Contact Plan Design for Cross-Linked GNSSs: An ILP Approach for Extended Applications

TL;DR

This work addresses the problem of extending GNSS ISLs to support external users without compromising core GNSS functionality. It introduces an ILP-based CPD that operates under a polling time-division duplex framework and a user-service model with a multi-stage service procedure, enabling continuous multi-slot ISLs for diverse external needs. Simulations using BeiDou show that the CPD maintains essential ranging and data-delivery capabilities while providing best-effort extended ISLs, and it demonstrates notable improvements in Earth–Moon LP orbit determination and clock synchronization when GNSS ISLs are available. The results establish GNSS as a more pervasive PNT infrastructure capable of interoperating with cislunar assets, enhancing navigation, timing, and data transport in future space architectures.

Abstract

Global Navigation Satellite Systems (GNSS) employ inter-satellite links (ISLs) to reduce dependency on ground stations, enabling precise ranging and communication across satellites. Beyond their traditional role, ISLs can support extended applications, including providing navigation and communication services to external entities. However, designing effective contact plan design (CPD) schemes for these multifaceted ISLs, operating under a polling time-division duplex (PTDD) framework, remains a critical challenge. Existing CPD approaches focus solely on meeting GNSS satellites' internal ranging and communication demands, neglecting their extended applications. This paper introduces the first CPD scheme capable of supporting extended GNSS ISLs. By modeling GNSS requirements and designing a tailored service process, our approach ensures the allocation of essential resources for internal operations while accommodating external user demands. Based on the BeiDou constellation, simulation results demonstrate the proposed scheme's efficacy in maintaining core GNSS functionality while providing extended ISLs on a best-effort basis. Additionally, the results highlight the significant impact of GNSS ISLs in enhancing orbit determination and clock synchronization for the Earth-Moon libration point constellation, underscoring the importance of extended GNSS ISL applications.

Figures (13)

• Figure 1: Hierarchical Topology Model: System periods are divided into Finite State Automaton (FSA) states, further segmented into superframes subdivided into time slots as the basic ISL allocation unit.
• Figure 2: User Model: The diagram illustrates the interaction between GNSS satellites and user types. Constellation users suitable for consolidation are represented as a single logical user.
• Figure 3: User Isolation: (a) Interaction between a GNSS satellite and a specific user. (b) Constellation users without consolidation, with GNSS providing ISLs to individual nodes and the constellation CPD managing internal links. (c) Consolidated overall logic user, with GNSS offering ISLs to the constellation as a whole, requiring the selection of an internal node to receive ISLs before performing the constellation CPD.
• Figure 4: User Procedures: Flowchart illustrating the GNSS CPD.
• Figure 5: Number of visible satellites for satellites in all FSA states.