Glass fiber networks offer high performance, but they are not available in wide rural areas. Outside of large metropolitan areas, an alternative for broadband connectivity are geostationary satellites. This is where the approach of the DLR scientists starts: Within the project THRUST (Terabit-throughput optical satellite technology), they developed an innovative transmission technology for the next generation of communications satellites. The idea was to connect the satellites to the terrestrial Internet by means of a laser link, with the goal of multi-terabit data rates. Communication with the users takes place via microwave connection in the Ka band, a widespread frequency band in satellite communications.
Already during first trials in October, the scientists succeeded in set a record. In a test bed in Upper Bavaria they established a data rate of 1.72 Terabit per second across a distance of 3 kilometers. “The high stability of the signal reception along with the performance reserves at three kilometers encouraged us to dare the next step,” explained project manager Juraj Poliak from the DLR Institute of Communications and Navigation.
The quality of the data connection depends to some extend from the properties of the atmosphere. Therefore, Poliak and his Team developed a maximum load test. In simulations they found that the data link into the space would underlie the same level of distortions as in a terrestrial transmission across ten kilometers – in the worst case. The team verified the simulation results on a laser transmission path between Weilheim and Hohenpeissenberg, which happens to have a distance of 10.4 kilometers, and succeeded.
After the feasibility proof in the worst case scenario, the focus is now on the stability of the optical link. In the next phase of the research, the scientists therefore will perform measurements that help them to better understand the influence of the atmosphere and establish a stable laser connection to the satellite in the long term. “The stability of the connection is extremely important, because even a short interruption in the magnitude of 10 milliseconds would cause a transmission reduction of 10 Gbps,” explained Ramon Mata Calvo, head of the Optical Technologies research group of the DLR Institute of Communications and Navigation. With their trials, the scientists were able to demonstrate that optical wireless data transmission in the terabit range is feasible. The research therefore will be continued.