Local Network Integration via Satellites

In the framework of a national activity and a project funded by the European Space Agency, a novel satellite communications system has been developed which supports the interconnection of computer networks, ISDN exchanges and isochronous services such as point-to-point and multi-point video conferencing. The project was carried out in close cooperation with the Institute of Applied Systems Technology (Joanneum Research) and the Institute of Computer Science (University of Salzburg). The satellite gateway utilizes the method of cell multiplexing. An efficient demand-assignment time division access scheme has been studied and implemented which makes optimum use of the available satellite capacity. Internally the method of cell multiplexing is adopted. Currently a user data rate of 4 Mbit/s is supported in single-frequency TDMA mode. An enhancement of the speed by utilising multi-frequency TDMA has been carried out. Thus, the capacity can be assigned in time and frequency. A frequency-agile demodulator allows the frequencies to be changed between bursts. This way the network capacity can be increased significantly without the need to increase the antenna size or the transmitter. An important aspect of the project is the investigation of powerful error-correction coding techniques. Special emphasis has been laid on Reed-Solomon block codes and concatenated schemes (Turbo codes).