## Unipolar vs bipolar waveforms

#### When signalling over a communications link, there are two common binary (two state) signalling formats, unipolar and bipolar. A unipolar scheme is characterized by the voltage states being 0 and +V volts, and thus has a dc component to the Fourier Series expansion. A bipolar format has a 0 dc mean with voltage states of +V and –V volts representing logic 1 and logic 0. The bipolar format is used on the serial output port of every computer conforming to the RS232 interface standard having voltage states of +12 volts and –12 volts. In the section on matched filtering in Chapter 3, it is shown that this bipolar format of signalling for data transmission is much more tolerant to noise than the unipolar equivalent for the same average symbol power. |