Performance Evaluation for Latency-Stability Tradeoff in Satellite-Terrestrial Integrated Networks

Low-Earth-Orbit (LEO) satellite constellation is promising to extend broadband Internet services to where the terrestrial networks cannot reach, forming a satellite-terrestrial integrated network (STIN). The tradeoff between communication latency and topology stability is the core of constellation design and STIN operation. In general, low-altitude orbits reduce the propagation delay of ground-satellite links (GSLs), but result in frequent handover for GSLs. Frequent GSL handover weakens the topology stability, which is often measured by satellite pass duration and communication session duration. In this paper, we investigate the latency-stability tradeoff in STIN, and propose a stochastic model to analyze and evaluate GSL latency and pass/session duration. We analytically derive the distributions and the expectations of these metrics in closed forms, and verify the theoretic results based on empirical distributions (obtained by trajectory simulation). Compared to previous studies, our results exhibit more concise expressions and arguments. We find that the above closed-form expressions take two key arguments, i.e., the orbit period and the maximal central angle. The expected pass/session duration is directly proportional to the product of the two arguments, and the coefficients can be obtained explicitly (e.g., 0.25 for pass duration). We also demonstrate how to utilize the analytic results to draw deep insights on constellation design, aiming to reduce the GSL latency and keep the topology stable. We believe that our results in this paper could empower the operators and researchers to obtain a rapid understanding on the latency-stability tradeoff of STIN without resorting to time-consuming simulations.