Downlink OTFS-RSMA Cross-Domain Transmission Scheme and Sum-Rate Maximization

Rate splitting multiple access (RSMA) is an emerging multiple access scheme that plays a significant role in improving user sum-rate. This letter proposes a downlink orthogonal time frequency space-RSMA (OTFS-RSMA) cross-domain transmission scheme based on heterogeneous mobile user grouping and multicast technology, where high-speed users are served in the delay-Doppler (DD) domain and low-speed users are served in the time-frequency (TF) domain. Specifically, the OTFS-RSMA scheme categorizes users into high-speed users group and low-speed users group based on their mobility and then uses multicast to send cross-domain signals to the respective user groups, with RSMA used for transmission within the groups. By jointly optimizing the rate allocation and power control, this letter proposes a two-stage algorithm based on the coati optimization algorithm (COA) to maximize user sum-rate under the constraints of base station transmission power and QoS rate requirements. Our simulation results show that the proposed OTFS-RSMA scheme significantly outperforms the OTFS-NOMA scheme in terms of improving sum-rate.