Research on Receiving Method of Code Shift Keying (CSK) Signal

摘要

Code Shift Keying (CSK) modulation type can obtain a high information transmission rate while maintaining the correlation characteristics of the spread spectrum signal, and has been attracting attention in the field of satellite navigation in recent years. Different from the conventional Direct Sequence Spread Spectrum (DSSS) method, demodulating CSK modulation data requires external time synchronization information. For this reason, the receiver can obtain the corresponding synchronization information from the pilot signal of the same frequency, or obtain the frequency and symbol synchronization information from the received signals of other frequencies of the same satellite to assist in demodulating the CSK modulation data when there is no pilot signal of the same frequency. In this paper, a signal receiving method is proposed, which can reduce the threshold of CSK signal data demodulation, aiming at one data signal which is modulated by BPSK DSSS and another modulated by CSK DSSS, both of them share the same carrier and have orthogonal phase. Namely, the dual auxiliary signal receiving method obtains the corresponding Doppler frequency offset information from the pilot signals of other frequencies of the same satellite to assist in tracking the BPSK DSSS data signal of the same frequency point as CSK signal, obtain the symbol synchronization information, and then assist in demodulating the CSK modulation data. Compared with the single auxiliary signal receiving method which only relies on BPSK signal of orthogonal multiplexing at the same frequency to demodulate CSK data with coherent demodulation or demodulate CSK data with noncoherent demodulation assisted by pilot signals at other frequencies, this method has better signal tracking robustness and lower data demodulation threshold. The method proposed in this paper combines cross-frequency pilot signal assistance and co-frequency signal coherent assistance, which can not only assist the coherent demodulation of CSK signal, but also assist non-coherent demodulation of CSK signal, and has better adaptability to complex environments. The theoretical calculation results show that the threshold of CSK signal demodulation can be reduced by about 3 dB by using the dual auxiliary signal receiving method proposed in this paper.