Enhanced suppression of multipath interference

• US 5,771,456 A
• Filed: 08/09/1996
• Issued: 06/23/1998
• Est. Priority Date: 08/09/1996
• Status: Expired due to Fees

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Pon, Rayman
• Primary Examiner(s): VO, NGUYEN THANH
• Application Number:
  US08/694,845
• Time in Patent Office: 683 Days
• Field of Search: 455/456, 455/457, 455/504, 455/505, 455/506, 455/65, 455/63, 340/988, 340/989, 340/993, 342/386-391, 342/421, 342/450, 342/461, 342/357, 342/352, 364/443, 364/449.1, 364/449.7, 364/449.8, 364/451, 364/452
• US Class Current: 455/456.2
• CPC Class Codes: G01S 1/045 Receivers
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/426 by combining or switching between position solutions or signals derived from different modes of operation in a single system
• CPC Class Codes: G01S 19/52 Determining velocity

Abstract

A method for suppressing the effects of multipath signals in determination of the location of a mobile user, using the speed or magnitude of the velocity v of the user to determine the procedure(s) to be used to determine the range or pseudorange values corresponding to the GPS, GLONASS, LORAN, FM subcarrier or other location determination (LD) signals received from a plurality of LD signal sources. Where the user velocity v satisfies v≦v1, or v≧v2 (v1 and v2 being two selected velocity threshold values with 0<v1<v2), the range or pseudorange values are determined by a first procedure and by a second procedure, respectively, that reduce or eliminate the effects of multipath signals. Where the user velocity v satisfies v1<v<v2, the range or pseudorange values are determined by a blend of the first and second procedures.

Claims

1. A method of suppressing the effects of multipath signals in determination of the location of a mobile user, the method comprising the steps of:

determining the location of a location determination (LD) unit, that is transported with a mobile user, that receives and processes LD signals from a plurality of LD signal sources numbered j=1, 2, . . . , J (J≧

2), and that determines the location coordinates x(t)=(x(t), y(t), z(t)) and the speed or magnitude v(t)=|v(t)| of the velocity vector v(t) of the LD unit as a function of time t, using a measured range p(t;

j) from the LD unit to each of the LD signal sources;

where the speed v of the LD unit is no greater than a first selected velocity threshold v1, determining the ranges ρ

=ρ

1(t;

j) (j=1, 2, . . . , J) by a first method that reduces the effects of presence of multipath signals in the LD signals received by anantenna of the LD unit;

where the speed v of the LD unit is no less than a second selected velocity threshold v2 (>

v1), determining the ranges ρ

=ρ

2(t;

j) (j=1, 2, . . . , J) by a second method that reduces the effects of presence of multipath signals in the LD signals received by the antenna; and

determining a blended range ρ

(t,j;

blend) that equals ρ

1(t;

j) when v(t)≦

v1, that equals ρ

2(t;

j) when v(t)≧

v2, and that varies continuously from ρ

1(t;

j) to ρ

2(t;

j) for speeds v(t) satisfying v1<

v(t)<

v2.

2. The method of claim 1, wherein said step of determining said blended range ρ

(t;

j;

blend) comprises the steps of;

selecting monotonically increasing functions f(t;

v;

dv/dt;

j), which may depend upon the variable t, the variable v=v(t) and the variable dv/dt, that satisfy ##EQU12## determining said blended range ρ

(t;

j;

blend) (j=1, 2, . . . , J) by the relation

space="preserve" listing-type="equation">ρ

(t;

j;

blend)= 1-f(t;

v;

dv/dt;

j)!ρ

1(t;

j) +f(t;

v;

dv/dt;

j) ρ

2(t;

j).

3. The method of claim 2, further comprising the step of selecting at least two of said monotonically increasing functions f(t;

v;

dv/dt;

j) to be equal for different values of j.

4. The method of claim 2, further comprising the step of choosing at least one of said selected functions f to be the function defined by ##EQU13## where A is a selected positive constant that may depend upon the index j.

5. The method of claim 2, further comprising the step of choosing at least one of said selected functions f to be the function defined by ##EQU14## where τ

is a selected time value parameter, C is a selected positive constant, t=t_thr indicates the time the velocity v(t) attains a value v1 with dv/dt >

0, and one or more of the parameters τ

, C and t_thr may depend upon the index j.

6. The method of claim 2, further comprising the step of choosing at least one of said selected functions f to be the function defined by ##EQU15## where E is a selected positive constant, D satisfies 0<

D≦

1, t_thr indicates the time the velocity v(t) attains a value v1 with dv/dt >

0, and one or more of the parameters D, E and t_thr may depend upon the index j.

7. The method of claim 1, wherein said step of determining said blended range ρ

(t;

j;

blend) comprises the steps of;

selecting monotonically decreasing functions f(t;

v;

dv/dt;

j), which may depend upon the variable t, the variable v=v(t) and the variable dv/dt, that satisfy ##EQU16## determining said blended range ρ

(t;

j;

blend) (j=1, 2, . . . , J) by the relation

space="preserve" listing-type="equation">ρ

(t;

j;

blend)=f(t;

v;

dv/dt;

j) ρ

1(t;

j) + 1-f(t;

v;

dv/dt;

j)!ρ

2(t;

j).

