  Vehicle-to-everything (V2X) is considered as one of the most important
applications of future wireless communication networks. However, the Doppler
effect caused by the vehicle mobility may seriously deteriorate the performance
of the vehicular communication links, especially when the channels exhibit a
large number of Doppler frequency offsets (DFOs). Orthogonal time frequency
space (OTFS) is a new waveform designed in the delay-Doppler domain, and can
effectively convert a doubly dispersive channel into an almost non-fading
channel, which makes it very attractive for V2X communications. In this paper,
we design a novel OTFS based receiver with multi-antennas to deal with the
high-mobility challenges in V2X systems. We show that the multiple DFOs
associated with multipaths can be separated with the high-spatial resolution
provided by multi-antennas, which leads to an enhanced sparsity of the OTFS
channel in the delay-Doppler domain and bears a potential to reduce the
complexity of the message passing (MP) detection algorithm. Based on this
observation, we further propose a joint MP-maximum ration combining (MRC)
iterative detection for OTFS, where the integration of MRC significantly
improves the convergence performance of the iteration and gains an excellent
system error performance. Finally, we provide numerical simulation results to
corroborate the superiorities of the proposed scheme.
