Performance Analysis of Nonorthogonal Multiple Access for Downlink Networks With Antenna Selection Over Nakagami-m Fading Channels

We investigate the system performance of a nonorthogonal multiple access (NOMA) based downlink amplify-and-forward relay network over Nakagami-$m$ fading channels with imperfect channel state information, where the base station and all users are provided with multiple antennas, while the relay is equipped with a single antenna. Two special conditions of interest (e.g., Nakagami-1, i.e., Rayleigh and Nakagami-2) are analyzed, and closed-form expression for the system outage probability is derived. Moreover, tight lower and upper bounds of the outage probability, and the outage probability in the high signal-to-interference-and-noise ratio regime, i.e., in the presence of error floor, which exists due to the channel estimation errors, are obtained. Finally, computer simulations are conducted to verify the accuracy of the numerical analysis and to confirm the superiority of the antenna selection and NOMA scheme.

I. Introduction

Non-orthogonal multiple access (NOMA) has been considered as a promising signaling scheme in 5G wireless networks, due to its high radio-frequency spectrum efficiency and potential features to secure user fairness [1]. In [2], the outage performance was investigated in a hybrid relaying network, where NOMA as well as orthogonal multiple access (OMA) were utilized within user pairing groups and among each group, respectively. In [3], the study in [2] was extended to demonstrate the superior level of NOMA over OMA under two conditions, i.e., permanent power allocation and cognitive radio. More practical analog networks were considered in [4], where the performance of NOMA was compared with OMA and the superiority of NOMA scheme was confirmed. In addition, in [5], the successive interference canceller (SIC) was used in a NOMA-based multiple-input multiple-output (MIMO) wireless system with a single user to analyze the system performance.