the fidelity of QCM compatible with the no-signaling constraint. This bound equals the fidelity of the Bu\v{z}ek-Hillery QCM. | eng_Latn | 5,378 |
Orthogonal space-time block codes (STBC), and the Alamouti scheme in particular, are of particular interest in multiple-input multiple-output (MIMO) systems since they achieve full spatial diversity over fading channels and are decoded from linear processing at the receiver. Nevertheless, due to the expensive spectral resource, increasing network capacity requires the development of interference cancellation (IC) techniques allowing several users to share the same spectral resources without impacting the transmission quality. In this context several IC schemes have been developed during this last decade, where each user is equipped with multiple antennas and employs STBC at transmission. However, these IC techniques require multiple antennas at reception, which remains a challenge at the handset level due to cost and size limitations. For this reason, low complexity single antenna interference cancellation (SAIC) techniques, currently operational in GSM handsets, have been developed recently for single antenna users using real-valued modulations or complex filtering of real-valued modulations, by using a widely linear (WL) filtering at reception. Extension to multiple antennas at reception is called multiple antenna interference cancellation (MAIC) technique. The purpose of this paper is to extend the SAIC/MAIC technology to users using both real-valued constellations, such as amplitude shift keying (ASK) constellations, and the Alamouti scheme at transmission. A WL minimum mean square error (MMSE) receiver, completely new for IC purposes in the context of radio communications systems using the Alamouti scheme, is proposed and analyzed. This receiver, which corresponds to the maximum likelihood (ML) receiver for synchronous intranetwork interferences, is able to separate up to 2 N Alamouti users from N antennas at reception, hence SAIC capability for N = 1. | The aim of this letter is to exhibit some advantages of using real constellations in large multiuser (MU) MIMO systems. It is shown that a widely linear zero-forcing (WLZF) receiver with M-ASK modulation enjoys a spatial-domain diversity gain, which linearly increases with the MIMO size even in fully- and over-loaded systems. Using the decision of WLZF as the initial state, the likelihood ascent search (LAS) achieves near-optimal BER performance in fully loaded large MIMO systems. Interestingly, for coded systems, WLZF shows a much closer BER to that of WLZF-LAS with a gap of only 0.9–2 dB in SNR. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,379 |
We present a novel frequency domain approach for the identification of a multiple-input multiple-output (MIMO) system driven by white, mutually independent unobservable inputs. Samples of the system frequency response are obtained based on parallel factorization (PARAFAC) of three-way tensors constructed based on third-order cross-spectra of the system outputs. The main difficulties in frequency domain methods are frequency dependent permutation and filtering ambiguities. We show that the information available in the higher-order spectra allows for the ambiguities to be resolved up to a constant scaling and permutation, and a linear phase ambiguity. The advantages of the proposed approach is that, it does not require exact channel length information, need no phase unwrapping, and unlike the majority of existing methods, need no pre-whitening of the system outputs | Equalization and estimation of the matrix impulse response function of multiple-input multiple-output (MIMO) digital communications channels in the absence of any training sequences is considered. An iterative, Godard (1980) cost-based approach is considered for spatio-temporal equalization and MIMO impulse response estimation. Stationary points of the cost function are investigated with particular attention to the case when finite-length equalizers exist. Sufficient conditions are derived under which all stable local minima correspond to desirable minima. The inputs are extracted and cancelled one by one. The matrix impulse response is then obtained by cross-correlating the extracted inputs with the observed outputs. Identifiability conditions are analyzed. | The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.). | eng_Latn | 5,380 |
Digital angle modulations having input symbol memory can be demodulated using maximum likelihood sequence estimation (MLSE or Viterbi decoding). The demodulation of the more bandwidth efficient of these can require a large number of computations. In this paper, lower complexity decoding approaches are presented. These decoders use a predetermined processing order and a reduced number of survivor signals, S , at every-time NT . Processing is performed on the signal sequences using metrics (likelihoods) obtained by a matched filter bank similar to that needed for MLSE. The decoders can achieve asymptotic optimality of error rate while being computationally faster and simpler than MLSE for many modulations. In addition, error rate performance can be traded for complexity reduction. Expected performance has been verified for representative modulations. | In this paper, we propose a new algorithm for the surviving path decision in M-algorithm convolutional decoders. Correct path loss introduces one of the most destructive effects