大规模MIMO下行预编码技术

[摘要] 考虑大规模多输入多输出（MIMO）中导频序列开销过大以及预编码复杂度的问题，提出了两种适用于大规模MIMO的预编码技术：基于用户调度和波束选择的波束分多址（BDMA）下行传输技术，即通过简单高效的贪婪算法进行用户调度和波束分配，使不同的用户在正交的波束上进行传输；基于用户分组的两级预编码技术，即基于用户分组的两级预编码方法，利用聚类算法将信道特性相似的用户分为一组，基站进行第一级组间干扰消除预编码，基站获取分组的等效瞬时信道后，进行第二级组内干扰消除预编码。研究结果证明：两种下行传输技术在解决大规模MIMO中导频开销过大和系统复杂度问题方面都是切实有效的。

[关键词] 大规模MIMO系统；用户调度；波束分多址；两级预编码

[Abstract] Considering the problem of costly pilot training and computation complexity in massive multiple input multiple output (MIMO) systems, two precoding techniques adapted to massive MIMO are proposed : beam division multiple access (BDMA) downlink transmission based on user scheduling and beam allocation, which can realize the orthogonal transmission of different users on non-overlapping beams by a simple and effective greedy algorithm; two-stage precoding technique based on user grouping, which partitions the users into multiple groups each with approximately channel covariance matrix by a clustering algorithm, the first-stage precoding aims to suppress inter-group interference, the second-stage precoding is conducted to mitigate intra-group interference after the base stations obtain the instantaneous effective channel of different groups. Research results demonstrate that both downlink techniques are practical in solving the costly pilot and complexity problem of massive MIMO.

[Keywords] massive MIMO system; user scheduling; beam division multiple access; two-stage beamforming