Doppler Zero-Insert Extension for OTFS Modulation with Fractional Doppler

Orthogonal time frequency space (OTFS) modulation can better handle Doppler shift and delay issues, which is a promising modulation method in future high-mobility scenarios. In the OTFS modulation system, the channel is expressed as a constant channel by delay information and Doppler information, which poses a huge challenge to OTFS transmission based on delay-Doppler domain channel estimation. The accuracy of the Doppler axes is not high enough, resulting in fractional Doppler parameters in most cases, which will cause great trouble to OTFS transmission and channel estimation. To solve this problem, we proposed a Doppler zero-insert extension scheme. In the delayed-Doppler domain, the signal is zero-inserted and extended in the Doppler direction to increase the total transmission time, thereby improving the accuracy of the Doppler axes direction. According to the extended received signal, channel estimation can be performed on the original fractional Doppler channel. We proved the feasibility of the proposed scheme for fractional Doppler channel detection through theoretical derivation, and obtained the performance improvement brought by the proposed scheme by analyzing the effect of converting fractional Doppler to integer Doppler. Finally, a relatively appropriate expansion parameter is selected through simulation, and the simulation results demonstrate the effective detection of our proposed scheme for fractional Doppler situations.