Abstract: In this paper, a Zero Forcing BeamForming (ZFBF) precoding scheme based on two-level codebook was proposed. The defect, that the performance of ZFBF precoding scheme was worse with fewer feedback bits in the multi-user Multiple Input Multiple Output (MIMO) system upon limited feedback, was well overcome by this scheme. In the proposed scheme, unitary matrix was combined with random vector codebook. The best beamforming vector in the one-level codebook was searched firstly and then the Signal to Interference and Noise Ratio (SINR) corresponding with the best beamforming vector in the disturbance range of orthogonal vector was calculated. Finally, the user's feedback information was decided by comparing the SINR calculated with the SINR threshold value set by system. At last, the codebook was adaptively changed and ZFBF precoding was finished by the station, according to the user's feedback information. The simulation results show that every user's average number of feedback bits is significantly reduced and a better sum rate performance with a lower feedback rate is gained. The codebook searching process is simplified and the sum rate performance is improved by this scheme successfully.

Key words: multi-user, Multiple Input Multiple Output (MIMO), limited feedback, two-level codebook, Zero Forcing BeamForming (ZFBF), adaptive precoding

摘要： 为了克服基于有限反馈的多用户多输入多输出(MIMO)系统中迫零波束成型(ZFBF)预编码方案反馈量小时性能较差的缺陷,提出一种基于二级码本的ZFBF自适应预编码方案。该方案的码本设计结合了酉矩阵和随机矢量码本,首先在一级码本中搜索最佳的波束成形矢量; 然后在扰动范围内计算最佳波束成形矢量对应的信干噪比(SINR),将其与系统设定的SINR门限值进行比较来决定用户的反馈信息; 最后基站根据用户的反馈信息自适应地改变码本,对用户进行ZFBF预编码。从而简化了用户端的码本搜索过程,并且在用户数较多的情况下用较少的反馈比特数达到较好的性能。仿真结果表明,该方案能够显著降低每用户的平均反馈比特数,以较低的反馈速率获得较好的和容量性能。

关键词: 多用户, 多输入多输出, 有限反馈, 二级码本, 迫零波束成型, 自适应预编码