Exploiting SWIPT for IoT NOMA-based Diamond Relay Networks

Combining non-orthogonal multiple access (NOMA) with cooperative relaying networks has been considered as a viable approach for increasing the spectral efficiency and capacity enhancement of the system. With the exponential growth of the Internet of Things (IoT), integrating simultaneous wireless information and power transfer (SWIPT) with NOMA and diamond relaying networks can increase capacity and energy efficiency at the same time. Moreover, a diamond network topology has been established as a standard cooperative relaying model in the 3rd Generation Partnership Project (3GPP). Therefore, in this paper, we investigate SWIPT for IoT NOMA-based diamond relay networks wherein a source node transmits two symbols to a destination node through two energy harvesting (EH) based decode-and-forward relay nodes using the principle of downlink NOMA in the first time slot. The two EH based relay nodes harvest the energy from the source's signal and then transmits the decoded symbol to the destination node using the uplink NOMA protocol in the next time slot. Analytical expressions for the achievable rate of the symbols and the achievable rate of the considered system are derived and verified with the simulation results. Moreover, an asymptotic closed-form solution for the achievable rate is also provided for mathematical tractability and simplified analysis. Our results demonstrate the effect of energy harvesting parameters and the effectiveness of the considered system over the similar system model using conventional orthogonal multiple access.