Hybrid Relay and Reconfigurable Intelligent Surface Assisted Multiuser MISO Systems

Te Yi Kan, Ronald Y. Chang, Feng Tsun Chien, Bing Jia Chen, H. Vincent Poor

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Reconfigurable intelligent surfaces (RISs) are viewed as key enablers for next-generation wireless communications. This paper investigates a multiuser downlink multiple-input single-output (MISO) system in which a multiantenna base station (BS) transmits information to multiple single-antenna users with the aid of both a half-duplex decode-and-forward (DF) relay and a full-duplex RIS. Active beamforming at the BS and the DF relay, as well as passive beamforming at the RIS, are jointly designed for system sum-rate maximization. The design problem is challenging to solve due to coupled beamforming variables. An alternating optimization (AO) based algorithm is proposed to tackle this complex co-design problem. Numerical results demonstrate the superior performance of the proposed hybrid relay-RIS system with a judicious joint beamforming design. Convergence and complexity analysis shows that the convergence rate of the proposed algorithm is dominated by the numbers of users and RIS elements, and the proposed scheme can converge in a few iterations even in the configuration of large numbers of users and RIS elements. Interesting tradeoffs posed in the joint design are discussed. An extension of the proposed design method to a related energy efficiency (EE) optimization problem is also outlined and implemented.

Original languageEnglish (US)
Pages (from-to)7653-7668
Number of pages16
JournalIEEE Transactions on Vehicular Technology
Issue number6
StatePublished - Jun 1 2023
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Aerospace Engineering
  • Electrical and Electronic Engineering
  • Computer Networks and Communications
  • Automotive Engineering


  • Reconfigurable intelligent surfaces
  • alternating optimization
  • beamforming
  • decode-and-forward
  • multiuser MISO
  • relay


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