ADS-B receiver system with multipath mitigation

• US 8,917,201 B2
• Filed: 09/30/2011
• Issued: 12/23/2014
• Est. Priority Date: 09/30/2011
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Malaga, Alfonso
• Primary Examiner(s): BYTHROW, PETER M
• Application Number:
  US13/250,003
• Publication Number:
  US 20130082867A1
• Time in Patent Office: 1,180 Days
• Field of Search: 342 29- 51, 342159-164, 342/175
• US Class Current: 342/40
• CPC Class Codes: G08G 5/0008 with other aircraft
• CPC Class Codes: H04B 1/1081 Reduction of multipath noise by equalising H04B7/005
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04B 7/18506 Communications with or from aircraft, i.e. aeronautical mobile service
• CPC Class Codes: H04L 25/03019 adaptive, i.e. capable of adjustment during data reception

Abstract

Systems and methods for receiving ADS-B messages in environments where multipath propagation corrupts the messages or blocks the reception of the messages. An exemplary system combines RF signal processing and digital signal processing techniques to make it possible to receive ADS-B messages in the presence of multipath reflections from nearby structures and/or farther out structures. The system uses an array of horizontally spaced antennas. The RF signals from the antennas are combined by the receiver so as to form a set of beams with different azimuth antenna patterns to increase the probability that the multipath does not combine destructively with the line-of-sight path in at least one of the beams. This effectively removes multipath reflections where the delay of the multipath relative to the line-of-sight path is less than 100-200 nanoseconds. The system is also configured to remove multipath reflections with greater delays relative to the line-of-sight path.

Claims

1. A method comprising:

at a plurality of receivers,

receiving a plurality of signals from a plurality of diversity antennas;

at a device in communication with the plurality of receivers,

simultaneously processing the plurality of signals to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals to produce a signal that is free of interference from the short delay multipath signals;

removing interference from the long delay multipath signals from the produced signal; and

outputting an ADS-B message based on the produced signal that is free of short delay interference signals with the removed interference from long delay multipath signals.

2. The method of claim 1, wherein the plurality of diversity antennas comprise antennas configure to receive signals at 1090 MHz.

3. The method of claim 2, wherein the diversity antennas comprise a first pair of horizontally spaced antennas and simultaneous processing of the signals received by these two antennas comprises:

summing the signals received from first and second horizontally separated antennas to create a first sum signal;

subtracting the signals received from the first and second antennas to create a first difference signal; and

simultaneously processing the first sum signal and the first difference signal to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals.

4. The method of claim 3, wherein the diversity antennas comprise a second pair of antennas spaced horizontally in a plane perpendicular to the plane of the first pair of antennas and simultaneous processing of the signals received by this second pair of antennas comprises:

summing the signals received from third and fourth horizontally separated antennas to create a second sum signal;

subtracting the signals received from the third and fourth antennas to create a second difference signal; and

simultaneously processing the second sum signal and the second difference signal to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals.

5. The method of claim 4, wherein the plurality of signals comprise automatic dependent surveillance-broadcast (ADS-B) signals.

6. The method of claim 5, wherein the first and second antennas are vertically separated from the third and fourth antennas.

7. The method of claim 5, wherein the horizontal separation is approximately at least half of the wavelength of the ADS-B signals.

8. The method of claim 5, wherein the first and second antennas are horizontally and vertically separated and the second and fourth antennas are horizontally and vertically separated.

9. The method of claim 4, wherein outputting the ADS-B message in the presence of short delay and long delay multipath signals comprises:

performing preamble correlation for each of the first and second sum signals and first and second difference signals based on a previously known ADS-B message preamble configuration;

selecting one of the first and second sum and difference signals with associated start-of-message value, pulse-peak timing value and frequency offset value based on the performed preamble correlation and a predefined power threshold; and

storing each of the first and second sum and difference signals in a buffer, and

wherein removing the interference from long delay multipath signals comprises;

retrieving one of the stored sum and difference signals based on the selected signal;

correcting a frequency error of the retrieved signal based on a frequency offset value associated with the selected signal;

correlating the frequency error corrected signal with the previously known ADS-B message preamble configuration;

estimating the amplitude and phase of the multipath signals at delay intervals of 500 ns based on the output of the correlation between the frequency error corrected selected signal with the known ADS-B preamble configuration that precedes the ADS-B message bits; and

cancelling any corruption of the ADS-B message bits that follow the preamble by long delay multipath signal interference based on the estimated amplitude and phase of multipath signals at delay intervals of 500 ns.

