Multiuser Precoding and Channel Estimation for Hybrid Millimeter Wave MIMO Systems

TL;DR

This paper introduces a low-complexity, efficient channel estimation method for hybrid millimeter wave MIMO systems that estimates the strongest AoAs without requiring explicit CSI feedback, enabling effective multiuser precoding.

Contribution

The paper presents a novel channel estimation algorithm for hybrid mmWave MIMO systems that reduces complexity and feedback, applicable to both sparse and non-sparse channels, and demonstrates significant rate improvements.

Findings

Achieves higher achievable rates than fully digital systems.

Reduces signaling overhead proportional to the number of users.

Provides a tight upper bound on system achievable rate.

Abstract

In this paper, we develop a low-complexity channel estimation for hybrid millimeter wave (mmWave) systems, where the number of radio frequency (RF) chains is much less than the number of antennas equipped at each transceiver. The proposed channel estimation algorithm aims to estimate the strongest angle-of-arrivals (AoAs) at both the base station (BS) and the users. Then all the users transmit orthogonal pilot symbols to the BS via these estimated strongest AoAs to facilitate the channel estimation. The algorithm does not require any explicit channel state information (CSI) feedback from the users and the associated signalling overhead of the algorithm is only proportional to the number of users, which is significantly less compared to various existing schemes. Besides, the proposed algorithm is applicable to both non-sparse and sparse mmWave channel environments. Based on the estimated CSI, zero-forcing (ZF) precoding is adopted for multiuser downlink transmission. In addition, we derive a tight achievable rate upper bound of the system. Our analytical and simulation results show that the proposed scheme offer a considerable achievable rate gain compared to fully digital systems, where the number of RF chains equipped at each transceiver is equal to the number of antennas. Furthermore, the achievable rate performance gap between the considered hybrid mmWave systems and the fully digital system is characterized, which provides useful system design insights.