Analysis of Transmit Antenna Selection/Maximal-Ratio Combining in Rayleigh Fading Channels

In this paper, we investigate a multiple-input-multiple-output (MIMO) scheme combining transmit antenna selection and receiver maximal-ratio combining (the TAS/MRC scheme). In this scheme, a single transmit antenna, which maximizes the total received signal power at the receiver, is selected for uncoded transmission. The closed-form outage probability of the system with transmit antenna selection is presented. The bit error rate (BER) of the TAS/MRC scheme is derived for binary phase-shift keying (BPSK) in flat Rayleigh fading channels. The BER analysis demonstrates that the TAS/MRC scheme can achieve a full diversity order at high signal-to-noise ratios (SNRs), as if all the transmit antennas were used. The average SNR gain of the TAS/MRC is quantified and compared with those of uncoded receiver MRC and space-time block codes (STBCs). The analytical results are verified by simulation. It is shown that the TAS/MRC scheme outperforms some more complex space-time codes of the same spectral efficiency. The cost of the improved performance is a low-rate feedback channel. We also show that channel estimation errors based on pilot symbols have no impact on the diversity order over quasi-static fading channels.     

Optimum mode-switching-assisted constant-power single- and multicarrier adaptive modulation

A set of optimum mode-switching levels is derived for a generic constant-power adaptive-modulation scheme based on a closed-form expression of the average bit error ratio (BER) and the average bits-per-symbol (BPS) throughput of the adaptive-modulation scheme. This results in a constant BER, variable-throughput arrangement. The corresponding BPS throughput performance and the achievable signal-to-noise ratio (SNR) gain are investigated for the optimum mode-switching assisted constant-power adaptive-modulation schemes employing various diversity schemes, including maximal ratio combining (MRC) receive-antenna diversity, a two-dimensional RAKE receiver, as well as transmit-diversity aided space-time (ST) coding, when communicating over various fading scenarios. The BPS throughput of our constant-power adaptive quadrature amplitude modulation (AQAM) scheme approaches the throughput of variable-power variable-rate AQAM within 1 dB. However, the achievable throughput gain of the adaptive-modulation scheme, in comparison to conventional fixed-mode modems, is substantially reduced as the diversity order of the receiver is increased. Hence, adaptive modulation constitutes a lower complexity alternative to multiple-transmitter and receiver-based systems when considering the range of techniques that can be used for mitigating the effects of the channel-quality fluctuations imposed by wireless channels.     

Performance bounds for space-time block codes with receive antenna selection

In this correspondence, we present a comprehensive performance analysis of orthogonal space-time block codes (STBCs) with receive antenna selection. For a given number of receive antennas M, we assume that the receiver uses the best L of the available M antennas, where, typically, L/spl les/M. The selected antennas are those that maximize the instantaneous received signal-to-noise ratio (SNR). We derive explicit upper bounds on the bit-error rate (BER) performance of the above system for any M and L, and for any number of transmit antennas. We show that the diversity order, with antenna selection, is maintained as that of the full complexity system, whereas the deterioration in SNR is upper-bounded by 10log/sub 10/(M/L) decibels. Furthermore, we derive a tighter upper bound for the BER performance for any N and M when L=1, and derive an expression for the exact BER performance for the Alamouti scheme when L=1. We also present simulation results that validate our analysis.     

瑞利衰落信道下最大比发射联合选择接收技术的性能分析

本文设计了一种新的MIMO传输技术,它在发射端(基站)按最大比发射(MRT),接收端则基于信噪比最大的原则仅选择一根接收天线来处理信号,记MRT/RAS.其目标就是为了提高系统性能并降低接收端(移动台)的硬件复杂度.根据随机矩阵和排序统计的最新理论,推导出瑞利衰落信道下MRT/RAS系统的中断概率、误码率(BER)等性能指标的确切表达式.仿真结果表明MRT/RAS系统可以取得很好的阵列增益及满分集增益.仿真试验也证明了分析结果的正确性.     

Space-time trellis codes with transmit antenna selection

A scheme combining transmit antenna selection (TAS) and space-time trellis code (STTC), which is referred to as the TAS/STTC scheme, is considered. In this scheme, two transmit antennas, which maximise the signal-to-noise ratio (SNR) at the receiver, are chosen to transmit the baseline STTCs designed for two transmit antennas. It is shown by simulation that, similar to two other transmit antenna selection schemes investigated previously by the authors, this scheme also achieves a full diversity order as if all the transmit antennas were used. In addition, this scheme has a fixed low decoding complexity no matter how high the diversity order. Unlike the traditional STTC, this scheme does not have the requirement for minimum memory order to achieve a full diversity order.     

