Adaptive multipath equalization
First Claim
Patent Images
1. A method for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the method comprising the steps of:
- receiving a signal s(t) at a receiver that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;
selecting a grid of values {τ
g }g (g=1, 2, . . . , G) of the time variable t lying in the interval -Tc ≦
t≦
Tc ;
selecting a set of sampling times (τ
'"'"'j)j (j=1, . . . , J;
J a selected integer≧
2) for a correlation function R(τ
), and determining the correlation function values R(τ
'"'"'j)=xj, where the correlation function R(τ
) is defined by ##EQU10## and T is a selected time satisfying T>
>
Tc ;
choosing complex numbers bg so that a sum ##EQU11## is minimized, where q is a selected positive number;
arranging the magnitudes |bg | of the complex numbers bg in a sequence {|bgk |}gk in decreasing order of magnitude so that |bg1 |≧
|bg2 |≧
|bg3 |≧
. . . , and choosing H members of this sequence, where H is a selected positive integer;
designating the time t=τ
g1 as the time of arrival of the direct signal and the times t=τ
gk (k=2, . . . , H) as the times of arrival of multipath signals; and
interpreting a difference signal ##EQU12## as a signal from which at least one multipath signal has been removed.
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Abstract
Method and apparatus for using a plurality of correlators to improve an estimate of direct signal arrival time by identifying features of a correlation function at and adjacent to the correlation peak. In a first embodiment, the errors in location of the center point of a correlation function R(τ), formed by the incoming composite signal and a stored copy of the expected signal, are assumed to be strongly correlated for narrow sample spacing and wide sample spacing of the correlation function. In a second embodiment, multipath signal strengths and phases are estimated, using multiple sampling of the correlation function R(τ). This approach assumes that path delays of the direct signal and of the multipath signals can be determined separately. Path delays can be determined by any of at least three approaches: (1) identification of slope transition points in the correlation function; (2) Cepstrum processing of the received signal, using Fourier transform analysis; and (3) use of a grid of time points on the correlation function domain, and identification of time values, associated with certain solution parameters of the least mean squares analysis that have the largest absolute values, as times of arrival of the direct and multipath signals. Separate identification of multipath time delays reduces the least mean squares analysis to a linear problem. A modified signal is constructed, with the multipath signal(s) approximately removed from the incoming composite signal. This modified signal allows a better estimate of the arrival time of the direct signal.
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Citations
23 Claims
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1. A method for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the method comprising the steps of:
-
receiving a signal s(t) at a receiver that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;selecting a grid of values {τ
g }g (g=1, 2, . . . , G) of the time variable t lying in the interval -Tc ≦
t≦
Tc ;selecting a set of sampling times (τ
'"'"'j)j (j=1, . . . , J;
J a selected integer≧
2) for a correlation function R(τ
), and determining the correlation function values R(τ
'"'"'j)=xj, where the correlation function R(τ
) is defined by ##EQU10## and T is a selected time satisfying T>
>
Tc ;
choosing complex numbers bg so that a sum ##EQU11## is minimized, where q is a selected positive number;
arranging the magnitudes |bg | of the complex numbers bg in a sequence {|bgk |}gk in decreasing order of magnitude so that |bg1 |≧
|bg2 |≧
|bg3 |≧
. . . , and choosing H members of this sequence, where H is a selected positive integer;designating the time t=τ
g1 as the time of arrival of the direct signal and the times t=τ
gk (k=2, . . . , H) as the times of arrival of multipath signals; andinterpreting a difference signal ##EQU12## as a signal from which at least one multipath signal has been removed. - View Dependent Claims (2, 3, 4)
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5. A method for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the method comprising the steps of:
-
receiving a signal s(t) at a receiver that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;forming a correlation function R(τ
