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摘要中继可以提高频谱利用率和无线传输可靠性，减少基站覆盖盲区、干扰和功率消耗。双向中继同单向中继相比，可在 2 个而不是 3-4 个时隙内完成用户间信息交换，因而具有更高的频谱效率，双向中继技术是目前无线通信领域的一个研究热点。 本文研究了无线协作通信系统中的双向中继波束成形技术。论文主要有如下几方面的工作： (1).研究对比了基于 AF 双向中继的三种波束成形技术，分别是最大和速率（Maximizing sum- rate，MSR）方案，最小均方根误差（Minimum mean square error ，MMSE）方案，迫零（Zero- forcing，ZF）方案。仿真结果表明在和速率与误码率的性能上，MSR 方案优于 MMSE 方案，MMSE 方案优于 ZF 方案。但在计算复杂度上，7484
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MSR方案最复杂，ZF 方案最简单； (2).研究了信道估计误差对双向中继的影响。引入信道估计误差模型，仿真了修正后的MSR方案，发现随着信道估计误差的增大，系统性能会变差； (3).仿真了一种基于功率分配的波束成形算法，讨论了两种情况，一是在限定的接收信噪比下求解最小总功率，二是在总功率限制下，求解最大的接收信噪比。
关键词 双向中继 多输入多输出 波束成形 迫零 最小均方误差 和速率 信道误差
功率分配
Title Beamforming Study for Two-way Relaying Cooperative
Wireless Communication Systems
Abstract
Relaying can improve spectral efficiency and reliability and reduce blind areas of
coverage, interference and power consumption of base-station. In two-way relaying
systems, unlike one-way relaying, users can exchange information during 2 slots rather
than 3-4 time slots and thus shows a higher spectral efficiency. Therefore, two-way
relaying techniques currently become a hot research topic in the field of wireless
communications.
This paper studies the two-way relay beamforming techniques in wireless
cooperative communication system. The main works of this paper are as follows:
1. Three relay beamforming methods based on AF two-way relaying are
investigated and compared as follows: maximizing sum-rate (MSR), minimum mean
square error (MMSE), zero- forcing (ZF). Simulation results show that the MSR
performs better than the MMSE in terms of sum-rate and bit error rate and the MMSE
is better than the ZF. However, for complexity, three beamformers have the decreasing
order: MSR> MMSE>ZF.
2. The impact of channel estimation error is studied in two-way relaying system.
A channel estimation error model is introduced. Simulation shows that the sum-rate
performance of system will become worse with the increase of channel estimation
error.
3. A beamforming algorithm based on power allocation (PA) is investigated for
two-way relay networks. The problem of minimizing the transmit power under the SNR
constraint and the problem of maximizing SNR under the power constraint are
discussed.
Keywords Two-way relay multi - input multi -output (MIMO) beamforming
zero-forcing (ZF) minimum mean square error(MMSE) sum-rate
channel error power distribution