Learning-Based Adaptive IRS Control with Limited Feedback Codebooks

Abstract

Intelligent reflecting surfaces (IRS) consist of configurable meta-atoms, which can change the wireless propagation environment through design of their reflection coefficients. We consider a practical setting where (i) the IRS reflection coefficients are achieved by adjusting tunable elements embedded in the meta-atoms, (ii) the IRS reflection coefficients are affected by the incident angles of the incoming signals, (iii) the IRS is deployed in multi-path, time-varying channels, and (iv) the feedback link from the base station to the IRS has a low data rate. Conventional optimization-based IRS control protocols, which rely on channel estimation and conveying the optimized variables to the IRS, are not applicable in this setting due to the difficulty of channel estimation and the low feedback rate. Therefore, we develop a novel adaptive codebook-based limited feedback protocol where only a codeword index is transferred to the IRS. We propose two solutions for adaptive codebook design: random adjacency (RA) and deep neural network policy-based IRS control (DPIC), both of which only require the end-toend compound channels. We further develop several augmented schemes based on the RA and DPIC.Numerical evaluations show that the data rate and average data rate over one coherence time are improved substantially by our schemes.

Deep Reinforcement Learning-Based Adaptive IRS Control with Limited Feedback Codebooks

“…1) Dependency between Meta-Atoms' Reflection Phase Shift and Attenuation: Much of the existing work on IRS reflec-A more comprehensive version of this paper is under review in IEEE Transactions on Wireless Communications [1]. C. G. Brinton was supported in part by the National Spectrum Consortium (NSC) under Grant W15QKN-15-9-1004 and Office of Naval Research (ONR) under Grant N00014-21-1-2472.…”

“…Let θ [t] denote the incident angle of the -th channel path to the IRS. 1 Under a far-field assumption where θ [t] is the same across all the meta-atoms, the impedance of meta-atom n can be described as [9]…”