A Rate-Splitting Empowered NOMA Network: Power Allocation and User Pairing

In this article, the harmony between non-orthogonal multiple access (NOMA) and rate-splitting (RS) is explored in a multi-antenna scenario, where a RS-NOMA system is proposed to implement dynamically transformation between these two transmission schemes. Specifically, a common signal is generated at the base station (BS) and transmitted with the users' private signals. By utilizing successive interference cancellation (SIC), the common signal is decoded and removed at each user, and then the private signals can be decoded based on NOMA schemes. By jointly design power allocation and user pairing, a weighted sum rate maximization problem is formulated with quality of service (QoS) constraints, where the priority of different signals is presented. By analyzing the monotonicity, the optimal power allocation is expressed in several cases, and then the strategy of each user to achieve the QoS threshold is obtained in all cases. To solve the user pairing problem, a matching based algorithm is developed, where the property is analyzed. Simulation results indicate that: i) the proposed RS-NOMA system outperforms the conventional RS and NOMA systems in general; ii) the developed power allocation strategy and user pairing algorithm can improve the RS-NOMA system in terms of the weighted sum rate and outage probability.