On the Average Rate and Power Allocation of Uplink Multi-Antenna NOMA Systems

In this paper, we consider low-complexity design of multi-antenna uplink non-orthogonal multiple access (NOMA) system. There are 2N user equipments (UEs) distributed uniformly in a circle, where the N UEs nearer to the base station (BS) are called strong UEs and the other N farther UEs are called weak UEs. The BS decodes the strong UEs' signals by zero-forcing (ZF) detector first, and subtracts the strong UEs' signals. Then, the BS decodes the weak UEs' signals by ZF detector. For the proposed scheme we obtain the closed-form expressions of the average rate under three scenarios. In addition, a power allocation policy is proposed to reduce the interference between the UEs and maximize the average sum rate. Numerical results verify the analytical results and show that the average sum rate of the proposed NOMA scheme outperforms that of the orthogonal multiple access scheme employing time division multiple access.