NOMA in Cooperative Underlay Cognitive Radio Networks under Imperfect SIC

Dinh-Thuan Do, Anh-Tu Le, Byung Moo Lee
2020 IEEE Access  
In conventional cognitive radio (CR), the users in secondary network (SN) can only access the idle spectrum when users in primary network (PN) are absent. This novel strategy provides higher spectrum efficiency when detecting the presence of the PN. Hence, spectrum utilization of the traditional scheme can be further improved as exploiting application of non-orthogonal multiple access (NOMA). As combination of CR and NOMA, such CR-NOMA has been proposed to improve spectrum efficiency to adapt
more » ... ficiency to adapt to requirements in 5G communications. In this study, the relaying scheme is employed in the SN of the proposed CR-NOMA and the relay is allowed to energy harvesting (EH) from the secondary transmitter to serve signal forwarding to distant secondary users. With this regard, the complex model of EH-assisted CR-NOMA is explored in outage behavior and throughput performance as awareness on imperfect successive interference cancellation (SIC) at the receiver. As most important results, the exact closed-form of the exact outage probability is derived for each NOMA destination by assuming that the channel coefficients among considered links follow Rayleigh distribution. Furthermore, performance gap between two NOMA users can be controlled by various parameters such as transmit power, energy harvesting coefficients and levels of imperfect SIC. Simulation results verify our analytical results. INDEX TERMS Energy harvesting, imperfect SIC, NOMA, outage probability, underlay cognitive radio. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see VOLUME 8, 2020 D.-T. Do et al.: NOMA in Cooperative Underlay CR Networks Under Imperfect SIC of successive interference cancellation (SIC), each NOMA user detects all weaker users' signals by determining stronger users' messages as a noise before decoding the own message [12]. A. RELATED WORKS In addition, the explosive increment of diverse mobile devices and the rapid development of high-rate services, it is required to explore new paradigms to provide higher spectral efficient and energy-efficient communication networks. However, to attain a high spectral efficiency (SE) the fixed spectrum allocation scheme meets a major disadvantage. Recently, cognitive radio (CR) network has been introduced to allow the primary network to share its frequency band with the secondary network with respect to improved SE [13]. Besides SE, other increasing attention is that energy efficiency (EE), especially in both energy constraint devices and wireless powered systems [14]. In energy-efficient architecture, there are two kinds of energy aware systems. The first kind considers on maximizing EE [15]. In [16], a novel NOMA system was investigated in term of EE power allocation. In particular, they examined a low-complexity sub optimal algorithm which comprises power allocation and sub channel assignment. The second kind is energy harvesting (EH). Recently, radio-frequency (RF) signals have been proposed as promising sources for EH. The EE of the wireless communication networks can be enhanced by examining RFbased EH technique as [17] and [18]. Moreover, information transmission and EH are joint processed due to the dual properties of RF, the authors in [19]-[23] investigated a developing technique, namely simultaneous wireless information and power transfer (SWIPT). Regarding improved SE, CR-inspired NOMA (CR-NOMA) and NOMA with fixed power allocation are analyzed under several circumstances to prove that channel quality of a user with a poor channel condition could strictly guarantee in the CR-NOMA [24] . In addition, the better fairness in term of spectrum allocation can be obtained in CR-NOMA compared NOMA with the fixed power allocation. In addition, the power allocation is presented for two secondary user to improve the SE in the underlay CR-NOMA by using interference cancellation technique [25] . Thus, to greatly improve the spectrum utilization it is natural to employ NOMA together with CR with power constraints. Furthermore, a large-scale underlay CR system is developed by using stochastic geometry along with NOMA. They derived expressions of the outage probability for the NOMA users to evaluate the performance of the considered networks [26] . Regarding improved EE, joint SWIPT and NOMA was introduced to encourage strong users to forward weak users' signal and then this dual-hop transmission will not drain their batteries [27], [28] . To increase the individual data rate, wireless powered communication networks (WPCN) is proposed to combine with NOMA uplink as [29] . Benefiting from the harvested energy in the first time slot, the strong users in [30] are able to forward to the weak users' signals in
doi:10.1109/access.2020.2992660 fatcat:sf463iqemffgzeirvy56vkevne