High-Sensitivity, Large-Doppler-Range DSSS-GMSK Signal Acquisition Algorithm for Earth-Moon Space Satellite Communication.

With the intensifying competition among countries in lunar and deep-space exploration, the forward communication bands between Earth and the Moon are becoming increasingly congested. Spread-spectrum communication is poised to replace conventional unified-carrier wave systems as the dominant telemetry and tracking technology. Compared with Phase-Shift Keying (PSK) modulation, Gaussian-Filtered Minimum-Shift Keying (GMSK) offers lower transmit sidelobes and higher spectral efficiency, making it a promising alternative to Quadrature Phase-Shift Keying (QPSK) as a communication scheme integrated with spread-spectrum systems. This paper compares the direct-sequence spread-spectrum Gaussian-Filtered Minimum-Shift Keying (DSSS-GMSK) modulation scheme with the widely adopted DSSS-BPSK scheme and demonstrates the advantages of DSSS-GMSK, including higher spectral efficiency and improved signal acquisition performance over a wide Doppler dynamic range. This paper also proposes a deep-space DSSS-GMSK signal acquisition algorithm capable of achieving signal acquisition at a carrier-to-noise density ratio (C/N0) of 34 dB-Hz over a Doppler range from -350 kHz to +350 kHz, demonstrating the feasibility and potential of DSSS-GMSK. The algorithm requires minimal computational hardware resources, and its feasibility has been verified through simulations. Furthermore, its resistance to false locking is analyzed and discussed.