Iterative receiver for orthogonal time frequency space with index modulation via structured prior-based hybrid belief and expectation propagation

Orthogonal Time Frequency Space (OTFS) signaling with index modulation (IM) is a promising transmission scheme characterized by high transmission efficiency for high mobility scenarios. In this paper, we study the receiver for coded OTFS-IM system. First, we construct the corresponding factor graph, on which the structured prior incorporating activation pattern constraint and channel coding is devised. Then we develop a iterative receiver via structured prior-based hybrid belief propagation (BP) and expectation propagation (EP) algorithm, named as Str-BP-EP, for the coded OTFS-IM system. To reduce the computational complexity of discrete distribution introduced by structured prior, Gaussian approximation conducted by EP is adopted. To further reduce the complexity, we derive two variations of the proposed algorithm by using some approximations. Simulation results validate the superior performance of the proposed algorithm.