System-level evaluation of downlink non-orthogonal multiple access (NOMA) for non-full buffer traffic model

For the past few years, we proposed non-orthogonal multiple access (NOMA) as a promising multiple access scheme for further improvement of spectrum efficiency for LTE enhancements and the 5th generation mobile communications system (5G). Currently, the system performance of NOMA, considering practical assumptions, different deployment scenarios and NOMA specific functionalities, including multi-user pairing, transmit power allocation, and combination with MIMO is being evaluated and discussed in academia, industry, and standardization [5-16]. In addition, the most of existing evaluations for NOMA focus on the full buffer traffic model, which is widely adopted for the evaluation of mobile radio access system. However, further investigations with non-full buffer traffic model are also important to clarify the system performance of NOMA for different types of the traffic. This paper investigates the system-level performance of NOMA with non-full buffer traffic model for different levels of packet arrival rates and sizes. In addition, the impact of the scheduling algorithm such as α-fair gradient scheduler, which controls the fairness level of the resource allocation, is also discussed. Based on computer simulations, we show that for the non-full buffer case, NOMA can still provide a large performance gain compared to that of orthogonal multiple access (OMA) in particular for small packet sizes. It is also shown that under full buffer traffic model, α-fair gradient scheduler is able to trade-off between average user packet throughput and 5% user packet throughput; however, this does not hold for the case of non-full buffer traffic model.