Pulse-Shaped OTFS for V2X Short-Frame Communication with Tuned One-Tap Equalization

Abstract:
The recently proposed orthogonal time frequency and space (OTFS) waveform promises significant performance advantages for high mobility users. OTFS is a pulse-shaped multicarrier scheme with Gabor (Weyl-Heisenberg) structure and additional time-frequency (TF) spreading. The spreading of the symbols over the TF domain is utilizing the symplectic Fourier transform (SFFT). For coherent communication OTFS requires proper channel information and the use of appropriated equalizers to exploit the full spreading gain. The doubly-dispersive channel is first estimated with pilot and guard symbols placed in the delay-Doppler (DD) domain. One-tap equalization, favored due to their lower complexity, is then performed in the TF domain. However, an accurate estimation of the self-interference power is necessary to exploit full diversity with such linear equalizer. To enable short-frame vehicle-to-everything (V2X) communication, we propose to instantaneously estimate the selfinterference power using pilot and guard symbols for tuning the minimum mean square error (MMSE) equalizer. We evaluate this approach for vehicular channels generated by the geometricstatistical channel simulator Quadriga and with an OTFS transceiver architecture based on a polyphase implementation for orthogonalized Gaussian pulses. Comparing to a IEEE 802.11p compliant design, we show that in such vehicular scenarios OTFS significantly outperforms cyclic-prefix based orthogonal frequency-division multiplexing (OFDM) when instantaneously tuning the equalizer. Our results also indicate that with such an approach the promised OTFS gains can indeed be obtained with a linear equalizer.