  A continuous-time model for the additive white Gaussian noise (AWGN) channel
in the presence of white (memoryless) phase noise is proposed and discussed. It
is shown that for linear modulation the output of the baud-sampled filter
matched to the shaping waveform represents a sufficient statistic. The analysis
shows that the phase noise channel has the same information rate as an AWGN
channel but with a penalty on the average signal-to-noise ratio, the amount of
penalty depending on the phase noise statistic.
