Communication Channel

 1.Telephone channels:Telephone channels are based on circuits switching mechanism to establish an end to end communication link on a temporary basic. Telephone channels support only the transmission of electrical signal. Therefore appropriate transducers are used at the transmitting and receiving end of the channel. Further telephone channel are essentially a linear band width limited channel.

2.Optical fiber:

An optical fiber is a dielectric wave guide which transports light signals from one place to another. Just as a metallic wire pair or a coaxial cable. Just as a metallic wire pair or a coaxial cable transport electrical signal. There are numerous advantages of optical fibers.

1. It has innermost potential bandwidth which is around 2*10^14Hz.
2. Low transmission losses.
3. Immunity to electromagnetic interference
4. Small size and weight.
5. Ruggedness and flexibility.

Mobile Radio Channel:

It extends the capability of public telecommunication network by introducing mobility into the network by virtue of its ability to broadcast. Basically there is no ‘line-sight’ path for communication rather radio propagation takes place multi path and mainly by the way scattering from the surface of surrounding building and by defraction over them. Therefore, the energy reaches the receiving antenna via more than one path. Therefore, in a mobile radio environment, we face a problem of multi path phenomenon in the sense that the various incoming radio waves reach their destination from different directions and with different time delays. Because of this, the received signal strength varies with location in a very complicated manner and therefore, a mobile radio channel may be viewed as a linear time- varying channel that is statistical in nature.

Satellite channel:

It provides broad area coverage in a continential as well as intercontinential sense. In almost all satellite communication system satellite are placed in Geo stationary orbit which is at an altitude of 22,300 miles (36000kms) satellite communication provides broad area coverage, reliable transmission links with wide transmission bandwidth. Most popular frequency band for satellite communication is 601Hz-uplink and 401-downlink. These frequencies are used because these used relatively in expensive microwave equipment the signal are less attinuatated due to rainfall. In 6/401 Hz typical satellite is assigned, a 500 MHZ bandwidth i.e. divided amount 12 transponders on board the satellite. Signal transponders can carry at least one color television signal, 12 hundred voice signal or digital data at a rate of 50Mbps.