Slotted Aloha-NOMA with MIMO Beamforming for Massive M2M Communication in IoT Networks

This paper proposes an uncoordinated random medium access protocol for Internet of Thing (IoT) networks incorporating conventional slotted Aloha (SA) with power domain non-orthogonal multiple access (PD-NOMA) and multiple-input multiple-output beamforming (MIMO BF). The number of active IoT devices, which is not known a priori, is detected at the IoT gateway via multiple hypothesis testing. The proposed protocol referred to as BF-SA-NOMA is not only scalable and compatible with the power-limited IoT devices, but it also uses beamforming to significantly improve the throughput to 1.31 compared with 0.36 in conventional slotted Aloha when 6 active IoT devices can be successfully separated using 2×2 MIMO and a SIC (Successive Interference Cancellation) receiver with 3 optimum power levels. The simulation results further show that the proposed protocol achieves higher throughput than Aloha-NOMA with a lower average channel access delay.