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STAR-RIS Assisted Downlink Active and Uplink Backscatter Communications with NOMA

Ao Huang, Xidong Mu, Li Guo

TL;DR

Numerical results demonstrate that compared with the baseline schemes employing conventional RISs or space division multiple access, the proposed scheme achieves higher performance gains; and higher UL rate gain is obtained at a cost of DL performance degradation, as a remedy, a more flexible performance tradeoff can be achieved by introducing the STAR-RIS.

Abstract

A simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted downlink (DL) active and uplink (UL) backscatter communication (BackCom) framework is proposed. More particularly, a full-duplex (FD) base station (BS) communicates with the DL users via the STAR-RIS's transmission link, while exciting and receiving the information from the UL BackCom devices with the aid of the STAR-RIS's reflection link. Non-orthogonal multiple access (NOMA) is exploited in both DL and UL communications for improving the spectrum efficiency. The system weighted sum rate maximization problem is formulated for jointly optimizing the FD BS active receive and transmit beamforming, the STAR- RIS passive beamforming, and the DL NOMA decoding orders, subject to the DL user's individual rate constraint. To tackle this challenging non-convex problem, we propose an alternating optimization (AO) based algorithm for the joint active and passive beamforming design with a given DL NOMA decoding order. To address the potential high computational complexity required for exhaustive searching all the NOMA decoding orders, an efficient NOMA user ordering scheme is further developed. Finally, numerical results demonstrate that: i) compared with the baseline schemes employing conventional RISs or space division multiple access, the proposed scheme achieves higher performance gains; and ii) higher UL rate gain is obtained at a cost of DL performance degradation, as a remedy, a more flexible performance tradeoff can be achieved by introducing the STAR-RIS.

STAR-RIS Assisted Downlink Active and Uplink Backscatter Communications with NOMA

TL;DR

Numerical results demonstrate that compared with the baseline schemes employing conventional RISs or space division multiple access, the proposed scheme achieves higher performance gains; and higher UL rate gain is obtained at a cost of DL performance degradation, as a remedy, a more flexible performance tradeoff can be achieved by introducing the STAR-RIS.

Abstract

A simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted downlink (DL) active and uplink (UL) backscatter communication (BackCom) framework is proposed. More particularly, a full-duplex (FD) base station (BS) communicates with the DL users via the STAR-RIS's transmission link, while exciting and receiving the information from the UL BackCom devices with the aid of the STAR-RIS's reflection link. Non-orthogonal multiple access (NOMA) is exploited in both DL and UL communications for improving the spectrum efficiency. The system weighted sum rate maximization problem is formulated for jointly optimizing the FD BS active receive and transmit beamforming, the STAR- RIS passive beamforming, and the DL NOMA decoding orders, subject to the DL user's individual rate constraint. To tackle this challenging non-convex problem, we propose an alternating optimization (AO) based algorithm for the joint active and passive beamforming design with a given DL NOMA decoding order. To address the potential high computational complexity required for exhaustive searching all the NOMA decoding orders, an efficient NOMA user ordering scheme is further developed. Finally, numerical results demonstrate that: i) compared with the baseline schemes employing conventional RISs or space division multiple access, the proposed scheme achieves higher performance gains; and ii) higher UL rate gain is obtained at a cost of DL performance degradation, as a remedy, a more flexible performance tradeoff can be achieved by introducing the STAR-RIS.
Paper Structure (30 sections, 2 theorems, 57 equations, 9 figures, 1 table, 3 algorithms)

This paper contains 30 sections, 2 theorems, 57 equations, 9 figures, 1 table, 3 algorithms.

Table of Contents

  1. Introduction
  2. Prior Works
  3. Studies on BackCom Systems
  4. Studies on STAR-RIS assisted Systems
  5. Motivations and Contributions
  6. Organization and Notation
  7. System Model and Problem Formulation
  8. System Model
  9. NOMA Based UL and DL Communications
  10. UL passive backscatter communication
  11. DL active communication
  12. Problem Formulation
  13. Discussion
  14. Proposed Solution Based on Alternating Optimization
  15. Active FD BS Transmit Beamforming Optimization
  16. ...and 15 more sections

Key Result

Lemma 1

For any two Hermitian matrices ${\mathbf{A}} \in {{\mathbb{H}}^M}$ and ${\mathbf{B}} \in {{\mathbb{H}}^M}$ having the same size, we have the following equality:

Figures (9)

  • Figure 1: Illustration of the STAR-RIS assisted DL active and UL backscatter communications.
  • Figure 2: The simulated setup.
  • Figure 3: Convergence of Algorithm 2.
  • Figure 4: System weighted sum rate versus the number of STAR-RIS element $M$.
  • Figure 5: System weighted sum rate versus the SI cancellation coefficient at the FD BS.
  • ...and 4 more figures

Theorems & Definitions (3)

  • Lemma 1
  • Theorem 1
  • proof