on the M-algorithm which mostly leads to catastrophic error. In the proposed M-algorithm survivor decision scheme, the M surviving states are not selected solely based on their own path metric. Among the M surviving states, some states with the best path metrics survive and also some other states whose ancestors have had the best path metrics survive. This way of survivor selection enables us to avoid correct path loss if an abrupt noise deteriorates the correct path metric severely. Simulation results show that the error rate performance of the ancestor-based survivor decision in some cases is slightly better than currently-best survivor decision scheme in the presence of the additive white Gaussian noise (AWGN). However, it is expected that the proposed algorithm offer better performance than the conventional methods in the presence of abrupt noise (short-term high value noise) like shot noise or over fading channel | MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity. | eng_Latn | 5,381 |
We propose a probing-based link adaptation scheme that is incorporated into the aggregation with fragment retransmission (AFR) scheme for high data rate wireless LANs (WLANs). Thanks to the frame structure of multiple fragments in AFR, the proposed scheme can significantly reduce the probing overhead by transmitting a few fragments in a frame at a higher data rate. At the same time, it can easily estimate the fragment error rate in the MAC layer. To maximize the throughput and maintain the average fragment error rate below the target value, the data rate can be switched to a higher data rate based on the probing result or a more robust data rate based on the estimated fragment error rate. The proposed scheme does not need a calibration process, which is a major difficulty in implementing the exponential effective SNR mapping based fast link adaptation (FLA/EESM) scheme. Moreover, it is less affected by imperfect channel matrix estimation compared to the FLA/EESM scheme. In the performance evaluation for several channel models, the proposed scheme provides 3~10% and 5~15% more throughput than the FLA/EESM scheme with perfect and imperfect channel matrix estimations, respectively, while maintaining the average fragment error rate below the target value. | Wireless networks are under constant pressure to provide ever-higher data rates to increasing numbers of users with greater reliability. This book is an accessible introduction to every fundamental aspect of space-time wireless communications. Space-time processing technology is a powerful tool for improving system performance that already features in the UMTS and CDMA2000 mobile standards. The ideal volume for graduate students and professionals, it features homework problems and other supporting material on a companion website. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,382 |
NMR diffusion measurements have proven to be a very powerful technique for probing the solution dynamics of polymer systems. In theory, it is possible to extract a range of useful information including molecular weights from the diffusion data. In practice, especially outside the infinite dilution regime, the data analysis is further complicated by numerous effects including macroscopic and microscopic averaging. Here the averaging effects in dilute bimodal narrow molecular weight poly(methyl methacrylate) in deuterated chloroform solutions are studied at 298 K and cogent models developed to analyze the data. Simulations are performed which represent different limits of diffusive behavior in bimodal solutions and the suitability of the simulations are found to be dependent on the ratio of the molecular weights in the solution. | Molecular crowding occurs when the total concentration of macromolecular species in a solution is so high that a considerable proportion of the volume is physically occupied and therefore not accessible to other molecules. This results in significant changes in the solution properties of the molecules in such systems. Macromolecular crowding is ubiquitous in biological systems due to the generally high intracellular protein concentrations. The major hindrance to understanding crowding is the lack of direct comparison of experimental data with theoretical or simulated data. Self-diffusion is sensitive to changes in the molecular weight and shape of the diffusing species, and the available diffusion space (i.e., diffusive obstruction). Consequently, diffusion measurements are a direct means for probing crowded systems including the self-association of molecules. In this work, nuclear magnetic resonance measurements of the self-diffusion of four amino acids (glycine, alanine, valine and phenylalanine) up to their solubility limit in water were compared directly with molecular dynamics simulations. The experimental data were then analyzed using various models of aggregation and obstruction. Both experimental and simulated data revealed that the diffusion of both water and the amino acids were sensitive to the amino acid concentration. The direct comparison of the simulated and experimental data afforded greater insights into the aggregation and obstruction properties of each amino acid. | We summarize the enabling technologies for photonics-assisted broadband millimeter-wave (mm-wave) communication, which is a promising candidate for the enhanced mobile broadband (eMBB) communications, one of the three main typical