Double-Active-IRS Aided Wireless Communication: Deployment Optimization and Capacity Scaling

TL;DR

This paper investigates the deployment and capacity scaling of a double-active-IRS aided wireless system, optimizing reflection, placement, and resource allocation to maximize data rates, and analyzing how SNR scales with system parameters.

Contribution

It introduces a joint optimization framework for deploying double-active IRSs, including placement and element allocation, and derives the asymptotic SNR scaling laws under practical constraints.

Findings

SNR scales quadratically with the number of reflecting elements.

Optimal reflection and beamforming significantly improve system performance.

The proposed algorithm outperforms benchmark systems in simulations.

Abstract

In this letter, we consider a double-active-intelligent reflecting surface (IRS) aided wireless communication system, where two active IRSs are properly deployed to assist the communication from a base station (BS) to multiple users located in a given zone via the double-reflection links. Under the assumption of fixed per-element amplification power for each active-IRS element, we formulate a rate maximization problem subject to practical constraints on the reflection design, elements allocation, and placement of active IRSs. To solve this non-convex problem, we first obtain the optimal active-IRS reflections and BS beamforming, based on which we then jointly optimize the active-IRS elements allocation and placement by using the alternating optimization (AO) method. Moreover, we show that given the fixed per-element amplification power, the received signal-to-noise ratio (SNR) at the user increases asymptotically with the square of the number of reflecting elements; while given the fixed number of reflecting elements, the SNR does not increase with the per-element amplification power when it is asymptotically large. Last, numerical results are presented to validate the effectiveness of the proposed AO-based algorithm and compare the rate performance of the considered double-active-IRS aided wireless system with various benchmark systems.