A study on code synchronization for time diversity in helicopter satellite communications

In helicopter satellite communications, the periodic blockage of the channel due to the rotor blades degrades the bit error rate (BER) performance. Although time diversity is attractive in order to overcome the periodic blockage, the combining process in the receiver requires the code synchronization. The pre-detection combining is suitable for time diversity because it is superior to the post-detection combining in terms of the BER performance. However, a sync word cannot be applied to the code synchronization in the pre-detection combining. To solve this problem, we propose a novel code synchronization scheme. The proposed scheme estimates the timing offset between the transmitter and the receiver on the basis of the cross-correlation of all possible pairs of the encoded sequences to combine. Results of computer simulation show that the proposed scheme achieves excellent synchronization performance without sync word even in the severe environment of helicopter satellite communications.