Research On The Modulation Of Inter-Navigation Satellite Laser Link

Inter-Satellite Link(ISL) is a significant part of the modern Global Navigation Satellite System(GNSS). And the ranging and communication function of ISL can make the navigation system still work normally in the absence of ground stations' support. The second generation of Chinese COMPASS satellite navigation system is developed systematically. Meanwhile, the goal of high speed data transmission and precise distance measurement can be achieved by laser link compared with the traditional RF link.First the Intensity Modulation/Direct Detection( IM/DD) and coherent optical communication system for ISL are respectively introduced in this thesis. And the principle of their modulation and demodulation are also discussed. According to the complete space satellite constellation of next generation COMPASS system, the link characteristics such as available connectivity, link distance and Doppler frequency shift are studied in a whole period via STK software. Under the circumstances of actual parameters of satellites optical system, a link budget is calculated.By comparing the performances of IM/DD and coherent optical modulations, a signal scheme using coherent optical system is proposed with the purpose of ranging and data communication between navigation satellites. The scheme, divided into data channel and pilot channel, uses QPSK modulation. The pilot channel is designed for high precision ranging without data modulation, while the data channel is used for high speed communication. Then the performance of this system, with homodyne coherent detection scheme, is tested by simulation software. It has come to the conclusion that the BER performance and ranging accuracy of this scheme both are much better than RF link or IM/DD optical communication system for ISL, which is under the circumstances of 92.3dB-Hz CNR and 100 Mbps information rate in data channel.