Hybrid Beamforming for Reconfigurable Intelligent Surface based Multi-User Communications: Achievable Rates with Limited Discrete Phase Shifts

Boya Di, Hongliang Zhang, Lingyang Song, Yonghui Li, Zhu Han, H. Vincent Poor

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Reconfigurable intelligent surfaces (RISs) have drawn considerable attention from the research community recently. RISs create favorable propagation conditions by controlling the phase shifts of reflected waves at the surface, thereby enhancing wireless transmissions. In this paper, we study a downlink multi-user system where the transmission from a multi-antenna base station (BS) to various users is achieved by an RIS reflecting the incident signals of the BS towards the users. Unlike most existing works, we consider the practical case where only a limited number of discrete phase shifts can be realized by a finite-sized RIS. A hybrid beamforming scheme is proposed and the sum-rate maximization problem is formulated. Specifically, continuous digital beamforming and discrete RIS-based analog beamforming are performed at the BS and the RIS, respectively, and an iterative algorithm is designed to solve this problem. Both theoretical analysis and numerical validations show that the RIS-based system can achieve good sum-rate performance by setting a reasonable size of the RIS and a small number of discrete phase shifts.

Original languageEnglish (US)
Article number9110889
Pages (from-to)1809-1822
Number of pages14
JournalIEEE Journal on Selected Areas in Communications
Volume38
Issue number8
DOIs
StatePublished - Aug 2020

All Science Journal Classification (ASJC) codes

  • Computer Networks and Communications
  • Electrical and Electronic Engineering

Keywords

  • Reconfigurable intelligent surface
  • hybrid beamforming
  • limited discrete phase shifts
  • multi-user communications
  • non-convex optimization

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