Channel capacity of adaptive transmission with maximal ratio combining in correlated Rayleigh fading

We derive closed-form expressions for the single-user capacity of maximal ratio combining diversity systems taking into account the effect of correlation between the different branches. We consider a Rayleigh fading channel with two kinds of correlation: 1) equal branch signal-to-noise ratios (SNRs) and the same correlation between any pair of branches and 2) unequal branch SNRs and arbitrary correlation between branches such that the eigenvalues of the branch covariance matrix are all distinct. Three adaptive transmission schemes are analyzed: 1) optimal simultaneous power and rate adaptation; 2) optimal rate adaptation with constant transmit power; and 3) channel inversion with fixed rate.     

On spectral efficiency of low-complexity adaptive MIMO systems in Rayleigh fading channel

Adaptive MQAM modulation is used to maximize spectral efficiency of Multiple-Input Multiple-Output (MIMO) systems while keeping bit error rate (BER) under a target level. Closed-form expressions of the average spectral efficiency, coined as discrete-rate spectral efficiency (DRSE), are derived for adaptive modulation MIMO systems using different algorithms. To further enhance the spectral efficiency, a low complexity adaptation scheme is suggested to switch across different algorithms based on the DRSE. In the current letter, we investigate the adaptation scheme that switches between Orthogonal Space-Time Block Codes (OSTBC) and spatial multiplexing with zero-forcing (ZF) detection for MIMO systems with two transmit antennas. Two types of operating environment are considered: flat Rayleigh fading channel without spatial correlation and spatially correlated Rayleigh fading channel with transmit correlation.     

Ergodic capacity formula of MIMO-OFDM systems under correlated frequency selective Rayleigh fading channels

An explicit formula for the ergodic capacity of Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) systems under correlated frequency selective Rayleigh channels is derived,by simplifying the channel response matrix in frequency domain into the so-called Kronecker model composed of three kinds of correlations,i.e.multipath tap gain correlation and spatial fading correlations at both transmitter and receiver.The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity.If taps are independent,there is a very simple expression for the ergodic capacity.In case of tap correlation,the capacity formula could be further given in an integral expression.The validity of the new formula is verified and the effects of correlations,delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.     

Performance analysis of adaptive loading OFDM under Rayleigh fading

In this paper, we investigate the performance of adaptive loading orthogonal frequency-division multiplexing (OFDM) under Rayleigh fading with maximal ratio-combining (MRC) diversity at the receiver. We assume that channel-state information is available at both the transmitter and the receiver. Closed-form expressions for the lower bound on the average capacity of OFDM transmission under Rayleigh fading are provided for ideal MRC diversity. Simple approximate expressions for the average capacity of the Rayleigh-fading channel are also provided for the high signal-to-noise ratio (SNR) case. In the second part of this paper, a maximum-rate adaptive-loading strategy is derived for uncoded quadrature-amplitude-modulation modulated OFDM. Simple lower bound expressions and high-SNR approximations are provided for the average spectral efficiency of the maximum-rate adaptive-loaded uncoded OFDM under Rayleigh-fading channel conditions. According to the results, the performance of the uncoded adaptive-loading OFDM is about 8.5 dB inferior to the capacity bound at 10/sup -5/ symbol error probability under frequency-selective Rayleigh fading.     

Average channel capacity for Rayleigh fading spread spectrum MIMO systems

In this paper, a novel approach to the problem of estimating the average channel capacity (in the Shannon sense) assigned to each user of a spread spectrum (SS) multiple‐input multiple‐output (MIMO) system operating in a Rayleigh fading environment, is presented. The analysis leads to a closed‐form expression which fully conforms to the upper bound of the channel capacity value of a non‐fading AWGN channel when the transmitted signal bandwidth tends to infinity proving the validity of the described analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

Ergodic capacity of switch-and-examine combining under flat Rayleigh fading channels

Switch-and-examine combining (SEC) is an interesting diversity technique that is simpler than selection combining (SC), whereas its performances is similar in terms of bit error rate (BER) and diversity order. As ergodic capacity is also a key performance index in modern wireless systems, this article analyzes the ergodic capacity of the SEC system. The numerical results show that the ergodic capacity of SEC with optimal threshold is similar to that of SC for arbitrary number of diversity branches.     

MIMO-DCSK通信系统在瑞利衰落信道下的误码性能分析

对多输入多输出差分混沌相移键控(MIMO-DCSK)通信系统在瑞利衰落信道下的性能进行了分析,给出了基于中心极限定理的高斯近似误码率表达公式,并与计算机仿真数据进行比较。仿真结果表明:随着扩频因子的增大,高斯近似误码率曲线与实际仿真误码率曲线的一致性也随之增强;相比DCSK系统,随着发送天线数量和接收天线数量的增加,MIMO-DCSK系统的误码性能有较大提升,且增加接收天线的数量可以比增加发送天线的数量获得更大的增益;随着发送天线数量的增多,不同天线间信号的非正交性导致理论误码率曲线与仿真曲线出现差别,在扩频因子增大后趋于一致。     

