MISO Wireless Communication Systems via Intelligent Reflecting Surfaces : (Invited Paper)

Intelligent reflecting surfaces (IRSs) have received considerable attention from the wireless communications research community recently. In particular, as low-cost passive devices, IRSs enable the control of the wireless propagation environment, which is not possible in conventional wireless networks. To take full advantage of such IRS-assisted communication systems, both the beamformer at the access point (AP) and the phase shifts at the IRS need to be optimally designed. However, thus far, the optimal design is not well understood. In this paper, a point-to-point IRS-assisted multiple-input single-output (MISO) communication system is investigated. The beamformer at the AP and the IRS phase shifts are jointly optimized to maximize the spectral efficiency. Two efficient algorithms exploiting fixed point iteration and manifold optimization techniques, respectively, are developed for solving the resulting non-convex optimization problem. The proposed algorithms not only achieve a higher spectral efficiency but also lead to a lower computational complexity than the state-of-the-art approach. Simulation results reveal that deploying large-scale IRSs in wireless systems is more efficient than increasing the antenna array size at the AP for enhancing both the spectral and the energy efficiency.

I. Introduction

The capacity of current wireless networks has to exponentially increase to meet the rapidly growing demands for high-data-rate multimedia access. The network capacity can be boosted by deploying large-scale antenna arrays, network densification with small cells, and uplifting the carrier frequency to the millimeter-wave (mm-wave) bands [1], [2]. However, additional cost and power consumption are inevitably incurred by deploying more antenna elements, access points (APs), and radio frequency (RF) chains at extremely high frequencies (EHF) [3]. Therefore, new paradigms that are both spectral- and energy-efficient are needed for the design of future wireless communication systems.