ICI mitigation for high-speed OFDM communications in high-mobility vehicular channels

Abstract

The performance of an Orthogonal Frequency Division Multiplexing (OFDM) system to transmit high bandwidth data from a vehicle to a base station can suffer from Inter-Carrier Interference (ICI) created by high Doppler shifts. In current communication systems, high Doppler shifts can happen because of the high speed of the vehicles such as fixed wings unmanned aircraft vehicles (UAVs) and high speed trains (HST). In next generation wireless systems with high carrier frequency, such as 5G cellular data systems at center frequency between 27.5–71 GHz, even a vehicle moving with moderate speed can cause Doppler shift of several kilohertz. To cancel the ICI, the time variant channel matrix should be estimated in the frequency domain. In this paper, a new channel estimation scheme is presented suitable for high Doppler scenarios. To estimate the channel in the frequency domain, a training sequence in the time domain is transmitted, and both channel amplitudes and Doppler shifts are estimated in time domain. Then, the complete frequency domain channel matrix is constructed from the estimated parameters and used for ICI mitigation. In contrast to conventional methods that only estimate diagonal elements of the frequency domain channel matrix or other partial section of the matrix to reduce the complexity, this new method estimate the complete matrix. Simulation results show significant gain in performance for the complete channel estimation as compared to conventional methods using least square and minimum mean square diagonal elements of the channel estimators in high Doppler scenarios.