Intelligent Reflecting Surface Enhanced Wireless Network via Joint Active and Passive Beamforming

Abstract

Intelligent reflecting surface (IRS) is a revolutionary and transformative technology for achieving spectrum and energy efficient wireless communication cost-effectively in the future. Specifically, an IRS consists of a large number of low-cost passive elements each being able to reflect the incident signal independently with an adjustable phase shift so as to collaboratively achieve three-dimensional (3D) passive beamforming without the need of any transmit radio-frequency (RF) chains. In this paper, we study an IRS-aided single-cell wireless system where one IRS is deployed to assist in the communications between a multi-antenna access point (AP) and multiple single-antenna users. We formulate and solve new problems to minimize the total transmit power at the AP by jointly optimizing the transmit beamforming by active antenna array at the AP and reflect beamforming by passive phase shifters at the IRS, subject to users' individual signal-to-interference-plus-noise ratio (SINR) constraints. Moreover, we analyze the asymptotic performance of IRS's passive beamforming with infinitely large number of reflecting elements and compare it to that of the traditional active beamforming/relaying. Simulation results demonstrate the significant performance gain achieved by the proposed scheme with IRS over a benchmark massive MIMO system without using IRS. We also draw useful insights into optimally deploying IRS in future wireless systems. Index TermsIntelligent reflecting surface, joint active and passive beamforming, phase shift optimization.

Using Intelligent Reflecting Surfaces for Rank Improvement in MIMO Communications

“…The metasurface technology has recently gained interest in wireless communications, under names such as IRS [7], large intelligent surface [8], and software-controlled metasurfaces [9,10]. Several promising use cases of this technology, such as for range extension to users with obstructed direct links [7,8,11,12], joint wireless information and power transmission in internet of things (IoT) networks [13], physical layer security [14,15], unmanned air vehicle (UAV) communications [16] have been studied. Still, the IRS-aided wireless communication systems are new and remain largely unexplored.…”

Resource Allocation for Intelligent Reflecting Surface Enabled Heterogeneous Networks

“…The channel vector between PU i and the secondary BS and the channel vector between PU i and the IRS are denoted by l D,i ∈ C NT and l R,i ∈ C M , respectively. Matrix Ψ = diag e jψ1 , · · · , e jψM represents the phase shift matrix of the IRS [16], [17] with ψ m , ∀m ∈ M, denoting the phase shift of the m-th reflector of the IRS. The channel between the secondary BS and the IRS is denoted by matrix F ∈ C M ×NT .…”

A Hardware Architecture For Reconfigurable Intelligent Surfaces with Minimal Active Elements for Explicit Channel Estimation

“…Differently from conventional relaying systems [11], [12], recent RIS designs are mainly based on metamaterials and are comprised of periodically aligned subwavelength elements, termed as unit cells, which are capable of offering overall control over the metasurface's EM behavior [8], [9], [13]. Considering RIS as a means to assist data communication between a Base Station (BSs) and User Equipments (UEs), [11], [14] presented design algorithms for the phase shifting values of the RIS unit cells under the assumption of perfect availability of the wireless channels where RIS is involved. However, estimating those channels and then sharing this information is a challenging task with the currently available metasurface architectures, which consist of nearly passive elements.…”