Low Complex Inter-Doppler Interference Mitigation for OTFS Systems via Global Receiver Windowing

Orthogonal time frequency space (OTFS) waveform has been considered as a potential candidate for affording a wide range of emerging communications and sensing applications in beyond 5G wireless technologies. OTFS takes advantage of both time and frequency selectivity of the doubly dispersive wireless environment, which has been considered as one of the limiting factors in classical wireless communication technologies. However, the performance of OTFS-based wireless systems is severely affected by fractional Doppler that arises due to inevitable and inherent characteristics of the wireless channel taps of not being always integer Doppler values in the delay-Doppler plane. Thus, this results in severe inter-Doppler interference (IDI) and a low channel sparsity in delay-Doppler (DD) domain. To this end, this work introduces a novel receiver (Rx) windowing technique to combat the impact of fractional Doppler on error performance of the OTFS-based transmission with practical pulse shaping filters at the transceiver. Specifically, we introduce a global cyclic prefix (CP) based raised cosine (RC) windowing at Rx in order to alleviate the effect of IDI on the received signal. To do so, the proposed scheme changes the pulse shape of the OTFS signal in DD domain that defines the IDI level and sparsity of the effective channel. Furthermore, we assess the performance of the proposed Rx windowed OTFS (RW-OTFS) scheme under various practical communication scenarios. The obtained numerical and simulation results validate the accuracy of the proposed IDI mitigator for OTFS systems in practical high-mobility scenarios.