SYSTEM AND METHOD FOR PROVIDING TIMING SERVICES AND DME AIDED MULTILATERATION FOR GROUND SURVEILLANCE

• US 20110156878A1
• Filed: 07/20/2010
• Published: 06/30/2011
• Est. Priority Date: 07/20/2009
• Status: Active Grant

• Current Assignee: SAAB Cars
• Original Assignee: Sensis Pty Limited (Telstra Group Ltd.)
• Inventors: Wu, Ryan Haoyun, Lefebvre, Kevin
• Granted Patent: US 8,063,744 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• CPC Class Codes: G01S 13/785 Distance Measuring Equipment [DME] systems
• CPC Class Codes: G01S 5/0081 Transmission between base stations
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence

Abstract

The present invention utilizes the existing DME transponder system infrastructure to augment existing ground surveillance multilateration (MLAT) capabilities by providing additional measurements for determining the position of an aircraft equipped with a DME transponder. DME listeners receive DME interrogation signals and DME reply signals, determine TDOA between the DME transponder and each DME listener, and transmit data to a central computer that clusters TDOAs between the DME transponder and the DME listeners and computes the aircraft position using the clustered TDOAs. The DME-aided MLAT can be used as a backup surveillance system when GNSS-based systems are unavailable. The DME-aided MLAT can be integrated with SSR receive units (RUs) performing multilateration (MLAT) calculations.

Claims

1. A method DME aided multilateration, the method comprising:

transmitting interrogation pulses from at least one DME interrogator that are received by at least one DME transponder;

transmitting reply pulses from at least one DME transponder in response to the interrogation pulses received from the at least one DME interrogator;

providing at least one DME listener for

receiving and demodulating the interrogation pulses transmitted by the at least one DME interrogator and the reply pulses transmitted by the at least one DME transponder,

cross correlating the received interrogation pulses and reply pulses and determining a cross correlation output;

determining an interrogation pattern of the received interrogation pulses and reply pulses by selecting overlapping pulses of the received interrogation pulses and reply pulses when a maximum peak for cross correlation occurs in the cross correlation output,

determining a time difference of arrival (TDOA) for the associated interrogation pulses and reply pulses using the position of the maximum peak of cross correlation, known time delay of the DME transponder and known distance between the at least one DME transponder and the at least DME listener,

transmitting at least the determined TDOA, interrogation pattern information, and the ID of the DME listener to a central computer;

wherein the central computer

receives at least the determined TDOA interrogation pattern information, and DME listener ID from the at least one DME listener,

associates the determined TDOA to a specific transmission of interrogation pulses from the at least one DME interrogator using the interrogation pattern information to form a DOA cluster, and

determines a position for the at least one DME interrogator when three or more TDOAs are clustered.

2. The method of claim 1, wherein the TDOA is determined using the following equation:

TDOA=t₁−

t₃=(t₂−

τ

₂−

t_d)−

t₃

where;

τ

₂=Known propagation time between DME transponder and DME listener;

t₁=time of arrival of DL signal at DME transponder and t₁=t₂−

τ

₂−

t_d;

t₂=time of arrival of UL signal at DME listener;

t₃=time of arrival of DL signal at DME listener;

t_d=Known DIME transponder delay; and

t₂−

t₃ is obtained by XCORR {UL, DL}.

3. The method of claim 1, further comprising determining an identity for the at least one DME interrogator using at least one of Mode A ID or Mode S address.

4. The method of claim 1, further comprising synchronizing clocks between a first DME listener and a second DME listener using a reference transmitter, wherein clock offset is determined before determining the TOA for the received interrogation pulses and reply pulses at each of the first and second DME listeners using the following equation:

Clock Offset=τ

₂−

τ

₁−

(t₂−

t₁)

where;

t₂−

t₁ is obtained by XCORR {UL @ DME listener #1, UL @ DME listener #2}, and

τ

₂, τ

₁=(known DME transponder to DME listener distance)/(speed of light).

5. The method of claim 4, wherein the reference transmitter is shared with Mode S multilateration receiving units (RUs).

6. The method of claim 1, further comprising integrating DME aided multilateration and Mode A/S multilateration by receiving a Mode A/S transponder transmission at two or more Mode S receiving units (RUs), from a target that includes the at least one DME interrogator, wherein at least two Mode S RUs are each co-located with a DME listener, deriving at least one Mode A/S signal TDOA measured at the more than one RU, and associate at least one DME signal derived TDOA with the at least one Mode A/S signal derived TDOA based on similarities in TDOA and TDOA rate values within a predetermined time window.

7. The method of claim 6, wherein the Mode A/S derived TDOA is used to improve position accuracy to the determined position for the at least one DME interrogator.

