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In wireless transmission media, communication devices communicate with each other and data is communicated through the air or space using broadcast radio signals, microwave signals and infrared signals. This transmission medium is used when it is impossible to install the cables. The data can be transmitted all over the world through this medium. The commonly used wireless transmission media are discussed below.
i. Broadcast Radio
It is a wireless transmission medium that is used to communicate information through radio signals in air, over long distance such as between cities and countries. In this medium, a transmitter is required to send messages (signals) and receiver is required to receive them. To receive the broadcast radio signal, the receiver has an antenna that is located in the range of signal. Some networks use a special device called transceiver used to send and to receive messages in the form of radio signals. The data transmission speed of broadcast radio is up to 54Mbps.
ii. Cellular Radio
Cellular radio is a form of broadcast radio that is used for mobile communications such as cellular telephones and wireless modems. A cellular telephone is a telephone device that uses high frequency radio waves to transmit voice and digital messages. Some mobile users connect their laptop computer or other mobile device to a cellular telephone to access the Web, send and receive e-mail etc. while away from a standard telephone line.
iii. Microwaves
Microwaves are radio waves that provide a high speed transmission. In Microwaves transmission, data is transmitted from one station to another. Microwave station contains an antenna, transceiver (transmitter & receiver) and other equipments that are required for microwave communication. Microwave uses the line-of-sight transmission, which means that in microwave transmission system the data signals travel in a straight path and cannot bend. Microwave stations or antennas are usually installed on the high towers or buildings. Thus microwave stations need to be placed within 20 to 30 miles of each other. Each microwave station receives signals from the previous stations. In this way, data is transmitted from one place to another.
The data transmission speed of microwave transmission is up to 150 Mbps. Microwave transmission is used in environments where installing physical transmission media is impossible and where line-of-sight transmission is available. It is used in wide-open areas. Today, it is used by telephone companies, cable television providers, universities etc.
Microwave Transmission System
iv. Communication Satellite
A communication satellite is a space station that receives microwave signals from earth microwave station (earth based station). The earth based stations often are microwave stations. Other devices, such as PDAs and OPS receivers, also functions as earth based stations. Transmitting a signal from ground or earth station to a satellite station in space is called up-linking and the reverse is called the down- linking.
Communication Satellite Transimssion System
Now-a-days, television & radio broadcast, global positioning systems and Internet also use the communication satellites. The communication satellite is launched about 22300 miles (or more) above the earth into space. The communication satellite consists of solar powered, transceiver that receives and sends signals. The signals are transmitted from one earth station to the satellite. The satellite receives and amplifies the signals and sends them to another earth station. This entire process takes only a few seconds. To communicate information from one country to another country more than one satellites are required. The data transmission speed of communication satellite is very high such as up to 1 Gbps.