Robust Downlink Transmission: An Offset-Based Single-Rate-Splitting Approach

We consider a multi-user multiple-input single-output downlink system that provides each user with a prespecified level of quality-of-service. The rate-splitting (RS) approach to this problem involves splitting the messages of each user into common and private portions that are transmitted in superposition and decoded sequentially. By adjusting the rates of each portion, the RS approach is able to mitigate the interference that conventional linear beamforming (CLB) schemes incur when users have channels that are closely aligned. However, the transmitter design problem for the RS approach can be quite challenging to solve. In this paper we develop a single-rate-splitting approach, in which RS is applied only to the user with the channel that is “most aligned” with the other channels. This approach greatly reduces the computational cost of RS designs, and admits an offset-based variant that provides robustness to channel estimation errors. Despite its simplifications, our simulation results indicate that the proposed approach retains most of the performance advantage of RS transmission over CLB.