This paper investigates the outage performance of secondary users (SUs) in underlay cognitive radio-based nonorthogonal multiple access (CR-NOMA) networks. We consider down link scenario for the secondary network, which consists of a secondary transmitter (ST) and two SUs, ie, a near user and far user. The ST uses NOMA signaling to transfer the information to the down link SUs. A dedicated node is used as the full-duplex decode-and-forward (DF) relay for delivering the message to the far-user. We derive exact expressions for the outage probabilities experienced by the SUs for full duplex (FD)/half duplex (HD)-based CR-NOMA networks, in independent, nonidentically distributed Rayleigh fading channels. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. We compare the performance of the proposed FD/HD-based CR-NOMA networks against that of a CR network, which use conventional orthogonal multiple access (OMA) scheme. We establish that the performance of CR-NOMA network is better as compared to CR-OMA networks. We then consider finding the optimal location for the FD relay node that minimizes the outage probability of far-user. We formulate an optimization problem that is solved using genetic algorithm. Numerical results show that optimized relay location significantly improves the outage performance of the far-user. The analytical results are validated by extensive simulation studies.Trans Emerging Tel Tech. 2019;30:e3701.wileyonlinelibrary.com/journal/ett
To achieve high data rates expected from beyond 5G communications, higherorder modulation techniques have been explored. The energy-efficient modulation technique with a high data rate has encouraged researches towards an optimum two-dimensional hexagonal-shaped constellation, namely, hexagonal quadrature amplitude modulation (HQAM). Thus, in this work, we analyze the average symbol error rate (ASER) of HQAM schemes by considering a two-user nonorthogonal multiple access (NOMA) pair. Closed-form expressions for ASER of HQAM schemes for users are derived over generalized Nakagami-m fading channels. Further, for the HQAM constellation feasibility in two-user downlink NOMA systems, the power allocation criterion for the users is presented. Furthermore, the impact of modulation order of the users over the systems ASER analysis is investigated and valuable insights are drawn.
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