Properties of Satellite Communications

This article describes General Properties of Satellite Communications in data Communication.

General Properties of Satellite Communications
Satellite Communications systems consist of antennae and reflective dishes, much as in a terrestrial microwave. The dish servers to focus the signal from a transmitting antenna to a receiving antenna. The send/receive dishes that make up the earth segment are of varying sizes, depending on power levels and frequency bands. They are generally mounted on a tripod or other type of brace, which is anchored to the earth, pad or roof, or attached to a structure such as a building.
Cables connect the antennae to the actual transmit/receive equipment. The terrestrial antennae support a single frequency band.
Satellites can support multiple transponders and therefore, substantial bandwidth, with each transponder generally providing increments in bandwidth.
Error Performance
Satellite transmission is susceptible to environmental interference, particularly at frequencies above 20 GHz. Sunspots and other types of electromagnetic interference affect satellite and microwave transmission.
Satellite is not considered to be limited in terms of distance as the signal largely travels through the vacuum of space. Each signal travels approximately 36000 kms in each direction.
Propagation Delay
Geostationary satellites, by virtue of their high orbital altitude, impose rather significant propagation delay on the signal. Hence, highly interactive voice, data and voice applications are not effectively supported via two way satellite communications.
As is the case with all microwave and other radio system, satellite transmission is inherently not secure. Satellite transmission is especially vulnerable to interception, as the signal is broadcast over the entire area of the footprint. Therefore, the unauthorized user must know only the satellite and associated frequency range being employed to access the signal. Security must be imposed through encryption of the signal.
The acquisition, deployment and rearrangement costs of the space segment of satellite systems can be quite high , to the tune of several millions dollars. However, the satellite can be shared by a large number of users, with each user connecting a large number of sites. As a result. Satellite networks often compare very favorably with cabled systems or microwave systems for many point to multipoint applications.
Applications :

Satellite applications are many and increasing rapidly as the traditional voice and data services have been augmented. Traditional international voice and data services have been supplanted to a considerable extent by submarine fiber optic cable system.
Applications included a international vice and data, television and radio broadcast, maritime navigation, videoconferencing, inventory management and control through VSATs, disaster recovery and paging. More recent and emerging applications include air navigation, mobile voice and data because of Low Earth Orbit Satellites (LEOs), Advanced Traffic Management Systems (ATMS), integrated Digital Services Network (ISDN), interactive television, and interactive multimedia.


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