This paper seeks to highlight the concept of multi-channel communications satellite systems, the concept of systems operation, the advantages and disadvantages of the system and how to improve performance and reliability of the system in the presence of man-made interference and atmospheric noise.
Satellite communication, heavily relies on the use of a spacecraft in orbit around the Earth. The spacecraft is able to receive and re-transmit signals mainly radio signals. The use of satellite systems for communication, have over time undergone evolution. They have been in use for some time now and many changes have been made enabling higher performance of these satellites. Communications satellites are not only able to amplify and route signals but they are also able to sort these signals. Earlier on they used to function like the ground microwave repeaters but as mentioned earlier, these systems have undergone great evolution and now they are quite different from ground microwave repeaters. Whereas ground microwave repeaters relay radio signals between two fixed points, the satellite communication systems are able to interconnect a multiple of locations both fixed and mobile. This is the superiority of these systems over the ground microwave repeaters. As far as evolution of these systems is concerned, the current functions of both switching and rerouting of signals with the switchboards being onboard and airborne.
Communications Satellite Orbits
The choice of orbit is very important to the performance of communications satellites. In fact, the height of the satellite which is in a circular orbit determines not only the time of orbit but also the coverage. For instance, a 35,860 km orbital satellite has a corresponding orbital period of about 23 hours 56 minutes and 4 seconds (roughly one day). The orbit of the satellite may coincide with the equatorial plane and this will therefore mean that the satellite will hover in one fixed point in relation to the rotating earth and as such it is said to be geostationary. A geostationary satellite has the capacity of supporting two fifths coverage of the earth's surface and this therefore implies that three geostationary satellites are able to support world coverage. Most of the satellites that support communications (fixed and mobile) are the satellites which are in geosynchronous equatorial orbit (Korhonen, 2003: pp1-7).
The geostationary satellites have much capacity for coverage but are not able to cover the high latitude regions. These regions require that other types of satellites are used which are inclined at an angle with respect to the equatorial plane. For instance, the Russians launched a satellite with its orbit inclined at 63.50 in 1965. This satellite was meant for their domestic communications. The Molniya system is the type of this satellite system because it is found in the Molniya orbit and it was launched at 63.50 orbit inclination with respect the equatorial plane with the following specifications:
Perigee - 500 km
Apogee - 40,000 km
Orbital period - 12 hours
As far as the above inclination is concerned, there is no rotation of line of the aphides and as such there is reduced orbit correction sand manoeuvres (Takashi et al, 2003: pp168-172).
The satellites need