s to offer services to both the public and government [11, 12]. Example 11.3: Australian National Broadband Network The Australian NBN roll-out is expected to provide connectivity to some 3-4% of Australians using a K band satellite system. This system is expected to use transponders with a 300-600 MHz bandwidth to provide services using a VSAT architecture. Transmission rates in the downlink are expected to be in the order of 12 Mbps, and the systems is expected to support a total traffic of 80 gigabits per second (Gbps) [13]. The network architecture is expected to follow that of VSAT systems as illustrated in Figure 11.9. Mobile Communications Satellite Systems Usage of GEO satellites for international voice and TV broadcast service requires large capacity links and therefore high-gain antennas which can be directed to the satellite. However, satellites may provide other applications which do not require large capacity, and therefore the link budget can be met with smaller, less directional antennas. Such receivers on the ground may be non-stationary, and therefore incapable of maintaining the direction of an antenna towards a GEO satellite. These satellites may also support non-real-time applications: a spy satellite may collect information from a point on the Earth and download the data to a ground station during its next pass over. Two classes of satellites relevant to telecommunications exist beside GEO. One class is the LEO satellite systems, with an orbital altitude of less than 2000 km. LEO satellites are pri- marily used in mobile communications systems. The other class is the MEO satellites with an orbital altitude of between 2000 km and 35 786 km. Some MEO satellites are used for broad- band telecommunications and another set for positioning services such as in GPS. Since the altitude of these two classes of satellite systems is lower than for the GEO satellite, the path loss experienced by their signals is smaller and therefore smaller antennas can be used for achieving their link budget. Moreover, 