An Efficient Symbol-by-Symbol Aided Expectation Propagation Detector for OTFS With Index Modulation

In this letter, an efficient symbol-by-symbol aided expectation propagation (SS-EP) detector is designed for orthogonal time frequency space (OTFS) with index modulation (IM). Specifically, the null symbol of the OTFS-IM scheme is utilized to the expanded constellation symbol for expectation propagation. A varied zero sequence is designed based on the index mapping principle for our proposed SS-EP detector to improve the performance. Moreover, low-complexity SS-EP (LC-SS-EP) detector is developed, where the successive updating method is designed to update the statistical variables to reduce the operations of matrix inversion in each iteration. The simulated results show that the proposed SS-EP detectors are capable of providing significant performance gains over the existing detectors for both uncoded and coded OTFS-IM system.