最大比发射/选择接收技术的性能研究

为了提高系统性能并降低接收端(移动台)的硬件复杂度,提出一种新的MIMO传输技术。即在发射端(基站)按最大比发射(MRT,maximal-ratio transmit)技术,接收端则基于信噪比最大的原则仅选择一根接收天线来处理信号,记作MRT/RAS(maximal-ratio transmit/receiver antenna selection)。根据随机矩阵和排序统计的最新理论,推导出瑞利衰落信道下MRT/RAS系统的中断概率、误码率(BER)等性能指标的确切表达式。仿真结果表明MRT/RAS系统可以取得很好的阵列增益及满分集增益。相同频谱条件下,性能超过某些复杂的空时编码系统。而且在准静态衰落信道下,信道估计错误对取得的分集阶数并没有影响。仿真试验也证明了分析结果的正确性。     

Average SNR of a generalized diversity selection combining scheme

The average signal-to-noise ratio (SNR) of a generalized selection combining scheme, in which the m diversity branches (m⩽L, where L is the total number of diversity branches available) with the largest instantaneous SNRs are selected and coherently combined, is derived. A Rayleigh fading channel is assumed, and a simple closed-form expression for the SNR is found which is upper bounded by the average SNR of maximal ratio combining, and lower bounded by average SNR of conventional selection combining     

Selection diversity combining with multiple antennas for MM-waveindoor wireless channels

Presents predetection and postdetection combining schemes for selection diversity reception with multiple antennas for MM-wave indoor radio channels. For those combining schemes, a reduction in complexity is achieved by limiting the number of combined signals to small values and by increasing the number of received signals. Bit error rate (BER) performance of binary phase shift keying (BPSK) with predetection combining of selected signals (CSS) and BER performance of differential BPSK with postdetection CSS are analyzed for slow fading and Rayleigh-distributed envelope statistics. Predetection maximal ratio combining of signals that comes from a single group or several groups of diversity channels as well as postdetection combining of received signals for groups of channels are considered. In comparing predetection combining with groups (PCG) and predetection combining of the best signals (PCB), we observe that the required SNR for achieving a certain BER is approximatively the same (with PCG having a slight advantage of 0.5 dB) for a given number, N, of diversity channels and L combined signals. Furthermore. PCG is equivalent to PCB for L=N since both techniques then correspond to conventional predetection maximal ratio combining (MRC), PCG and PCB are also equivalent when L=1 as both schemes then correspond to conventional selection combining. A small degradation of approximately 2 dB in the required SNR is observed when postdetection diversity reception with groups (PDG) is used instead of PCG. For L=N, PDG reduces to post detection MRC. The PDG technique is considered more suitable than PCB or PCG for MM-indoor wireless systems     

Switching rate and receiver performance of binary modulations with the selection‐and‐stay combining over independent and correlated Nakagami‐m fading channels

The dual‐branch selection‐and‐stay combining (SSTC) is analyzed for diversity reception on independent and correlated Nakagami‐m fading channels, where the conventional selection combining (SC) is employed only at the switching instance, and the receiver uses the selected branch till its signal‐to‐noise ratio (SNR) estimation is lower than a preset threshold. In this combining scheme, the receiver only needs to continuously estimate the SNR of the single selected branch. For the performance analysis of SSTC, the switching rate and the average bit error rates (BERs) of different binary coherent and non‐coherent modulations are evaluated. Numerical results based on the analysis and simulations are illustrated. According to the analysis and numerical results, the SSTC outperforms the existing switch‐and‐stay combining in the senses of the average BER and switching rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Joint Optimization Of “Transmission Rate” and “Outer-Loop SNR Target” Adaptation Over Fading Channels

Joint optimization of signal-to-noise ratio (SNR) target and transmission rate adaptation is examined for multilevel quadrature amplitude modulation (MQAM) over flat-fading channels, to maximize the spectral efficiency subject to an average transmit power constraint. We propose an adaptive transmission scheme in which the outer-loop SNR target and data rate are adapted to bit-error rate (BER), where total or truncated channel-inversion strategies are exploited for the (fast) inner-loop power control. We obtain the optimal solutions for both continuous and discrete rate adaptation, and consider cases where diversity combining is performed in the receiver. We show that by using this BER-based adaptive scheme, spectral efficiency can be improved compared with optimal SNR-based variable-rate variable-power MQAM. We also show that for continuous rate adaptation, the optimal SNR target monotonically increases with BER, while it descends within a BER range with constant rate     

