# Channel Estimation and Hybrid Precoding for Distributed Phased Arrays Based MIMO Wireless Communications

## TL;DR

This paper introduces a novel DPA-MIMO architecture enabling efficient channel estimation and hybrid precoding in mmWave systems, leveraging sparse recovery algorithms and sub-array grouping to improve performance and reduce training overhead.

## Contribution

It proposes a coordinated pilot design, two sparse channel recovery algorithms, and a SIC-based hybrid precoding method tailored for DPA-MIMO systems, advancing the state-of-the-art in reconfigurable mmWave MIMO.

## Key findings

- The proposed estimators effectively exploit channel sparsity.
- Hybrid precoding achieves good performance with low complexity.
- Reduced training overhead compared to traditional methods.

## Abstract

Distributed phased arrays based multiple-input multiple-output (DPA-MIMO) is a newly introduced architecture that enables both spatial multiplexing and beamforming while facilitating highly reconfigurable hardware implementation in millimeter-wave (mmWave) frequency bands. With a DPA-MIMO system, we focus on channel state information (CSI) acquisition and hybrid precoding. As benefited from a coordinated and open-loop pilot beam pattern design, all the sub-arrays can perform channel sounding with less training overhead compared with the traditional orthogonal operation of each sub-array. Furthermore, two sparse channel recovery algorithms, known as joint orthogonal matching pursuit (JOMP) and joint sparse Bayesian learning with $\ell_2$ reweighting (JSBL-$\ell_2$), are proposed to exploit the hidden structured sparsity in the beam-domain channel vector. Finally, successive interference cancellation (SIC) based hybrid precoding through sub-array grouping is illustrated for the DPA-MIMO system, which decomposes the joint sub-array RF beamformer design into an interactive per-sub-array-group handle. Simulation results show that the proposed two channel estimators fully take advantage of the partial coupling characteristic of DPA-MIMO channels to perform channel recovery, and the proposed hybrid precoding algorithm is suitable for such array-of-sub-arrays architecture with satisfactory performance and low complexity.