In this letter, an orthogonal time frequency space (OTFS) based non-orthogonal multiple access (NOMA) scheme is investigated for the coordinated direct and relay transmission system, where a source directly communicates with a near user with high mobile speed, and it needs the relaying assistance to serve the far user also having high mobility. Due to the coexistence of signal superposition coding and multi-domain transformation, the performance of OTFS-based NOMA is usually challenging to be measured 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 the outage sum rate by using the Inversion formula and characteristic function. Numerical results verify the performance superiority and the effectiveness of the proposed scheme.

翻译：在这封信中,正在调查一个基于正方位时频空间(OTFS)的非正方位多重访问(NOMA)计划,用于协调的直接和中继传输系统,在这个系统中,一个源直接与移动速度高的近用户通信,需要转发协助为远端用户服务,因为信号叠加编码和多域转换同时存在,基于OTFS的NOMA的性能通常难以从理论角度加以衡量。为了准确评估拟议方案的系统性能,我们通过使用 Inversion 公式和特征功能,得出了超值概率和超值总和率的封闭式表达方式。数字结果验证了拟议方案的业绩优势和有效性。</s>