Performance analysis of multiuser diversity with antenna selection in MIMO MRC systems

Homogeneous versus heterogeneous lunar mantle: Constraints from secondary crust production

In this paper, we present a comprehensive performance analysis for multiple‐input multiple‐output (MIMO) systems with multiuser diversity over Rayleigh fading channels. We derive exact closed‐form expressions of the outage probability and the average bit error rate (BER) for different MIMO schemes, including the selective combining (SC), maximum ratio combining (MRC) and space‐time block codes (STBC). We also provide the explicit upper bounds on the BER performance. Finally, the mathematical formalism is verified by numeric results that study the interaction between the antenna diversity and the multiuser diversity. It is observed that the system performance is deteriorated as the number of transmit antennas increases in multiuser scenario, which is unlike the case in single‐user systems. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper, we present a performance analysis for the user scheduling for the multiuser MRC MIMO systems exploiting the user and antenna diversities. We consider two scheduling schemes including absolute SNR-based scheduling and normalized SNR-based scheduling schemes. We propose the utilization of an antenna selection scheme to overcome the drawback of channel hardening in multiuser MIMO systems and to improve the system performance. We derive new closedform expressions for the average bit error rate of the presented schemes for two scenarios: Heterogeneous (independent nonidentically distributed SNRs- i.ni.d.) and Homogeneous (independent identically distributed SNRs- i.i.d.) cases. Using mathematical analysis and numerical simulations, we compare the presented schemes.

There has been an increasing interest in digital transmission in the field of mobile radio. In a mobile communication system, because of multipath propagation, the communication channel is modeled as a Rayleigh fading channel. One of the most efficient techniques to reduce the fading effect and improve the system performance is space diversity reception. The average bit error rate (BER) performance of TC M-ary PSK with 2 branch selection combining (SC) and maximal ratio combining (MRC) diversity systems on a correlated Rayleigh fading channel is analysed, and some numerical results are shown. Although the correlation between branch causes signal-to-noise (SNR) loss (relative to the uncorrelated fading case) for SC and MRC diversities, the diversity can lead one to achieve the diversity gain compared to a system without diversity. It is found that the diversity gain of TC 8PSK with SC and MRC diversities is decreased with increasing the fading correlation parameter /spl xi//sup 2/, the diversity gain of TC 8PSK with MRC diversity is larger than TC 8PSK with SC diversity.

Smart antennas can greatly improve the performance of wireless communication systems by providing better link quality and immunity to interference. A simple smart antenna structure is fixed beamforming and beam selection. More complex structures require combining of the signals from multiple receivers. In this paper we compare the performance of beam and antenna selection and combining techniques. Our results are based on recently reported statistical and measurement based spatial channel models and in most cases include impact of co-channel interference. We derive the probability density function (pdf) of SINR in space- and frequency-selective multiple clustered Rayleigh fading channel with finite angle spread (AS). We also analyze the outage capacity and probability of beam selection in flat fading assuming both correlated and independent fading between the antennas. Our analysis also includes the impact of erroneous beam or antenna selection. Furthermore, theoretical bounds for a hybrid of beam/antenna selection and maximal ratio combining (MRC) are presented. We show that beam selection techniques can be very effective against both multipath fading and co-channel interference. We also show that simple fixed beamforming networks such as Butler matrices are nearly as effective as more complex fixed beamforming networks.

The performance analysis of multiuser multiple-input multiple-output (MIMO) system with rate-adaptive modulation and antenna selection over Rayleigh fading channels is presented. By means of exact expression of bit error rate (BER), the suboptimal switching thresholds (ST) of fading gain subject to a target BER constraint are derived. It is shown that this suboptimal ST are very close to the optimal ST, and is more accurate than the conventional ST based on approximate BER expression. By the ST, we obtain exact closed-form expressions of the spectrum efficiency (SE) and average BER. Moreover, a tightly approximate BER is derived to simplify the calculation of exact BER, which has more accuracy than the existing approximate BER. Simulation results for SE and BER are in good agreement with the derived theoretical expressions. The results show that the multiuser MIMO with adaptive modulation can provide better SE than the single user counterpart, and the system SE using suboptimal ST is also higher than that using conventional ST.