High capacity wireless multimedia transmission with unequal error protection over Rayleigh fading channel

Efficient use of the available bandwidth and power resources for real-time multimedia transmission with high data rate and quality of service guarantee is one of the main challenges for next generation wireless systems. In image and video applications, the reception quality is highly sensitive to transmission delay, data loss, and error performance. Therefore, feasible transmission techniques over realistic channel conditions and detection methods are required to meet the increasing demands of multimedia services. In this paper, adaptive real-time communication (ARTC) system based superposition coding and layered detection is proposed for higher capacity visual data transmission over Rayleigh fading channel with unequal error protection (UEP). In the transmitter side, the source data is splitted into two streams depending on their importance, high priority and low priority. These two bit streams are modulated individually using different adjustable power allocation ratio according to partial feedback of channel state information with a constraint of total transmitted power during every symbol period. The received signal is detected using low complexity layered receiver with successive interference cancellation. To evaluate the system performance, constellation constrained capacity formula is derived. Under same resources of bandwidth, power, and time, extensive simulation results demonstrate the effectiveness of proposed ARTC scheme and shows significant improvement in capacity and bit-error-rate compared with the conventional direct single stream transmission and hierarchical modulation. Furthermore, the unequal importance characteristics of visual data are well exploited to attain reliable communication with UEP property.     

协同通信系统中差分调制在Rayleigh衰落信道中的误码性能分析

根据源-中继-目的节点链路的等效信噪比模型,推导了检测传送和选择检测传送两种协议下目的节点瞬时信噪比的概率密度函数和特征函数,基于此推导了协同DMPSK调制近似误符号率的闭合表达式.推导结果不含积分表达式,方便计算,为系统设计和功率分配提供了理论基础.最后通过仿真验证了推导结果的正确性.     

Shannon capacity of STBC in Rayleigh fading channels

Space-time block coding (STBC) is a powerful transmit diversity scheme for multiple antenna systems. A closed-form expression for the Shannon capacity of MIMO systems is derived using STBC under independent and quasi-static flat Rayleigh fading channels. The Shannon capacity of STBC over such channels is expressed as a finite sum of functions that are easy to evaluate, thereby avoiding the need for numerical integration or Monte Carlo simulation.     

Effective capacity of a correlated Rayleigh fading channel

The next generation wireless networks call for quality of service (QoS) support. The effective capacity (EC) proposed by Wu and Negi provides a powerful tool for the design of QoS provisioning mechanisms. In their previous work, Wu and Negi derived a formula for effective capacity of a Rayleigh fading channel with arbitrary Doppler spectrum. However, their paper did not provide simulation results to verify the accuracy of the EC formula derived in their paper. This is due to difficulty in simulating a Rayleigh fading channel with a Doppler spectrum of continuous frequency, required by the EC formula. To address this difficulty, we develop a verification methodology based on a new discrete‐frequency EC formula; different from the EC formula developed by Wu and Negi, our new discrete‐frequency EC formula can be used in practice. Through simulation, we verify that the EC formula developed by Wu and Negi is accurate. Furthermore, to facilitate the application of the EC theory to the design of practical QoS provisioning mechanisms in wireless networks, we propose a spectral‐estimation‐based algorithm to estimate the EC function, given channel measurements; we also analyze the effect of spectral estimation error on the accuracy of EC estimation. Simulation results show that our proposed spectral‐estimation‐based EC estimation algorithm is accurate, indicating the excellent practicality of our algorithm. Copyright © 2010 John Wiley & Sons, Ltd.     

Estimate of channel capacity in Rayleigh fading environment

The channel capacity in a Rayleigh fading environment is derived. The result shows that the channel capacity in a Rayleigh fading environment is always lower than that in a Gaussian-noise environment. When operating a digital transmission in a mobile radio environment that has Rayleigh fading statistics, it is very important to know the degradations in channel capacity due to Rayleigh fading, and also to what degree the diversity schemes can raise the channel capacity in a Rayleigh fading environment. The curves are generated to show the degradation of channel capacity in a Rayleigh fading environment and its improvement by diversity schemes     

Capacity analysis for distributed antenna systems using cooperative transmission schemes in fading channels

Wireless systems equipped with distributed antennas can provide enhanced data throughput as well as improved signal quality when appropriate cooperative transmission schemes among antennas are employed. In this paper, the performance of distributed antenna systems (DAS) under the influence of Rayleigh fading and log-normal shadowing effects is investigated for different cooperation strategies, and corresponding statistical distributions for both the signal-to-interference ratio (SIR) and the capacity are presented. Specifically, the ergodic capacity per remote antenna (RA) is determined when n RAs cooperatively transmit the desired signal to the target receiver, which is compared with the non-cooperative single-antenna transmission (SAT) case. Using the results, a preferable mode of operation for given geographic locations of the receiver is determined. We further propose to perform an adaptive operation between the cooperative and non-cooperative modes under the capacity maximization criteria, and quantify exact amounts of capacity gain over individual transmission modes.     