8. The method of claim 1, wherein the central computer is selected from the group consisting of DME transponder, DME listener, and Secondary Surveillance Radar (SSR) transponder based RU.

9. A method DME aided multilateration, the method comprising:

transmitting interrogation pulses from at least one DME interrogator that are received by at least one DME transponder;

transmitting reply pulses from at least one DME transponder in response to the interrogation pulses received from the at least one DME interrogator;

providing at least one DME listener for

receiving and demodulating the interrogation pulses transmitted by the at least one DME interrogator and the reply pulses transmitted by the at least one DME transponder,

cross correlating the received interrogation pulses and reply pulses and determining a cross correlation output;

determining an interrogation pattern of the received interrogation pulses and reply pulses by selecting overlapping pulses of the received interrogation pulses and reply pulses when a maximum peak for cross correlation occurs in the cross correlation output,

determining a time difference of arrival (TDOA) for the associated interrogation pulses and reply pulses using the position of the maximum peak of cross correlation, known time delay of the DME transponder and known distance between the at least one DME transponder and the at least one DME listener,

transmitting at least the determined TDOA, interrogation pattern information, and the ID of the DME listener to a central computer;

wherein the central computer

receives at least the determined TDOA interrogation pattern information, and DME listener ID from the at least one DME listener,

associates the determined TDOA to a specific transmission of interrogation pulses from the at least one DME interrogator using the interrogation pattern information to form a TDOA cluster,

determines Mode C information for the DME interrogator from another source, and

when two or more TDOAs are clustered, determines a position for the DME interrogator from the two TDOAs and the Mode C information.

10. The method of claim 9, wherein the TDOA is determined using the following equation:

TDOA=t₁−

t₃=(t₂−

τ

₂−

t_d)−

t₃

where;

τ

₂=Known propagation time between DME transponder and DME listener;

t₁ time of arrival of DL signal at DME transponder and t₁=t₂−

τ

₂−

t_d;

t₂=time of arrival of UL signal at DME listener;

t₃=time of arrival of DL signal at DME listener;

t_d=Known DME transponder delay; and

t₂−

t₃ is obtained by XCORR {UL, DL}.

11. The method of claim 9, further comprising determining an identity for the DME interrogator using at least one of Mode A ID or Mode S address.

12. The method of claim 9, further comprising synchronizing clocks between a first DME listener and a second DME listener using a reference transmitter, wherein clock offset is determined before determining the TOA for the received interrogation pulses and reply pulses at each of the first and second DME listeners using the following equation:

Clock Offset=τ

₂−

τ

₁−

(t₂−

t₁)

where;

t₂−

t₁ is obtained by XCORR {UL @ DME listener #1, UL @ DME listener #2}, and

τ

₂, τ

₁=(known DME transponder to DME listener distance)/(speed of light).

13. The method of claim 9, wherein the central computer assumes an altitude for the DME interrogator and determines a coarse position for the DME interrogator before using the Mode C information to determine a refined position for the DME interrogator.

14. The method of claim 9, wherein the central computer is selected from the group consisting of DME transponder, DME listener, and SSR transponder based RU.

15. A method for DME aided multilateration, the method comprising:

transmitting interrogation pulses from at least one DME interrogator that are received by at least one DME transponder;

transmitting reply pulses from at least one DME transponder in response to the interrogation pulses received from the at least one DME interrogator;

providing at least two DME listeners for

receiving and demodulating the interrogation pulses transmitted by the at least one DME interrogator and the reply pulses transmitted by the at least one DME transponder,

determining a time of arrival (TOA) of each pulse pair in the received interrogation pulses and reply pulses and a received signal strength (RSS) for the received interrogation pulses and reply pulses at each of the at least two DME listeners, and

transmitting at least the determined TOA of each pulse pair and RSS for the received interrogation pulses and reply pulses and the ID of the DME listener from each of the at least two DME listeners to a central computer;

wherein the central computer

receives at least the determined TOA of each pulse pair and RSS for the received interrogation pulses and reply pulses and DME listener ID from each of the at least two DME listeners,

associates the received interrogation pulses and reply pulses using the received TOA of each pulse pair and RSS,

derives TDOAs between each DME listener of the at least two DME listeners and the at least one DME transponder from the received TOA of each pulse pair and RSS of associated interrogation pulses and reply pulses and the known distance between each DME listener of the at least two DME listeners and the at least one DME transponder,

clusters the derived TDOAs to a specific transmission of interrogation pulses from the at least one DME interrogator, and

determines a position for the at least one DME interrogator when three or more TDOAs are clustered.