) defined by ##EQU13## where T is a selected time satisfying T>
>
Tc ;
determining a first pair of distinct time values τ
=τ
1,w and τ
=τ
2,w which produce equal values of the correlation function magnitude |R(t)|, using a difference Δ
τ
w,sp =τ
2,w -τ
1,w in the range 0.4 Tc ≦
Δ
τ
w,sp ≦
Tc, and computing τ
w,avg =(τ
1,w +τ
2,w)/2;determining a second pair of distinct time values τ
=τ
1,n and τ
=τ
2,n which produce equal values of the correlation function magnitude |R(t)|, using a difference Δ
τ
n,sp =τ
2,n -τ
1,n in the range 0.01 Tc ≦
Δ
τ
n,sp ≦
0.2 Tc, and computing τ
w,avg =(τ
1,w +τ
2,w)/2, where Δ
τ
n =τ
n,avg -τ
peak and Δ
τ
w =τ
w,avg -τ
peak and τ
peak is the value of τ
, to be determined, for the peak of the correlation function magnitude;providing a collection {(Δ
τ
w,k,sim -Δ
τ
n,k,sim, Δ
τ
n,k,sim)}k of a selected number K of coordinate pairs of simulated values of the variables Δ
τ
w -Δ
τ
n and Δ
τ
n, and determining real parameters a and b that provide an optimal approximation to this collection of coordinate pairs by the equation Δ
τ
n,sim =a(Δ
τ
w,sim -Δ
τ
n,sim)+b;determining the time value τ
peak of the correlation function magnitude by the relation τ
peak =τ
n,avg -a(Δ
τ
w -Δ
τ
n)-b; andinterpreting the time value τ
peak as the time a direct signal arrives at the receiver. - View Dependent Claims (6)
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7. Apparatus for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the apparatus comprising:
-
a receiver that receives a signal s(t) that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;a signal processor, connected to the receiver, that; (1) forms a correlation function R(τ
) defined by ##EQU15## where T is a selected time satisfying T>
>
Tc ;
(2) determines a sequence of N time values (N a selected integer≧
2) {τ
m }m, each of which is estimated to correspond to a time of arrival of a direct signal or of a multipath signal at the receiver;(3) selects a sequence of sampling times {τ
'"'"'j }j (j=1, . . . , J;
J a selected integer≧
2) for the correlation function R(τ
) and determines the correlation function values R(τ
'"'"'j)=xj ;(4) determines complex numbers bm so that a sum ##EQU16## is minimized, where q is a selected positive number; and
(5) interprets a difference signal ##EQU17## as a signal from which at least one multipath signal has been removed. - View Dependent Claims (8, 9, 10, 11)
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-
12. Apparatus for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the apparatus comprising:
-
a receiver that receives a signal s(t) that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;a signal processor, connected to the receiver, that; (1) forms a correlation function R(τ
) defined by ##EQU18## where T is a selected time satisfying T>
>
Tc ;
(2) selects a sequence of values {τ
g }g of the time variable τ
lying in the interval -Tc ≦
τ
≦
Tc,(3) selects a sequence of sampling times {τ
'"'"'j }j (j=1, . . . , J;
J a selected integer≧
2) for the correlation function R(τ
) and determines the correlation function values R(τ
'"'"'j)=xj ;(4) determines complex numbers bg so that a sum ##EQU19## is minimized, where q is a selected positive number;
(5) arranges the magnitudes |bg | of the complex numbers bg in a sequence {|bgk |} in decreasing order of magnitude so that |bg1 |≧
|bg2 |≧
|bg3 |≧
. . . , and chooses H members of this sequence, where H is a selected positive integer;(6) designates the time t=τ
g1 as the time of arrival of the direct signal and at least one of the times t=τ
gk (k=2, . . . , H) as the times of arrival of multipath signals; and(7) interprets a difference signal ##EQU20## as a signal from which at least one multipath signal has been removed. - View Dependent Claims (13, 14, 15)
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-
16. Apparatus for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the apparatus comprising:
-
a receiver that receives a signal s(t) that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;a signal processor, connected to the receiver, that; (1) forms a correlation function R(τ
) defined by ##EQU21## where T is a selected time satisfying T>
>
Tc ;
(2) determines a first pair of distinct time values τ
=τ
1,w and τ
=τ
2,w which produce equal values of the correlation function magnitude |R(t)|, using a difference Δ
τ
w,sp =τ
2,w -τ
1,w in the range 0.4 Tc ≦
Δ
τ
w,sp ≦
Tc, and computes τ
w,avg =(τ
1,w +τ
2,w)/2;(3) determines a second pair of distinct time values τ
=τ
1,n and τ
=τ
2,n which produce equal values of the correlation function magnitude |R(t)|, using a difference Δ
