Integrating Cognitive Radio in NOMA-based B5G Networks: Architecture and Research Challenges

The integration between cognitive radio (CR) technology and non-orthogonal multiple access (NOMA) technique has been recently configured as a promising solution to meet the unprecedented requirements of beyond fifth generation (B5G) networks, especially those related to Internet-of-Things (IoT) applications. Specifically, power domain NOMA multiplexing allows many users to share the same orthogonal resource blocks, on the other hand, CR allows secondary users (SUs) to access the licensed spectrum frequency without interrupting the primary users' activities. In such a CR-based NOMA network, the licensed frequency is split into several channels, and a set of SUs is served in each channel using the NOMA scheme. This paper provides an overview and analysis of the state-of-the-art NOMA, CR, and CR-based NOMA network architecture. Furthermore, we present the main unique design challenges related to the practical implementation of such systems. Finally, some future research directions and open issues are provided and discussed.