  Non-terrestrial networks (NTN), particularly low Earth orbit (LEO) satellite
networks, have emerged as a promising solution to overcome the limitations of
traditional terrestrial networks in the context of next-generation (6G)
wireless systems. In this paper, we focus on analyzing the timeliness of
information delivery in NTN through the concept of Age of Information (AoI). We
propose an on-off process to approximate the service process between LEO
satellites and a source node located on the Earth's surface. By utilizing
stochastic geometry, we derive a closed-form expression for the time-average
AoI in an NTN. This expression also applies to on-off processes with one
component following an exponential distribution while the other has its
probability density function supported on a bounded interval. Numerical results
validate the accuracy of our analysis and demonstrate the impact of source
status update rate and satellite constellation density on the time-average AoI.
Our work fills a gap in the literature by providing a comprehensive analysis of
AoI in NTN and offers new insights into the performance of LEO satellite
networks.
