Patent ID: 6493378
Filing Date: 2002-12-10
Classification: G01S,H04B

Abstract:
A method of tracking an input code signal comprising a repeating sequence of chips, each chip having a time duration &Dgr; and a value determined by a preselected series of numbers, each chip in the sequence corresponding to a respective number in the series, said method comprising the steps of:(a) generating a reference code signal (S(t)) comprising a repeating sequence of strobes, the start of each strobe being spaced in time from the start of the next strobe by an integer number of chip durations &Dgr;, each strobe having a duration of less than &Dgr; and having a non-zero average value over its duration, the average values of said strobes being related to the preselected series of numbers, said reference code signal being generated such that the start of its strobe sequence may be adjusted in time with an adjustable time shift &egr; from the start of the sequence of the input code signal, the value of said time shift &egr; having a first polarity when the sequence start of the reference code signal leads the sequence start of the input code signal and a second polarity opposite to said first polarity when the sequence start of the reference code signal lags the sequence start of the input code signal, said time shift &egr; moving in a leading direction when the sequence start of the reference code is advanced in time and moving in a lagging direction when the sequence start of the reference code is retarded in time; (b) generating a correlation signal (dI) related to the correlation of the input code signal and said reference code signal, the value of said correlation signal being a function of said time shift &egr; and being equal to zero when said time shift &egr; is at a point &egr;0, the value of said correlation signal having a first polarity when said time shift &egr; moves in the leading direction away from said point &egr;0 and a second polarity opposite to said first polarity when said time shift &egr; moves in the lagging direction away from said point e0, said correlation signal further having a first peak value (dIE) when said time shift &egr; moves in the leading direction away from said point &egr;0 and having a second peak value (dIL) when said time shift &egr; moves in the lagging direction away from said point &egr;0, the second peak value (dIL) being greater than the first peak value (dIE); and (c) adjusting said time shift &egr; in response to the value of said correlation signal to move said time shift &egr; towards said point &egr;0, said correlation signal indicating that said time shift &egr; should be advanced when the value of the correlation signal has its second polarity and indicating that said time shift &egr; should be retarded when the value of the correlation signal has its first polarity, said point &egr;0 thereby being a point of steady balance and the generation of said reference code signal thereby tracking the input code signal by being adjusted toward maintaining a constant time shift between the sequence starts of the two code signals.