Gang Li

As the BeiDou Navigation Satellite System (BDS) is developed form BDS-2regional services to BDS-3 global services, the regional-serving GEO and IGSOsatellites are transformed into global-serving MEO satellites. The observation arcof MEO satellites by regional ground stations is about 1/3. The accuracy of MEOorbit determination and time synchronization would become worse, which wouldmake the global positioning accuracy become unacceptable. It is very hard to pro-vide Radio Navigation Satellite System (RNSS) service and effectively managethe satellite constellation. Different from GPS, GLONASS and Galileo adopt-ing a worldwide ground-stations method, BDS-3 creatively established a globaloperations and services architecture with regional stations and Ka-band Inter-Satellite Links (ISLs). The architecture's contributions to BDS-3 include not onlycombined orbit determination and time synchronization, but autonomous navi-gation, global operations and services. The BDS-3 on-orbit operation results arepresented in the paper to verify the designed capabilities. Compared with BDS-2,the orbit determination accuracy is improved from 0.6m to 0.15m, and the time synchronization accuracy is improved from 6.67ns to 1.16ns. Under autonomousnavigation, the 30-day orbit maintenance accuracy reaches 16m and the timesynchronization accuracy reaches 3.74ns. The success rate of data transmissionreaches 99%, and the delay is better than 12.9s. In the future, laser ISLs will beused to enhance the system structure and further improve global operation andservice capabilities.

Massive global Low Earth Orbit (LEO) constellations have been developed rapidly with the characteristics of higher number and shorter orbital periods of LEO satellites in recent years. The increasing requirements of real-time orbit determination and emergency data transfer in full arc can hardly meet by traditional regional ground stations. An integrated communication and navigation service architecture based on the third phase of the BeiDou system(BDS-3) Global Short Message Communication (GSMC) is proposed, which enables global coverage and random access. The GSMC downlink single-frequency signal is used for real-time orbit determination, and is further combined with B1C navigation signal for real-time dual-frequency high-precision orbit determination. Considering fast moving of LEO satellites and short burst of uplink messages, the uplink BDS-3 satellite selection strategy based on carrier-to-noise ratio, and uplink high-precision compensation of frequency shift are adopted to increase the communication success rate. The service architecture proposed can improve the precision of the autonomous orbit determination and enhance the capability of real-time command transmission of LEO satellites even without the traditional ground stations involved. According to the simulated analysis and first on-board test data, the integrated communication and navigation service has been validated. The precision of single-frequency real-time orbit determination can reach 2.83m, and the precision of dual-frequency can reach 0.26m. The average time delay of communication is about 11.45s, and the success rate is about 99.8%. The method may provide alternative means of real-time high-precision orbit determination and emergency data transfer of LEO satellites.