Enabling Cooperative Hybrid Beamforming in TDD-based Distributed MIMO Systems

TL;DR

This paper introduces a low-complexity calibration method for distributed MIMO systems that compensates RF impairments, enabling effective cooperative hybrid beamforming in TDD-based wireless networks.

Contribution

A novel reciprocal tandem concept and a two-step calibration approach are proposed for joint AP calibration and downlink channel estimation in distributed MIMO.

Findings

Calibration improves beamforming accuracy

Numerical simulations validate effectiveness

Reduces complexity of calibration process

Abstract

Distributed massive MIMO networks are envisioned to realize cooperative multi-point transmission in next-generation wireless systems. For efficient cooperative hybrid beamforming, the cluster of access points (APs) needs to obtain precise estimates of the uplink channel to perform reliable downlink precoding. However, due to the radio frequency (RF) impairments between the transceivers at the two en-points of the wireless channel, full channel reciprocity does not hold which results in performance degradation in the cooperative hybrid beamforming (CHBF) unless a suitable reciprocity calibration mechanism is in place. We propose a two-step approach to calibrate any two hybrid nodes in the distributed MIMO system. We then present and utilize the novel concept of reciprocal tandem to propose a low-complexity approach for jointly calibrating the cluster of APs and estimating the downlink channel. Finally, we validate our calibration technique's effectiveness through numerical simulation.