application scenarios of 5G wireless networks. These enabling technologies, mainly focusing on the improvement of the system structure, include broadband mm-wave signal generation with simple and cost-effective schemes, multiple-input multiple-output architecture with polarization-multiplexing optical mm-wave signal, advanced multilevel modulation, optical or electrical multicarrier modulation, antenna polarization multiplexing and the employment of the high-gain mm-wave antenna, multi-band multiplexing, and broadband mm-wave signal detection. We also review the advanced digital signal processing (DSP) for heterodyne coherent detection, which can be applied into the photonics-assisted mm-wave communication systems, to further enhance the system performance for a given system structure and certain available devices. Based on these enabling technologies and advanced DSP, we have realized over 1 Tb/s wireless signal transmission at D-band and over 2.5 km wireless transmission with a bit rate up to 54 Gb/s at W-band. Our work verifies the photonics-assisted broadband mm-wave communication can meet the high-data-rate demand of eMBB. | eng_Latn | 5,383 |
A new method allowing a reduction in the probability of clipping in discrete multitone (DMT)-based transceivers is described. The method does not use any kind of precoding and can easily be implemented within conventional DMT-transceivers. The main advantage of the proposed method is an improvement of system performance in terms of overall signal-to-noise ratios (SNRs): with the simplest implementation option of the proposed method, up to about 8 dB improvement in the SNR as compared with previously reported brute force clipping methods can be achieved. | This paper addresses the joint design of transmit and receive beamforming or linear processing (commonly termed linear precoding at the transmitter and equalization at the receiver) for multicarrier multiple-input multiple-output (MIMO) channels under a variety of design criteria. Instead of considering each design criterion in a separate way, we generalize the existing results by developing a unified framework based on considering two families of objective functions that embrace most reasonable criteria to design a communication system: Schur-concave and Schur-convex functions. Once the optimal structure of the transmit-receive processing is known, the design problem simplifies and can be formulated within the powerful framework of convex optimization theory, in which a great number of interesting design criteria can be easily accommodated and efficiently solved, even though closed-form expressions may not exist. From this perspective, we analyze a variety of design criteria, and in particular, we derive optimal beamvectors in the sense of having minimum average bit error rate (BER). Additional constraints on the peak-to-average ratio (PAR) or on the signal dynamic range are easily included in the design. We propose two multilevel water-filling practical solutions that perform very close to the optimal in terms of average BER with a low implementation complexity. If cooperation among the processing operating at different carriers is allowed, the performance improves significantly. Interestingly, with carrier cooperation, it turns out that the exact optimal solution in terms of average BER can be obtained in closed form. | In this paper, we present a finite-granularity, loading algorithm for a discrete multitone (DMT) modulation system. The proposed algorithm offers significant implementational advantages over the well-known water-pouring method and the earlier Hughes-Hartogs algorithm, while typically suffering only negligible performance degradation relative to the optimal solution. We also present simulation results of this loading algorithm applied to the newly proposed asymmetric digital subscriber lines (ADSL) service. > | eng_Latn | 5,384 |
Following a strong trend towards cognitive connected cars, modern automobiles are equipped with a multitude of wireless communication systems. In order to ensure proper functionality, reliability, and resilience of these systems, the development of suitable test facilities and verification methods is of great interest in current research. An established testing method is the concept of channel emulation, in which temporal and spatial characteristics of mobile communications are reconstructed in a lab environment, in order to allow for reproducible and stable test conditions. Under the roof of the Thuringian Center of Innovation in Mobility in Ilmenau, Germany, the virtual road simulation and test area - VISTA was installed and laid out for virtual drive testing. This paper presents a distributed spatial channel emulator, which is based on multiple commercially available software-defined-radio modules and can be deployed in an over-the-air measurement setup. Pursuing a cluster-based measurement concept, it allows for reconstructing essential features of electromagnetic wave propagation in the wireless automotive communication channel. In this paper, the implementation of the distributed channel emulator is described and its feasibility demonstrated in principle. | This paper presents a joint calculation of the precoding matrix indicator (PMI) and rank indicator (RI) in multiple-input multiple-output (MIMO) downlink third generation partnership project (3GPP) universal mobile telecommunications system (UMTS)/long-term evolution (LTE) systems. The standard codebook based precoding is used where the mobile station estimates and sends some measures related to the channel state information to the base station for link adaptation purpose. We study the system performance using link-level simulation under realistic assumptions. Specifically, we use K-best MIMO decoding in the presence of perfect and imperfect estimation of the channel and the noise variance, as well as white and colored noise plus interference defined by the 3GPP LTE specification documents. Similar to some previous results, our method for calculating the PMI/RI is based on maximizing the mutual information between the transmitted and received symbols with respect to the precoding matrix. We evaluate the system performance using two channel measures when computing the mutual information. The first measure is the estimated channel whereas the second one is the estimated channel covariance matrix. Although these two measures have been used in different literature, there have not been conclusive results on which one should be used in different practical scenarios. We assess the system performance using Monte Carlo simulations and compare different test cases, e.g., 3GPP channel models, wideband, and subband PMI/RI calculation, white/color noise plus interference, etc. We then conclude our work with technical recommendations for different scenarios. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,385 |
This paper proposes a high capacity carrier interferometry/multicarrier code division multiple access (CI/MCCDMA)system through the simultaneous support of highand low data rate transmission. High data rate users transmitdata through all sub-carriers while alternate odd andeven subcarriers are shared by the low data rate users.The usage of alternate sub-carriers suggests to split CIcodes in odd and even parts leading to an increase incapacity. The cross-correlations among the code patternsare reduced through the phase shift of even (odd) CI codeusing odd (even) sub-carriers by an amount of π/2 andodd (even) CI code using odd (even) sub-carriers by -π/2,all measured with respect to orthogonal codes assigned tosupport high data rate transmission. Performance in termof BER (bit error rate) is then analyzed by carrying outsimulation on frequency selective Rayleigh fading channel.The MAI (multiple access interference) effect is subtractedat the subcarrier projection domain leading to the reductionin high computation cost inherent in parallel interferencecancelation. Performance improvement for different combinationsof low and high data rate users are shown comparedto the conventional CI/MC-CDMA system as well as blockPIC scheme. | Consider a Gaussian multiple-access channel shared by K users who transmit asynchronously independent data streams by modulating a set of assigned signal waveforms. The uncoded probability of error achievable by optimum multiuser detectors is investigated. It is shown that the K -user maximum-likelihood sequence detector consists of a bank of single-user matched filters followed by a Viterbi algorithm whose complexity per binary decision is O(2^{K}) . The upper bound analysis of this detector follows an approach based on the decomposition of error sequences. The issues of convergence and tightness of the bounds are examined, and it is shown that the minimum multiuser error probability is equivalent in the Iow-noise region to that of a single-user system with reduced power. These results show that the proposed multiuser detectors afford important performance gains over conventional single-user systems, in which the signal constellation carries the entire burden of complexity required to achieve a given performance level. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,386 |
This paper proposes a new coding algorithm of speech compressing, which is based on Best Wavelet Packet Transform and SPIHT coding algorithm. The new approach applies the wavelet packet transform to process speech signal to obtain optimal wavelet tree to allocate the dynamic bits, and then uses the modified SPIHT coding algorithm to compress the coefficients from the wavelet packet transform. The entropy coding is also used to increase the compression ratio. The experiments indicate that the new approach can gain better quality signal reconstruction at high compression ratios and have a low-complexity and low-delay. | Frequency -warped signal processing techniques are attractive to many wideband speech and audio applications since they have a clear connection to the frequency resolution of human hearing. A warped version of the linear predictive coding (LPC) for speech compression is implemented in this paper and an analysis of the application of Set Partitioning In Hierarchical Trees (SPIHT) algorithm to the compression of speech signals is performed. It has been shown that the proposed scheme i.e. Warped LPC with MLT_SPIHT algorithm produces an enhancement in speech quality. The proposed scheme is based on the combination of the Modulated Lapped Transform(MLT) and SPIHT. Comparisons are made with Plain LPC Coder, Voice Excited LPC Coder with the coding of the residual signal with DCT, Voice Excited LPC Coder with the coding of the residual signal with MLT and SPIHT. The performance of the coders described has been assessed by computer simulation in terms of a) Signal -to -noise ratio (SNR) b) Compression ratio c) Informal subjective listening test. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,387 |
