Mobile satellite communications systems: Toward global personalcommunications

The constraints imposed by the RF environment are reviewed. An overview of present and planned mobile satellite systems is given. Present systems refer to those already in operation, while planned systems refer to those that have authority to offer the services and have either a satellite in orbit or one being built to support the systems. Future directions for mobile satellite communications systems are discussed. One approach emerging is the use of large satellites, with large antennas. operating at much higher carrier frequencies. A second approach is to use low-earth orbit (LEO) satellites. in order to reduce the path loss. The LEO approach also results in much smaller propagation delays than those experienced with geostationary satellites