NOMA Design With Power-Outage Tradeoff for Two-User Systems

This letter proposes a modified non-orthogonal multiple-access (NOMA) scheme for systems with a multi-antenna base station (BS) and two single-antenna users, where NOMA transmissions are conducted only when the absolute correlation coefficient (ACC) between the user channels exceeds a threshold and the BS uses matched-filter (MF) precoding along the user with the stronger average channel gain. We derive the average required transmit power to guarantee the signal-to-interference-plus-noise-ratio (SINR) levels of both users. Our results show that the average required transmit power grows logarithmically in the reciprocal of the ACC threshold and a non-zero threshold is necessary for finite average transmit power. Further, for the massive MIMO scenario, we derive scaling laws of the average transmit power and outage probability with respect to the antenna numbers, as well as their tradeoff law. Simulation results are shown to validate our theoretical results.

I. Introduction

Non-orthogonal multiple-access (NOMA) is a potential technique for next generation mobile communications. With superposition coding at the transmitting base station (BS) and successive interference cancellation (SIC) at the receiving users, NOMA can provide improved performance via the extra degree-of-freedom in the power domain compared to orthogonal multiple-access (OMA) schemes [1], [2].