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Variable suppression of multipath signal effects

  • US 5,923,703 A
  • Filed: 08/24/1998
  • Issued: 07/13/1999
  • Est. Priority Date: 05/20/1996
  • Status: Expired due to Term
First Claim
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1. A method of formation of an autocorrelation difference function of an incoming signal that reduces effects of presence of a multipath signal in the incoming signal, the method comprising the steps of:

  • (1) receiving an incoming digital signal s(t) that can vary with the time t and that has a digital signal bit period with a selected length Δ

    τ

    chip ;

    (2) forming a first signal product difference
    
    
    space="preserve" listing-type="equation">Δ

    s.sub.1 (t;

    τ

    ;

    t.sub.E ;

    t.sub.L ;

    qE;

    qL)=s(t)S.sub.d (t+τ

    -t.sub.E)w1(t+τ

    -t.sub.E ;

    qE)-s(t)S.sub.d (t+τ

    -t.sub.L)w1(t+τ

    -t.sub.L ;

    qL),where Sd (t) is a selected reference signal, w1(t;

    q) is a first selected, non-constant weighting signal that may depend upon one or more parameters q, τ

    is a selected time shift, tE and tL are first and second selected time values satisfying 0<

    tL -tE <



    τ

    chip ;

    (3) forming a second signal product difference
    
    
    space="preserve" listing-type="equation">Δ

    s.sub.2 (t;

    τ

    ;

    t.sub.E ;

    t.sub.L ;

    qE;

    qL)=s(t)S.sub.d (t+τ

    -t.sub.E)w1 (t+τ

    -t.sub.E ;

    qE)-s(t)S.sub.d (t+τ

    -t.sub.L)w1 (t+τ

    -t.sub.L ;

    qL),where w1 (t;

    q) is a second selected weighting signal that may depend upon one or more parameters q;

    (4) selecting an integer n≧

    2 and setting an accumulation An-1 =0;

    (5) examining the incoming digital signal bit value bn, for the time interval defined by nΔ

    τ

    chip

    t<

    (n+1)Δ

    τ

    chip, and the immediately preceding digital bit value bn-1 of the reference signal Sd (t);

    (6) when bn-1

    bn, computing the contribution of the first signal product difference over a time interval In ={t'"'"'|tn-1

    <

    t'"'"'≦

    tn

    }, where Δ

    is a selected time value satisfying 0≦

    Δ

    <

    Δ

    τ

    chip, to an autocorrelation difference function Δ

    AC#(τ

    ;

    q) for the incoming digital signal s(t), and adding this contribution to An-1 to form An ;

    (7) when bn-1 =bn, computing the contribution of the second signal product difference over the time interval In to the autocorrelation difference function Δ

    AC#(τ

    ;

    q) for the incoming digital signal s(t), and adding this integral or sum to An-1 to form An ;

    (8) replacing the integer n by the integer n+1 and repeating steps (5), (6) and (7) at least once;

    (9) interpreting the accumulation AN for a selected positive integer N as the autocorrelation difference function Δ

    AC#(τ

    ;

    q) for the incoming digital signal s(t);

    (10) determining at least one value t0 of the time shift variable τ

    for which the autocorretation difference function Δ

    AC#(τ

    ;

    q) changes sign; and

    (11) interpreting the time value t=t0 as an estimate of the time at which a signal, which is substantially free of the presence of a multipath signal, was received.

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