Phaselock threshold correction

DETAILED DESCRIPTION In accordance with the present invention, there is provided a noise estimator for threshold correction of phaselock in a receiver where a noise estimating circuit provides threshold correction of phaselock as a function of input noise power to mitigate a bias introduced by the AGC circuit at the output of a quadrature phase detector.
The noise power estimator of the present invention utilizes the ergodic properties of the input signal and time averaging to arrive at a statistical average of input signal envelope.
This time average of the input signal is subtracted from the instantaneous value of the detected envelope and the computed instantaneous error resulting from this subtraction is squared and time-averaged, resulting in an estimate of the input noise power.
In accordance with the present invention, there is provided a noise estimator for computing the noise estimate of an input signal where the input signal comprises a signal component and a noise component.
The estimator circuit includes a filter for removing wideband noise from the input signal.
Further, the noise estimator of the present invention includes a square-law power detector responsive to the output of the low pass filter and an envelope detector coupled to the output of the square-law power detector.
A time-averaged envelope of the input signal is output from a low pass filter performing time averaging, and this output is applied to a subtractor that also receives the instantaneous value of the input envelope to generate an instantaneous error signal.
This instantaneous error signal is squared and applied to a low pass filter that also performs time averaging.
The resultant signal from the time averaging function is a noise estimate on the input signal.
This noise estimate is then utilized for threshold correction for phaselock of a receiver to a transmitter.