Capacity Enhancement of D2D Aided Coordinated Direct and Relay Transmission Using NOMA

Abstract

This letter investigates a device-to-device (D2D) communication aided coordinated direct and relay transmission (CDRT) using non-orthogonal multiple access (NOMA) framework, where a cell-center user (CU) is served by a base station (BS) directly while a cell-edge user (EU) needs the help of a relaying user (RU) to communicate with BS. Specifically, with the use of the NOMA principle, we propose to exploit a D2D communication link from RU to CU for transmitting a new signal during the information forwarding of RU in the second phase, so as to enhance the network spectrum efficiency. Analytical closed-form expressions of the system ergodic sum capacity are derived and verified by computer simulations. Both analytical and simulation results demonstrate that the D2D aided NOMA scheme achieves higher sum rates than the conventional CDRT scheme and orthogonal multiple access (OMA) scheme.