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Line Communication , Wireless or Radio Communication , classification of digital communication system :-
Regarding the mode of propagation, communication may be divided in the following two forms:
(i) Line Communication
(ii) Wireless or Radio Communication
1.5.1. Line Communication
In line communication, the medium of transmission is a pair of conductors called transmission line. This is also called as line channel. This means that in line communication, the transmitter and the receiver are connected through a wire or line. However, the installation and maintenance of a transmission line is not only costly and complex but also overcrowds the open space. Apart from this, its message transmission capability is also limited.
1.5.2. Wireless or Radio Communication
In wireless or radio communication, a message is transmitted through open space by electromagnetic waves called as radio waves. Radio waves are radiated from the transmitter in open space through a device called antenna. A receiving antenna intercepts the radio waves at the receiver. All the radio, TV and satellite broadcasting are wireless or radio communication. The advantages of wireless communication are cost effectiveness, possible long distance communication and simplicity.
* Inter symbol interference (ISI) is an important aspect in digital communication and shall be discussed in detail in chapter 5.