Optimal Pilot Signal Design and Two-Stage Hybrid-Field Channel Estimation for Extremely Large-Scale MIMO Systems

The paper proposes a co-design of pilot signal and channel estimator tailored for hybrid-field communications in extremely large-scale MIMO systems. It introduces a novel pilot signal design algorithm based on the alternating direction method of multipliers (ADMM) to minimize the mutual coherence of the sensing matrix, and a two-stage channel estimation algorithm that sequentially estimates the line-of-sight (LoS) channel component and the hybrid-field scattering channel components.