Optimization-based Phase-shift Codebook Design for Large IRSs

TL;DR

This paper introduces an optimization-based method for designing phase-shift codebooks for large IRSs, improving power efficiency and reducing complexity compared to existing designs.

Contribution

It proposes a novel optimization framework for both continuous and discrete phase-shift codebook design, including an optimal algorithm for discrete and a low-complexity solution for continuous phases.

Findings

Discrete phase-shift design with 2-bit quantization approaches continuous performance.

Proposed algorithms enable flexible codebook sizes and beamwidths.

Significant transmit power savings over existing codebook designs.

Abstract

In this paper, we focus on large intelligent reflecting surfaces (IRSs) and propose a new codebook construction method to obtain a set of pre-designed phase-shift configurations for the IRS unit cells. Since the complexity of online optimization and the overhead for channel estimation scale with the size of the phase-shift codebook, the design of small codebooks is of high importance. We consider both continuous and discrete phase-shift designs and formulate the codebook construction as optimization problems. To solve the optimization problems, we propose an optimal algorithm for the discrete phase-shift design and a low-complexity sub-optimal solution for the continuous design. Simulation results show that the proposed algorithms facilitate the construction of codebooks of different sizes and with different beamwidths. Moreover, the performance of the discrete phaseshift design with 2-bit quantization is shown to approach that of the continuous phase-shift design. Finally, our simulation results show that the proposed designs enable large transmit power savings compared to the existing linear and quadratic codebook designs [1], [2].