A primary design goal of the cell-free~(CF) massive MIMO architecture is to provide uniformly good coverage to all the user equipments~(UEs) connected to the network. However, it has been found that this requirement may not be satisfied in case the channels between the access points~(APs) and the UEs are mixed LoS/NLoS. In this paper, we try to address this issue via the use of appropriate power control in both the uplink and downlink of a CF massive MIMO system under mixed LoS/NLoS channels. We find that simplistic power control techniques, such as channel inversion-based power control perform sub-optimally as compared to max-min power control. As a consequence, we propose a particle swarm algorithm~(PSA) based power control algorithm to optimize the performance of the system under study. We then use numerical simulations to evaluate the performance of the proposed PSA-based solution and show that it results in a significant improvement in the fairness of the underlying system while incurring a lower computational complexity.

翻译：无小区大规模MIMO架构的主要设计目标是为网络中所有用户设备提供均匀良好的覆盖。然而，研究发现，当接入点与用户设备之间的信道为LoS/NLoS混合场景时，这一要求可能无法得到满足。本文尝试通过在上行链路和下行链路中采用适当的功率控制来解决该问题。我们发现，与最大最小公平功率控制相比，信道反转等简单功率控制技术性能次优。为此，我们提出一种基于粒子群算法的功率控制算法来优化系统的性能。通过数值仿真评估所提基于PSA的解决方案，结果表明该方法在显著提升系统公平性的同时，计算复杂度更低。