
46 Principles of Synchronous Digital Hierarchy
The experiments of Harry Nyquist in 1933 showed that, to reproduce a
signal exactly from its samples, the sampling frequency is required to be at
least double the bandwidth of signal, i.e.,
Fs > 2 × BW
where Fs is the sampling frequency and BW is the bandwidth of the signal.
This relationship is known as “sampling theorem” or “Nyquist sampling
theorem.” This sampling theorem forms the basis of all the digital commu-
nication systems in use today.
Note that the sampling frequency has to be “greater than” twice the band-
width of the signal, and not equal to it. If the sampling frequency is equal
to ...