Cooperative non-orthogonal multiple access with D2D communication and opportunistic relaying in large-scale cellular networks.

In order to improve the spectrum efficiency , communication robustness, we propose a cooperative non -orthogonal multiple access (NOMA) scheme in large-scale cellular networks with Device-to-Device (D2D) communication and opportunistic relaying. The distribution of base stations (BSs) is assumed to follow homogeneous Poisson Point Process (PPP). Each BS communicates to both a near-user (CU1) and a far-user (CU2) in its coverage area. A collaborative region is defined between each BS and CU2, wherein there are multiple D2D transmitters (DTs) uniformly distributed and intending to communicate with a common D2D receiver (DR). Among all the DTs that has correctly decoded the data of CU2, one is selected to perform the single-hop decode-and-forward relaying. The selected DT superimposes its own data onto CU2's data , broadcasts the composite signal. If there is no DT available to forward the cellular data, the DT with the best channel quality towards DR will be selected to transmit the pure D2D data. Through properly modeling the aggregate interference, we analyze the throughput of each terminal. Numerical results show that with specific parameter settings, the NOMA scheme with optimal relay selection can greatly outperform random relay selection in terms of the far-user's throughput and the system throughput. With optimal relay selection, the proposed NOMA scheme can achieve much higher throughput than the orthogonal multiple access scheme.