Channel estimation for wideband doubly selective UAS channels

Reliable high-speed wireless communication is essential for abundant new unmanned aircraft system's (UAS) applications. While orthogonal frequency division multiplexing (OFDM) has been widely used for wideband communications because of its efficiency and its robustness to multipath propagation, high Doppler shift of UAS channels makes the implementation of OFDM challenging for UAS applications. Doppler shift makes the communication channel to vary with time and therefore, destroys the orthogonality between the subcarriers in OFDM and results in inter carrier interference (ICI). To mitigate ICI, channel state information (CSI) is needed at the receiver. In numerous scenarios, UAS wideband wireless channel is sparse. Therefore, compressed sensing (CS) methods can be implemented for the channel estimation. In this paper, both the sparsity of the delay spread and Doppler shift of the UAS payload communication channel are considered for channel estimation and three major adjustments to a regular CS method are proposed in order to enhance the channel estimation performance for high Doppler shift scenarios of UAS. The proposed modifications take into account the precise frequency domain channel model, the Doppler shift statistics of UAS wireless channels, and the ICI effect of the data on the channel estimation precision. Simulation results indicate that the proposed modifications enhance the channel estimation accuracy considerably for high Doppler shift scenarios.