Performance of a Multicarrier CDMA System with Rayleigh Fading Multipath Channels

This paper examines the performance of a multicarrier CDMA system in a Rayleigh fading channel without a RAKE receiver. Since the multicarrier technique is a diversity reception technique used in the frequency domain, the signal is transmitted at different frequency bands and undergoes different fading. The superimposed signal of the multipath components after going through the mobile channel will be processed by an Fourier Transform to enter the frequency domain, where the time delays in various paths are converted to the phase shifts in the compound signal. In this paper, we use sounding bits to extract the characteristics of the mobile channel and to partly remove the multipath effect. From the simulation, it is found that the multicarrier technique is simpler than the technique used in the single carrier system with a RAKE receiver while producing a better performance than that of the RAKE receiver.     

瑞利衰落信道MDPSK相位比较解调性能

本文提出一种适合于瑞利衰落信道多进制差分相移键控系统相位比较解调的性能分析方法，推导出符号错误率解析表示式，考虑了瑞利衰落、时间选择性衰落和高斯白噪声对体制性能的影响，并针对衰落功率谱为高斯型和矩形分别对二进制、四进制和八进制情形进行了数值计算。     

Joint Detection and Diversity Techniques in CDMA Mobile Radio Systems

CDMA mobile radio systems suffer from intersymbol interference (ISI) and multiple access interference (MAI) which can be combated by using joint detection (JD) techniques. Furthermore, the time variation of the radio channels leads to degradations of the receiver performance due to fading. These degradations can be reduced by applying diversity techniques. Three suboptimum detection techniques based on matched filters (MF), zero forcing (ZF) and minimum mean square-error (MMSE) equalization are considered. For further improvements, switched and equal gain diversity techniques are employed to combat fading. The performance is depicted in terms of the average bit error probability versus the average SNR per bit in a single cell environment showing an appreciable improvement over the non diversity situation. Theoretical results for the SNR at the front end of the receiver and the BER for ideal channel are obtained and compared with the simulation results.     

Channel capacity per user in a power and rate adaptive hybrid DS/FFH‐CDMA cellular system over Rayleigh fading channels

The theoretically achievable average channel capacity (in the Shannon sense) per user of a hybrid cellular direct sequence/fast frequency hopping code‐division multiple‐access (DS/FFH‐CDMA) system, operating in a Rayleigh fading environment, was examined. The analysis covers the downlink transmission and leads to the derivation of a novel expression between the average channel capacity available to each system's user under simultaneous optimal power and rate adaptation and the system's parameters, providing an optimistic upper bound, useful for practical modulation and coding schemes. The final derived closed‐form expression can be useful for the design of the DS/FFH‐CDMA system because it provides a theoretical tool for the initial quantitative analysis. Finally, avoiding the application of complex theoretical algorithm or lengthy simulation, we theoretically derived numerical results to illustrate the presented analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Tradeoffs of Source Coding, Channel Coding and Spreading in Frequency Selective Rayleigh Fading Channels

This paper investigates the tradeoffs of source coding, channel coding and spreading in CDMA systems. We consider a system consisting of an image source coder, a convolutional channel coder, an interleaver, and a direct sequence spreading module. With different allocations of bandwidth to source coding, channel coding and spreading, the system is analyzed over a frequency selective Rayleigh fading channel. The performance of the system is evaluated using the cumulative distribution function of peak signal-to-noise ratio. Tradeoffs of different components of the system are determined through simulations. We show that, for a given bandwidth, an optimal allocation of that bandwidth can be found. Tradeoffs among the parameters allow us to tune the system performance to specific requirements.     

Vector Channel Estimation and Multiuser Detection for Multicarrier DS CDMA in Time and Frequency Selective Fading Channels

In a multicarrier direct-sequence code-division multiple access (MC DS CDMA) system, different fading channels for different users and/or different carriers are correlated in general; thus a vector channel model is more appropriate than disjoint scalar channel models. For multiuser MC DS CDMA systems, we propose (1) a generalized vector autoregressive model which accounts for correlation between different user/carrier fading channels, (2) the use of a two-phased algorithm to obtain the proposed model’s parameters, and (3) a receiver structure that consists of a generalized decorrelator followed by maximal-ratio combining (MRC) of uncorrelated carrier channel outputs of each user. The estimated fading coefficients provide the necessary quantities to MRC. The computer simulation results show that the proposed scheme has performance close to the case in which the channel is perfectly known, and outperforms separate scalar channel estimation case.     

Selection and MRC Diversity for a DS/CDMA Mobile Radio System through Nakagami Fading Channel

Spatial diversity is an attractive technology for coping with the fadingchannels encountered in mobile communications.In this paper, the bit error rate (BER) is analyzed theoretically fordiversity reception with a RAKE receiver in aNakagami fading environment using either selection or maximal ratio combining.A coherent binary phase-shiftkeying (CBPSK) direct sequence code division multiple access (DS/CDMA) systemis considered. An arbitrary branchcorrelation is also considered for any diversity order in the case ofidentical fading severity on the branches.     

一种基于空时相关的MIMO OFDM系统信道估计算法

提出了一种基于空时相关的MIMO OFDM系统信道估计算法,该算法以时域最小二乘信道估计(TD-LS-CE)为初始估计,充分利用在接收端已知的空时相关性,通过最小化FIR窗内多符号平均意义上的信道估计均方误差(MSE),获得对初始信道估计进行空时滤波的最优权系数,并进一步利用奇异值分解的方法大大降低该信道估计算法的复杂度。最后仿真结果表明,在相同的条件下,该信道估计算法在MSE、BER方面优于传统滑动平均(MA)信道估计算法在其最佳窗长时的性能,且在一定条件下可逼近理想信道估计性能。此外,空时相关性的增强还可进一步改善该信道估计算法的性能。