Outage Performance of RIS-aided Cooperative FD-SWIPT-NOMA in Nakagami-m Channels

In this work we {derive new} analytical expressions for the outage probability (OP) of the downlink (DL) cooperative full-duplex (FD) simultaneous wireless information power transfer (SWIPT) non-orthogonal multiple access (NOMA) system aided by reconfigurable intelligent surfaces (RIS). The expressions for both the strongest and weakest NOMA users are devised assuming Nakagami-$m$ channel fading. The derived analytical OP expressions are simple to compute yet accurate for a wide range of RIS passive elements configurations, energy harvesting (EH) coefficient, and residual self-interference (SI) levels, being extensively validated by numerical simulations, demonstrating the correctness and accuracy of the proposed analytical method. The OP expressions reveal how paramount is to mitigate the SI in the FD relay mode, since for reasonable values of residual SI coefficient ($\bar{\omega}\geq -13$dB), it is notable its detrimental effect over the system performance; hence, new SI reduction methods for FD relays are useful for low number of passive elements. Also, applying the proposed OP expressions to predict the behaviour of the RIS-NOMA system equipped with a higher number of passive elements ($N\geq 30$) reveals a substantial reduction of the SI effect, motivating the implementation of the cooperative FD communications. Furthermore, we found the asymptotic behavior of outage probability of both clustered users, as well as the equal diversity order for both users, given by $\frac{N\mu^2}{2-2\mu^2}$ if the fraction of the harvest energy $\rho =0$ or $0$ if $\rho\neq0$, indicating the influence of channel parameters and number of RIS elements in the performance.Comment: 23 pages, 8 figures, full pape

Performance analysis of power-splitting relaying protocol in SWIPT based cooperative NOMA systems

This paper investigates a relay assisted simultaneous wireless information and power transfer (SWIPT) for downlink in cellular systems. Cooperative non-orthogonal multiple access (C-NOMA) is employed along with power splitting protocol to enable both energy harvesting (EH) and information processing (IP). A downlink model consists of a base station (BS) and two users is considered, in which the near user (NU) is selected as a relay to forward the received signal from the BS to the far user (FU). Maximum ratio combining is then employed at the FU to combine both the signals received from the BS and NU. Closed form expressions of outage probability, throughput, ergodic rate and energy efficiency (EE) are firstly derived for the SWIPT based C-NOMA considering both scenarios of with and without direct link between the BS and FU. The impacts of EH time, EH efficiency, power-splitting ratio, source data rate and distance between different nodes on the performance are then investigated. The simulation results show that the C-NOMA with direct link achieves an outperformed performance over C-NOMA without direct link. Moreover, the performance of C-NOMA with direct link is also higher than that for OMA. Specifically, (1) the outage probability for C-NOMA in both direct and relaying link cases is always lower than that for OMA. (2) the outage probability, throughput and ergodic rate vary according to β, (3) the EE of both users can obtain in SNR range of from -10 to 5 dB and it decreases linearly as SNR increases. Numerical results are provided to verify the findings