8. The method of claim 7, further comprising the step of selecting at least two of said monotonically decreasing functions f(t;

v;

dv/dt;

j) to be equal for different values of j.

9. The method of claim 7, further comprising the step of choosing at least one of said selected functions f to be the function defined by ##EQU17## where A is a selected positive constant that may depend upon the index j.

10. The method of claim 7, further comprising the step of choosing at least one of said selected functions f to be the function defined by ##EQU18## where τ

is a selected time value parameter, C is a selected positive constant, t_thr indicates the time the velocity v(t) attains a value v2 with dv/dt <

0, and one or more of the parameters τ

, C and t_thr may depend upon the index j.

11. The method of claim 7, further comprising the step of choosing at least one of said selected functions f to be the function defined by ##EQU19## where E is a selected positive constant, D satisfies 0<

D≦

1, t_thr indicates the time the velocity v(t) attains a value v2 with dv/dt<

0, and one or more of the parameters D, E and t_thr may depend upon the index j.

12. The method of claim 1, further comprising the step of causing a LD signal receiver/processor to determine the location coordinates (x(t), y(t), z(t)) of said user, using a blended range value of ρ

(t;

j;

blend).

13. The method of claim 1, further comprising the step of selecting said LD signals that are received and processed from the class of signals consisting of GPS signals, GLONASS signals, LORAN signals, TACAN signals, Omega signals, Decca signals, JTIDS Relnav signals, PLRS signals and FM subcarrier signals.

14. Apparatus for suppressing the effects of multipath signals in determination of the location of a mobile user, the apparatus comprising:

a location determination (LD) unit, including a microprocessor, that is transported with a mobile user, that receives and processes LD signals from a plurality of LD signal sources numbered j=1, 2, . . . , J (J≧

2), and that determines the location coordinates x(t)=(x(t), y(t), z(t)) and the speed or magnitude v(t)=|v(t)| of the velocity vector v(t) of the LD unit as a function of time t, using a measured range ρ

(t;

j) from the LD unit to each of the LD signal sources, where the microprocessor is programmed so that;

where the speed v of the LD unit is no greater than a first selected velocity threshold v1, the microprocessor determines the ranges ρ

=ρ

1(t;

j) (j=1, 2, . . . , J) by a first method that reduces the effects of presence of multipath signals in the LD signals received by an antenna of the LD unit;

where the speed v of the LD unit is no less than a second selected velocity threshold v2(>

v1), the microprocessor determines the ranges ρ

=ρ

2(t;

j) (j=1, 2, . . . , J) by a second method that reduces the effects of presence of multipath signals in the LD signals received by the antenna; and

where the speed v of the LD unit satisfies v1<

v(t)<

v2, the microprocessor determines a blended range ρ

(t;

j;

blend) that equals ρ

1(t;

j) when v(t)≦

v1, that equals ρ

2(t;

j) when v(t)≧

v2, and that varies continuously from ρ

1(t;

j) to ρ

2(t;

j) for speeds v(t) satisfying v1<

v(t)<

v2.

15. The apparatus of claim 14, wherein said microprocessor determines said blended range ρ

(t;

j;

blend) by (1) using selected monotonically increasing functions f(t;

v;

dv/dt,j), which may depend upon the variable t, the variable v=v(t) and the variable dv/dt, that satisfy ##EQU20## and (2) determining said blended range ρ

(t;

j;

blend) (j=1, 2, . . . , J) by the relation

space="preserve" listing-type="equation">ρ

(t,j;

blend)= 1-f(t;

v;

dv/dt,j)!ρ

1 (t;

j) +f(t;

v;

dv/dt;

j) ρ

2(t;

j).

16. The apparatus of claim 15, wherein at least two of said selected monotonically increasing functions f(t;

v;

dv/dt;

j) are equal for different values of j.

17. The apparatus of claim 14, wherein said microprocessor determines said blended range p(t;

j;

blend) by (1) using selected monotonically decreasing functions f(t;

v(t);

dv/dt;

j), which may depend upon the variable t, the variable v=v(t) and the variable dv/dt, that satisfy ##EQU21## and (2) determining said blended range ρ

(t;

j;

blend) (j=1, 2, . . . , J) by the relation

space="preserve" listing-type="equation">ρ

(t;

j;

blend)=f(t;

v;

dv/dt;

j)ρ

1(t;

j) + 1-f(t;

v;

dv/dt;

j)!ρ

2(t;

j).

18. The apparatus of claim 17, wherein at least two of said selected monotonically decreasing functions f(t;

v;

dv/dt;

j) are equal for different values of j.

19. The apparatus of claim 14, wherein said LD signals that are received and processed are drawn from the class of signals consisting of GPS signals, GLONASS signals, LORAN signals, TACAN signals, Omega signals, Decca signals, JTIDS Relnav signals, PLRS signals and FM subcarrier signals.