Abstract
This paper considers non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) system, where the base station (BS) directly communicates with the nearby users while it requires the help of a dedicated relay to communicate with the cell-edge users. We derive exact closed form expression for the outage probabilities experienced by the downlink users and the system outage probability of the considered CDRT network with full-duplex relaying (FDR) technique. Further, we derive approximate closed form expressions for the ergodic rates achieved by the users. The channel of all the links experience Nakagami fading distribution and the analysis takes into account the residual interference generated due to the imperfect successive interference cancelation (I-SIC) technique. We provide numerical and simulation results to identify the impact of key system parameters on the outage and ergodic rate performance of the users and the system outage performance. The outage and ergodic rate performance of users in the considered FDR-based NOMA-CDRT system has been observed to be significantly improved compared to a FDR-based OMA (orthogonal multiple access)-CDRT system. It is observed that random selection of NOMA power allocation coefficients at the BS leads to higher outage for the near users compared to the far users. We determine numerical results for the NOMA power allocation coefficient that leads to equal outage performance for both the users. Finally, we derive analytical expression for the optimal power allocation (OPA) coefficient at the BS that minimizes the system outage probability. Through extensive numerical and simulation studies, we establish that OPA can lead to significant reduction of system outage probability compared to random selection of power allocation coefficients at the BS.
Highlights
Non-orthogonal multiple access (NOMA) has been identified as an effective multiple access technique to improve the spectrum efficiency in the fifth generation (5G) wireless networks
6.3 Evaluation of ergodic rates of user 1 (U1) and user 2 (U2) Figures 13 and 14 respectively show the ergodic rate achieved by the users and the ergodic sum rate of the network, for full-duplex relaying (FDR)-based non-orthogonal multiple access (NOMA)-coordinated direct and relay transmission (CDRT) system
Ergodic rate of U1 does not depend on k2πrr, as this quantity does not influence the Signal to interference plus noise ratio (SINR) at U1
Summary
Non-orthogonal multiple access (NOMA) has been identified as an effective multiple access technique to improve the spectrum efficiency in the fifth generation (5G) wireless networks. NOMA technique allows multiple users to coexist and share the same time-frequency resource block via power domain multiplexing mechanism [1, 2]. In this case, a NOMA enabled BS will apply the superposition coding technique to combine. In [4], the authors have considered the application of NOMA in two-user HDR based CDRT system and analyzed the outage and ergodic sum rate performance. In [16], the authors have analyzed the outage and ergodic rate performance of the near and the far users in HDR-based NOMACDRT system, where an energy harvesting relay has been employed to assist the BS for delivering message to the far user. Notice that all the above papers consider the performance evaluation of HDR-based NOMA-CDRT system
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