A Spatial Similarity-Guided Pilot Assignment and Access Point Selection for Cell-Free Massive MIMO Networks

TL;DR

This paper investigates pilot assignment and access point (AP) selection strategies for uplink cell-free massive multiple-input multiple-input multiple-output (CF-mMIMO) systems to improve interference management and spectral efficiency (SE).

Abstract

This paper investigates pilot assignment and access point (AP) selection strategies for uplink cell-free massive multiple-input multiple-output (CF-mMIMO) systems. We propose channel similarity-aware pilot assignment (CAPA) and AP selection schemes to improve interference management and, consequently, spectral efficiency (SE). The pilot assignment strategy dynamically allocates pilot sequences by evaluating inter-user channel similarity, ensuring that users (UEs) with high channel similarity are assigned orthogonal pilots to mitigate pilot contamination. Subsequently, an AP selection algorithm is introduced that prioritizes the selection of low-correlation APs to reduce interference and enhance spatial diversity. This selection process maintains robust UE-AP links while minimizing inter-AP redundancy. The combined approach significantly improves SE, particularly in dense network deployments. Simulation results are provided to demonstrate the effectiveness of the proposed strategies under dynamic UE scenarios.

Figures (2)

• Figure 1: SE per UE with different schemes
• Figure 2: 95% likely SE comparison with different number of pilot sequences $\tau_p$ for $L=100$, $N=4$, and $K=50$.