With the explosive growth of Internet devices, the 5G new radio (NR) system faces congestion and high latency issues due to the low access efficiency of traditional orthogonal multiple access (OMA).Besides this, the performance of the orthogonal frequency-division multiplexing (OFDM)-based system is severely degraded due to the Doppler effect in high-speed scenarios.To meet the low-latency, high-reliability, and massive connection requirements of 6G communication in high-mobility scenarios, firstly, a novel orthogonal time frequency space (OTFS)-based pattern division multiple access (PDMA) scheme, shortened as OTFS-PDMA, was proposed.Then, the system input-output relationship of different types of PDMA codeword allocation schemes in the delay-Doppler (DD) domain was derived.Finally, a low-complexity expectation propagation algorithm (EPA)-based receiver was proposed.Simulation results illustrate that the proposed OTFS-PDMA scheme achieves significant performance gains over the conventional OTFS-OMA scheme.For regular PDMA patterns, the PDMA codeword allocation has a slight impact on the system performance.For irregular patterns, the centralized spreading method outperforms the discrete one.For discrete spreading scheme, the system can achieve better performance by assigning irregular PDMA spread signals along the Doppler direction.In addition, the proposed EPA receiver outperforms its conventional counterparts.
