On the Performance of Doubly-Selective Fading Estimations in High Mobility Systems

This paper studies the theoretical performance of channel estimations in high mobility wireless communication systems operating with doubly-selective (both time-selective and frequency-selective) fading. High mobility communications result in fast time-selective fading with a Doppler spread as high as a few kilo-Hertz. The fast fading variation can be estimated and tracked with pilot-assisted minimum mean squared error (MMSE) channel estimation. The percentage of pilot symbols among the transmitted symbols plays a critical role. A higher pilot percentage can lead to a better channel estimation, but also more overhead. The impacts of the pilot percentage on channel estimations are identified through the derivation of the asymptotic mean squared error (MSE) of channel estimations. The results are expressed as a closed-form expression of various system parameters, including the pilot percentage, the maximum Doppler spread, the signal-to-noise ratio (SNR), etc.