Channel and Phase Shift Estimation for TM-aided OTFS Railway Communications

In this paper, we suggest a new framework for wireless communications on railways aided by transmissive metasurfaces (TMs) and investigate the channel and phase shift estimation when orthogonal time frequency space (OTFS) is used. Specifically, we first establish the OTFS transmitter, end-to-end channel, and OTFS receiver models, and then define the input-output signal relation in vector form. Based on signal relation, we develop a channel and phase shift estimator that initially adopts the linear minimum mean squared error method to obtain the end-to-end channel and iteratively optimize the phase shift using the majorization-minimization (MM) method. Finally, numerical results are provided to show both convergence and performance of our MM-based estimation algorithm.