Frequency reuse in land mobile-satellite systems

The author reviews the current methods of re-using the radio spectrum in the land mobile satellite service (LMSS) using satellites in the geostationary satellite orbit. The methods described relate to the performance of the satellite and mobile antennas. It is acknowledged that the satellite antenna provides a good method of frequency reuse through the use of multiple spot beams. However, when two or more satellite systems plan to provide services to the same geographical area, the mobile antenna plays an important part in facilitating sharing of frequencies. Developments in mobile Earth station design are lead to use of directional antennas combined with an antenna tracking mechanism. It is proposed that their lower sidelobe gain be used to protect other co-frequency LMSS operations, recognising also a requirement for sufficient orbital separation of the satellites