NOMA Based Multiuser Uplink Signalling with Energy Harvesting IoT Nodes

This paper investigates the performance of an uplink multiuser IoT network in which green self-sustaining IoT users utilize the energy harvested from the downlink signal for uplink signalling using NOMA principles. The uplink user with best link signal-to-noise (SNR) is first chosen. To increase spectral efficiency, another user is also picked for concurrent transmission using non-orthogonal multiple access (NOMA) principles. We demonstrate that the choice of the second user depends on the target rate and number of users, and is not always the user with the second-best SNR. The users are selected using a timer-based mechanism, and no feedback of channel estimates is involved. Considering the time-switching protocol for energy harvesting, we obtain expressions for outage probability and throughput of this scheme. Unlike in traditional uplink NOMA networks, the transmit powers here are random, and this makes the analysis and user selection mechanism interesting. Accuracy of the derived expressions is illustrated by computer simulations.