RIS Partition-Assisted Non-Orthogonal Multiple Access (NOMA) and Quadrature-NOMA With Imperfect SIC

Abstract

Reconfigurable intelligent surface (RIS)-assisted power-domain non-orthogonal multiple access (PD-NOMA) system has emerged as a revolutionary technology to enhance the spectrum efficiency for future wireless networks. This work introduces two novel RIS systems, namely, RIS partition-assisted (RISP) PD-NOMA (RISP-PD-NOMA) and RISP-Quadrature-NOMA (RISP-Q-NOMA), to improve the signal quality of all users by dedicating fixed RIS units to each user for phase cancellation. The closed-form expressions of average sum-rate, outage probability, and diversity order of both systems are evaluated under the Rician fading channel for perfect and imperfect successive interference cancellation (SIC). Further, the performance of both systems is compared with RIS-division PD-NOMA (RISD-PD-NOMA) system where the RIS subsurface assigned to one user is not exposed to another user. It is noticed from the analysis that under perfect SIC, RISP-PD-NOMA outperforms RISP-Q-NOMA and RISD-PD-NOMA. However, under imperfect SIC, RISP-Q-NOMA demonstrates superior performance than other systems, due to lesser number of SIC operations that lead to less stringent constraints on the power allocation, reduce detection delay, and improve SIC stability. Furthermore, the analytical expression for bit error rate (BER) of RISP-PD-NOMA and RISP-Q-NOMA is derived, and then closed-form expression of average-BER is evaluated. Numerical results demonstrate that RISP-Q-NOMA is superior to RISP-PD-NOMA and RISD-PD-NOMA.

Effective capacity analysis of configurable intelligent surface-assisted NOMA communications systems

“…wherein T and B represent the block length and the bandwidth, respectively. The parameter ν v > 0 is the QoS exponent, defined as (15):…”

Joint Phase Shift Design and Resource Management for a Non-Orthogonal Multiple Access-Enhanced Internet of Vehicle Assisted by an Intelligent Reflecting Surface-Equipped Unmanned Aerial Vehicle

“…Additionally, the non-orthogonal multiple access (NOMA) technique has been emerging as a potential solution in UAV-assisted networks, which can achieve timely, reliable, and seamless data exchange [31]. Therefore, some recent efforts in [32,33] combined IRS-equipped UAVs with the NOMA technique to obtain the benefits of both. The sum data rate maximization schemes used to fully exploit the advantages of NOMA-enhanced, IRS-equipped UAVs, are presented in [34][35][36].…”

“…Third, compared with the hover mode, the mobile IRS-equipped UAV can further maintain aerial LoS links. Unfortunately, this issue has been overlooked in [33,35]. Finally, due to the highly complex coupling among optimization variables (e.g., the power, subcarrier, and phase shift) and mixed combinatorial features, it is difficult to solve the sum data rate maximization problem in the context of the considered scenarios.…”

Reconfigurable Intelligent Surface Enabled Over-the-Air Uplink NOMA

“…For example, while the power difference required in power domain NOMA is generally conducted at the Tx or Rx, a hybrid RIS with active and passive partitions has been utilized to enable the power difference over the air in UL scenario [29]. In [31] and [32], two RIS partitioned systems are introduced to maximize diversity order and improve signal quality, and an RIS assisted UE pairing THz-NOMA system has been proposed that pairs UEs based on the distance and power allocation between them to enhance their bit error rate (BER) performance, respectively. Other works also investigate the physical layer security for RIS-NOMA systems, joint active and passive beamforming for MISO RIS-aided NOMA to maximize the sum rate [33], joint location and beamforming designs for STAR-RIS assisted NOMA systems, and attach an RIS to an unmanned aerial vehicles (UAV) to assist in communication to other base station (BS) to UAV or UE communications [34]- [36].…”