Cooperative position location via wireless data link using broadcast digital transmissions

• US 8,063,825 B1
• Filed: 05/07/2009
• Issued: 11/22/2011
• Est. Priority Date: 05/07/2009
• Status: Expired due to Fees

• Current Assignee: Chun Yang
• Original Assignee: Chun Yang
• Inventors: Yang, Chun
• Primary Examiner(s): Tarcza; Thomas
• Assistant Examiner(s): MCGUE, FRANK J
• Application Number:
  US12/436,868
• Time in Patent Office: 929 Days
• Field of Search: 342/458
• US Class Current: 342/458
• CPC Class Codes: G01S 5/0072 Transmission between mobile stations, e.g. anti-collision systems
• CPC Class Codes: G01S 5/009 Transmission of differential positioning data to mobile
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

A cooperative position location device (CPLD) that integrates a broadcast digital transmission (BDT) receiver, a data link transceiver, and a displacement sensor; a computer program product tangibly stored in computer-readable media; and associated methods for receiving and processing special codes embedded in BDT signals from a plurality of transmitters to produce time of arrival (TOA) measurements thereof; for sending and receiving special messages between cooperative position location devices (CPLDs) to produce time difference of arrival (TDOA) of common events of BDT at and time of flight (TOF) measurements between the CPLDs; and for integrating differential and relative ranges between CPLDs to a plurality of BDT transmitters and displacement measurements to yield a joint position solution of the CPLDs.

Claims

1. A method of determining the location of a plurality of mobile users in an area using existing digital signals of opportunity transmitted from a plurality of transmitters proximate said area, said method comprising the steps of:

providing each of said plurality of mobile users with a displacement sensor that detect displacements incurred within said area as said plurality of mobile users move through said area, therein producing displacement measurements;

establishing a communications link between each of said plurality of mobile users, wherein each of said plurality of mobile users receives said digital signals of opportunity from each of said transmitters at different times, and wherein said different times are communicated among said plurality of mobile users using said communications link to determine time difference of arrival measurements;

utilizing said time different of arrival measurements to form a compensated differential range measurement between at least two of said mobile users and at least one of said transmitters;

forming a corrected relative range measurement between at least two of said mobile users using said communications link;

transforming said compensated differential range measurement, said corrected relative range measurement collected, and said displacement measurements into a location for at least one of said mobile users; and

determining a position location for each of said mobile users utilizing said differential range measurements, said corrected relative range measurements, and said displacement measurements.

2. The method according to claim 1, wherein said transmitters are selected from a group consisting of surface transmitters, airborne transmitters, and satellite transmitters.

3. The method according to claim 1, wherein said digital signals of opportunity are broadcast digital transmissions, each containing a known periodic code selected from a set comprising a synchronization code embedded in said broadcast digital transmissions and a modulated pseudonoise sequence superimposed onto said broadcast digital multimedia signals.

4. The method according to claim 3, wherein said step of forming a compensated differential range measurement between at least two of said mobile users and at least one of said transmitters, further includes the substeps of:

receiving said broadcast digital transmissions from at least one of said transmitters by at least two of said mobile users;

providing a local time base at each of said mobile users;

determining a measured time of arrival of said known periodic code at said mobile users relative to said local time base of said cooperative devices; and

generating said compensated differential range measurement between at least two of said mobile users from said time of arrival from at least one of said transmitters.

5. The method according to claim 4, wherein said step of generating said compensated differential range measurement between at least two of said mobile users from said time of arrival from at least one of said transmitters, further includes the substeps of:

exchanging said time of arrival of a same known periodic code from at least one of said transmitters between said mobile users via said communications link;

generating a differential time of arrival by subtracting said measured time of arrival of one of said mobile users from another of said mobile users; and

applying compensations to said differential time of arrival, yielding said compensated differential range measurement.

6. The method according to claim 5, wherein said step of applying compensations to said differential time of arrival, further includes the substeps of:

obtaining a clock offset estimate between said time bases of said mobile users;

obtaining a correction of line of sight distance for topographic distortion caused by terrain elevation in a vicinity of said mobile users;

obtaining an atmospheric propagation velocity of light according to weather conditions in a vicinity of said mobile users;

applying said clock offset estimate to said differential time of arrival,

scaling clock offset-compensated differential time of arrival by said atmospheric propagation velocity of light; and

applying said correction of line of sight distance for topographic distortion.

7. The method according to claim 4, wherein said step of receiving broadcast digital transmissions, further includes the substeps of:

obtaining a center frequency from a channel selector for each of said transmitters;

tuning a local oscillator to down-convert said broadcast digital transmissions from said center frequency to a predetermined intermediate frequency signal;

applying stages of mixing, bandpass filtering and amplification to said intermediate frequency signal; and

digitizing said intermediate frequency signal, yielding received incoming signal time samples of said broadcast digital transmissions.

