Next Generation High Throuhgput Satellite System Based on Optical Feeder Links

High-data-rate ground-to-space optical links are envisioned to be an alternative and more probably a next step to radio-frequency links, after the Q/V band still under development [1] for the feeder links of next generation high throughput satellites. Indeed, optical links allow a significant increase of the available spectral resources per link. This enables a drastic reduction of the number of gateway stations required on the feeder link, making this approach highly attractive when it comes to serve a large number of small user beams (i.e. Terabit/s scenario). In this paper, a two co-located high throughput satellites solution covering EU27 is presented, implementing an innovative free-space optical feeder link to handle the large number of user beams. An affordable site diversity system based on several optical ground stations and an optical fiber network is considered to overcome cloud blockage of the feeder link. These OGS networks are optimized for reaching at least 99.9% feeder link availability while minimizing the overall cost of the system. To achieve required high throughput on the feeder link, a trade-off has been carried out between two potential transmission scheme candidates, i.e. analog and digital optical modulations. The study has shown that both options could be feasible in the 2025-2030 time frame (assuming significant technical /technological developments), and that link budget could be closed by using the relevant atmospheric perturbation mitigation methods implemented in the optical ground station or in the on-board terminal. An end-to-end performance analysis has been carried out considering 150 user beams per satellite operating in Ka band and assuming a DVB-S2 improved air interface performances, proving that both satellite jointly obtain a total aggregated throughput beyond 1Tbps. This work has been carried out in the frame of EU FP7 BATS project, aimed at integrate broadband access across the EU for 2020 and beyond.