MIMO系统中基于树形码本的高效反馈方案

为了进一步降低有限反馈系统的反馈量,提出一种基于树形码本的高效反馈方案.对于具有时间相关性的信道,下一时刻最优码字的分布取决于当前时刻波束成形矢量,树形码本的特点是同一支上的码字在矢量空间上距离较近,在已知当前时刻码字的条件下,将搜索范围限定在一个小码本内,从中搜索最优码字,从而降低反馈量.仿真结果表明:基于树形码本设计的高效反馈方案能在不降低系统性能的前提下有效地减少系统反馈信息量;反馈量的减少和信道多普勒频偏有关,多普勒频偏越小,信道的变化越缓慢,搜索码本也越小,反馈量改善效果就越明显.因此,在具有时间相关信道中,利用所提出的基于树形码本的高效反馈方案,能以较低的反馈量获取与传统方案相似的系统性能.

Efficient feedback approach based on tree-structured codebook for MIMO systems

In order to get a further reduction in amount for the limited feedback system,an efficient scheme is proposed based on the tree-structured codebook. When the channel is time correlated,the distribution of the optimum codeword for the next time-slot depends on the beam forming vector at present.The tree-structured codebook is characterized by the short distance in the vector space when the code words are in the same branch.The searching range for the next moment is restricted in a small codebook when the optimum codeword is known at present; therefore the feedback amount is reduced.Simulation results show that the new approach can improve the feedback amount without performance degradation.Moreover,the feedback amount depends heavily on the Doppler frequency.With a smaller frequency,the variation of the channel is slower and the searching codebook is smaller,which leads to a more noticeable feedback performance improvement.By utilizing the channel correlation information in the time domain,the new scheme obtains the same performance as the traditional feedback scheme while the required feedback information is significantly reduced.