This article studies a novel distributed precoding design, coined team minimum mean-square error (TMMSE) precoding, which rigorously generalizes classical centralized MMSE precoding to distributed operations based on transmitter-specific channel state information (CSIT). Building on the so-called theory of teams, we derive a set of necessary and sufficient conditions for optimal TMMSE precoding, in the form of an infinite dimensional linear system of equations. These optimality conditions are further specialized to cell-free massive MIMO networks, and explicitly solved for two important examples, i.e., the classical case of local CSIT and the case of unidirectional CSIT sharing along a serial fronthaul. The latter case is relevant, e.g., for the recently proposed radio stripe concept and the related advances on sequential processing exploiting serial connections. In both cases, our optimal design outperforms the heuristic methods that are known from the previous literature. Duality arguments and numerical simulations validate the effectiveness of the proposed team theoretical approach in terms of ergodic achievable rates under a sum-power constraint.

中文翻译：

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使用无细胞大规模 MIMO 应用的团队 MMSE 预编码

本文研究了一种新颖的分布式预编码设计，即团队最小均方误差(TMMSE) 预编码，它将经典的集中式 MMSE 预编码严格推广到基于发射机特定信道状态信息 (CSIT) 的分布式操作。基于所谓的团队理论，我们以无限维线性方程组的形式推导出一组最优 TMMSE 预编码的充分必要条件。这些最优条件进一步专门用于无蜂窝大规模 MIMO 网络，并明确解决了两个重要示例，即本地 CSIT 的经典情况和沿串行前传的单向 CSIT 共享情况。后一种情况是相关的，例如，对于最近提出的无线电条纹概念和利用串行连接的顺序处理的相关进展。在这两种情况下，我们的优化设计都优于以前文献中已知的启发式方法。对偶论证和数值模拟验证了所提出的团队理论方法在总和功率约束下遍历可实现速率的有效性。