A Partial Channel Reciprocity-based Codebook for Wideband FDD Massive MIMO

TL;DR

This paper introduces a novel CSI feedback framework for wideband FDD massive MIMO systems leveraging partial channel reciprocity, resulting in improved performance, reduced complexity, and lower feedback overhead compared to existing 5G codebooks.

Contribution

The paper proposes a partial channel reciprocity (PCR) codebook based on the low-rankness of the channel covariance matrix, enhancing CSI acquisition in wideband FDD massive MIMO.

Findings

PCR codebook outperforms 5G codebook in simulations

Achieves higher CSI accuracy with less feedback

Reduces complexity at user and base station sides

Abstract

The acquisition of channel state information (CSI) in Frequency Division Duplex (FDD) massive MIMO has been a formidable challenge. In this paper, we address this problem with a novel CSI feedback framework enabled by the partial reciprocity of uplink and downlink channels in the wideband regime. We first derive the closed-form expression of the rank of the wideband massive MIMO channel covariance matrix for a given angle-delay distribution. A low-rankness property is identified, which generalizes the well-known result of the narrow-band uniform linear array setting. Then we propose a partial channel reciprocity (PCR) codebook, inspired by the low-rankness behavior and the fact that the uplink and downlink channels have similar angle-delay distributions. Compared to the latest codebook in 5G, the proposed PCR codebook scheme achieves higher performance, lower complexity at the user side, and requires a smaller amount of feedback. We derive the feedback overhead necessary to achieve asymptotically error-free CSI feedback. Two low-complexity alternatives are also proposed to further reduce the complexity at the base station side. Simulations with the practical 3GPP channel model show the significant gains over the latest 5G codebook, which prove that our proposed methods are practical solutions for 5G and beyond.