FDD Massive MIMO Based on Efficient Downlink Channel Reconstruction

TL;DR

This paper proposes a novel framework for downlink channel reconstruction in massive MIMO systems, enabling accurate CSI estimation with minimal training and feedback, thus enhancing spectral efficiency.

Contribution

It introduces an efficient downlink training scheme combined with an enhanced NOMP algorithm for accurate channel reconstruction in FDD massive MIMO systems.

Findings

eNOMP algorithm accurately extracts frequency-independent parameters

Downlink channel gains estimated with limited pilot overhead

System sum-rate approaches perfect CSI performance

Abstract

Massive multiple-input multiple-output (MIMO) systems deploying a large number of antennas at the base station considerably increase the spectrum efficiency by serving multiple users simultaneously without causing severe interference. However, the advantage relies on the availability of the downlink channel state information (CSI) of multiple users, which is still a challenge in frequency-division-duplex transmission systems. This paper aims to solve this problem by developing a full transceiver framework that includes downlink channel training (or estimation), CSI feedback, and channel reconstruction schemes. Our framework provides accurate reconstruction results for multiple users with small amounts of training and feedback overhead. Specifically, we first develop an enhanced Newtonized orthogonal matching pursuit (eNOMP) algorithm to extract the frequency-independent parameters (i.e., downtilts, azimuths, and delays) from the uplink. Then, by leveraging the information from these frequency-independent parameters, we develop an efficient downlink training scheme to estimate the downlink channel gains for multiple users. This training scheme offers an acceptable estimation error rate of the gains with a limited pilot amount. Numerical results verify the precision of the eNOMP algorithm and demonstrate that the sum-rate performance of the system using the reconstructed downlink channel can approach that of the system using perfect CSI.