[21] Appl. No.: 09/138,767 [22] Filed: Aug. 24, 1998
Related U.S. Application Data
[62] Division of application No. 08/650,338, May 20, 1996.
[51] Int. CI.6 H04K 1/00; H04L 25/08
[52] U.S. CI 375/209; 375/346
[58] Field of Search 375/208, 209,
375/343, 346, 285, 267, 347
[56] References Cited
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Primary Examiner—Tesfaldet Bocure
Attorney, Agent, or Firm—Wagner, Murabito & Hao
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 tsxchip. Two or three consecutive bit values b„_2, bn_1 and b„ of the direct (ideal) signal are examined. If a test condition for these bit values is satisfied, a first non-uniform weighting function wl(t) is used to compute the contribution of a time interval I„={t'|t„_1+A<t' = t„+A}, where A is a selected time value satisfying 0=A<Axchip, to first and second autocorrelation functions AC#(x;E) and AC#(x;L) with respective selected first and second time shifts x=tE and x=tL (>cE). If the test condition is not satisfied, a second weighting function wl"(t) is used to compute the contribution of the time interval \n to AC#(x;E) and AC#(x;L). An autocorrelation difference function AAC#(x)=AC#(x;E) and AC#(x;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 AAC(x)=AC (x;E)-AC(x;L).
18 Claims, 24 Drawing Sheets
