Phase shift keyed demodulator using recovered carrier with controlled phase offset
AssigneeThe Post Office
InventorRichard P. Scott
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Abstract
This invention relates to an adaptive demodulator for use in a phase shift keyed microwave communication system. The adaptive demodulator improves the system error rate at a particular carrier to noise ratio by monitoring the output of the demodulator and optimizing the phase offset of the carrier signal recovered in the demodulator to provide a high output. A particular example continuously varies the phase offset of the recovered carrier signal about the highest output value to track variations in the optimum phase offset.
Claims8
A demodulation apparatus for use in a phase shift keyed microwave communication system comprising:
- carrier signal recovery means for recovering a carrier from a modulated signal and having a first input for receiving a phase shift modulated input signal, a second input for receiving a phase change signal, and an output for outputting a recovered carrier signal;
- demodulation means for demodulating a modulated carrier, having a first input for said phase shift modulated signal, a second input for said recovered carrier signal, and an output for demodulated signals;
- amplitude monitoring means having an input for said demodulated signal, and an output for outputting a signal dependent upon the amplitude of the demodulated signal applied to its input;
- control means, having an input connected to said output of said amplitude monitoring means and an output, for outputting a phase change signal;
- means connecting said output of said carrier signal recovery means to said second input of said demodulation means;
- means connecting said output of said demodulation means to said input of said amplitude monitoring means;
- and
- means connecting the output of said control means to said second input of said carrier signal recovery means whereby said signal applied to said second input of said carrier signal recovery means controls the phase of said recovered carrier signal to maintain said output from said demodulation means at a high level.
A method of optimising the phase position of a carrier signal recovered from a phase shift modulated signal to maximise the pulse amplitude of said signal on demodulation comprising recovering a carrier signal from said phase shift modulated input signal, demodulating said phase shift modulated input signal by reference to the phase of said recovered carrier signal, monitoring the amplitude of said demodulated signal derived by reference to the phase of said recovered carrier signal, and controlling the phase of said recovered carrier signal in dependence upon said monitored amplitude of said demodulated output signal to maintain said amplitude at a high value.
Dependencies are inferred from the claim text.