In this paper, we investigate the average throughput of a multi-antenna wireless powered communication network where an energy-constrained user harvests energy from a hybrid access-point (AP) equipped with multiple antennas in the downlink, and then transmits information to the AP in the uplink using the harvested energy. Specifically, we consider a more practical scenario, i.e., nonlinear energy harvester, as compared with the traditional linear model. In order to evaluate the key parameters, such as the transmit power, antenna numbers, time-splitting, channel fading severity, on the performance of thecconsidered system, we derive closed-form expressions of thecaverage throughput for both delay tolerant and delay intolerant transmission modes in Nakagami-m fading channel. In addition,cto further exploit the insights on the application of the consideredcsystem, the asymptotic analysis for the achievable throughput are also provided in two special cases, i.e., high transmit power regime and high saturation threshold regime. Finally, our results demonstrate that the considered system exhibits the throughput saturation phenomenon, and the parameters of channel fading severity produce a different impact on the average throughput in the two transmission modes. | Performance of wireless powered relay with amplify-and-forward protocol is studied for Nakagami- $m$ fading channels. Different from the existing literature, we consider the nonlinearity of the energy harvester. An analytical expression is derived for the complementary cumulative distribution function (CCDF) of the end-to-end signal-to-noise ratio. Using the CCDF, outage capacity is calculated. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,388 |
As converged services are becoming the standard for corporate networks, concerns have been arising on the best way to ensure efficient use of expensive WAN bandwidth. Achieving excellent quality of multimedia and voice communication requires the allocation of large bandwidth for these services. In most cases, lossy compression codecs are used to reduce bandwidth requirements resulting in lower quality of service. The codec selection is maintained even during low bandwidth utilization. In this paper, we present a codec interface that combines high-fidelity high-bitrate and low-fidelity low-bitrate codecs. Audio packets from the low-bitrate codec are transmitted on the highest priority class of service of differentiated services networks. This ensures that these packets always arrive at destination. Audio packets from the high-bitrate codec are transmitted on the lowest priority class of service. At low bandwidth utilization, the high-fidelity high-bitrate packets will be used and during congestions, these packets would be dropped. This ensures achieving the best possible voice quality during varying network loads. Simulation results measuring the mean opinion score of voice quality show that superior voice quality can be achieved with this method over using standalone codecs while maintaining excellent quality of service for data traffic as well. | In this paper, we present an optimal UEP framework for transmitting packetized audio streams over MIMO wireless links. Our proposed framework aims at maximizing the expected end-to-end Segmented SNR of a received audio sequence. It reduces the packetization overhead of small audio frames while protecting audio streams against temporarily correlated bit errors introduced by wireless transmission medium. To reduce the packetization overhead, our framework suggests a frame grouping technique distributing the transmission overhead of one packet among multiple audio frames. To mitigate the effects of random bit errors, our framework utilizes a UEP RS channel coding scheme to assign parity bits according to the combined perceptual importance of frames embedded in individual packets. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,389 |
This paper proposes a new adaptive source-channel coding scheme in the context of subband coding. We first express the total mean-squared distortion suffered by the source in terms of source and channel distortions of the subbands. We then minimize this total distortion by an appropriate choice of source and channel coding rates for the subbands. This corresponds to casting the conventional bit allocation problem in a joint source-channel coding context. The choice of rates depends on the state of the physical channel, modeled by a binary symmetric channel (BSC). We then use a finite state Markov model for a fading channel to generalize results obtained for the BSC. This results in a joint source-channel coding scheme that is optimized to the current state of a fading channel. | This paper presents a low-complexity method of transmitting digitally compressed imagery through AWGN and fading channels. The proposed method combines a wavelet-based image coder that employs phase scrambling and trellis-coded quantization (TCQ), and source adaptive modulation (SAM). We present two versions of SAM that utilize BPSK (SAM-TCQ) and 16-ary PPM (OSAM-TCQ), respectively. We then compare the performance of the OSAM system to that of a system that utilizes unequal error protection (UEP). In our previous work, the SAM-TCQ system was shown to perform as well as UEP-TCQ at high bit error rates (BER), and within 1 dB of the UEP-TCQ system at low bit error rates. In this work, we show that the OSAM-TCQ system performs nearly 4 dB better than UEP-TCQ at high bit error rates, and the same as the UEP-TCQ system at low bit error rates, with much lower complexity than the UEP-based system. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,390 |
