Hierarchical Full-Duplex Underwater Acoustic Network: A NOMA Approach

Underwater acoustic is the prevalent technology in underwater wireless communications. The sum rate in underwater acoustic channels is limited by the underwater environment properties. This paper attempts to increase the sum rate of underwater channels without utilizing additional resources, through adding a relay and employing full duplex (FD) and non-orthogonal multiple access (NOMA) technologies. The adopted system model has two sensors and two robotic arms communicating with a buoy via a relay. Employing FD-NOMA allows multiple uplink and downlink transmissions to occur simultaneously, using the same time and frequency resources. The main challenge for this deployment is the interference between the transmissions. Interference cancellation techniques, successive interference cancellation and self-interference cancellation, are employed to mitigate the interference due to NOMA and FD, respectively. In order to maximize the sum rate, an optimization problem over the power is formulated and solved as a convex optimization problem. The performance of the system is benchmarked with the performance of the non-relay (NR) aided FD-NOMA and relay-aided (R) half duplex orthogonal multiple access (HD-NOMA). It is shown that R-FD-NOMA always has higher sum rate than NR-FD-NOMA, irrespective of the efficiency of interference cancelation. In addition, it is shown that at efficient interference cancellation, the sum rate of FD-NOMA is higher than HD-OMA.