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An Efficient Two-Dimension OTFS-NOMA Scheme Based on Heterogenous Mobility Users Grouping

Orthogonal time frequency space (OTFS) modulation recently has been widely studied for its superior performance in high-mobility scenarios. In order to explore the efficiency potential and performance, the concept of non-orthogonal multiple access (NOMA) is extended to OTFS as a key technique to enhance its spectral efficiency. As for diverse schemes of NOMA formulated in different domains, we propose a two-dimension OTFS-NOMA (2D-OTFS-NOMA) transmission scheme based on heterogenous mobility users grouping by exploiting both power-domain and code-domain. Specifically, power-domain NOMA (PD-NOMA) is implemented between the users under high-mobility and low-mobility, while sparse code multiple access (SCMA) technique is applied to the users under the subgroup of low-mobility. Moreover, a high dimensional codebook design is also proposed based on Signature matrix construction methodology, which has a great extensibility for larger number of users' scenarios. We also validate the corresponding detection approach and present the analyses of its performance. Simulation results demonstrate that the proposed two-dimension OTFS-NOMA transmission scheme outperforms the other existing PD-NOMA scheme for OTFS systems in terms of spectral efficiency performance.