A period detector for pseudo-periodic signals

The spreading codes of direct sequence spread spectrum signals are often periodic. From a segment of signal containing multiple periods, this periodicity can be detected and the period estimated. The approach taken is to bandlimit the signal (to introduce variation into the envelope), compute the envelope of the filtered signal (to remove the information), and compute the autocorrelation of the envelope. The autocorrelation function contains a peak at an offset equal to the period. The peak-to-noise ratio can be used to obtain an estimate of the input signal-to-noise ratio. Narrowband interference can corrupt the process, so it can be important to precede application of the technique by a pre-whitening filter. The technique applies even for "featureless" signals, in which measures have been taken to suppress rate lines in the outputs of quadratic or higher-order chip rate detectors.