Han Tongzhou, Zhao Danfeng
College of Information and Communication Engineering, Harbin Engineering University, Harbin 150001, China.
Entropy (Basel). 2021 Nov 22;23(11):1552. doi: 10.3390/e23111552.
In centralized massive multiple-input multiple-output (MIMO) systems, the channel hardening phenomenon can occur, in which the channel behaves as almost fully deterministic as the number of antennas increases. Nevertheless, in a cell-free massive MIMO system, the channel is less deterministic. In this paper, we propose using instantaneous channel state information (CSI) instead of statistical CSI to obtain the power control coefficient in cell-free massive MIMO. Access points (APs) and user equipment (UE) have sufficient time to obtain instantaneous CSI in a slowly time-varying channel environment. We derive the achievable downlink rate under instantaneous CSI for frequency division duplex (FDD) cell-free massive MIMO systems and apply the results to the power control coefficients. For FDD systems, quantized channel coefficients are proposed to reduce feedback overhead. The simulation results show that the spectral efficiency performance when using instantaneous CSI is approximately three times higher than that achieved using statistical CSI.
在集中式大规模多输入多输出（MIMO）系统中，会出现信道硬化现象，即随着天线数量的增加，信道表现得几乎完全是确定性的。然而，在无小区大规模MIMO系统中，信道的确定性较低。在本文中，我们提出使用瞬时信道状态信息（CSI）而非统计CSI来获得无小区大规模MIMO中的功率控制系数。在缓慢时变信道环境中，接入点（AP）和用户设备（UE）有足够的时间来获取瞬时CSI。我们推导了频分双工（FDD）无小区大规模MIMO系统在瞬时CSI下的可达下行链路速率，并将结果应用于功率控制系数。对于FDD系统，提出了量化信道系数以减少反馈开销。仿真结果表明，使用瞬时CSI时的频谱效率性能比使用统计CSI时高出约三倍。
