The maximum-likelihood estimator developed in Problem 8.6 can be used bit by bit to estimate the phase on every received bit of a binary FSK waveform. Is the demodulator that results equivalent to, better than, or poorer than a non coherent FSK demodulator? If these demodulators are not equivalent, explain the difference and decide whether this means that there is some weakness in the theory.
Problem 8.6
With data treated as a random nuisance parameter, derive the likelihood function for the phase of a binary FSK waveform. Sketch a coherent receiver designed around the maximum-likelihood estimator. Explain how the nonlinearity in the phase estimator may be approximated in a way that results in a decision-directed estimator.