Characteristics of Satellite Systems
- Satellites have been launched for various applications and are placed at different altitudes. Moreover their weights are also dissimilar.
- Provides connections between the Earth-based base station and the satellites.
- The GEO satellites, which are at an altitude of 35,768 km, orbit in the equatorial plane with zero degree inclination and complete exactly one rotation in a day.
- The antennas are at fixed positions, and an uplink bank (reverse band) of 1634.5 to 1660.5 MHz and a downlink band (forward band) in the range of 1530 to 1559 MHz, are employed.
- Ku band frequencies (11 and 13 GHz) are employed for connection between the base station (earth station) and the satellites.
- A satellite typically has a large footprint, which can be up to 34% of the earth's surface covered, and therefore it is difficult to reuse frequencies.
- The global coverage of small mobile phones and data transmission typically cause high latency in the range of about 275 ms.
- LEO satellite are divided into little and big satellites.
- Little LEOs are smaller in size and are in the frequency range of 148 to 150.
- They cause alphanumeric displays at low bit rates (of the order of 1 kb/s) for two ?way message and positioning information.
- Big LEO satellites have adequate power and bandwidth to provide various global mobile services (i.e. data transmission, paging, facsimile, and position location) along with good quality voice services for mobile systems such as handled devices and vehicular transceivers.
- Big LEO transmits in the frequency range of 1610 to 1626.5 MHz (uplink) and 2483.5 to 2500MHz (downlink) and orbit at about 500 to 1500km above the earth surface.
- The latency is around 5 to 10 ms, and the satellite is visible for about 10 to 40 ms.
- Several satellites are needed to ensure global coverage. The same frequency spectrum is also used by MEO and GEO.
- In MEO systems, the slow- moving satellites orbit at a height of about 5,000 to 12,000 km above the earth and have a latency of about 70to 80 ms.
- Specialized antennas are used to provide smaller footprints and higher transmitting power.