Doppler Mitigation in OFDM-Based Aeronautical Communications

Doppler spectrum in an aeronautical channel is modeled with dual-Doppler shift instead of classical Jakes model. Orthogonal frequency division multiplexing (OFDM)-based systems are sensitive to Doppler shifts/spread, since the time variation of the channel causes inter-carrier interference (ICI). ICI analysis is provided here for OFDM-based systems in the aeronautical channel. The effect of ICI on the received signal is presented and its power is derived. As compared with terrestrial channels, where ICI is generally overcome by increasing the subcarrier spacing and bounding the normalized Doppler frequency (NDF), we propose to mitigate the effect of Doppler shifts in aeronautical channels, as follows. First, we use parametric spectrum estimation methods to extract the Doppler shifts by exploiting the predictable number of paths. Then, a beamforming-based method is introduced to resolve the incoming rays by separating them individually. Finally, paths are Doppler-compensated and combined using diversity combining techniques. Computer simulations are performed to provide numerical results. It is shown that a mean square error (MSE) performance ofis achieved with the parametric estimation methods, and bit error rate (BER) performance approaching the no-Doppler scenario is obtained with the beamforming-based mitigation method.