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.
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