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

Design of Non-Orthogonal Multiple Access Enhanced Backscatter Communication

Backscatter communication (BackCom), which allows a backscatter node (BN) to communicate with the reader by modulating and reflecting the incident continuous wave from the reader, is considered a promising solution to power the future Internet-of-Things. In this paper, we consider a single BackCom system, where multiple BNs are served by a reader. We propose using the power-domain non-orthogonal multiple access (NOMA), i.e., multiplexing the BNs in different regions or with different backscattered power levels, to enhance the spectrum efficiency of the BackCom system. To better exploit power-domain NOMA, we propose setting the reflection coefficients for multiplexed BNs to be different. Based on this considered model, we develop the reflection coefficient selection criteria. To illustrate the enhanced system with the proposed criteria, we analyze the performance of the BackCom system in terms of the average number of bits that can be successfully decoded by the reader for the two-node pairing case and the average number of successful BNs for the general multiplexing case. Our results show that NOMA achieves the much better performance gain in the BackCom system as compared to its performance gain in the conventional system, which highlights the importance of applying NOMA to the BackCom systemThis work was supported by the Australian Research Council’s Discovery Project Funding Scheme under Project DP170100939

Security outage probability analysis of cognitive networks with multiple eavesdroppers for Industrial Internet of Things

The Industrial Internet of Things (IIoT) has been recognised as having the potential to benefit a range of industrial sectors substantially. However, widespread development and deployment of IIoT systems are limited for some reasons, the most significant of which are a shortage of spectrum resources and network security issues. Given the heterogeneity of IIoT devices, typical cryptographic security techniques are insufficient since they can suffer from challenges including computation, storage, latency, and interoperability. This paper presents a physical layer security analysis of the underlying cognitive radio networks for IIoT. Through consideration of the spectrum, IIoT devices can opportunistically utilise the primary spectrum, thereby improving spectrum efficiency and allowing access by an increased number of devices. Specifically, we propose two cognitive relay transmission (CRT) schemes, optimal single CRT (O-SCRT) and multiple CRT (MCRT), to improve transmission reliability further. Since it is challenging to obtain channel state information in the wiretap link, we provide a sub-optimal single CRT scheme and derive closed-form expressions of security outage probability by invoking both selection combination and maximal ratio combination techniques at the eavesdropper. To provide a benchmark, the round-robin single CRT scheme is also analysed. Simulation results are provided to verify our analysis and show that O-SCRT provides the best system security outage performance