A Simple Variational Bayes Integrated Communication and Sensing Approach for MIMO-OTFS Systems

Integrated sensing and communication (ISAC) has emerged as a promising technology for next-generation wireless communications. In this paper, we present a simple ISAC approach for MIMO (multi-input multi-output)-OTFS (orthogonal time-frequency space) systems, leveraging the power of variational Bayes. By factorizing the a posteriori probability (APP), we construct a factor graph for the received symbols in the MIMO-OTFS system. Parametric message passing algorithms for ISAC functionality are then derived by minimizing the variational free energy. Specifically, we decouple the original problem into three subproblems, referred to as data detection, channel coefficient estimation, and kinematic parameter sensing, and derive the corresponding message update rules. Simulation results demonstrate the superior performance of the proposed approach.