IoT-Based Coordinated Direct and Relay Transmission with Non-Orthogonal Multiple Access

This letter studies an Internet-of-Things (IoT)-based coordinated direct and relay transmission (CDRT) adopting non-orthogonal multiple access (NOMA), where an information source directly communicates with a strong user while a weak user needs the help of an IoT master node. Different from traditional NOMA-CDRT systems, in which NOMA protocol is only deployed at the information source to serve users, the proposed novel system, i.e., IoT-assisted NOMA-CDRT, have two stages: (1) information source transmits the information data to users and (2) IoT master node operating as a relay to decode and forward data of the weak user along with IoT-U. Under the considered system setup, we derive exact closed-form expressions for the outage probability of users as well as approximated expressions for the ergodic sum capacity. Our results show that the proposed system may not perform well in terms of outage performance at the strong user during the cooperative transmission phase, but achieves higher ergodic sum capacity in whole communication process, and enhances efficient spectrum usage, compared with conventional CDRT and orthogonal multiple access systems.