Cross-layer techniques represent efficient means to enhance throughput and increase the transmission reliability of wireless communication systems. In this paper, a cross-layer design of aggressive adaptive modulation and coding (A-AMC), truncated automatic repeat request (T-ARQ), and user scheduling is proposed for multiuser multiple-input-multiple-output (MIMO) maximal ratio combining (MRC) systems, where the impacts of feedback delay (FD) and limited feedback (LF) on channel state information (CSI) are also considered. The A-AMC and T-ARQ mechanism selects the appropriate modulation and coding schemes (MCSs) to achieve higher spectral efficiency while satisfying the service requirement on the packet loss rate (PLR), profiting from the feasibility of using different MCSs to retransmit a packet, which is destined to a scheduled user selected to exploit multiuser diversity and enhance the system's performance in terms of both transmission efficiency and fairness. The system's performance is evaluated in terms of the average PLR, average spectral efficiency (ASE), outage probability, and average packet delay, which are derived in closed form, considering transmissions over Rayleigh-fading channels. Numerical results and comparisons are provided and show that A-AMC combined with T-ARQ yields higher spectral efficiency than the conventional scheme based on adaptive modulation and coding (AMC), while keeping the achieved PLR closer to the system's requirement and reducing delay. Furthermore, the effects of the number of ARQ retransmissions, numbers of transmit and receive antennas, normalized FD, and cardinality of the beamforming weight vector codebook are studied and discussed.

Yucca Mountain has been proposed by the U.S. Department of Energy as the nation’s long-term, permanent geologic repository for spent nuclear fuel or high-level radioactive waste. The potential repository would be located in Yucca Mountain’s unsaturated zone (UZ), which acts as a critical natural barrier delaying arrival of radionuclides to the water table. Since radionuclide transport in groundwater can pose serious threats to human health and the environment, it is important to understand how much and how fast water and radionuclides travel through the UZ to groundwater. The UZ system consists of multiple hydrogeologic units whose hydraulic and geochemical properties exhibit systematic and random spatial variation, or heterogeneity, at multiple scales. Predictions of radionuclide transport under such complicated conditions are uncertain, and the uncertainty complicates decision making and risk analysis. This project aims at using geostatistical and stochastic methods to assess uncertainty of unsaturated flow and radionuclide transport in the UZ at Yucca Mountain. Focus of this study is parameter uncertainty of hydraulic and transport properties of the UZ. The parametric uncertainty arises since limited parameter measurements are unable to deterministically describe spatial variability of the parameters. In this project, matrix porosity, permeability and sorption coefficient of the reactive tracer (neptunium) of the UZ are treated as random variables. Corresponding propagation of parametric uncertainty is quantitatively measured using mean, variance, 5th and 95th percentiles of simulated state variables (e.g., saturation, capillary pressure, percolation flux, and travel time). These statistics are evaluated using a Monte Carlo method, in which a three-dimensional flow and transport model implemented using the TOUGH2 code is executed with multiple parameter realizations of the random model parameters. The project specifically studies uncertainty of unsaturated flow and radionuclide transport caused by multi-scale heterogeneity at the layer and local scales. Typically, in studies of Yucca Mountain, the layer scale refers to hydrogeologic layers with layer-wise average properties, and the local scale refers to the spatial variation of hydraulic properties within a layer. While most studies of radionuclide transport in the UZ have been conducted at the layer scale, the uncertainty at the local scale within a layer is also important, since it affects flow path, velocity, and travel time of radionuclide. This report first presents the uncertainty caused by layer-scale heterogeneity of matrix permeability, porosity, and sorption coefficients of reactive tracers. Homogeneous fields of the parameters are generated at each hydrogeologic layer for Monte Carlo simulations. This study is referred to as the homogeneous case. To assess the uncertainty caused by local-scale heterogeneity, the sequential Gaussian simulator (SGSIM) of GSLIB (Deutsch and Journel, 1998) is used to generate heterogeneous parameter fields within each layer, and Monte Carlo simulations are conducted. This study is referred to as the heterogeneous cases. For the homogeneous and heterogeneous cases, the mean, variance, 5th and 95th percentiles of simulated state variables are estimated for uncertainty assessment. In addition, the statistics of the two cases are compared to investigate effect of local-scale heterogeneity on the unsaturated flow and radionuclide transport. It is found that the local-scale heterogeneity increased the predictive uncertainty of percolation flux and cumulative mass arrival for computational blocks below the footprint of proposed repository, whereas mean predictions are hardly affected. The local-scale heterogeneity significantly affects travel times to the water table for both conservative and reactive tracers. In the early simulation period, tracer mean travel times are delayed, whereas the influence of local-scale heterogeneity diminishes during the late simulation period. Simulated state variables in this project are more realistic than those of using one- or two dimensional models, due to a three-dimensional numerical model used in the project to characterize hydrological conditions at the UZ. Therefore, we expect that results of this project can be used directly to facilitate DOE site performance analysis and decision making.

