On the Outage Performance of Overlay Cognitive STBC-NOMA System With Imperfect SIC

This letter investigates an overlay cognitive Alamouti’s space-time block code-aided non-orthogonal multiple access (STBC-NOMA) system. Approximate closed-form expressions for the system throughput (ST) and the outage probability (OP) of both the primary and secondary networks under imperfect successive interference cancellation (SIC) are derived over Rayleigh fading channels. Moreover, asymptotic expressions of the ST and OP at high signal-to-noise ratio (SNR) regime are also evaluated. It is shown that the proposed system outperforms the system presented by Liping et al. (2020), in terms of both the ST and OP. The letter further investigates the impact of power allocation coefficients on the OP.

I. Introduction

Non-orthogonal multiple access (NOMA) has been recognized as a key multiple access technology for better spectrum utilization in next generation wireless networks [1]. NOMA employs superposition coding at the source and successive interference cancellation (SIC) at the destination allowing multiple users to simultaneously access the network at the same time and the same frequency resource. Moreover, to improve the spectrum efficiency, cognitive radio (CR) is another promising technique and has received a considerable attention as an application to enhance the performance of emerging technologies [2]. In CR, the secondary network (SN) can be allowed to utilize the license spectrum of the primary network (PN). CR basically operates under three paradigms, namely, the underlay mode, the overlay mode, and the interweave mode. Integration of CR with NOMA (CR-NOMA) has envisioned to meet the massive connectivity, high throughput, and low latency requirements of next generation wireless networks [3], [4]. Thus, CR-NOMA is expected to provide more intelligent spectrum sharing.