While cell-free massive MIMO (CF-mMIMO) offers high network-wide throughput in static networks, especially for the worst-served users, its performance in mobile networks is not yet fully addressed. In this paper, we evaluate the performance of a mobile CF-mMIMO network under a comprehensive throughput model and show that it suffers from large performance degradation due to the combined effect of channel aging and handover delay. To restore the performance of CF-mMIMO under mobility, we formulate a novel optimization problem to maximize the nett throughput given by our comprehensive throughput model. We propose a near-optimal handover scheme, nearOpt, by directly solving the relaxed optimization problem with Newton's method. We then design a heuristic scheme, FairDiff, to prioritize handovers for the poorly-served users using a policy threshold based on Jain's fairness index, which achieves equivalently good performance as nearOpt but with an order of magnitude lower complexity. We present an extensive evaluation of the mobile throughput performance of our handover schemes under realistic urban network distributions and UE mobility patterns. Our results show that, unlike the existing literature benchmarks that either obtain very low throughput for the worst-performing users or high throughput at the cost of very high computational complexity, our FairDiff scheme consistently achieves the highest network-wide throughput with the lowest computational complexity among all considered schemes. We thus for the first time propose a handover scheme that delivers the promise of uniformly good throughput for mobile CF-mMIMO, making it a feasible architecture for practical mobile networks.

翻译：尽管无蜂窝大规模MIMO（CF-mMIMO）在静态网络中能够提供较高的全网吞吐量，尤其对服务最差的用户而言，但其在移动网络中的性能尚未得到充分研究。本文基于一个综合吞吐量模型评估移动CF-mMIMO网络的性能，结果表明由于信道老化与切换延迟的共同影响，其性能会出现显著下降。为恢复移动环境下CF-mMIMO的性能，我们构建了一个新颖的优化问题，旨在最大化综合吞吐量模型给出的净吞吐量。我们通过牛顿法直接求解松弛优化问题，提出了一种近似最优的切换方案nearOpt。随后，我们设计了一种启发式方案FairDiff，该方案基于Jain公平性指数设定策略阈值，优先为服务状况较差的用户执行切换，在实现与nearOpt相当性能的同时将计算复杂度降低一个数量级。我们在现实城市网络分布与用户设备移动模式下，对所提切换方案的移动吞吐量性能进行了广泛评估。结果表明，现有文献基准方案要么使性能最差用户获得极低吞吐量，要么以极高计算复杂度为代价换取高吞吐量；而我们的FairDiff方案在所有对比方案中始终以最低计算复杂度实现最高的全网吞吐量。因此，我们首次提出了一种能够为移动CF-mMIMO实现均匀优质吞吐量的切换方案，使其成为实际移动网络中可行的架构。