常见分集合并系统的性能分析

在移动通信中,分集技术是一种最有效的抗衰落技术。本文对3种常见的线性合并分集技术进行简要分析,给出它们的基带表示和合并器输出信噪比的概率密度函数(pdf),由此给出它们的合并增益。针对系统采用MPSK调制的情况,对瑞利衰落信道的3种合并分集系统的比特误码率(BER)性能进行理论研究,分别给出选择性合并(SC)和最大比率合并(MRC)系统的理论比特误码率表达式;对于等增益合并(EGC)分集,给出了一种近似的EGC系统的输出信噪比的pdf,由此导出EGC的一种近似的BER表达式,由蒙特卡罗仿真结果可以看出此近似的BER数值结果是准确的。数值结果显示:MRC性能最好,EGC性能稍差,而SC性能较差。文中给出的分析方法对于实际分集系统的理论研究具有普遍的指导意义。     

Performance of partially coherent selection combining receiver in α-μ fading channel

In this paper the impact of the imperfect reference signal extraction is investigated, the bit error rate (BER) performance of multibranch selection combining (SC) receiver for binary and quaternary phase-shift keying (BPSK and QPSK) signals in a generalized α-μ fading channel are shown. The combined effects of imperfect phase estimation of the received signal, diversity order, fading severity and average signal-to-noise ratio (SNR) per bit on BER values are examined. The analytical results are verified by Monte Carlo simulations.     

一种双天线发射分集方案的性能分析

在平坦的瑞利衰落信道中,通过分析一种简单的双发射天线分集方案(即Alamouti编码方案,简称ACS)接收信号的统计特性和输出信噪比.在多相相移键控调制下,推导了该方案的传输比特误码率的一般理论分析式,证明了采用ACS技术的移动通信系统与采用2分集阶的最大比率合并接收分集技术的误码性能相同.Monte-Carlo仿真结果也验证此结论.这一理论成果可推广到采用正交空时分组码的多天线发射分集系统.     

High reliability of real-time visual data transmission using superposition coding with receiver diversity

Supporting visual data applications in the real-time communication systems are among the most challenging issues over the next generation wireless communication systems. This challenge is further magnified by the fact that the quality of reception is highly sensitive to transmission delay, data losses and bit error rate (BER) in such applications. In this paper, we proposed Superposition Coding with Receiver Diversity (SPC-RD) scheme, which employs unequal error protection (UEP) to improve the error performance, maximize the received signal to noise ratio (SNR) and optimize the reliability of the transmission system. In the transmitter side, the visual data is divided into a number of different priority layers based on their effects on the reception quality. These layers are modulated individually where the highest priority layer is modulated with the highest UEP level against error-prone channels, and vice versa. These modulated signals are then superimposed together and transmitted via wireless Single-Input Multiple-Output (SIMO) Rayleigh fading channel. In the receiver side, three different diversity combining approaches; selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered. The combined signal is then passed through a multiuser demodulator so-called the ordered successive interference cancellation (O-SIC) demodulator to reconstruct and separate the data layers. This demodulation technique is evaluated and compared with the traditionally maximum likelihood joint detection (MLJD) technique. Extensive simulations have been carried out to validate the various assertions. Under the assumption of equal transmission power, the simulation results illustrate that the proposed SPC-RD scheme provides a SNR gain of 14.5 dB over the Rayleigh fading channel at the diversity order of three for the acceptable BER level of 10^?3 when BPSK scheme is exploited compared to the traditional equal error protection system. In addition, the proposed scheme with O-SIC demodulation technique achieves almost similar performance compared to MLJD technique but using less computational complexity.     

Performance comparison of selection combining schemes for binary DPSK on nonselective Rayleigh-fading channels with interference

This paper is concerned with the error performance analysis of binary differential phase shift keying (DPSK) with differential detection over the nonselective Rayleigh-fading channel with selection diversity reception and with an additive, correlated, Gaussian interference process in each diversity channel. The fading process is assumed to have an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. The selection schemes investigated are: 1) the selection combining (SC) scheme based on signal-to-noise power ratio (SNR); 2) the SC scheme based on signal-plus-noise (S+N); and 3) the SC scheme based on maximum output (MO). New, exact, closed-form bit-error probability (BEP) expressions are derived, and a performance comparison among the three SC schemes and combining diversity reception is given. The results obtained reduce to previously known results when the correlated interference process is absent, and when the fading process does not fluctuate over the duration of several symbol intervals. The results indicate that the performance of each scheme depends on the tradeoff between the number of diversity branches, the SNR, the interference level, and the correlation of the interference process. However, the SC-(S+N) scheme generally performs worse than the SC-SNR scheme, the SC-MO scheme and combining diversity reception scheme. The findings presented here are not only of fundamental theoretical value, but are also of practical interest to the designers of future mobile communication systems.     

