Position calculation method and storage medium storing a program threrefor

• US 20060068810A1
• Filed: 08/11/2005
• Published: 03/30/2006
• Est. Priority Date: 09/27/2004
• Status: Active Grant

• Current Assignee: Maxell, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Ogino, Atsushi
• Granted Patent: US 7,299,058 B2
• Time in Patent Office: Days
• US Class Current: 455/456.100
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A position calculation method includes a step of calculating error degradation quantities about respective measurement results (“distance-ranging results”) on distances between respective reference stations and a detection-target station from the respective distance-ranging results and positions of the respective reference stations, a step of calculating weight-assigning factors about the respective distance-ranging results based on the respective error degradation quantities, a step of checking the number of valid distance-ranging results, and a step of calculating the position of the detection-target station based on the respective distance-ranging results, the positions of the respective reference stations, and the respective weight-assigning factors.

Claims

1. A position calculation method, comprising the steps of:

receiving radio signals between a plurality of respective reference stations and a detection-target station by either said plurality of reference stations or said detection-target station, said plurality of reference stations being radio devices whose positions have been already known, said detection-target station being a radio device whose position has been unknown,

measuring physical quantities about distances thereby to measure absolute distances or relative distances between said plurality of respective reference stations and said detection-target station, respectively, and

calculating position of said detection-target station based on distance-ranging results and positions of said respective reference stations, said distance-ranging results being said respective distances measured,

wherein said calculating step comprises the steps of;

calculating respective error degradation quantities Δ

Ei from said respective distance-ranging results Ri and said positions Pi of said respective reference stations, said respective error degradation quantities being quantities of respective errors by which said respective distance-ranging results influence minimum value of square error function to solve the position of said detection-target station,

evaluating said respective distance-ranging results based on said respective error degradation quantities, and updating weight-assigning factors Wi about said respective distance-ranging results, and

calculating said position P of said detection-target station based on said respective distance-ranging results, said positions of said respective reference stations, and said respective weight-assigning factors updated.

2. The position calculation method according to claim 1, wherein said error degradation quantities Δ

E_i are defined using

Δ

E_i=E₀−

E_i0, i=1, . . . ,n

where Eo is the minimum value of said square error function using all measurements, n is a number of measurements, and Eio is a minimum value of square error function E not including distance-ranging result R.

3. The position calculation method according to claim 2, wherein said error degradation quantities Δ

E_i are determined using variable values P and T acquired using

$E_0=\underset{P,T}{\min }<br><br>\left(E<br><br>\left(P,T\right)\right),E<br><br>\left(P,T\right)=\underset{k=1}{\overset{n}{\sum <br><br>}}<br><br>W_k<br><br>{\left\{R_k+\mathrm{cT}-<br><br>P_k-P<br><br>\right\}}^2$ $E_i<br><br>\left(P,T\right)=\underset{\underset{k\ne <br><br>i}{k=1}}{\overset{n}{\sum <br><br>}}<br><br>W_k<br><br>{\left\{R_k+\mathrm{cT}-<br><br>P_k-P<br><br>\right\}}^2,i=1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},n$ $E_{\mathrm{i0}}=\underset{P,T}{\min }<br><br>\left(E_i<br><br>\left(P,T\right)\right),i=1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},n$

where P is a position, T is offset of a clock selected as the reference, W_k are weight-assigning factors, c is a speed of the radio waves, and R_k are distance-ranging results.

4. The position calculation method according to claim 2, wherein said error degradation quantities Δ

E_i are determined using variable values P and T acquired using

$E_0=\underset{P,T}{\min }<br><br>\left(E<br><br>\left(P,T\right)\right),E<br><br>\left(P,T\right)=\underset{k=1}{\overset{n}{\sum <br><br>}}<br><br>W_k<br><br>{\left\{R_k+\mathrm{cT}-<br><br>P_k-P<br><br>\right\}}^2$ $E_i<br><br>\left(P,T\right)=\underset{\underset{k\ne <br><br>i}{k=1}}{\overset{n}{\sum <br><br>}}<br><br>W_k<br><br>{\left\{R_k+\mathrm{cT}-<br><br>P_k-P<br><br>\right\}}^2,i=1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},n$ $E_{\mathrm{i0}}=E_i<br><br>\left(P_0,T_0\right),E<br><br>\left(P_0,T_0\right)=E_0,i=1,\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>},n$

where P is a position, T is offset of a clock selected as the reference, Po and To are P and T providing Eo, W_k are weight-assigning factors, c is a speed of the radio waves, and R_k are distance-ranging results.

5. The position calculation method according to claim 3, wherein said step of updating said weight-assigning factors is a step of updating values of said weight-assigning factors based on comparisons between said respective error degradation quantities and a threshold value determined in advance.

6. The position calculation method according to claim 5, wherein said step of updating said weight-assigning factors about said distance-ranging results is a step of updating said values of said weight-assigning factors to zero if said error degradation quantities about said distance-ranging results have exceeded said threshold value determined in advance.

7. The position calculation method according to claim 6, wherein, before executing said step of calculating said position of said detection-target station, a step of checking the number of valid distance-ranging results is executed in order to judge possibility or impossibility of said execution of said position calculating step.

8. The position calculation method according to claim 7, wherein said checking of the number of said valid distance-ranging results is a checking based on a comparison between the number of said weight-assigning factors which become non-zero with respect to said respective distance-ranging results and a threshold value determined in advance.

9. The position calculation method according to claim 1, further comprising a step of calculating Dilution of Precision after having executed said step of calculating said position of said detection-target station, and judging success or failure of said position calculation of said detection-target station in accordance with a calculation value of said Dilution of Precision.

10. A computer-readable storage medium for storing a position calculation program for implementing a position calculation method in a position calculation apparatus,

said position calculation apparatus, comprising:

an input unit for inputting physical quantities about distances,

a processing unit, and

an output unit, said physical quantities about said distances being measured such that radio signals between a plurality of respective reference stations and a detection-target station are received by either said plurality of reference stations or said detection-target station, said plurality of reference stations being radio devices whose positions have been already known, said detection-target station being a radio device whose position has been unknown,

said position calculation method being executed by said processing unit, comprising the steps of;

calculating, from said physical quantities about said distances, absolute distances or relative distances between said plurality of respective reference stations and said detection-target station, respectively, and

calculating position of said detection-target station based on distance-ranging results and positions of said respective reference stations, said distance-ranging results being said respective distances measured,

wherein the calculating step includes the steps of;

calculating respective error degradation quantities from said respective distance-ranging results and said positions of said respective reference stations, said respective error degradation quantities being quantities of respective errors by which said respective distance-ranging results influence least square error,

evaluating said respective distance-ranging results based on said respective error degradation quantities, and updating weight-assigning factors about said respective distance-ranging results, and

calculating said position of said detection-target station based on said respective distance-ranging results, said positions of said respective reference stations, and said respective weight-assigning factors updated.