10. A system comprising:

a plurality of diversity antennas configured to receive a plurality of signals;

a plurality of receivers configured to receive the plurality of signals from the plurality of diversity antennas;

a device in communication with the plurality of receivers, the device configured to;

simultaneously process the plurality of signals to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals to produce a signal that is free of interference from the short delay multipath signals;

remove interference from the long delay multipath signals from the produced signal; and

output an ADS-B message based on the produced signal that is free of short delay interference signals with the removed interference from long delay multipath signals.

11. The system of claim 10, wherein the plurality of diversity antennas comprise antennas configure to receive signals at 1090 MHz.

12. The system of claim 11, wherein the diversity antennas comprise a first pair of horizontally spaced antennas and the device simultaneous processes by:

summing the signals received from first and second horizontally separated antennas to create a first sum signal;

subtracting the signals received from the first and second antennas to create a first difference signal; and

simultaneously processing the first sum signal and the first difference signal to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals.

13. The system of claim 12, wherein the diversity antennas comprise a second pair of antennas spaced horizontally in a plane perpendicular to the plane of the first pair of antennas and the device simultaneous processes by:

summing the signals received from third and fourth horizontally separated antennas to create a second sum signal;

subtracting the signals received from the third and fourth antennas to create a second difference signal; and

simultaneously processing the second sum signal and the second difference signal to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals.

14. The system of claim 13, wherein the plurality of signals comprise automatic dependent surveillance-broadcast (ADS-B) signals.

15. The system of claim 14, wherein the first and second antennas are vertically separated from the third and fourth antennas.

16. The system of claim 14, wherein the horizontal separation is approximately at least half of the wavelength of the ADS-B signals.

17. The system of claim 14, wherein the first and second antennas are horizontally and vertically separated and the second and fourth antennas are horizontally and vertically separated.

18. The system of claim 13, wherein the device outputs the ADS-B message in the presence of short delay and long delay multipath signals by:

performing preamble correlation for each of the first and second sum signals and first and second difference signals based on a previously known ADS-B message preamble configuration;

selecting one of the first and second sum and difference signals with associated start-of-message value, pulse-peak timing value and frequency offset value based on the performed preamble correlation and a predefined power threshold; and

storing each of the first and second sum and difference signals in a buffer, and

wherein the device removes the interference from long delay multipath signals by;

retrieving one of the stored sum and difference signals based on the selected signal;

correcting a frequency error of the retrieved signal based on a frequency offset value associated with the selected signal;

correlating the frequency error corrected signal with the previously known ADS-B message preamble configuration;

estimating the amplitude and phase of the multipath signals at delay intervals of 500 ns based on the output of the correlation between the frequency error corrected selected signal with the known ADS-B preamble configuration that precedes the ADS-B message bits; and

cancelling any corruption of the ADS-B message bits that follow the preamble by long delay multipath signal interference based on the estimated amplitude and phase of multipath signals at delay intervals of 500 ns.

19. A system comprising:

a means for receiving a plurality of signals from a plurality of diversity antennas, wherein the diversity antennas are at least one of spaced horizontally on a vehicle by a plurality of ADS-B signal wavelengths or each of the diversity antennas produces a different azimuth antenna pattern; and

a means for

simultaneously processing the plurality of signals to detect the reception of an ADS-B message in the presence of short delay and long delay multipath signals to produce a signal that is free of interference from the short delay multipath signals;

removing interference from the long delay multipath signals from the produced signal; and

outputting an ADS-B message based on the produced signal that is free of short delay interference signals with the removed interference from long delay multipath signals.