Approximate distribution of capacity of Rayleigh fading MIMO channels

Approximate closed-form density and distribution functions for the capacity of multiple-input multiple-output (MIMO) radio systems in spatially semi-correlated Rayleigh fading channels are derived. The approximations are given in terms of the Meijer G-function, hence allowing easy numerical evaluation of capacity outage probabilities with, for example, Maple or Mathematica.     

频率选择性衰落环境中MIMO系统信道容量研究

提出了一种频率选择性环境中多输入多输出系统信道容量的分析方法.该方法基于接收均匀圆阵构建了蕴含天线间距、散射角大小和多径数等模型物理参数的衰落空间相关模型。分析了MIMO OFDM系统信道衰落的统计特性。在此基础上利用Wishart分布的性质详细推导了任意天线数的MIMO OFDM系统的信道容量及其上下限。该方法回避了已有方法需要求取信道衰落相关特征值概率密度函数的问题，降低了运算量；并且可以有效地分析在频率选择性环境中模型物理参数对信道容量的影响。仿真结果表明，随着天线间距的增大，系统的平均信道容量也逐渐增大；但当天线间距增大到一定程度后,信道容量变化不明显，散射角越大，信道容量的增长速率越快，当接收信噪比较高时,平均信道容量的上下限接近于其实际值。     

On multicell cooperative transmission in backhaul-constrained cellular systems

Recent work has shown that multicell cooperative signal processing in cellular networks can significantly increase system capacity and fairness. For example, multicell joint transmission and joint detection can be performed to combat intercell interference, often mentioned in the context of distributed antenna systems. Most publications in this field assume that an infinite amount of information can be exchanged between the cooperating base stations, neglecting the main downside of such systems, namely, the need for an additional network backhaul. In recent publications, we have thus proposed an optimization framework and algorithm that applies multicell signal processing to only a carefully selected subset of users for cellular systems with a strongly constrained backhaul. In this paper, we consider the cellular downlink and provide a comprehensive summary and extension of our previous and current work. We compare the performance obtained through centralized or decentralized optimization approaches, or through optimal or suboptimal calculation of precoding matrices, and identify reasonable performance–complexity trade-offs. It is shown that even low-complexity optimization approaches for cellular systems with a strongly constrained backhaul can yield major performance improvements over conventional systems.     

Application of best relay selection approach to cooperative DF IDMA systems over Rayleigh/Weibull fading channels

This paper analyzes the performance of cooperative decode‐and‐forward (DF) interleave‐division multiple‐access (IDMA) networks with best relay selection over Rayleigh/Weibull fading environments. In the analysis, approximate outage probability (OP) and bit error probability (BEP) expressions are derived for the considered system. Further, a 2‐hop DF IDMA system is also designed to compare with cooperative one. We propose OP and BEP expression for 2‐hop DF IDMA systems. Numerical results are obtained by changing the number of relays and the value of fading parameter in the proposed expressions. Also, simulations are provided to corroborate the exactness of the derived approximate OP and BEP expressions.     

Still image transmission using ARQ over Rayleigh fading channels

The authors propose a new ARQ scheme suitable for image transmission over radio channels. The proposed scheme detects only serious degradation and so attains higher throughput performance than the conventional ARQ scheme     

Performance of adaptive MC-CDMA detectors in rapidly fading Rayleigh channels

Multicarrier code-division multiple access (MC-CDMA) combines multicarrier transmission with direct sequence spread spectrum. Different approaches have been adopted which do not assume a perfectly known channel. We examine the forward-link performance of decision-directed adaptive detection schemes, with and without explicit channel estimation, for MC-CDMA systems operating in fast fading channels. We analyze theoretically the impact of channel estimation errors by first considering a simpler system employing a threshold orthogonality restoring combining (TORC) detector with a Kalman channel estimator. We show that the performance deteriorates significantly as the channel fading rate increases and that the fading rate affects the selection of system parameters. We examine the performance of more realistic schemes based on the minimum mean square error (MMSE) criterion using least mean square (LMS) and recursive least square (RLS) adaptation. We present a discussion which compares the decision-directed and pilot-aided approaches and explores the tradeoffs between channel estimation overhead and performance. We find that there is a fading rate range where each method provides a good tradeoff between performance and overhead. We conclude that the MMSE per carrier decision-directed detector with RLS estimation combines good performance in low to moderate fading rates, robustness in parameter variations, and relatively low complexity and overhead. For higher fading rates, however, only pilot-symbol-aided detectors are appropriate.     

On the capacity of slotted Aloha with Rayleigh fading: the roleplayed by the number of interferers

The role played by the number of interferers and the modulation choice in the performance of slotted Aloha networks with Rayleigh fading is investigated and discussed; the case of multiple transmitted power classes is also considered. A new capture model which takes the number of actual interferers into account is proposed. The network capacity is analytically estimated, and significant differences (depending on the modulation scheme) are found with respect to previously published results carried out by means of more common (and less accurate) capture models, also when the case of different transmitted power classes is considered