An Adaptive MAC Layer Protocol for ATM-based LEO Satellite Networks

German Aerospace Center (DLR), Fraunhofer FOKUS.cats, and Tesat-Spacecom have designed a future multimedia ATM-based LEO satellite network. Part of the development was an adaptive MAC and FEC scheme which is presented in this paper. The FEC implementation switches on the fly during a connection between several FEC and modulation modes to guarantee a maximum ATM cell error rate of 10−6. In order to prevent influences of the changing FEC scheme on the user– level data rate, the MAC dynamically changes its packet lengths. Additionally, to minimize contention on the up–link, the MAC structures its TDMA frame into a fixed assigned part and a contention specific part. The boarder in between the two is dynamically altered according to the current link utilization.