Abstract: Submarines only surface when necessary, which greatly restricts realtime communication and positioning. The blue-green laser has advantages of high penetration in deep-water and a low attenuation coefficient, which has been verified in airborne and space-borne communication with submarines. Considering the principle of GNSS signal generation, combining the integration of the blue-green laser communication ranging with the precise orbit determination of the LEO satellite, a submarine positioning algorithm based on blue-green laser was proposed. By integrating carrier phase modulation into laser communication, pseudorange measurement of the submarine was achieved, and combined with its elevation measurement, underwater positioning was realized. For the service of the Belt and Road area, especially the South China Sea region, the constellation parameters were optimized, and a sparse constellation composed of three LEO satellites was designed. The submarine remained stable within the coverage area of the constellation. It completed communication ranging and navigation message reception at least twice with the interval of 1 to 3 minutes, and performed positioning calculation with two sets of observation data, precise ephemeris and elevation measurement. Considering the accuracy of satellite orbit determination, the laser propagation error in atmosphere and seawater, simulation shows that the positioning error in X and Z direction is less than 100m, and the error in Y direction is about 100 to 150 meters, which will help improve combat capability for submarines. 

Key words: LEO satellite, sparse constellation, blue-green laser, communication ranging, submarine positioning