The receiving station can be mobile, which offers coverage from a single satellite. Within the coverage range of a single satellite, circuit cost is independent of distance. Large amounts of bandwidth are available over satellite circuits, making voice, video, and high-speed data circuits available. Advantages
A transponder is a radio relay station on board the satellite.
Transponders The downlinksignal is applied to a high-power amplifier, using a traveling wave tube orsolid-state amplifier as the output device. Echostar 9 (also known as Telstar 13 and Intelsat Americas 13), which was launched in August 2003, has 2 Ka-, 32 Ku-, and 24 C-bandtransponders.
A spin-stabilized satellite rotates on its axis at about 100 rpm. three-axis stabilization, which consists of a gyroscopic stabilizer inside the vehicle. Attitude Control Apparatus
Satellites are powered by solar batteries. Power is conserved by turning offunused equipment with signals from the Earth. Solar cell life is a major factor that limits the workinglife of a satellite. Power Supply
Iridium launched commercial voice, fax, paging, and narrow-band data service in 2001, using a network of 66 operational satellites plus six in-orbit backups. Satellites are connected via intersatellite links to the four nearest neighbors and to an Earth station. Low Earth Orbiting Satellite
The hubs control demand assignment to the satellite and monitor and diagnose network performance. Demand is allocated in one of the four ways -pure aloha -slotted aloha -TDMA and spread spectrum. The first three methods generally are used on Ku-band and the last on C-band. VSAT provides bandwidth as high as T1/E1 and as low as the customer needs to go.
The remote station has an antenna and a receiving unit, which is about the size of a personal computer base unit. The primary application for VSAT is data, although it can also carry voice and video. Typically, C-band VSATs carry 9.6 Kbps data, and Ku-band VSATs carry 56 or 64 Kbps data; some systems carry a full or fractional T1/E1. The primary advantage of VSAT is its ability to support multiple locations.
In one sense, satellite applications diminish as terrestrial and undersea fiber-optic circuits become more plentiful and economical, but satellite services are still uniquely suited for many applications. SATELLITE APPLICATION ISSUES