Variable suppression of multipath signal effects

Abstract

Method and apparatus for formation of an autocorrelation difference function of an incoming digital signal that reduces the effects of presence of a multipath signal or of noise in an incoming digital composite signal. An incoming digital composite signal, including direct and multipath signals, is received that has a bit value transition interval of length .DELTA..tau..sub.chip. Two or three consecutive bit values b.sub.n-2, b.sub.n-1 and b.sub.n of the direct (ideal) signal are examined. If a test condition for these bit values is satisfied, a first non-uniform weighting function w1(t) is used to compute the contribution of a time interval I.sub.n ={t'.vertline.t.sub.n-1 +.DELTA.<t'.ltoreq.t.sub.n +.DELTA.}, where .DELTA. is a selected time value satisfying 0.ltoreq..DELTA.<.DELTA..tau..sub.chip, to first and second autocorrelation functions AC#(.tau.;E) and AC#(.tau.;L) with respective selected first and second time shifts .tau.=t.sub.E and .tau.=t.sub.L (>t.sub.E). If the test condition is not satisfied, a second weighting function w1 (t) is used to compute the contribution of the time interval I.sub.n to AC#(.tau.;E) and AC#(.tau.;L). An autocorrelation difference function .DELTA.AC#(.tau.)=AC#(.tau.;E)-AC#(.tau.;L) is formed in which the effects of noise or of multipath signals is suppressed, relative these effects in a conventionally computed autocorrelation difference function .DELTA.AC(.tau.)=AC(.tau.;E)-AC(.tau.;L).