Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Coexisting Passive RIS and Active Relay Assisted NOMA Systems

Ao Huang, Li Guo, Xidong Mu, Chao Dong, Yuanwei Liu

TL;DR

Numerical results demonstrate that the proposed coexisting RIS and relay assisted transmission framework is capable of achieving a significant user performance improvement than conventional schemes without RIS or relay and the H-NOMA and F- NOMA protocols are generally preferable for ensuring user rate fairness and enhancing user sum rate.

Abstract

A novel coexisting passive reconfigurable intelligent surface (RIS) and active decode-and-forward (DF) relay assisted non-orthogonal multiple access (NOMA) transmission framework is proposed. In particular, two communication protocols are conceived, namely Hybrid NOMA (H-NOMA) and Full NOMA (F-NOMA). Based on the proposed two protocols, both the sum rate maximization and max-min rate fairness problems are formulated for jointly optimizing the power allocation at the access point and relay as well as the passive beamforming design at the RIS. To tackle the non-convex problems, an alternating optimization (AO) based algorithm is first developed, where the transmit power and the RIS phase-shift are alternatingly optimized by leveraging the two-dimensional search and rank-relaxed difference-of-convex (DC) programming, respectively. Then, a two-layer penalty based joint optimization (JO) algorithm is developed to jointly optimize the resource allocation coefficients within each iteration. Finally, numerical results demonstrate that: i) the proposed coexisting RIS and relay assisted transmission framework is capable of achieving a significant user performance improvement than conventional schemes without RIS or relay; ii) compared with the AO algorithm, the JO algorithm requires less execution time at the cost of a slight performance loss; and iii) the H-NOMA and F-NOMA protocols are generally preferable for ensuring user rate fairness and enhancing user sum rate, respectively.

Coexisting Passive RIS and Active Relay Assisted NOMA Systems

TL;DR

Numerical results demonstrate that the proposed coexisting RIS and relay assisted transmission framework is capable of achieving a significant user performance improvement than conventional schemes without RIS or relay and the H-NOMA and F- NOMA protocols are generally preferable for ensuring user rate fairness and enhancing user sum rate.

Abstract

A novel coexisting passive reconfigurable intelligent surface (RIS) and active decode-and-forward (DF) relay assisted non-orthogonal multiple access (NOMA) transmission framework is proposed. In particular, two communication protocols are conceived, namely Hybrid NOMA (H-NOMA) and Full NOMA (F-NOMA). Based on the proposed two protocols, both the sum rate maximization and max-min rate fairness problems are formulated for jointly optimizing the power allocation at the access point and relay as well as the passive beamforming design at the RIS. To tackle the non-convex problems, an alternating optimization (AO) based algorithm is first developed, where the transmit power and the RIS phase-shift are alternatingly optimized by leveraging the two-dimensional search and rank-relaxed difference-of-convex (DC) programming, respectively. Then, a two-layer penalty based joint optimization (JO) algorithm is developed to jointly optimize the resource allocation coefficients within each iteration. Finally, numerical results demonstrate that: i) the proposed coexisting RIS and relay assisted transmission framework is capable of achieving a significant user performance improvement than conventional schemes without RIS or relay; ii) compared with the AO algorithm, the JO algorithm requires less execution time at the cost of a slight performance loss; and iii) the H-NOMA and F-NOMA protocols are generally preferable for ensuring user rate fairness and enhancing user sum rate, respectively.
Paper Structure (39 sections, 2 theorems, 62 equations, 8 figures, 1 table, 3 algorithms)

This paper contains 39 sections, 2 theorems, 62 equations, 8 figures, 1 table, 3 algorithms.

Table of Contents

  1. Introduction
  2. Prior Works
  3. Studies on RIS-aided Systems
  4. Studies on RIS-NOMA Systems
  5. Motivations and Contributions
  6. Organization and Notation
  7. System Model and Problem Formulation
  8. System Model
  9. Communication Protocols
  10. Signal Model
  11. IB-stage
  12. IR-stage
  13. H-NOMA
  14. F-NOMA
  15. Problem Formulation
  16. ...and 24 more sections

Key Result

Theorem 1

The subproblem is feasible if and only if the following conditions hold. where $\alpha_n^{\min}$, $\alpha_n^{\max}$, $\beta_d^{\min}$ and $\beta_d^{\max}$ are expressed, respectively, as

Figures (8)

  • Figure 1: Illustration of the considered coexisting RIS and relay assisted NOMA transmission framework and resource allocation strategies. (a) System model design. (b) Resource allocation based on each communication protocol.
  • Figure 2: The simulated setup (top view).
  • Figure 3: Convergence behaviour of proposed algorithms.
  • Figure 4: Execution time ratio $\zeta$ between the proposed algorithms AO and JO versus the number of RIS elements $M$.
  • Figure 5: Optimal rate versus the number of RIS elements $M$.
  • ...and 3 more figures

Theorems & Definitions (7)

  • Theorem 1
  • proof
  • Remark 1
  • Lemma 1
  • proof
  • Remark 2
  • Remark 3