In this paper, the performance of a mixed Terahertz/free-space optical (THz/FSO) wireless transmission system is studied, where the joint effects of channel fading and pointing errors are considered for both THz and FSO links. Employing the semi-blind amplify-and-forward protocol, we derive the cumulative distribution function and probability density function of the end-to-end signal-to-noise ratio. By applying the derived statistics, exact expressions for the outage probability (OP), average bit error rate (BER), and average channel capacity are obtained. In order to attain useful physical insights, asymptotic OP and average BER expressions are also presented. Based on them, the diversity gain is determined, which is shown to depend on channel fading and pointing errors of both links. In addition, by taking into account the hardware impairments, the OP of the non-ideal hardware system is derived. Moreover, the analysis is extended to multi-antenna scenarios and the asymptotic OP is obtained. Finally, illustrative numerical results are plotted and it can be observed that the path loss, channel fading, pointing errors and hardware impairments lead to a considerable degradation in system performance.

SummaryIn this paper, the performance of an underlay cognitive radio system with random mobility and imperfect channel state information (CSI) is investigated. The mobile user (MU) utilises maximum ratio combining (MRC) and selection combining (SC) diversity techniques as signal reception to improve the quality of received signal‐to‐noise ratio (SNR). Under the Rayleigh fading, random waypoint mobility model is employed to characterised the effect of the MU random mobility on the system performance. Thus, novel probability density function (PDF) and cumulative distribution function (CDF) for the two considered diversity techniques are derived. Through these, the outage probability and average bit error rate (ABER) closed‐form analytical expressions are then obtained to quantify the system performance under the MRC and SC schemes. The results illustrate the effect of imperfect CSI, user mobility which is characterised by pathloss and the network topology on the system performance. Also, the results depict that MRC offers the system better performance compared with SC under the same system conditions. The accuracy of the derived analytical expressions is verified through Monte‐Carlo simulations.

In this paper, we introduce a novel performance analysis of the η-μ generalized radio fading channels with integer value of the μ fading parameter, i.e. with even number of multipath clusters. This fading model includes other fading models as special cases such as the Nakagami-rn, the Hoyt, and the Rayleigh. We obtain novel unified and generic simple closed-form expressions for the average bit error rates and ergodic channel capacity in the additive white generalized Gaussian noise (AWGGN), which includes the additive Gaussian, the gamma, the Laplacian, and the impulsive noise as special cases. The receiver is assumed to be an L-branch maximal ratio combiner where we study the effect of having more deployed receiver antenna. Numerical evaluation as well as results from technical wireless literature validate the generality and the accuracy of the derived unified expressions under the studied test cases.

Reliable vehicular communications is fast becoming a necessity. Vehicle to infrastructure (V2I) communication, which is critical for safety, is often interrupted when vehicles travel in tunnels. Leaky Feeder (LF) or radiating cable have been the primary solution to provide wireless access in tunnels and mines, but being overlooked until now. The LF is a natural multi antenna transceiver ideal for broadband short rage access. In this work, we model the LF as a linear antenna array and derive the average bit error rate (BER) in Rayleigh fading channel considering Quadrature Phase Shift Keying (QPSK) and M-Array Quadrature Amplitude (M-QAM) Modulations. We consider maximal ratio transmission (MRT) at the transmission end and coherent detection and maximal ratio combining (MRC) at the receiving end. Analytical expressions are derived for the BER. The effects of slot spacing and carrier frequency on the BER are also studied. Numerical evaluations show that the LF is a strong candidate for tunnels with much lower BER than a single antenna transmitter with the same SNR.

