Distributed vs. Centralized Precoding in Cell-Free Systems: Impact of Realistic Per-AP Power Limits

2026-03-04

AI Summary

This work addresses the practical limitations of centralized precoding in cell-free massive MIMO systems, which often assumes idealized power constraints and thus fails to realize its theoretical performance gains in real-world deployments. By rigorously comparing centralized and distributed precoding under strict per-access-point (AP) instantaneous power constraints, the study evaluates their realistic performance and introduces two heuristic adaptation strategies: global power scaling and local normalization. The results demonstrate that, once practical per-AP power constraints are enforced, the performance advantage of centralized precoding vanishes and can even become inferior to distributed precoding. This finding highlights the superior robustness and practicality of distributed precoding in hardware-constrained scenarios, offering a more realistic perspective for system design.

Technology Category

• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Search and Optimization: Distributed Search
• Planning, Routing, and Scheduling: Applications

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Security and Privacy: Large-scale security measurements

Abstract

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}.

Problem

• cell-free massive MIMO
• centralized precoding
• per-AP power constraint
• distributed precoding
• power allocation

Innovation

• cell-free massive MIMO
• centralized precoding
• distributed precoding
• per-AP power constraint
• power scaling