Contents I. Introduction
The giant low-earth-orbit (LEO) constellation as a promising candidate to offer the capability of the network accessing all over the earth has attracted extensive attentions in recent years, especially after the commercial success by SpaceX [1, 2]. The LEO system has also been considered as an effective approach to implement the next-generation 6G network, supporting the high-bandwidth wireless accessing and information delivering [3]. Therefore, the networking performance in LEO system, both over the radio-frequency (RF) and the optical laser (OL) was intensively investigated [4]. With the increase of the LEO constellation scale, the ultrahigh bandwidth is necessary to the satellite systems. The free-space laser communication between satellites becomes the only solution to such high performance, although the much higher transmission loss suffered in the laser carrier [5]. The investigations on the giant LEO have focused on the routing strategy, networking form or satellite-end upgrading [6]. The few works are on the transmission performance, which could be used to quantify the signal quality when passing through the selected routing path. In this paper, we carry out the joint optimization by connecting the routing strategy and the signal quality, to reveal the dynamic transmission performance for the real LEO optical networks. The results show that the optimized delay of 48.75ms and the signal quality of EVM% could be simultaneously achieved by the routing strategy of the shortest path algorithm. The severe degradations would be further observed when the sun outages and the doppler frequency shift happened in the LEO transmission system.