Progressive image transmission over space-time coded OFDM-based MIMO systems with adaptive modulation

This paper considers a progressive image transmission system over wireless channels by combining joint source-channel coding (JSCC), space-time coding, and orthogonal frequency division multiplexing (OFDM). The BER performance of the space-time coded OFDM-based MIMO system based on a newly built broadband MIMO fading model is first evaluated by assuming perfect channel state information at the receiver for coherent detection. Then, for a given average SNR (hence, BER), a fast local search algorithm is applied to optimize the unequal error protection design in JSCC, subjected to fixed total transmitted energy for various constellation sizes. This design allows the measurement of the expected reconstructed image quality. With this end-to-end system performance evaluation, an adaptive modulation scheme is proposed to pick the constellation size that offers the best reconstructed image quality for each average SNR. Simulation results of practical image transmissions confirm the effectiveness of our proposed adaptive modulation scheme.     

Boosted space-time diversity scheme for wireless communications

A novel concept of space-time diversity is developed. It is similar to 2 times 2 bit-interleaved space-time coded modulation with iterative decoding (BI-STCM-ID), except for labelling maps, which are different for the signals transmitted through particular antenna. In such an approach the so-called waterfall region of BER curves is observed at lower SNRs than for BI-STCM-ID systems. At the same time the proposed timesboostedtimes scheme is characterised by good BER against SNR asymptotic performance, which is proved by the results of Extrinsic Information Transfer (EXIT) Chart analysis, error-free feedback (EF) bounds, and results of the overall system simulation. It is shown that numerous labelling maps can be combined with a Gray one to meet specific requirements.     

Energy Savings in OFDM Systems through Cooperative Relaying

Energy savings in orthogonal frequency division multiplexing (OFDM) systems is an active research area. In order to achieve a solution, we propose a new cooperative relaying scheme operated on a per subcarrier basis. This scheme improves the bit error rate (BER) performance of the conventional signal‐to‐noise ratio (SNR)‐based selection relaying scheme by substituting SNR with symbol error probability (SEP) to evaluate the received signal quality at the relay more reliably. Since the cooperative relaying provides spatial diversity gain for each subcarrier, thus statistically enhancing the reliability of subcarriers at the destination, the total number of lost subcarriers due to deep fading is reduced. In other words, cooperative relaying can alleviate error symbols in a codeword so that the error correction capability of forward error correction codes can be fully exploited to improve the BER performance (or save transmission energy at a target BER). Monte‐Carlo simulations validate the proposed approach.     

基于准正交空时分组码的多中继协作方案

根据准正交空时分组码提出了一种基于选择中继协议的多中继协作方案。从两个方面讨论了该方案的空间分集性能,通过分析成对差错概率证明,若所有的中继都正确译码,该方案可以获得全分集增益;若某些中继不能正确译码,该方案仍可以获得部分分集增益。将所提方案与使用正交空时分组码的协作方案进行比较,仿真结果表明,在信噪比较高时,两个方案都可获得全分集增益,但所提方案具有更高的编码增益。而当信噪比变低时,所提方案具有更高的分集增益和编码增益。     

Exact error performance of square orthogonal space- time block coding with channel estimation

Consider a wireless communication system in flat fading with N transmit and M receive antennas using space-time block coding, where N/spl times/1 code vectors are transmitted over L symbol intervals, resulting in an N/spl times/L code matrix. A least-squares estimate (LSE) as well as a minimum mean-square estimate (MMSE) of the M/spl times/N channel matrix is obtained from a sequence of pilot code vectors. For the case of linear square (i.e., with N=L) orthogonal codes over constant envelope constellations, we obtain an expression for the exact decoding error probability (DEP) for coherent maximum-likelihood decoding. We also find the coding gain for high average signal-to-noise ratio (SNR) per diversity branch in the case of Rayleigh fading. A comparison between both channel-estimation techniques is done in terms of the average pilot-power-to-signal-power ratio (APPSPR). It is found that MMSE requires lower pilot power than LSE for the same DEP and the same average SNR per diversity branch. In addition, the error performance with LSE approaches that with MMSE, with an increase of average SNR per branch or an increase of APPSPR.