# 2.4 Calculation of channel capacity

## Limitation due to finite bandwidth

#### In order to determine the maximum rate at which data can be sent over a channel, we need to know the maximum symbol rate that can be supported in a channel as a function of the channel bandwidth. For the moment, let us consider only 'lowpass' or 'baseband' channels where we can assume that the channel can pass signals with frequencies within the range 0 Hz to B Hz. This is called the channel passband. #### Shown here is an example of an 8-ary symbol stream which just happens to begin to alternate between the maximum and minimum voltage levels. This looks like a square wave, for which the harmonic structure is known from its Fourier series expansion. The fundamental of this square-wave is at a frequency of 0.5 x 1/Ts, where Ts is the symbol period. |