Noise that affect the channel

In the image there is term called (1/g)and term and sigma(t). Both attenuating the signal,but i cannot understand the difference between them. Thank you

In the image there is term called (1/g)and term and sigma(t). Both attenuating the signal,but i cannot understand the difference between them.

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The term 1/G is attenuating the signal.
The sigma(t) is adding to the attenuated signal.

The effect of each term is different.

JimB

1/G is attenuating the signal x(t).

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1)what attenuate the signal.i mean attenuation caused by what

The sigma(t) is adding to the attenuated signal.

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2)what types of noise in general,how its added to the signal.I mean if i send i signal through wire,how the noise signal is being added

i think it is some kind of basic ,so i don't mind even if u give a link that leads to leads to my answer