An Accurate Time Diversity Combining with a Novel Channel Estimation for Helicopter Satellite Communications

One of the most important problems in helicopter satellite communications is that the periodic blockage of the received signal due to rotor blades significantly degrades the bit error rate (BER) performance. Time diversity is attractive in order to solve this problem. In a previous study, we proposed a time diversity combining scheme performing maximal ratio combining (MRC) on the basis of the channel blockage information estimated with a pseudo BER. However, in the low carrier-to-noise power ratio region, the BER performance of this conventional scheme is inferior to that of the ideal MRC because the channel estimation error is increased. In this paper, an accurate time diversity combining with a novel channel estimation scheme is proposed. The proposed scheme extracts the line spectrum of the periodic blockage from the envelope of the received signal by using the fast Fourier transform (FFT). The channel blockage information is estimated from the inverse FFT of the extracted line spectrum. The results of computer simulation show that the proposed scheme achieves the excellent BER performance very close to that of the ideal MRC.