Beamforming Optimization for Intelligent Reflecting Surface with Discrete Phase Shifts

By Qingqing Wu, Rui Zhang. IEEE International Conference on Acoustics, Speech, and Signal Processing, 2018

303 citations recorded by the source corpus.

Intelligent reflecting surface (IRS) is a cost-effective solution for achieving high spectrum and energy efficiency in future wireless communication systems by leveraging massive low-cost passive elements that are able to reflect the signals with adjustable phase shifts. Prior works on IRS mostly consider continuous phase shifts at each reflecting element, which however, is practically difficult to realize due to the hardware limitation. In contrast, we study in this paper an IRS-aided wireless network, where an IRS with only a finite number of phase shifts at each element is deployed to assist in the communication from a multi-antenna access point (AP) to a single-antenna user. We aim to minimize the transmit power at the AP by jointly optimizing the continuous transmit beamforming at the AP and discrete reflect beamforming at the IRS, subject to a given signal-to-noise ratio (SNR) constraint at the user receiver. We first propose a suboptimal and low-complexity solution to the problem by applying the alternating optimization technique. Then, we analytically show that as compared to the ideal case with continuous phase shifts, the IRS with discrete phase shifts achieves the same squared power gain in terms of asymptotically large number of reflecting elements, while a constant performance loss is incurred that depends only on the number of phase-shift levels. Simulation results verify our analytical result as well as the effectiveness of our proposed design as compared to different benchmark schemes.

Subfields: Aerospace Engineering, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/753fbdf0cbcf625e820f73563063caaf82bab90b

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Citations in the corpus

Deep Reinforcement Learning Based Intelligent Reflecting Surface Optimization for MISO Communication Systems (2020, methodology): “Note that, for a ﬁxed phase shift matrix Φ , the optimal beamforming method that maximizes the received SNR is the maximum-ratio transmission (MRT) [8], i.e., The optimization problem for the phase shift matrix Φ to maximize γ can be formulated as where Φ i , i is the i -th diagonal element of Φ .”
Intelligent Reflecting Surface Enhanced Wireless Network via Joint Active and Passive Beamforming (2018, background): “The design of IRS with discrete phase shifts is left for our future work [6], [19].”
Reconfigurable Intelligent Surfaces for Wireless Communications: Principles, Challenges, and Opportunities (2020, methodology): “, [32], [37], and focused on devising algorithms to configure the RIS given channel knowledge.”
Capacity Characterization for Intelligent Reflecting Surface Aided MIMO Communication (2019, background): “To characterize the capacity limit of IRS-aided MIMO systems, we assume that the phase-shift by each IRS element can be continuously adjusted, while the results of this paper can be readily extended to the practical setup with discrete phase-shift levels [17], [18].”
Large Intelligent Surface-Assisted Wireless Communication Exploiting Statistical CSI (2018, background): “Modern LIS also includes reflector array, which can reflect the electromagnetic wave, offering support to traditional wireless systems [6]–[9].”
Prospective Multiple Antenna Technologies for Beyond 5G (2019, background): “Hence, an IRS is an array of meta-atoms that each scatter the incoming signals with a controllable phase-shift [149], [163], [164], so that the joint effect of all phase-shifts is a reﬂected beam in a selected direction.”
Massive Access for 5G and Beyond (2020, methodology): “Considering a finite number of phase shifts for each reflecting unit in practice, IRS beamforming was optimized to minimize the total power consumption in [159].”
Smart Radio Environments Empowered by Reconfigurable Intelligent Surfaces: How it Works, State of Research, and Road Ahead (2020, background): “In [190], the authors consider a single-user system, in which an RIS with finite-resolution phase shifters aids the communication from a multi-antenna transmitter to a singleantenna receiver.”
Intelligent Reflecting Surface: Practical Phase Shift Model and Beamforming Optimization (2019, background): “Following similar steps as in [13], problem (P0) can be reformulated as”
Intelligent Reflecting Surface-Aided Wireless Communications: A Tutorial (2020, methodology): “, two-level (reflecting or absorbing) amplitude control, and/or two-level (0 or π) phase-shift control [45], [49].”
Wireless Communications Through Reconfigurable Intelligent Surfaces (2019, background): “In their follow-up study [77], the authors considered the same power minimization problem by assuming discrete (finite resolution) RIS phase shifts.”
Toward Smart Wireless Communications via Intelligent Reflecting Surfaces: A Contemporary Survey (2019, methodology): “The large size of the IRS’s scattering elements can make the overall phase tuning more ﬂexible, even with limited phase shifts at an individual scattering element, e.g., [128], [130], [146], [156].”
Intelligent Reflecting Surface: A Programmable Wireless Environment for Physical Layer Security (2019, methodology): “Moreover, since achieving continuous reflecting coefficients on the reflecting elements is costly in practice due to the hardware limitation, the SNR maximization problem and transmitter power minimization problem were studied in [18]–[20] by considering discrete reflecting coefficients on the refle”
Hybrid Beamforming for Reconfigurable Intelligent Surface based Multi-User Communications: Achievable Rates With Limited Discrete Phase Shifts (2019, background): “To exploit the potential of RIS techniques, many existing works have considered the RIS as a reflection-type surface deployed between sources and destinations in either point-to-point communications [5], [10]–[12] or multi-user systems [13]–[16] for higher data rates or energy saving.”
Secrecy Rate Maximization for Intelligent Reflecting Surface Assisted Multi-Antenna Communications (2019, background): “Different from the above works that focused on continuous phase shifts at the IRS, discrete phase shifts were further concerned for both single-user [13] and multiuser [14] MISO systems.”