Performance of OTFS-NOMA Scheme for Coordinated Direct and Relay Transmission Networks in High-Mobility Scenarios

This letter proposes an orthogonal time frequency space (OTFS) modulation based non-orthogonal multiple access (NOMA) scheme for the coordinated direct and relay transmission system, where a source communicates directly with a nearby mobile user, and serves a distant user with high-mobility relying on the relaying assistance. However, the coexistence of signal superposition coding and multi-domain transformation presents a challenge in measuring the performance of OTFS-based NOMA from a theoretical perspective. To accurately evaluate the system performance of the proposed scheme, we derive the closed-form expressions for the outage probability and outage sum rate using the inversion formula and characteristic function under both perfect SIC and imperfect SIC. Numerical results verify the performance superiority and the effectiveness of the proposed scheme.