Limited Feedback Hybrid Precoding for Multi-User Millimeter Wave Systems

TL;DR

This paper proposes a low complexity hybrid analog/digital precoding method for multi-user millimeter wave systems, improving sum rates over analog-only solutions with minimal training and feedback.

Contribution

It introduces a hybrid precoding algorithm tailored for mmWave systems that balances performance and hardware constraints, with analysis and simulations demonstrating its effectiveness.

Findings

Hybrid precoding outperforms analog-only beamforming in sum rate.

Performance approaches unconstrained digital beamforming with small codebooks.

Algorithm requires minimal training and feedback overhead.

Abstract

Antenna arrays will be an important ingredient in millimeter wave (mmWave) cellular systems. A natural application of antenna arrays is simultaneous transmission to multiple users. Unfortunately, the hardware constraints in mmWave systems make it difficult to apply conventional lower frequency multiuser MIMO precoding techniques at mmWave. This paper develops low complexity hybrid analog/digital precoding for downlink multiuser mmWave systems. Hybrid precoding involves a combination of analog and digital processing that is inspired by the power consumption of complete radio frequency and mixed signal hardware. The proposed algorithm configures hybrid precoders at the transmitter and analog combiners at multiple receivers with a small training and feedback overhead. The performance of the proposed algorithm is analyzed in the large dimensional regime and in single path channels. When the analog and digital precoding vectors are selected from quantized codebooks, the rate loss due to the joint quantization is characterized and insights are given into the performance of hybrid beamforming compared with analog-only beamforming solutions. Analytical and simulation results show that the proposed techniques offer higher sum rates compared with analog-only beamforming solutions, and approach the performance of the unconstrained digital beamforming with relatively small codebooks.