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 Analysis of Common Diversity Combining Systems

Diversity is an effective technique on combating channel fading in mobile communications.The three common linear combining diversity approaches are analyzed,the base-band representation over combining branches of diversity system is described,and Probability Density Function(pdf) of output signal-to-noise ratio(SNR) of combination system and three diversity combining gains are evaluated.In flat Rayleigh fading channel,the bit-error-rate(BER) performance of three combining techniques for M-ary phase-shifting key(MPSK) are studied in theory,the BER expressions of selective combining(SC) and maximal ratio combining(MRC) are evaluated,respectively.Utilizing an approximate pdf of equal gain combining(EGC),a closed-form expression is obtained for the EGC diversity system.The Monte-Carlo simulation results verify that the approximate EGC values can replace the true values of EGC system in practical applications.Finally,the numerical values of selection combining(SC),MRC and EGC show that MRC performance is optimal,EGC is sub-optimal,and SC is the worst.The analysis methods given in this paper can provide guidance function in practical diversity system applications.