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The signal-to-noise ratio which is the ratio of the power in a signal to the power contained in the noise that is present at a particular point in the transmission. Typically, this ratio is measured at a receiver, because it is at this point that an attempt is made to process the signal and recover the data. For convenience, this ratio is often reported in decibels:

SNR dB= 10 log 10signal powernoise power

This expression the amount, in decibels, that the intended signal exceeds the noise level. A high SNR will mean a high-quality signal and low number of required intermediate repeaters .

The signal-to-noise ratio is important in the transmission of digital data because it sets the upper bound on the achievable data rate. Shannon’s result is that the maximum channel capacity, in bits per second, obeys the equation

C= B log2(1+SNR)

Where C is the capacity of the channel in bits per second and B is the bandwidth of the channel in hertz .