16. The method of claim 15, wherein the TDOA is determined using the following equation:

TDOA=t₁−

t₃=(t₂−

τ

₂−

t_d)−

t₃

where;

τ

₂=Known propagation time between DME transponder and DME listener;

t₁=time of arrival of DL signal at DME transponder and t₁=t₂−

τ

₂−

t_d;

t₂=time of arrival of UL signal at DME listener;

t₃=time of arrival of DL signal at DME listener;

t_d=Known DME transponder delay; and

t₂−

t₃ is obtained by XCORR {UL, DL}.

17. The method of claim 15, further comprising determining an identity for the DME interrogator using at least one of Mode A ID or Mode S address.

18. The method of claim 15, further comprising synchronizing clocks between a first DME listener and a second DME listener using a reference transmitter, wherein clock offset is determined before determining the TOA for the received interrogation pulses and reply pulses at each of the first and second DME listeners using the following equation:

Clock Offset=τ

₂−

τ

₁−

(t₂−

t₁)

where;

t₂−

t₁ is obtained by XCORR {UL @ DME listener #1, UL @ DME listener #2}, and

τ

₂, τ

₁=(known DME transponder to DME listener distance)/(speed of light).

19. The method of claim 15, wherein the at least one DME listener transmits demodulated signal waveforms for the received interrogation pulses and reply pulses from each of the at least two DME listeners to a central computer, and the central computer cross correlates the received interrogation pulses with reply pulses and determines TDOA using the peak position of the correlation output.

20. The method of claim 15, wherein the central computer is selected from the group consisting of DME transponder, DME listener, and SSR transponder based RU.

21. A method for DME aided multilateration, the method comprising:

transmitting interrogation pulses from at least one DME interrogator that are received by at least one DME transponder;

transmitting reply pulses from at least one DME transponder in response to the interrogation pulses received from the at least one DME interrogator;

providing at least two DME listeners for

receiving and demodulating the interrogation pulses transmitted by the at least one DME interrogator and the reply pulses transmitted by the at least one DME transponder,

determining a time of arrival (TOA) of each pulse pair and a received signal strength (RSS) for the received DME interrogation pulses and reply pulses at each of the at least two DME listeners, and

transmitting at least the determined TOA of each pulse pair and RSS for the received interrogation pulses and reply pulses and the ID of the DME listener from each of the at least two DME listeners to a central computer;

wherein the central computer

receives at least the determined TOA of each pulse pair and RSS for the received interrogation pulses and reply pulses and DME listener ID from each of the at least two DME listeners,

associates the received interrogation pulses and reply pulses using the received TOA of each pulse pair and RSS,

derives TDOA between each of the at least two DME listeners and the at least one DME transponder from the received TOA of each pulse pair and RSS of associated interrogation pulses and reply pulses and the known distance between each of the at least two DME listeners and the at least one DME transponder,

clusters the derived TDOAs to a specific transmission of interrogation pulses from the at least one DME interrogator, and

determines Mode C information for the DME interrogator from another source; and

when two or more TDOAs are clustered, determines a position for the DME interrogator from the two TDOAs and the Mode C information.

22. The method of claim 21, wherein the TDOA is determined using the following equation:

TDOA=t₁−

t₃=(t₂−

τ

₂−

t_d)−

t₃

where;

τ

₂=Known propagation time between DME transponder and DME listener;

t₁=time of arrival of DL signal at DME transponder and t₁=t₂−

τ

₂−

t_d;

t₂=time of arrival of UL signal at DME listener;

t₃=time of arrival of DL signal at DME listener;

t_d=Known DME transponder delay; and

t₂−

t₃ is obtained by XCORR {UL, DL}.

23. The method of claim 21, further comprising determining an identity for the DME interrogator using one of Mode A ID or Mode S address.

24. The method of claim 21, further comprising synchronizing clocks between a first DME listener and a second DME listener using a reference transmitter, wherein clock offset is determined before determining the TOA for the received interrogation pulses and reply pulses at each of the first and second DME listeners using the following equation:

Clock Offset=τ

₂−

τ

₁−

(t₂−

t₁)

where;

t₂−

t₁ is obtained by XCORR {UL @ DME listener #1, UL @ DME listener #2}, and

τ

₂, τ

₁=(known DME transponder to DME listener distance)/(s

25. The method of claim 21, wherein the central computer assumes an altitude for the DME interrogator and determines a coarse position for the DME interrogator before using the Mode C information to determine a refined position for the DME interrogator.

26. The method of claim 21, wherein the at least one DME listener transmits demodulated signal waveforms for the received interrogation pulses and reply pulses from each of the at least two DME listeners to a central computer, and the central computer cross correlates the received interrogation pulses and reply pulses and determines TDOA using the peak position of the correlation output.

27. The method of claim 21, wherein the central computer is selected from the group consisting of DME transponder, DME listener, and SSR transponder based RU.