Margin Leveling Algorithm for Fully Saturated Satellite Transponder with CDMA (Code Division Multiple Access) Signalling

摘要

For satellite communications in a noninterfering environment, a specific downlink carrier-to-noise ratio (CNR) is needed to achieve a desired bit error rate. In an interfering environment, and additional CNR or margin is needed to overcome interfering effects. A situation may arise where the desired margins cannot be achieved due to limited uplink and satellite transmit power. If this is the case, margin leveling should occur in order to decrease the desired margins in a specific manner until all margins are achieved. The goal of this thesis is to develop a margin leveling algorithm under specific constraints. The satellite under study is assumed to be operating with the traveling wave tube amplifier in full saturation. The signalling scheme used is direct sequence code division multiple access (CDMA) communications. Two methods of margin leveling are created--the first being the margin leveling of only the links in which the desired margins are not achieved; the second being the margin leveling of all links whether the desired margins are achieved or not. In the latter case, all links are leveled by an equal amount. It is found that the computer time needed to perform margin leveling increases proportionally to the square of the number of links accessing the satellite.