Asymptotic Orthogonality Analysis of Time-Domain Sparse Massive MIMO Channels

TL;DR

This paper proves that realistic sparse massive MIMO channels can achieve asymptotic orthogonality of user channels, supporting favorable propagation conditions similar to ideal Gaussian models, with simulations confirming the theory.

Contribution

It provides the first theoretical proof that sparse massive MIMO channels satisfy asymptotic orthogonality, bridging the gap between practical channels and ideal models.

Findings

Sparse massive MIMO channels satisfy asymptotic orthogonality.

Favorable propagation condition holds in realistic sparse channels.

Simulation results confirm theoretical analysis.

Abstract

The theoretical analysis of downlink massive MIMO usually assumes the ideal Gaussian channel matrix with asymp- totic orthogonality of channel vectors associated with different users, since it can provide the favorable propagation condition. Meanwhile, recent experiments have shown that massive MIMO channels between a certain user and massive base station antennas appear the spatial common sparsity (SCS) in both the time domain and angle domain. This motivates us to investigate whether realistic sparse massive MIMO channels could provide the favorable propagation condition, and reveal the capacity gap between massive MIMO systems over realistic sparse channels and that under the ideal Gaussian channel matrix assumption. This paper theoretically proves that channel vectors associated with different users in massive MIMO over realistic sparse channels satisfy the asymptotic orthogonality, which indicates that the favorable propagation condition can also be provided. Moreover, the simulation results confirm the theoretical analysis.