Hybrid Message Passing Based Receiver for Orthogonal Time Sequency Multiplexing Modulation System Without Zero Padding

In high-speed wireless communication scenarios, the orthogonal time sequency multiplexing (OTSM) exhibits performance comparable to orthogonal time frequency space (OTFS) with reduced complexity. By inserting zero padding (ZP) between blocks, conventional Gauss-Seidel (GS) receivers can leverage the diagonal block structure of the time-domain channel to achieve good BER performance. However, their complexity is quite high for the OTSM system without ZP. To this end, we propose an iterative receiver employing variational inference and belief propagation for the OTSM system without ZP. With a factor graph representation of the joint posterior distribution, a hybrid message passing receiver under a serial schedule is proposed for data detection in the OTSM system without ZP. Further extension is made for practical systems where the noise precision is unknown. Simulation results illustrate the advantages of the proposed variational receiver via comparison with the GS algorithm.