A satellite is a smaller object or body that revolves around a much larger object in space in a fixed well defined path.
Example: A moon is a natural satellite of the earth.
Types of satellites, they are two types
For example, the earth revolves around the sun, so it is a satellite. The moon revolves around the earth, so it is also a satellite. But they are Natural satellites.
Artificial satellites are specifically designed and launched into space for a variety of purposes such as weather monitoring, navigation, TV, and mobile communication.
PRINCIPLE OF SATELLITE COMMUNICATION
The process of communication begins at an earth station, the earth station is an installation designed to transmit and receive signals from a satellite in orbit around the earth.
Earth station sends information in the form of high-power, high-frequency signals to the satellite that receives and retransmits the signals back to earth. These retransmitted signals are then received by other earth stations in the coverage area of the satellite.
The area which receives the signal from the satellite is known as the satellite footprint. The transmission system from the earth station to the satellite is called the uplink and the transmission system from the satellite to the earth station is called the downlink.
To avoid confusion, the uplink and downlink frequencies are kept different. Before designing a satellite communication system, we must choose the orbit in which the satellite is to be placed. Orbits are of three types, namely;
A geostationary orbit is the type of orbit the satellite takes 24 hours to circle the earth since the period of revolution of the satellite is equal to the period of rotation of the earth.
The satellite appears to be stationary in the sky, for this reason, a 35900Km high equatorial orbit is called a geostationary orbit.
This is a type of orbit that is placed a thousand kilometers above the earth’s surface. It passes over the poles. The angle of inclination of this orbit is 90 degrees, it scans the whole earth every 12 hours.
Satellites are used for weather monitoring and are launched into the polar orbit.
It is used for establishing communication with regions at high latitudes, the angle of inclination is equal to 63 degrees.
SATELLITE COMMUNICATION SYSTEM
The satellite communication system is composed of three segments:
Consists of one or more active and spare satellites.
Contain all ground facilities for the control and monitoring of the satellites and management of the traffic of the satellite system.
Contain the traffic of earth stations.
The space segment consists of Payload and Platform.
The payload consists of receiving and transmitting antennas and all electronic equipment.
Consists of an attitude control subsystem, propulsion system, electric power, TTC, and Thermal control structure.
Ground segment terminals consist of three types;
Access the satellite while remaining fixed on the ground.
Is a movable terminal but remains fixed while transmission.
Designed to communicate with satellite while in motion. Mobile terminals are also defined as land mobile.
Control segment terminals consist of two types;
Tracking, telemetry, command, and monitoring station provide management and control functions to keep the satellite operating safely in orbit.
Used for non-real-time management function of the connection and associated resources allocated to a single satellite network.
SATELLITE LINK PARAMETERS
Communication Satellite air links are;
Space radio communication service: