OTFS-PDMA Scheme With EPA-Based Receivers for High-Mobility IoT Networks

The sixth-generation (6G) network is considered a promising enabler of the Internet of Things (IoT), with potential applications spanning from terrestrial to non-terrestrial terminals. In this paper, a novel orthogonal time frequency space (OTFS)-based pattern division multiple access (PDMA) scheme, shortened as OTFS-PDMA, is proposed to meet the low-latency, high-reliability, and massive connection requirements of 6G networks in high-mobility scenarios. A combined detection approach is proposed for the OTFS-PDMA scheme based on the expectation propagation algorithm (EPA). To mitigate the detrimental effect of base station antenna correlation, we design a vector EPA (V-EPA) receiver by combining different receive antennas at each delay-Doppler domain resource element. A pattern-aware serial mechanism is proposed to facilitate the convergence of the proposed EPA and V-EPA receivers by exploiting the convergence-amenable property of the PDMA scheme. An iterative detection and decoding (IDD) structure with parallel interference cancellation (PIC) is integrated into the proposed receivers to further improve the system performance. Simulation results illustrate that the proposed OTFS-PDMA scheme with EPA-based receivers achieves significant performance gains over the conventional OTFS-OMA scheme. Moreover, the proposed V-EPA receiver provides a good performance-complexity trade-off, particularly in spatially correlated multiple-input multiple-output (MIMO) channels.