Monitor link assignment for reentry users based on BeiDou inter-satellite links

Abstract

The BeiDou Navigation Satellite System (BDS) has equipped its new-generation satellites with inter-satellite link (ISL) payloads to improve navigation services and system operation. When the inter-satellite ranging and communication are satisfied, we analyze the exploitation of the spare ISL capability for serving atmospheric reentry users. These users can be monitored over the atmospheric reentry segment with ISL transmission, even in the absence of visibility to ground stations and escaping the blackout. We modeled the problem and proposed a link assignment method combining parallel assignment of ISLs and dynamic access of monitor links. First, ISLs were assigned for inter-satellite ranging and communication, which were quantified with the number of different links and timeslot delays respectively. Corresponding assignment algorithm operated in the stations and the computing resource was abundant. Therefore, the heuristic algorithm was used to search the shortest route and the fitness function was determined with a shortest path algorithm. Based on the ISL assignment, extended users were accessed to the ISL network dynamically without influencing performances of the constellation. Because of the uncertainty of users’ states, the monitor link assignment was implemented onboard with short-term predicted states and therefore the computing resource was scarce. Short-term predicted states conquered the deviation of satellite-user visibility. And a simple smallest delay strategy was used to determine the access nodes for users. To evaluate performances of the algorithm, link assignments were implemented for the BeiDou global constellation with 3 users. Each satellite was linked with at least 10 satellites and communicated with stations within 3 timeslots on the basis of ISL assignments. The assignment of monitor links demonstrated the user access did not influence the ranging and communication index of the ISL network and 1-, 2-, and 3-timeslot route delays of users occupy the main parts and the total ratio is larger than 95%.