Abstract: Method and apparatus for improving the accuracy of a received composite signal s(t) that contains a known reference signal S.sub.d (t) with a known bit transition period .DELTA.tchip and that may contain a multipath signal S.sub.m (t;.chi.;b) with an unknown multipath time delay b and an unknown multipath gain factor .chi. (-1.ltoreq..chi..ltoreq.1). Autocorrelation functions AC(.tau.) and AC(.tau.;d) for the incoming signal and for the reference (direct) signal are determined, dependent upon a time shift variable .tau., and a double difference autocorrelation function .DELTA..DELTA.AC(.tau.)=AC(.tau.)-AC(.tau.-.tau.LE)-AC(.tau.;d)+AC(.tau.-. tau.LE;d) is formed, where .tau.LE is a selected time shift displacement satisfying 0 <.tau.LE.ltoreq..DELTA..tau..sub.chip. Two integrals or sums of .DELTA..DELTA.AC(.tau.) are measured over different selected time shift intervals. The ratio of these two integrals or sums provides a quadratic equation in the time delay variable b that is solved for b.