基于空域相关矩阵反馈的 Massive MIMO 双级预编码研究

作为未来移动通信系统的关键技术，Massive MIMO可以通过布置大量天线显著提升移动通信系统性能。然而，天线数的大幅增加使传统单级预编码技术不再适用于Massive MIMO系统。国内外文献提出了基于信道空域相关特性的双级预编码技术，将传统单级预编码分解成一级预编码和二级预编码，以实现高效的Massive MIMO预编码。一级预编码“看到”的等效信道尺寸较小，可以直接使用传统预编码技术；二级预编码取决于信道空域相关矩阵。由于基站侧的信道空域相关矩阵一般是未知的，本课题借鉴有限反馈思路提出了信道空域相关矩阵的“估计、量化和反馈”方案：移动台首先利用接收信号估计基站侧信道空域相关矩阵，然后对相关矩阵估值量化并将量化结果反馈给基站，基站利用得到的相关矩阵信息构造二级预编码矩阵。随着反馈比特数增加，本课题方案将逐渐逼近最优二级预编码矩阵，为二级预编码器的最优设计提供可靠的理论支撑。

As the key technology for future mobile communication, Massive MIMO can significantly improve the system performance by installing a lot of antennas. However, traditional single-stage precoding technique can be hardly used in Massive MIMO systems due to the large antenna number. To achieve a low complexity precoding scheme with low feedback cost, a dual-stage precoding technique has been proposed in existing works where the single-stage precoding is replaced by a dual-stage precoding, including a first stage precoding and a second stage precoding. The first stage precoding can see an equivalent channel with low dimension and thus the traditional precoding technique can be directly used for the first stage precoding. The second stage precoding depends on the channel spatial correlation which is usually unknown. In this proposal, we propose a scheme based on the estimation, quantization and feedback of the channel spatial correlation matrix: the mobile terminal first estimate the spatial correlation matrix through the received signal, quantize the estimation results and then feed the quantization results back to the base station. The feedback information for the correlation matrix can be used for constructing the second stage precoding matrix at the base station. As the increasing of number of the feedback bits, the proposed scheme can achieve the optimal second stage precoding asymptotically, which provides a reliable theoretical framework for the optimal design of the second stage precoding.