A New NOMA-Based Two-Way Relaying Scheme

Two-Way Relaying (TWR) has been widely investigated in the literature as an efficient relaying scheme for dual-hop cooperative transmissions. In TWR, two nodes exchange data through an intermediate relay, where both nodes simultaneously send signals towards the relay in the first time slot. The relay, in turn, combines both received signals into one signal and sends it back to both nodes on the second time slot. In this paper, the spectral efficiency is further enhanced in TWR scheme by adopting Non-Orthogonal Multiple Access (NOMA) technique. Specifically, the transmitted signals from the nodes in the first time slot are composed based on NOMA transmission and intended to multiple intermediate relay-nodes. Consequently, each relay will extract its own symbols, combine them and send them in the second time slot. The improvement of the spectral efficiency in our system, as compared to the Conventional TWR, is linearly proportional to the number of relay-nodes that can be installed. The performance of the proposed scheme is mathematically analyzed in terms of the spectral efficiency and error performance, shown significant gain when compared to the conventional TWR scheme.