Phase synchronization of access points (APs) in a distributed multiple-input multiple-output (D-MIMO) system is critical to leverage the performance benefits of D-MIMO. Existing over-the-air phase synchronization methods assume that APs can communicate directly to perform necessary measurements. However, this assumption might not hold in scenarios where inter-AP signaling is too weak for effective communication. To address this, in this paper, we propose a novel over-the-air calibration scheme that uses repeater nodes to facilitate phase synchronization when direct AP signaling is infeasible. We give the steps of the algorithm for phase calibration in closed form, and show how it enables coherent joint transmission (CJT) by the APs. The framework expands the applicability of D-MIMO systems to challenging environments, where existing over-the-air synchronization techniques fall short.

翻译：在分布式多输入多输出（D-MIMO）系统中，接入点（AP）的相位同步对于发挥D-MIMO的性能优势至关重要。现有的空中相位同步方法假设接入点能够直接通信以执行必要的测量。然而，当接入点间信号过于微弱而无法有效通信时，这一假设可能不成立。针对此问题，本文提出了一种新颖的空中校准方案，该方案利用中继节点在直接AP信令不可行的情况下促进相位同步。我们给出了相位校准算法的闭式步骤，并展示了该算法如何实现接入点间的相干联合传输（CJT）。该框架将D-MIMO系统的适用性扩展到现有空中同步技术难以奏效的挑战性环境中。