IRS

RondoHan

Intelligent reflflecting surface (IRS) is a revolutionary and transformative technology for achieving
spectrum and energy effificient wireless communication cost-effectively in the future. Specififically, an IRS
consists of a large number of low-cost passive elements each being able to reflflect 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 reflflect 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 infifinitely large number of
reflflecting elements and compare it to that of the traditional active beamforming/relaying. Simulation
results demonstrate the signifificant 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.