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Improving the Coverage of Multiple Access Networks Using Reconfigurable Intelligent Surfaces

Rahimzare, Ahmad Reza | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55468 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Behroozi, Hamid; Mirmohseni, Mahtab
  7. Abstract:
  8. Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) are proposed as a new concept that, unlike conventional reflecting-only RISs, they can reflect a part of incident signals and transmit the other part at the same time. Using these surfaces enables full-space coverage instead of half-space coverage in the network, which creates a degree of freedom to place telecommunication devices on both sides of the surface. In this thesis, we investigate the coverage of a STAR-RIS aided two-user SISO network. To this end, we solve the network coverage maximization problem for orthogonal multiple access (OMA), non-orthogonal multiple access (NOMA), and rate-splitting multiple access (RSMA) methods. In fact, the users' distance from the surface is maximized given a minimum achievable rate. RSMA is a non-orthogonal method that divides users' messages into common and private parts. The receivers partially decode the interference and partially treat it as noise. It has been shown that RSMA outperforms some other multiple access methods such as OMA and NOMA in many cases. Therefore, we focus on the rate-splitting method and compare it with the other two methods in the results. We study the problem assuming perfect and imperfect channel state information (CSI) in the network as well as purely passive and semi-passive surfaces. For this purpose, we divide complex optimization problems into simpler convex subproblems. We also use alternative optimization algorithms to solve problems with purely passive surfaces. The simulation results show that the RSMA method with the help of STAR-RIS can improve the network coverage compared to other strategies.
  9. Keywords:
  10. Coverage ; Rate Splitting Multiple Access ; Multiple Access ; Reconfigurable Intelligent Surface (RIS) ; Simultaneously Transmitting And Reflecting Reconfigurable Intelligent Surfaces (STAR-RISs) ; Intelligent Surfaces

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