Distributed massive multiple-input multiple output (mMIMO) system for low earth orbit (LEO) satellite networks is introduced as a promising technique to provide broadband connectivity. Nevertheless, several challenges persist in implementing distributed mMIMO systems for LEO satellite networks. These challenges include providing scalable massive access implementation as the system complexity increases with network size. Another challenging issue is the asynchronous arrival of signals at the user terminals due to the different propagation delays among distributed antennas in space, which destroys the coherent transmission, and consequently degrades the system performance. In this paper, we propose a scalable distributed mMIMO system for LEO satellite networks based on dynamic user-centric clustering. Aiming to obtain scalable implementation, new algorithms for initial cooperative access, cluster selection, and cluster handover are provided. In addition, phase shift-aware precoding is implemented to compensate for the propagation delay phase shifts. The performance of the proposed user-centric distributed mMIMO is compared with two baseline configurations: the non-cooperative transmission systems, where each user connects to only a single satellite, and the full-cooperative distributed mMIMO systems, where all satellites contribute serving each user. The numerical results show the potential of the proposed distributed mMIMO system to enhance system spectral efficiency when compared to noncooperative transmission systems. Additionally, it demonstrates the ability to minimize the serving cluster size for each user, thereby reducing the overall system complexity in comparison to the full-cooperative distributed mMIMO systems.

翻译：分布式大规模多输入多输出（mMIMO）系统在低地球轨道（LEO）卫星网络中作为一项前景广阔的技术被引入，旨在提供宽带连接。然而，在LEO卫星网络中实施分布式mMIMO系统仍面临若干挑战。这些挑战包括：随着网络规模增大，系统复杂度增加，需要提供可扩展的大规模接入实现；另一个难题是，由于太空中分布式天线间的传播时延差异，用户终端接收到的信号异步到达，破坏了相干传输，进而降低了系统性能。本文提出一种基于动态用户中心集群的可扩展分布式mMIMO系统，用于LEO卫星网络。为实现可扩展实施，我们提供了初始协作接入、集群选择及集群切换的新算法。此外，为补偿传播时延引起的相位偏移，实现了相位感知预编码。我们将所提出的用户中心分布式mMIMO系统与两种基线配置进行性能比较：非协作传输系统（每个用户仅连接一颗卫星）和全协作分布式mMIMO系统（所有卫星共同服务每个用户）。数值结果表明，与非协作传输系统相比，所提出的分布式mMIMO系统在提升系统频谱效率方面具有潜力；同时，该系统能够最小化每个用户的服务集群规模，从而相较于全协作分布式mMIMO系统降低整体系统复杂度。