Permutation index-quadrature spatial modulation: A spectral efficient spatial modulation for next generation networks

<p>This thesis considers the analysis of current and future cellular communication systems. The main focus is on multiuser multiple-input multiple-output (MU-MIMO) antenna systems. The goal of this work is to characterize the achievable spectral efficiency of MU-MIMO systems, as well as to analyze the performance of practical, linear MU-MIMO transceiver structures in heterogeneous propagation environments. The analytical derivations in this thesis are based on the mathematical theory of finite and large dimensional random matrices. A collection of new general random matrix theory results, which permit efficient numerical evaluation are derived. With downlink regularized zero-forcing (RZF) processing at a cellular base station (BS), a general framework for the analysis of the expected (average) signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral efficiency is developed for uncorrelated and semi-correlated Rayleigh fading, as well as uncorrelated Ricean fading propagation channels. In contrast to existing results, the presented analyses are extremely general, applicable to single-cellular, multi-cellular, as well as distributed antenna systems. These systems could consist of arbitrary numbers of transmit and receive antennas, link signal-to-noise-ratios (SNRs), equal and unequal transmit correlation structures, and line-of-sight (LoS) levels, respectively. Numerical results are presented for single-cellular, as well as for two-tier multi-cellular systems demonstrating the impact of novel BS coordination strategies to suppress dominant inter-cellular interference. With dominant LoS directions in the propagation channel, the instantaneous downlink zero-forcing (ZF) SNR of a given terminal is analyzed. The ZF SNR is shown to be approximated by a gamma distribution for any number of transmit and receive antennas, link SNRs, and LoS levels. Furthermore, for moderately sized MU-MIMO systems, simplified instantaneous and ergodic sum spectral efficiency analyses are presented with RZF, ZF and matched-filter (MF) transmission on the downlink, and minimum-mean-squared-error, ZF and maximum-ratio combining (MRC) on the uplink, respectively. The simple nature of the derived expressions lead to the discovery of several valuable system level insights as a function of the contributing network parameters. Numerical results are presented for conventional and moderate MU-MIMO systems. Considering downlink semi-correlated Rayleigh fading channels with spatial correlation at the BS, it is mathematically proven that common correlation patterns for each terminal predicts lower ergodic sum spectral efficiencies in comparison to terminal specific correlation patterns. Closed-form approximations for the expected SINR and ergodic sum spectral efficiency are derived for both MF and ZF precoding, demonstrating the sensitivity of unequal correlation structures on the expected signal, interference and noise powers, respectively. The presented numerical results provide a cautionary tale of the impact of unequal correlation patterns on MU-MIMO performance and the importance of modeling this phenomenon. Finally, an approximate uplink performance analysis of large MU-MIMO systems with MRC and space-constrained uniform linear antenna arrays (ULA) is presented for semi-correlated Ricean fading channels. A space-constrained channel model is proposed, encapsulating the effects of unequal receive spatial correlation, unequal LoS levels, and unequal link gains for each terminal. The per-terminal and cell-wide ergodic sum spectral efficiencies are characterized and numerous practical special cases are presented. A limiting analysis of the ergodic per-terminal and cell-wide spectral efficiencies is also carried out, as the number of BS antennas grow without bound with a finite number of terminals and fixed physical dimensions of the ULA. Numerical results demonstrate the impact of space-constrained ULAs on the MU-MIMO system performance with variation in the LoS levels, correlation structures, physical array dimensions, and system size, respectively.</p>

We focus on fairness and stability of the congestion control mechanisms adopted in several versions of TCP by investigating their time-transient behavior through an analytic approach. In addition to TCP Tahoe, TCP Reno, and TCP Vegas, we consider enhanced TCP Vegas which is proposed in this paper for fairness enhancements. We consider the homogeneous case, where two connections have the equivalent propagation delays, and the heterogeneous case, where each connection has different propagation delay. We show that TCP Tahoe and TCP Reno can achieve fairness among connections in the homogeneous case, but cannot in heterogeneous case. We also show that TCP Vegas can provide almost fair service among connection, but there is some unfairness caused by the essential nature of TCP Vegas. Finally, we explain the effectiveness of our enhanced TCP Vegas in terms of fairness and throughput.