Unguided Media
Unguided Media
Wireless media also called radiated media. As the name indicates, in networks that use wireless media, there is no physical wire along which information travels; instead, information is transmitted through the air, from one transmission station to the next. Networking examples include radio, cellular, microwave and satellite. Broadcast TV and FM radio use wireless transmission as well (though the underlying engineering is a little different).
Radio Transmission
The electromagnetic radio waves that operate at the audio frequency are also used to transmit computer data. this transmission is also known as Radio Frequency RF) transmission. The computers using RF transmission do not require a direct physical connection like wires or cable. Each computer attaches to an antenna hat can both send and receive radio transmission.
Microwave Transmission
Microwave transmission refers to the technique of transmitting information over a microwave link. Microwaves have a higher frequency than radio waves. Microwave transmission can be aimed at a single direction, instead of broadcasting in all directions (like in radio waves). Microwaves can carry more information than radio waves but cannot penetrate metals. Microwaves are used where there is a clear path between the transmitter and the receiver.
Microwave transmission has the advantage of not requiring access to all contiguous land along the path of the system, since it does not need cables. They suffer from the disadvantages: a) needing expensive towers and repeaters, and b) are subject to interference from passing airplanes and rain. Because microwave systems are line-of-sight media, radio towers must be spaced approximately every 42 km along the route.
Satellite Transmission
The communication across longer distances can be provided by combining radio frequency transmission with satellites. Geosynchronous satellites are placed in an orbit synchronized with the rotation of the earth at a distance of 36,000 km above the surface of the earth. Geosynchronous satellites appear to be stationary when viewed from the earth. The satellite consists of transponder that can receive RF signals and transmit them back to the ground at a different angle. A ground station on one side of the ocean transmits signal to the satellite which in turn sends the signal to the ground station on the other side of the ocean.