Multi-pulse position modulation (M-PPM) is advantageous in a visible light communication system due to its overall satisfactory performance in spectrum efficiency and dimming control. In this letter, we consider the joint dimming and communication design with M-PPM. We provide a model for the dimming control and address the balance between the dimming loss minimization and the transmission rate maximization. The dimming loss is modeled by the quantization loss within the dimming range for the discrete transmission power levels. The transmission rate is evaluated by the channel capacity. We propose two optimization formulations on the dimming requirement service and the transmission rate maximization. Numerical results show that the objective loss function may increase as either the lower limit of the dimming range approaches zero or the upper limit approaches the peak transmission power. | Visible light communication (VLC) uses solid-state lightings to transmit information; therefore, it is necessary that modulation schemes for VLC provide dimming control. In this letter, we propose a multiple pulse position modulation (MPPM) to offer both functions of modulating data-stream and controlling the brightness at the same time. According to the dimming level, we control the number of pulses of MPPM in one symbol duration. We analyze communication performance in terms of the normalized power requirement and spectral efficiency. From our studies, we show that MPPM is superior to variable on-off keying (VOOK) and variable pulse position modulation (VPPM) proposed in the IEEE 802.15 VLC task group. | In genome rearrangements, the mutational event \emph{transposition} swaps two adjacent blocks of genes in one chromosome. The \emph{Transposition Distance Problem} (TDP) aims to find the minimum number of transpositions (distance) required to transform one chromosome into another, both represented as permutations. Setting the target permutation as the identity permutation, makes the TDP equivalent to the problem of \emph{Sorting by Transpositions} (SBT). ::: TDP is $\mathcal{NP}$-hard and the best approximation algorithm with a $1.375$ ratio was proposed in 2006 by Elias and Hartman. Their algorithm employs a technique called \emph{simplification} to transform an input permutation $\pi$ into a \emph{simple permutation} $\hat{\pi}$, obtained by inserting new symbols into $\pi$ in a way that the lower bound of the transposition distance of $\pi$ is kept on $\hat{\pi}$. The assumption is that handling with simple permutations is easier than with normal ones. A sequence of transpositions sorting $\hat{\pi}$ can be mimicked to sort $\pi$. ::: In this work, we first show that the algorithm of Elias and Hartman may require one transposition above the intended approximation ratio of $1.375$, depending on how the input permutation is simplified. Then, we propose a new $1.375$-approximation algorithm to solve TDP based on an algebraic formalism which does not use simplification, ensuring the approximation ratio of $1.375$ for all the permutations in the Symmetric Group $S_n$. We also propose a new upper bound for the transposition distance. ::: Implementations of our algorithm and the one of Elias and Hartman were audited using GRAAu tool. The results show that, taking as input short permutations with maximum length $13$, in addition to keeping the approximation below the $1.375$ ratio, our algorithm returns a higher percentage of exact distances than the one of Elias and Hartman. | eng_Latn | 5,391 |
Realistic channel models are crucial in developing future wireless systems. Channel sounding and consequently propagation parameter estimation are key tasks in creating such models. In this paper we present an estimator for the angular distribution of the diffuse scattering component that is frequently observed in channel sounding measurements. Finding the Cramer-Rao lower bound and comparing the variances study the large sample performance of the estimator. The simulations show that the variance of the proposed estimation technique closely reaches the Cramer-Rao lower bound for small sample size and for any number of antennas. | The increased popularity of array antennas for wireless communication, has inspired investigations of the spatio-temporal properties of the radio channel, among others the azimuthal shape of the scattering clusters. Based on a statistical analysis, we show that trying to estimate the shape of the scattering is an ill-posed problem and that the heavy-tailed power azimuth spectra reported in the literature may be an artifact stemming only from the measurement procedure. | We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero. | eng_Latn | 5,392 |
