The agility link based navigation satellite network suffers from a lack of continuous end-to-end connectivity. Message transmitting relies on a store-forward mechanism-ie, data are sent from one node to another, depending on the communication opportunities, termed contacts, which arise when 2 nodes are connected by a link. To address the technical issues in such networks, the common approach is termed delay-tolerant networking. However, the problem becomes more complicated when the message is subdivided into several frames for the limited transmission capacity of one contact. In this paper, we formalize the multiframe message broadcast problem where node may possess different knowledge, such as contact plans and message distribution, which depict the state of network and is helpful for data transmission. With the different amount of the knowledge, we investigate several different transmission strategies. And we propose the theoretical models to evaluate the above transmission strategies. Simulations prove the accuracy of our model. We also find that, as expected, the strategy using more knowledge tends to perform better. To the best of our knowledge this is the first investigation of multiframe message broadcast issues in the agility link based navigation satellite network.
KEYWORDSagility link, delay-tolerant network, multiframe broadcast, knowledge oracles
INTRODUCTIONAutonomous navigation can enhance the satellite survivability. It can provide full navigation accuracy for a long time even if the control segment on the ground becomes inoperable. 1 Intersatellite link (ISL) is an indispensable technique for autonomous navigation. Through the mutual distance measurement and communication with ISL, the ephemeris update cycle can be shortened and the joint orbit determination of constellation can be realized, which can improve the positioning accuracy. Intersatellite link can also provide an independent method of ephemeris and clock reference verification to enhance the integrity of the system. As well, ISL can forward measurement and control signal to monitor and control the constellation indirectly, which solves the limitations of regional detection tracking network. Therefore, the world's major satellite navigation systems are actively exploring and constructing ISLs. It becomes the development trends of a new generation of global satellite navigation system.Intersatellite link with high-frequency band has advantages of large communication capacity and strong anti-interference ability and has gradually become the mainstream of the development of ISLs. Agility link is such an ISL. It is generally based on the phased array antenna equipped on the satellite operating at Ka band to communicate and range between satellites. The links switch and reconstruct frequently, and its pointer is changing with time. The time is divided into discrete and equal time slots, denoted Δt. During one time slot, the satellite completes the alignment, chain-building, and communication. In addition, transmission delay and propagation de...