Multipath meter

• US 6,541,950 B2
• Filed: 01/23/2001
• Issued: 04/01/2003
• Est. Priority Date: 01/26/2000
• Status: Active Grant

• Current Assignee: Novatel Incorporated (Hexagon AB)
• Original Assignee: Novatel Incorporated (Hexagon AB)
• Inventors: Townsend, Bryan, Jakab, Andy, Wiebe, Jonathan
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): Kerveros, James
• Application Number:
  US09/768,092
• Publication Number:
  US 20020036585A1
• Time in Patent Office: 798 Days
• Field of Search: 324/76.14, 324/76.56, 324/613, 324/614, 324/620, 375/148, 375/141, 342/363, 342/457, 342/360, 455/65, 455/66, 455/456
• US Class Current: 324/76.14
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/711 the interference being multi-path interference

Abstract

The invention is a multipath meter that analyses estimates of parameters associated with a direct signal component and one or more multipath signal components of a signal received by an antenna. The meter analyses the parameter estimates in order to facilitate the select of a location for an antenna, monitor signal quality at an existing antenna site, and/or to determine if satellite failure or some other type of signal failure has occurred. The multipath meter makes available to a user or for analysis information related to the contributions of the direct signal and the multipath signals to the received signal. The information includes estimates of various parameters such as delay, relative amplitude and phase of the direct and multipath signals. The meter calculates a ratio of the amplitudes of the direct and the multipath signals, to determine the severity of the multipath signals and, thus, the signal quality. The same ratio values may also be used to determine the advisability of the associated location as an antenna site. The meter further calculates multipath corrected correlator values and estimation residual values, to determine how well the receiver compensates for the multipath signals. The meter can then determine if the site and/or signal quality corresponds to a condition in which “excessive” multipath signals are introduced into the received signal, that is, a condition that is associated with rather substantial tracking errors. The meter further calculates normalized error ratios and normalized error values for selected correlators used by the receiver to produce the estimates of the signal parameters. Based on these ratios and values, and the determination of signal quality the meter determines if a satellite failure or other signal failure has occurred.

Claims

1. A meter for use in characterizing signals received by an antenna, the meter including:

A. a first subsystem for determining estimates of parameters associated with a direct signal component and one or more multipath signal components of the received signal, the first subsystem determining estimates for one or more of amplitude, delay and phase of the signal components;

B. a second subsystem for analyzing the parameters and determining if multipath signal components that adversely affect the processing of the direct signal components are present, the second subsystem analyzing a ratio of amplitudes that is based on the estimates of the amplitudes of the direct signal components and the multipath signal components and determining that the multipath signal components that adversely affect the processing are present if the ratio of amplitudes is consistently below a predetermined minimum value over a predetermined time period.

2. The meter of claim 1 further including a display for providing to a user an indication of the presence of the signal components that adversely affect the processing of the direct signal components.

3. The meter of claim 2 wherein the display presents a plot of one or more values associated with signal quality.

4. The meter of claim 1 wherein the second subsystem analyses the parameters associated with signals received over the predetermined time period to determine if a location is acceptable as an antenna site.

5. The meter of claim 4 wherein the second subsystem determines how far a reflector is located from the antenna based on the frequency of a sinusoid that represents the phase of one or more of the multipath signal components.

6. The meter of claim 5 wherein a user determines if the located reflector is a permanent structure to determine if the current site of the antenna is desirable as a permanent location of the antenna.

7. The meter of claim 1 wherein the second subsystem further

i. produces minimum detectable error values for selected correlators, where the minimum detectable error value is a direct signal correlation value normalized by the corresponding correlator value of a punctual correlator,

ii. produces minimum detectable ratio values for selected sets of correlators, where the minimum detectable ratio is the ratio of a direct signal tracking error of a set of correlators at one location and a set of correlators at a second location, and

iii. determines the presence of signal components that adversely affect the processing of the direct signal components when one or both of the error values and ratio values associated with signals from respective satellites exceed predetermined thresholds.

