Classification of Communication:
There are two basic classification of communication systems, baseband systems and passband systems.
In baseband systems, the signal is transmitted without modifying the frequency content. A simple intercom is an example of this approach. Here, a microphone senses the input or message signal, and injects the resulting signal into a cable or channel. At the receiver, the signal is filtered to remove noise, amplified and reproduced into sound using a speaker. The baseband transmission is preferred at low frequencies and for short distances. However, Inter Symbol Interference (ISI) is the major problem associated with the baseband transmission.
In passband communication systems, the message signal is modulated by translating its spectrum to a new frequency location called the carrier frequency, fc. Modulation offers numerous advantages over baseband communication including increased efficiency, frequency-domain multiplexing and reduced size of communication equipment like radio receivers, transmitters and antennas when higher frequencies are used. The passband transmission is generally used at high frequencies and for long distances. All television and satellite transmission are passband type. The passband transmission, like baseband transmission, may be both analog and digital. If the digital signal modulates the carrier, then it is known as digital passband transmission.
Classification of Communication systems may be divided into two forms depending on the medium/channel used for transmission of information. These are :
1. Line Communication : In line communication, the medium of transmission is a pair of conductors called the transmission line. This means that in line communication, the transmitter and 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 it, its message transmission capability is also limited.
2. Wireless or Radio Communication : In wireless or radio communication, a message is transmitted through open space by electromagnetic waves referred to 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.
Depending upon the message signal, communication may also be classified as analog communication and digital communication.
1. Analog Communication : Analog communication is that classification of communication in which the message or information signal to be transmitted is analog in nature. This means that in analog communication the modulating signal (i.e., baseband signal) is an analog signal. This analog message signal may be obtained from sources like speech, video shooting etc. Presently all the AM, FM radio transmission and TV transmission are of analog communication type. Analog modulation methods are employed in this system.
2. Digital Communication : In digital communication, the message signal to be transmitted is digital in nature. This means that the digital communication involves the transmission of information in digital form. Digital modulation methods are used in this system. This system provides high rate and accuracy in transmission. This communication system includes fax, electronic mail (e-mail), internet, mobile, telephone network, telemetry etc.