Performance Analysis of Non-Orthogonal Multiple Access With Underlaid Device-to-Device Communications

Non-orthogonal multiple access (NOMA) and device-to-device (D2D) communications are promising technologies for 5G cellular networks. In this paper, we investigate the impact of the integration of D2D communications with a downlink NOMA system. In a cluster of two cellular users and a D2D pair, we extract power control strategies for the base station (BS), which allow for cellular users to achieve a higher sum rate and higher individual rates in NOMA compared to an orthogonal multiple access (OMA). The D2D link has the same rate in both OMA and NOMA systems in our proposed scheme. We further derive the probability that both users obtain higher rates in NOMA under a fixed power control strategy. We provide numerical results that illustrate the performance of the proposed power control policies and demonstrate the accuracy of the derived closed-form expression for the probability that both cellular users obtain higher rates in NOMA. We also study the effects of the BS transmit power level and the power portion assigned to each user on the probability that both users outperform in NOMA through numerical results.