8. The meter of claim 1 wherein the second subsystem determines if the current site of the antenna is a good site for the antenna by examining the trend of the ratio of amplitudes over the predetermined time period.

9. The meter of claim 1 wherein the meter determines a satellite failure when the corresponding ratios of amplitudes are negative.

10. A meter for use in characterizing signals received by an antenna, the meter including:

A. a first subsystem for determining estimates of parameters associated with a direct signal component and one or more multipath signal components of the received signal, the first subsystem determining estimates for one or more of amplitude, delay and phase of the signal components; and

B. a second subsystem for analyzing the parameters and determining if multipath signal components are present, the second subsystem

i. producing correlation residual values for selected correlators used by the first subsystem, the second subsystem producing the correlator residual value for a given correlator by subtracting from a measured correlation value the contributions made by the direct and the one or more multipath signal components, and

ii. determining the presence of multipath signal components, and adversely affect the processing of the direct signal components if one or more of the correlator residual values are consistently above a predetermined threshold value.

11. The meter of claim 10 wherein the second subsystem further

iii. produces minimum detectable error values for selected correlators, where the minimum detectable error value is a direct signal correlation value normalized by the corresponding correlator value of a punctual correlator,

iv. produces minimum detectable ratio values for selected sets of correlators, where the minimum detectable ratio is the ratio of a direct signal tracking error of a set of correlators at one location and a set of correlators at a second location, and

v. determines the presence of multipath signal components that adversely affect the processing of the direct signal components when one or both of the error values and ratio values associated with signals from respective satellites exceed predetermined thresholds.

12. The meter of claim 11 wherein the signal components that adversely affect the processing of the direct signal components are signals associated with satellite failure, which is determined based on a combination of

the associated minimum detectable error values and minimum detectable ratio values being higher or lower than corresponding expected values, and

associated ratios of amplitudes, which are based on the amplitudes of the estimated direct signal components and the multipath signal components, having relatively low values.

13. The meter of claim 12 wherein the second subsystem monitors signal quality of the signals received from a given transmitting source and assigns confidence ratings to associated position measurements based on either or both of the associated ratios of amplitudes being below a predetermined minimum threshold and the corresponding correlator residuals being above an associated predetermined threshold.

14. The meter of claim 13 wherein the meter assigns a low confidence rating to the received signals that correspond to both relatively low ratios of amplitudes and relatively high corresponding correlator residuals.

15. The meter of claim 10 wherein the signal components that adversely affect the processing of the direct signals are excessive multipath signals, which are determined based on the corresponding correlator residuals being above a predetermined threshold.

16. The meter of claim 15 wherein the second subsystem further determines at what times the excessive multipath signals are present by determining when the corresponding correlator residuals fall below the predetermined threshold.

17. The meter of claim 16 wherein the second subsystem determines that a location is not acceptable as an antenna site if excessive multipath signals are present for more than a certain portion of the predetermined time period.

18. A system for use in characterizing signals received by an antenna, the system including:

A. a signal receiver for determining estimates of parameters associated with a direct signal component and one or more multipath signal components of the received signal, the receiver determining estimates for one or more of amplitude, delay and phase of the signal components;

B. a meter for analyzing the parameters and determining if signal components that adversely affect position measurements are present, the meter

i. producing mimimum detectable error values for selected correlators, where the minimum detectable error value is a direct signal correlation value normalized by the corresponding correlator value of a punctual correlator,

ii. producing minimum detectable ratio values for selected pairs of correlators, where the minimum detectable ratio is the ratio of tracking errors of correlator pairs at selected locations, and

iii. determining the presence of multipath signal components that adversely affect the processing of the direct signal components when one or both of the error values and ratio values associated with signals from respective satellites exceed predetermined maximum thresholds or fall below predetermined minimum thresholds.