This paper proposes chip coding using convolutional codes for fast frequency-hopping spread-spectrum multiple-access (FFH-SSMA) systems. Its performance is evaluated and compared with that of repetition coding which is most commonly used in FFH systems. In our proposal, an information symbol is encoded by a convolutional code of rate 1/n and n chips are transmitted through a frequency hopper. We consider three models when perfect side information (PSI) is available, no side information (NSI) is available, and the ratio threshold test (RTT) is used. The probability density functions (PDFs) of the received signal are derived for asynchronous hopping systems. The performances of convolutional coding with threshold decoding and Viterbi decoding are presented under the constraint of fixed total bandwidth and information bit rate. In comparison with repetition codes, it is found that convolutional codes drastically enhance the system performance. It is identified that Viterbi decoding with RTT offers the most significant performance improvement. | Performance of robust soft decoding metrics is examined for use in convolutional coded asynchronous fast frequency-hop spread-spectrum multiple-access networks using binary frequency-shift keying under Rayleigh fading channels. For comparison, maximum-likelihood metrics based on a Gaussian approximation are derived. Significant gains are observed compared to hard decision decoding by using appropriate soft metrics. | Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights. | eng_Latn | 5,393 |
Multimode fibers are normally known to have a channel for carrying a signal mainly by their 3-dB modal bandwidth ranging between 200 to 500 MHz-km, depending on the material and structure of the fiber. To use only this 3-dB modal bandwidth, a higher data rate signal cannot be successfully transmitted. Alternatively, it has been shown that the response of the multimode fibers at low-frequency region, defining as the frequency next to the 3-dB modal band, contains many passbands. Additionally, these low-frequency passbands have been shown to be predictable in terms of their peak frequencies; thus, suitable subcarrier frequencies can be obtained and used in SCM system. In this paper, the formula from the previous work for determining the peak frequency of all 6 low-frequency passbands is applied. These 6 passbands and the 3-dB modal band of the multimode fiber are used to convey a high data rate signal. The signal is separated into 7 subcarrier signals and transmitted over these 7 channels using SCM system. The performance of the received signal in terms of the bit-error-rate (BER) is determined and shown. Some modification and adjustment are done in order to improve the performance of the system. It is found that for a multimode fiber with a 200-MHz 3-dB modal bandwidth, a 500-Mbps data rate signal can be successfully transmitted with a BER of lower than 10-6 . The data rate transmitted over a multimode fiber can be increased 2.5 times comparing to the 3-dB modal bandwidth, without any coding technique applied. | The bandwidth-distance product limitations of multimode fiber caused by intermodal dispersion may be overcome by using subcarrier multiplexing. Since there are deep nulls in the frequency response within the frequency band of interest, it is necessary either to avoid these frequencies adaptively or to use an appropriate coding technique. We consider the case of using a training sequence to identify the subcarriers to be discarded, and also diversity coding in which the information may be recovered in the presence of the loss of a fixed number of subcarriers. Simulation results indicate that diversity coding, which is less complex than the use of training sequences, provides very good performance over a wide range of channel conditions. | By using a superluminescent diode as the light source and a depolariser inside the fibre coil, a constant scale factor is achieved without using polarisation control elements. For long-term behaviour an RMS-bias drift of 10 degrees/h is obtained. | eng_Latn | 5,394 |
Effect of Changing the Symbol Rate of QAM Modem on the Performance of 32kb/s ADPCM System | This paper presents three models of Quadrature Amplitude Modulation (QAM) modem operating at data rate of 16.8kb/s to be transmitted over 32kb/s Adaptive Differential Pulse Code Modulation (ADPCM) channel. These modems operate at symbol rates of 2400, 2800, and 3360 baud with associated number of bits per symbol of 7, 6, and 5 respectively. The performance of ADPCM is studied considering these modems with different constellations. The simulation results show that the performance of ADPCM degrades as the symbol rate decreases or number of bits per symbol increases. Also, the performance with circular constellation is better than rectangular one. | The structure of GMA is introduced. Static displacement-force model and magnetism-machine coupling model for helping understand the magnetostriction and establishes simulation model are given. Simulation result shows that response time of machine part is slowness. It brings some disbennifit affection if minish damp. For example,exceed quantity and undulation will argument. It is important to ameliorate dynamic characteristic of the system to append a reasonable adjustor. | eng_Latn | 5,395 |
