Over-the-Air Beamforming with Reconfigurable Intelligent Surfaces

TL;DR

This paper introduces over-the-air beamforming with active reconfigurable intelligent surfaces (RIS) for multi-user MISO systems, enabling efficient signal manipulation without complex hardware, and proposes a new index modulation scheme with promising performance.

Contribution

It presents a novel over-the-air beamforming method using active RIS, formulated as a QCQP problem and solved via SDR, along with a new high-rate index modulation scheme.

Findings

Enhanced sum-rate performance demonstrated

Improved bit error rate (BER) performance shown

Efficient optimization via SDR approach

Abstract

Reconfigurable intelligent surface (RIS)-empowered communication is a revolutionary technology that enables to manipulate wireless propagation environment via smartly controllable low-cost reflecting surfaces. However, in order to outperform conventional communication systems, an RIS-aided system with solely passive reflection requires an extremely large surface. To meet this challenge, the concept of active RIS, which performs simultaneous amplification and reflection on the incident signal at the expense of additional power consumption, has been recently introduced. In this paper, deploying an active RIS, we propose a novel beamforming concept, over-the-air beamforming, for RIS-aided multi-user multiple-input single-output (MISO) transmission schemes without requiring any pre/post signal processing hardware designs at the transmitter and receiver sides. In the proposed over-the-air beamforming-based transmission scheme, the reflection coefficients of the active RIS elements are customized to maximize the sum-rate gain. To tackle this issue, first, a non-convex quadratically constrained quadratic programming (QCQP) problem is formulated. Then, using semidefinite relaxation (SDR) approach, this optimization problem is converted to a convex feasibility problem, which is efficiently solved using the CVX optimization toolbox. Moreover, taking inspiration from this beamforming technique, a novel high-rate receive index modulation (IM) scheme with a low-complexity sub-optimal detector is developed. Through comprehensive simulation results, the sum-rate and bit error rate (BER) performance of the proposed designs are investigated.