# Parallel Eclipse-Aware Routing on FPGA for SpaceWire-Based OBC in LEO Satellite Networks
###### Abstract  
Low Earth orbit (LEO) satellite networks deliver superior real-time performance and responsiveness compared to conventional satellite networks, despite technical and economic challenges such as high deployment costs and operational complexity. Nevertheless, rapid topology changes and severe energy constraints of LEO satellites make real-time routing a persistent challenge. In this paper, we employ field-programmable gate arrays (FPGAs) to overcome the resource limitations of on-board computers (OBCs) and to manage energy consumption effectively using the Eclipse-Aware Routing (EAR) algorithm, and we implement the K-Shortest Paths (KSP) algorithm directly on the FPGA. Our method first generates multiple routes from the source to the destination using KSP, then selects the optimal path based on energy consumption rate, eclipse duration, and estimated transmission load as evaluated by EAR. In large-scale LEO networks, the computational burden of KSP grows substantially as connectivity data become more voluminous and complex. To enhance performance, we accelerate complex computations in the programmable logic (PL) via pipelining and design a collaborative architecture between the processing system (PS) and PL, achieving approximately a 3.83\(\times\) speedup compared to a PS-only implementation. We validate the feasibility of the proposed approach by successfully performing remote routing-table updates on the SpaceWire-based SpaceWire Brick MK4 network system. LEO network; K-Shortest Paths; Eclipse-Aware Routing; FPGA; SpaceWire +
Footnote †: journal: Sensor and Actuator Networks  
constitutes the pivotal backbone for global communication reliability and security [2]. The growing interest in satellite-based networks has led to the need for global satellite communication standards. Built to meet these demands is the SpaceWire protocol. SpaceWire is designed for real-time data transmission between space-mounted systems and built on the low-voltage differential signaling (LVDS) scheme, which consumes less power, and most satellites are operational with SpaceWire as their communication protocol [3]. In LEO spacecraft, SpaceWire serves as the on-board backbone bus, interconnecting sensors, the on-board computer (OBC), mass-memory units, and RF subsystems via low-power LVDS links that employ wormhole routing. Because each router exposes only a fixed-format routing table, a mechanism capable of dynamically managing and updating these tables is essential. Routing algorithms are indispensable in LEO satellite networks. However, the unique characteristics of low Earth orbit (LEO) make it impractical to apply conventional routing protocols. Compared to medium Earth orbit (MEO) and geostationary Earth orbit (GEO) satellites, LEO satellites operate at lower altitudes, which reduces latency and path loss but at the same time introduces significant challenges [4]. Because each LEO satellite's coverage area is much smaller than that of MEO or GEO systems, global coverage requires the deployment of hundreds or even thousands of satellites. Moreover, the rapid movement of LEO satellites generates a dynamic topology that is fundamentally different from terrestrial and traditional satellite networks, posing one of the major challenges for LEO constellations [5]. This fast mobility leads to frequent changes in inter-satellite connections and demands new routing strategies capable of managing these variations efficiently. Although real-time routing computations have been necessary in existing satellite systems, the complexity of routing in LEO networks places even greater demands on the real-time processing capabilities of on-board computers (OBCs). Consequently, extensive research efforts have been devoted to developing novel routing strategies specifically tailored for LEO satellite networks [6; 7; 8]. The strategic management of a satellite's energy resources is equally critical in LEO satellite networks.