Drift correction in periodic crosscorrelation schemes

In the evaluation of a periodic crosscorrelation for a time-invariant system, a simple-to-instrument method is described for eliminating error terms due to polynomial drift disturbances. The method is based on the periodic input perturbation signal being of inverse repeat form, and leads to the result that polynomial drift up to the rth degree may be eliminated by crosscorrelating over r + 2 half periods with appropriate constant weights associated with each half period.