Transmission impairment:
A
transmission impairment is a property of a transmission medium which causes the
signal to be degraded, reduced in amplitude, distorted or contaminated.
Impairment can introduce errors into digital signals.
Or
·
Signals travel
through transmission media, which are not perfect.
·
The imperfection
causes signal impairment.
·
This means that
the signal at the beginning of the medium is not the same as the signal at the
end of the medium.
·
What is sent is
not what is received.
1. Attenuation:
The strength of a signal decrease with the increase in distance
travelled over a medium. Attenuation means loss of energy. When any signal
travels over a medium or channel, it loses some of its energy in the form of
heat in the resistance of the medium. Attenuation decides the signal to noise
ratio hence the quality of received signal. Attenuation is given in decibels
as:
Attenuation (dB) = 10log10 (Pout/Pin)
Where, Pin= Power at the sending end
Pout= Power at the receiving end
2. Distortion (Harmonic):
Another meaning of distortion is change in shape of the signal.
This type of distortion is observed for the composite signals made by different
frequencies. If the medium is not perfect, then all the frequency components
present at the input will not only be equally attenuated and will not be
proportionally delayed.
3. Noise:
When the data travels over a transmission medium, noise gets
added to it. Noise is a major limiting factor in communication system
performance. Noise can be categorized into four types as follows:
(i) Thermal noise
(ii) Intermodulation noise
(iii) Crosstalk
(iv) Impulse noise
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