A Channel Estimation Method for Modified Walsh-Hadamard Code Division Multiplexing in Helicopter Satellite Communications and Its Application to Initial Acquisition

Modified Walsh-Hadamard code division multiplexing (MWHCDM) is a promising solution for the degradation of bit error rate (BER) performance due to the periodic blockage (PB) of the channel caused by rotor blades in helicopter satellite communications. While zero-forcing (ZF) enhances the anti-PB capability of MWHCDM, it requires channel information. This paper proposes a channel estimation method for MWHCDM, discussing its application to initial acquisition. The proposed channel estimation method reproduces the transmitted signal from the received signal by utilizing the structure of MWHCDM signals. It estimates the channel information based on the cross-correlation coefficient between the reproduced transmitted signal and the received signal. Computer simulation shows that introducing ZF combined with the proposed channel estimation method to initial acquisition significantly improves the acquisition performance in the PB channel, similar to the BER performance.