In cell-free massive MIMO, centralized precoding is {theoretically known} to {remarkably} outperform its distributed counterparts, albeit {with} high implementation complexity. However, this letter highlights a practical limitation {often overlooked:} {widely used closed-form} centralized {precoders} are typically derived under a sum-power constraint, which often demands unrealistic power allocation that exceeds hardware capabilities. {When two simple heuristics (global power scaling and local normalization) are applied to enforce the per-AP instantaneous power constraint}, the centralized performance superiority disappears, making distributed precoding {a robust option}.

翻译：在无蜂窝大规模MIMO系统中，集中式预编码在理论上显著优于分布式方案，但其实现复杂度较高。然而，本文指出一个常被忽视的实际限制：广泛使用的闭式集中式预编码器通常基于总功率约束推导，这种约束往往要求超出硬件能力的非现实功率分配。当采用两种简单启发式方法（全局功率缩放与本地归一化）来强制执行每接入点的瞬时功率约束时，集中式性能优势随之消失，使得分布式预编码成为稳健的选择。