# Codebook Design for Channel Feedback in Lens-Based Millimeter-Wave Massive MIMO Systems

## TL;DR

This paper introduces a novel dimension-reduced subspace codebook for lens-based millimeter-wave massive MIMO systems, significantly reducing feedback overhead and improving channel quantization performance.

## Contribution

It proposes a new codebook leveraging mmWave channel properties and lens-based beam selection, addressing the lack of dedicated feedback schemes for such systems.

## Key findings

- Reduced feedback overhead compared to conventional codebooks
- Superior channel quantization performance in simulations
- Effective utilization of mmWave channel sparsity

## Abstract

The number of radio frequency (RF) chains can be reduced through beam selection in lens-based millimeter-wave (mmWave) massive MIMO systems, where the equivalent channel between RF chains and multiple users is required at the BS to achieve the multi-user multiplexing gain. However, to the best of our knowledge, there is no dedicated codebook for the equivalent channel feedback in such systems. In this paper, we propose the dimension-reduced subspace codebook, which achieves a significant reduction of the feedback overhead and codebook size. Specifically, we firstly utilize the limited scattering property of mmWave channels to generate the high-dimensional vectors in the channel subspace. Then, according to the function of lens and beam selector, we propose the dimension-reduced subspace codebook to quantize the equivalent channel vector.Moreover, the performance analysis of the proposed codebook is also provided.Finally, simulation results show the superior performance of the proposed dimension-reduced subspace codebook compared with conventional codebooks.