Assessments of Sc-Containing Ternary Systems Al–Sc–Ti and Al–Sc–Zr Within the Thermodynamic Database for Aluminium Alloys, TCAL5 | This paper presents the assessment of two Sc-containing ternary systems, Al–Sc–Ti and Al–Sc–Zr , within the project for developing the thermodynamic database for aluminium alloys TCAL5. A brief review was made on the Al-rich phase equilibria, which are relevant to the (Al) matrix phase and the hardening precipitate Al3Sc. The assessment highlights the modeling of molar volume of the Al3Sc phase. Using the resulting dataset, the lattice mismatch between the Al3Sc precipitates and the (Al) matrix phase was calculated at different temperatures and different Ti and Zr contents. The lattice mismatch would be useful for estimating the critical size at which precipitates start to loss coherency. | In this work, we introduce a new space---time coding (STC) paradigm which is based on the joint design of quasi-orthogonal space---time block code (Q-OSTBC) and the successive interference cancellation (SIC) detector. Based on the proposed principle, two high-rate Q-OSTBCs for three and four transmit antennas are designed. The symbols of the proposed Q-OSTBCs are of judiciously designed diversity order which can be effectively exploited by the SIC based receiver to cancel interference as well as to obtain diversity gain. The proposed SIC-amenable STC's amicable quasi-orthogonal structure also lends itself to efficient low-complexity linear decoding. Simulation results show that the proposed STC schemes achieve better multiplexing-diversity tradeoffs than the existing conventional schemes. | kor_Hang | 5,396 |
Instantaneous Mutual Information and Eigen-Channels in MIMO Mobile Rayleigh Fading | In this paper, we study two important metrics in multiple-input multiple-output (MIMO) time-varying Rayleigh flat fading channels. One is the eigen-channel, and the other is the instantaneous mutual information (IMI). Their second-order statistics, such as the correlation coefficient, level crossing rate (LCR), and average fade/outage duration, are investigated, assuming a general nonisotropic scattering environment. Exact closed-form expressions are derived and Monte Carlo simulations are provided to verify the accuracy of the analytical results. For the eigen-channels, we found they tend to be spatio-temporally uncorrelated in large MIMO systems. For the IMI, the results show that its correlation coefficient can be well approximated by the squared amplitude of the correlation coefficient of the channel, under certain conditions. Moreover, we also found the LCR of IMI is much more sensitive to the scattering environment than that of each eigen-channel. | We propose and experimentally demonstrate a low-loss and low-crosstalk Mach-Zehnder mode/wavelength multi/demultiplexer for WDM/MDM transmission. A broadband 3dB mode divider, which is also newly devised here, makes it possible to compose Mach-Zehnder filter for “mode” and “wavelength” simultaneously. | eng_Latn | 5,397 |
Unitary ESPRIT-based DOA estimation using sparse linear dual size spatial invariance array | We consider the direction-of-arrival estimation problem with a particular class of sparse linear arrays, composed of multiple widely separated subarrays. A new unitary ESPRIT- based direction-finding approach is proposed for such class of sensor arrays. The unambiguous estimates of direction cosines based on a half-wavelength baseline (invariance) and ambiguous ones based on a larger baseline are combined to obtain a better estimation accuracy. Simulation results show that proposed technique outperforms the original unitary ESPRIT which is used together with a ULA | Network performance can be improved by allowing adaptive routing, but doing so introduces new possibilities of deadlock which can overwhelm the flexibility advantages. Planar-adaptive routing resolves this tension by limiting adaptive routing to a series of two-dimensional planes, reducing hardware requirements for deadlock prevention. The authors explore the performance of planar-adaptive routers for two, three, and four-dimensional networks. Under nonuniform traffic loads, the planar-adaptive router significantly outperforms the dimension-order router, while giving comparable performance under uniform loads. With equal resources, the planar-adaptive router provides performance superior to fully adaptive routers because it requires less resources for deadlock prevention, freeing resources to increase the number of virtual lanes. > | eng_Latn | 5,398 |
Hybrid modulation as beacon replacement in CubeSat picosatellites | At present a CW beacon with Morse code or OOK modulation is still commonly used in picosatellites (especially in CubeSats) for signaling that picosatellite is currently rising above the horizon and for limited telemetry transmission about picosatellite functionality. This transmission with limited EIRP could be replaced by proposing group of hybrid modulations DM-FSK/DQPSK and M-FSK/DQPSK with better performances. These modulations offer a better spectral and energy efficiency in comparison to OOK and also offer the possibilities of continual received signal quality evaluation. This is useful for modulation adaptation or switching in the main picosatellite radio transmission subsystem. The main advantages of conventional CW beacon (such as simple signal processing and good human audibility in the noisy channel) stay with using of proposed hybrid modulations, presented in this paper. | We present calculations for {sup 8}Be-{sup 8}Be cluster states in {sup 16}O based on our recent schematic coupled-channels model. We justify some of the approximations made in the schematic model in this paper. The present calculations broadly support our assumptions about the states in {sup 16}O which formed the basis of our previous calculations in {sup 24}Mg. {copyright} {ital 1996 The American Physical Society.} | eng_Latn | 5,399 |
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