Reliability and the accuracy of position-finding methods by estimation of the rice factor of a radio link

• US 20060012523A1
• Filed: 06/07/2005
• Published: 01/19/2006
• Est. Priority Date: 06/07/2004
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Infineon Technologies AG
• Inventors: Schmid, Andreas, Neubauer, Andre
• Granted Patent: US 7,248,218 B2
• Time in Patent Office: Days
• US Class Current: 342/451
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/428 using multipath or indirect path propagation signals in position determination
• CPC Class Codes: G01S 3/06 Means for increasing effective directivity, e.g. by combining signals having differently oriented directivity characteristics or by sharpening the envelope waveform of the signal derived from a rotating or oscillating beam antenna comparing amplitude of signals having differently oriented directivity characteristics to determine direction G01S3/16, G01S3/28

Abstract

In order to improve the reliability and the accuracy of a position-finding method such as the GPS method, the quality of a radio link which is used for the position-finding method is determined by estimating a parameter, in particular the Rice factor of the amplitude distribution density, which is characteristic of the ratio of the strength of a signal transmitted via a line-of-sight path, with respect to the strength of the signals transmitted via non-line-of-sight paths.

Claims

1. A method for determination of the quality of a radio link, in which the radio signals propagate via two or more propagation paths, comprising:

estimating a parameter that is characteristic of a signal strength of a received signal that is transmitted via a line-of-sight path, with respect to a strength of received signals transmitted via non-line-of-sight paths; and

assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using;

${\hat{K}}_2\approx <br><br>\frac{\hat{E}<br><br>\left\{R^2\right\}-2·<br><br>\hat{E}<br><br>\left\{{\left(R-\hat{E}<br><br>\left\{R\right\}\right)}^2\right\}}{2·<br><br>\hat{E}<br><br>\left\{{\left(R-\hat{E}<br><br>\left\{R\right\}\right)}^2\right\}}$

where R is the amplitude of the sample values of the received signal and Ê

{x} is approximated by a running averaging of x.

2. A method for determination of the quality of a radio link, in which the radio signals propagate via two or more propagation paths, comprising:

estimating a parameter that is characteristic of a signal strength of a received signal that is transmitted via a line-of-sight path, with respect to a strength of received signals transmitted via non-line-of-sight paths; and

assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using;

${\hat{K}}_{2,4}=\frac{\hat{E}<br><br>\left\{R^4\right\}-2·<br><br>{\left(\hat{E}<br><br>\left\{R^2\right\}\right)}^2-\hat{E}<br><br>\left\{R^2\right\}·<br><br>\sqrt{2·<br><br>{\left(\hat{E}<br><br>\left\{R^2\right\}\right)}^2-\hat{E}<br><br>\left\{R^4\right\}}}{{\left(\hat{E}<br><br>\left\{R^2\right\}\right)}^2-\hat{E}<br><br>\left\{R^4\right\}}$

where R is the amplitude of the sample values of the received signal and Ê

{x} is approximated by a running averaging of x.

3. A method for finding the position of a mobile station by means of a radio link between the mobile station and at least one reference station, comprising:

determining a quality of the radio link, wherein the quality determination comprises estimating a parameter that is characteristic of a signal strength of a received signal that is transmitted via a line-of-sight path, with respect to a strength of received signals transmitted via non-line-of-sight paths; and

using the parameter to decide whether the signal received from the reference station is to be used for position finding;

or

using the signals associated with the line-of-sight path and non line-of-sight paths for position finding after assigning weights to each of the signals by means of a weighting factor based on the value of the parameter for each of the signals.

4. The method of claim 3, wherein the signals that are received from the reference station are used for position finding only when the value of the parameter is greater than a first predetermined threshold value.

5. The method of claim 3, wherein the signals that are received from the reference station are used for position finding only when the value of the parameter is less than a second predetermined threshold value.

6. The method of claim 3, wherein the signals that are received from the reference station are weighted differently by using the signals to a greater or lesser extent for position finding, in accordance with their associated parameter.

7. The method of claim 3, wherein the position-finding method comprises a satellite-assisted method, and the reference station comprises a satellite with the position-finding method being carried out in the GPS system, the GLONASS system or in the European Galileo system.

8. The method of claim 3, further comprising:

assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using;

${\hat{K}}_s\approx <br><br>\frac{\hat{E}<br><br>\left\{R^2\right\}-2·<br><br>\hat{E}<br><br>\left\{{\left(R<br><br>\widehat{-E}<br><br>\left\{R\right\}\right)}^2\right\}}{2·<br><br>\hat{E}<br><br>\left\{{\left(R<br><br>\widehat{-E}<br><br>\left\{R\right\}\right)}^2\right\}}$

where R is the amplitude of the sample values of the received signal and Ê

{x} is approximated by a running averaging of x.

9. The method of claim 3, further comprising:

assuming a Rice distribution as the distribution function for the signal strength amplitude, wherein the estimated parameter comprises a Rice factor (K), and wherein the Rice factor is estimated using;

${\hat{K}}_{2,4}=\frac{\hat{E}<br><br>\left\{R^4\right\}-2·<br><br>{\left(\hat{E}<br><br>\left\{R^2\right\}\right)}^2<br><br>\widehat{-E}<br><br>\left\{R^2\right\}·<br><br>\sqrt{2·<br><br>{\left(\hat{E}<br><br>\left\{R^2\right\}\right)}^2<br><br>\widehat{-E}<br><br>\left\{R^4\right\}}}{{\left(\hat{E}<br><br>\left\{R^2\right\}\right)}^2<br><br>\widehat{-E}<br><br>\left\{R^4\right\}}$

where R is the amplitude of the sample values of the received signal and Ê

{x} is approximated by a running averaging of x.

10. The method of claim 3, wherein the signals employed to determine the quality of the radio link are received from a plurality of reference stations.

11. An apparatus for generating an estimated Rice factor for use in ascertaining the quality of a radio link, comprising:

a magnitude squaring device comprising an input configured to receive amplitude values of sampled received signals;

a first squaring device comprising an input connected to an output of the magnitude squaring device;

a first running averaging device comprising an input connected to an output of the first magnitude squaring device;

a second running averaging device comprising an input connected to an output of the first squaring device;

a second squaring device comprising an input connected to an output of the first running averaging device;

a first adder comprising a first input connected to an output of the second squaring device, and a second input connected to an output of the second running averaging device with its mathematical sign being reversed;

a times-two multiplier comprising an input connected to the output of the second squaring device;

a second adder comprising a first input connected to an output of the times-two multiplier, and a second input connected to the output of the second running averaging device with its mathematical sign being reversed;

a square-rooting device comprising an input connected to an the output of the second adder;

a multiplier comprising a first input connected to the output of the first running averaging device, and a second input connected to an output of the square-rooting device;

a third adder comprising a first input connected to the output of the times-two multiplier with its mathematical sign being reversed, a second input connected to an output of the multiplier with its mathematical sign being reversed, and a third input connected to the output of the second running averaging device; and

a combined multiplier/divider comprising a multiplier or numerator input connected to an output of the third adder, and a divider or denominator input connected to an output of the second adder, and configured to produce the estimated Rice factor at its output.