Research on Communication Delay Model for Narrow Beam Inter-satellite Links in a TDMA System

Navigation constellation inter satellite link (ISL) is one of the efficient ways to improve the service performance of global navigation satellite system (GNSS). The four major GNSSs have been equipped with ISLs or plan to equip in near future. Narrow beam inter satellite link in a time division multiple access (TDMA) system have advantages of fast beam switching, flexible networking, high communication speed and good security. For navigation constellation to improve service performance, the measurement values have to transfer back to the ground facilities in a short time, at the same time, facilities have to transfer telecommand and uplink ephemeris to satellites which are invisible to ground facilities as soon as possible. These all made a request to shorter communication delay. And it is very important to improve the performance of ISLs by rapidly assessing the quality of the connection and adjusting the unreasonable connection in time. In this paper, a communication time delay model for ISLs based on directed graphs is studied. By abstracting the ISL timeslot table into a directed graph, and based on the shortest path algorithm, the communication time delay can be obtained quickly. Simulation verifications have been carried out for different scenes. Results show that the proposed model works well.