Cooperative NOMA-based D2D communications: A survey in the 5G/IoT context

Non-orthogonal multiple access (NOMA) and device-to-device (D2D) communications have been recognized as promising techniques for the fifth generation (5G) networks due to their potential role in increasing the spectral efficiency. Cooperative NOMA presents a more attractive option since the two techniques are combined to provide better benefits and address some of 5G deployment purposes, and Internet of things (IoT) constraints and use cases. In this paper, considering recent and popular cooperative NOMA schemes, we first provide a compact taxonomical classification of the various approaches in the literature, and we present a comparative performance analysis based on outage probability and average throughput. Then, we illustrate the applicability of cooperative NOMA by a few use cases in industrial IoT environments. Finally, we discuss open research challenges that still need to be investigated in this area.