τ
n,sp =τ
2,n -τ
1,n in the range 0.01 Tc ≦
Δ
τ
n,sp ≦
0.2 Tc, and computes τ
w,avg =(τ
1,w +τ
2,w)/2, where Δ
τ
n =τ
n,avg -τ
peak and Δ
τ
w =τ
w,avg -τ
peak and τ
peak is the value of τ
, to be determined, for the peak of the correlation function magnitude;(4) provides a collection {(Δ
τ
w,k,sim -Δ
τ
n,k,sim, Δ
τ
n,k,sim)}k of a selected number K of coordinate pairs of simulated values of the variables Δ
τ
w -Δ
τ
n and Δ
τ
n, and determines real parameters a and b that provide an optimal approximation to this collection of coordinate pairs by the equation Δ
τ
n,sim =a(Δ
τ
w,sim -Δ
τ
n,sim)+b;(5) determines the time value τ
peak of the correlation function magnitude by the relation τ
peak =τ
n,avg -a(Δ
τ
w -Δ
τ
n)-b; and(6) interprets the time value τ
peak as the time a direct signal arrives at the receiver. - View Dependent Claims (17)
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18. A method for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the method comprising the steps of:
-
receiving a signal s(t) at a receiver that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;forming a correlation function R(τ
) defined by ##EQU23## where T is a selected time satisfying T>
>
Tc ;
determining a sequence of N time values (N a selected integer≧
2) {τ
m }m, each of which corresponds to a time of arrival, lying in the interval -Tc ≦
t≦
Tc, of a direct signal or of a multipath signal at the receiver, wherein the time values τ
m are determined by (i) forming the logarithm of a Fourier transform log{Φ
(s(t))} of the received signal s(t), (ii) forming an inverse Fourier transform X(t)=Φ
-1 {log {Φ
(s(t))}}, and (iii) identifying at least one value t=τ
m (m=1, 2, . . . , N) for which the magnitude |X(t)| has a peak;selecting a set of sampling times {τ
'"'"'k }k (k=1, . . . , K;
K a selected integer≧
2) for the correlation function R(τ
), and determining the correlation function values R(τ
'"'"'k)=xk ;choosing complex numbers bm so that a sum ##EQU24## is minimized, where q is a selected positive number; and
interpreting a difference signal ##EQU25## as a signal from which at least one multipath signal has been removed. - View Dependent Claims (19)
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-
20. A method for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the method comprising the steps of:
-
receiving a signal s(t) at a receiver that is the result of a transmitted message signal with frequency ω and
having a shape signal p(t) with frequency fc =1/Tc ;forming a correlation function R(τ
) defined by ##EQU26## where T is a selected time satisfying T>
>
Tc ;
determining a sequence of N time values (N a selected integer≧
2) {τ
m }m, each of which corresponds to a time of arrival, lying in the interval -Tc ≦
t≦
Tc, of a direct signal or of a multipath signal at the receiver, wherein the time values τ
m are determined by (i) identifying at least two slope transition points for the correlation function magnitude |R(τ
)|, and (ii) for each slope transition point identified, identifying at least one time value τ
m with each slope transition point;selecting a set of sampling times {τ
'"'"'k }k (k=1, . . . , K;
K a selected integer≧
2) for the correlation function R(τ
), and determining the correlation function values R(τ
'"'"'k)=xk ;choosing complex numbers bm so that a sum ##EQU27## is minimized, where q is a selected positive number; and
interpreting a difference signal ##EQU28## as a signal from which at least one multipath signal has been removed. - View Dependent Claims (21, 22, 23)
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Specification
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Current AssigneeTrimble Navigation Limited (Trimble Inc.)
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Original AssigneeTrimble Navigation Limited (Trimble Inc.)
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InventorsEnge, Per, Schipper, John F., Farmer, Dominic
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Primary Examiner(s)Eisenzopf, Reinhard J.
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Assistant Examiner(s)SOBUTKA, PHILIP
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Application NumberUS08/277,150Time in Patent Office1,029 DaysField of Search455/65, 455/52.3, 455/67.1, 455/226.1, 455/296, 455/302, 455/303, 455/304, 455/305, 455/306, 455/307, 375/209, 375/343US Class Current455/65CPC Class CodesG01S 19/22 Multipath-related issuesH04B 1/711 the interference being mult...H04B 7/005 Control of transmission; Eq...
