Inter-Satellite Link (ISL) are a key enabling technology for next-generation of GNSS satellites. ISL offers enhanced Monitoring and Control (M&C) and data dissemination capabilities, helps reducing the size of the ground segment network and ultimately leads to better Clock and Ephemeris Data (CED) accuracy thanks to inter-satellite ranging measurements and reduced Signal-in-Space Error (SISE) through faster on-board data refresh rates.
An ISL-enabled constellation operates as a network where nodes (satellites) communicate via a data routing logic. The ground segment interacts with the constellation through designated access points called “Gateways.” Data dissemination can occur either directly (single-hop) or through multiple nodes (multiple-hop). If each node has two active ISL payloads, Real-Time Ring (RTR) transmission is achievable using connection matrices that create single or multiple interconnecting rings.
This network-oriented approach enhances real-time command and monitoring of satellites while increasing bandwidth usage. However, its effectiveness relies on the availability of the ISL payloads; if a link is not active, the rings open and data cannot travel past that node.
Considering that a GNSS constellation will be constituted by satellites at very heterogeneous points of their operative life, the ageing of the ISL payloads is expected to introduce failures over time, either temporarily or permanently.
The present paper analyses the performances of an ISL-capable MEO network exchanging data using a RTR strategy and evaluates its robustness when progressively introducing failures. The benefits of using a half-duplex communication scheme are analyzed.
The effects of failures are analysed firstly assuming no intervention from Ground and then introducing mitigation actions by the ground segment including contact replanning based on failed links and isolation of faulty satellites.
The performance metric considered is the time taken to disseminate data from their generation to when they reach the target satellite. Simulation hypotheses, recommendations, and future work are also presented.
