Dynamic Doppler tracking for LTE-based broadband communications on high speed rails

This paper provides a comprehensive overview on frequency synchronizations in LTE (Long Term Evolution) downlink transmission and presents the necessity to carry out dynamic Doppler tracking for LTE-based broadband communication on high speed rails (HSRs). Firstly, the fundamentals of frequency synchronization are introduced, followed by the discussion of dynamic Doppler shifts in HSR scenarios. Then, targeting at LTE downlink, various frequency synchronization algorithms are described, exploiting specific signal structures of LTE. Furthermore, considering new features in broadband communications on HSRs, recent researches using these features to improve the dynamic Doppler shift tracking are introduced and discussed. It can be seen that although dynamic Doppler shifts are important features of broadband wireless channels on HSRs, limited research has been conducted in this area and a lot of work needs to be done in future.