On Non-orthogonal Multiple Access Technique For Relaying Networks

Cooperative communications technology aims to form a virtual multiple-input multiple-output(MIMO) system via sharing antennas with other scattering relay nodes. It has a vast application prospect owing to its strong capability of boosting throughput and reliability without requiring the equipment of multiple antennas and etc… Meanwhile, with a serious shortage of spectrum resource recently, Non-Orthogonal Multiple Access(NOMA) can achieve a superior spectral efficiency by using non-orthogonal transmission scheme. Therefore, NOMA is considered to be a promising candidate for 5G multiple access schemes.Considering the above two points, we investigate the performance of two kinds of NOMA downlink cellular communication system models based on the relaying networks. The first model is the NOMA for relaying system with the direct-path, and the second one is the NOMA for relaying system without the direct-path. The main contributions of this thesis can be summarized as follows:1) The outage performance of the two models' users are investigated through the simulation. What's more, we derive the diversity order, the closed-form expression and the asymptotic expression in the high SNR regions for the outage probability. The simulation results demonstrate that the two models can achieve nearly the same outage performance with the conventional multiple access(MA) scheme with an opportunistic user scheduling, and they are superior to the MA scheme with a randomly user scheduling and the conventional NOMA system without the relaying. The outage performance of NOMA depends critically on the choices of the users' target rate and power allocation coefficient. If the target rate and power allocation coefficient are not chosen appropriately, the outage probability is one, i.e. the target quality of service will never meet.2) The ergodic sum rate of the two system models and the upper bound of the ergodic sum rate are derived through two methods. The simulation results demonstrate that the analysis upper bound of the ergodic sum rate is close to the simulation results. The NOMA system can achieve nearly the same sum rate with conventional MA with an opportunistic user scheduling, and they are superior to the conventional NOMA system without the relaying, and what's more, NOMA can offer better spectral efficiency and user fairness since more users are served at the same time, same frequency and same spreading code.