## Constellation diagram for PSK

| The constellation diagram for binary PSK displays the characteristic of antipodal signalling. This means that the symbols used are equal and opposite to each other in the constellation space. Antipodal signalling is a prerequisite for achieving optimum data detection performance in noise, as was discovered when analysing the performance of bipolar baseband signalling in Chapter 3.
If we compare the PSK constellation diagram with that for ASK, we see that the 'antipodal' signalling condition is not satisfied for ASK and hence we do not get the optimum performance in noise. This is directly equivalent to the inferior performance of unipolar signalling compared with bipolar signalling which suffers the same 3 dB performance penalty. |