Multiple-Antenna-Assisted Non-Orthogonal Multiple Access

Non-orthogonal multiple access (NOMA) is potentially capable of circumventing the limitations of the classic orthogonal multiple access schemes. Hence, it has recently received significant research attention in both industry and academia. This article is focused on exploiting multiple antenna techniques in NOMA networks, with an emphasis on investigating the rate region of MIMO-NOMA, while reviewing two popular multiple antennas aided NOMA structures, as well as underlining resource management problems of both single-carrier and multi-carrier MIMO-NOMA networks. This article also points out several effective methods of tackling the practical implementation constraints of multiple-antenna NOMA networks. Finally, some promising open research directions are provided in the context of multiple- antenna-aided NOMA.

Introduction

Given the popularity of bandwidth-thirsty multimedia applications, such as online gaming and virtual reality, the bandwidth demand for high-rate services has been higher. Moreover, the proliferation of Internet of Things (IoT) devices imposes additional challenges on the next generation networks. Non-orthogonal multiple access (NOMA), is potentially capable of improving the spectral efficiency while supporting the connectivity of a myriad of devices [1]. Hence, NOMA has been considered as a promising candidate for the fifth generation (5G) networks [2]. The key concept of NOMA relies on allowing multiple users to occupy the same resource block, while identifying users based on their different power levels. More particularly, NOMA applies superposition coding (SC) at the transmitters for multiplexing users within the power domain and invokes successive interference cancellation (SIC) at receivers for detection.