Joint Geometric and QoS-Aware Routing in Optical LEO Satellite Networks via DRL
Optical inter satellite links ISLs are becoming the backbone of modern LEO constellations offering high capacity and low latency but introducing stringent geometric and physical layer constraints Routing in such networks must therefore account for time varying topology jitter induced outage and the heterogeneous reliability of intra and inter plane optical links aspects that classical shortest path or existing learning based schemes do not fully capture This paper develops a joint geometric and QoS aware routing framework for optical LEO networks We derive a closed form outage expression under Gaussian beam propagation with pointing errors and obtain analytical maximum feasible link ranges for different ISL classes These relations remove beam divergence from the optimization variables and embed optical feasibility directly into the routing layer leading to a latency reliability capacity constrained routing formulation that is proved to be NP hard To enable scalable decision making we cast snapshot routing as a Markov decision process and introduce an angle constrained masked deep Q network AC MDQN that integrates optical feasibility masks potential based latency shaping and a geometry aware corridor filter around the source destination great circle path This design significantly reduces the effective action space complexity while preserving near optimal routing choices Simulations on a Starlink like constellation demonstrate that AC MDQN achieves end to end latency within 1 to 2 percent of constrained shortest path solutions remains robust under varying pointing jitter and supports controllable hop latency trade offs through reward design The results confirm that the proposed framework provides an efficient and physically consistent routing solution for large scale optical LEO networks