Pre-detection time diversity combining with accurate AFC for helicopter satellite communications

In helicopter satellite communications, the periodic blockage of the received signal and the carrier frequency fluctuation are the most important problems. In this paper, we propose a novel pre-detection time diversity combining scheme with accurate automatic frequency controller (AFC) for helicopter satellite communications. In the proposed scheme, a novel AFC tracks and removes the carrier frequency fluctuation due to Doppler shift exactly, and the in-phase combining of the time diversity signal is performed before the coherent detection. Results of computer simulation show that the proposed scheme improves the BER performance of the previous post-detection combining scheme.