8. The method according to claim 4, wherein said step of determining a measured time of arrival, further includes the substeps of:

maintaining lock onto said known periodic code of said transmitters;

determining a direct correlation peak pertaining to each of said transmitters; and

interpolating for a refined location of said direct correlation peak, yielding said measured time of arrival.

9. The method according to claim 8, wherein said step of maintaining lock onto said known periodic code of said transmitters, further includes the substeps of:

obtaining an initial estimate of timing and frequency errors of said periodic code and said center frequency via search over a time and frequency uncertainty interval;

creating a local replica of said periodic code at said timing estimate and a local carrier at said center frequency estimate via a code and carrier generator;

performing correlation between said incoming signal samples and said local replicas at said timing and frequency estimates;

applying a code delay discriminator, a carrier phase discriminator and a frequency error discriminator to said correlation, yielding a code delay error, a carrier phase error and a frequency error;

processing said code delay error, said carrier phase error and said frequency error through a code tracking filter and a carrier tracking filter; and

sending an output of said tracking filter to said code and carrier generator, therein closing a code feedback loop and a carrier feedback loop, therein maintaining lock onto said known periodic code of said transmitters.

10. The method according to claim 1, wherein said step of forming a corrected relative range measurement, further includes the substeps of:

obtaining an apparent time of flight of a ranging message for request;

obtaining an apparent time of flight of a ranging message for reply;

scaling an average of times of flight of said ranging messages for request and reply by the speed of propagation, yielding an apparent relative range between mobile users;

scaling a difference between times of flight of said ranging messages for request and reply by a factor of two, yielding an estimate of clock offset between said mobile users; and

applying delay corrections to said apparent relative range, yielding said corrected relative range measurement, wherein said delay corrections are selected from a group consisting of atmospheric, topographic, protocol-related, and circuitry propagation.

11. The method according to claim 10, wherein said step of obtaining an apparent time of flight of a ranging message, further includes the substeps of:

forming a ranging message at an initiating device;

broadcasting said ranging message to said mobile users;

obtaining a send time tag of said ranging message leaving said initiating device;

obtaining a receive time tag of said ranging message arriving at said mobile users;

exchanging said send and receive time tags of said ranging message between said initiating device and said mobile users; and

subtracting said send time tag from said receive time tag, yielding said apparent time of flight of a ranging message.

12. The method according to claim 11, wherein said step of broadcasting said ranging message, further includes the substeps of:

formatting said ranging message in accordance with a predefined ranging and a communication protocol;

modulating formatted ranging message onto a carrier;

applying stages of mixing, bandpass filtering and amplification to said carrier, therein up-converting said modulated carrier to a predetermined radio frequency signal; and

sending said radio frequency signal to an antenna, therein broadcasting said ranging message.

13. The method according to claim 11, wherein said step of obtaining a receive time tag, further includes the substeps of:

receiving incoming signal samples of said ranging message;

providing a local time base;

maintaining lock onto said ranging message; and

determining a time of arrival of said ranging message relative to said local time base, therein yielding said receive time tag of said ranging message.

14. The method according to claim 13, wherein said step of receiving incoming signal samples of said ranging message, further includes the substeps of:

obtaining a center frequency for said initiating device;

tuning a local oscillator to down-convert said broadcast ranging message from said center frequency to a predetermined intermediate frequency signal;

applying stages of mixing, bandpass filtering and amplification to said intermediate frequency signal; and

digitizing said intermediate frequency signal, yielding said incoming signal time samples.

15. The method according to claim 13, wherein said step of maintaining lock onto said ranging message, further includes the substeps of:

obtaining an initial estimate of timing and frequency errors of said ranging message and said center frequency via search over a time and frequency uncertainty interval;

creating a local replica of said ranging message at said timing estimate and a local carrier at said center frequency estimate via a code and carrier generator;

performing correlation between said incoming signal samples and said local replicas at said timing and frequency estimates;

determining a direct correlation peak pertaining to said ranging message;

interpolating for a refined location of said direct correlation peak, therein yielding said measured time of arrival of said ranging message code;

applying a code delay error discriminator, a carrier phase error discriminator and a frequency error discriminator to said correlation, therein yielding a code delay error, a carrier phase error and a frequency error;

processing said code delay error, said carrier phase error and said frequency error through a code tracking filter and a carrier tracking filter to obtain a filtered output; and

sending said filtered output to said code and carrier generator, therein closing a code feedback loop and a carrier feedback loop, thus maintaining lock onto said ranging message.

16. The method according to claim 11, wherein said send and receive time tags of said ranging message between said initiating device and said cooperative devices can be exchanged using a procedure selected from a set of directly embedding time tags into ranging messages and sending time tags in separate data-only messages in accordance with a predefined protocol.

17. The method according to claim 16, wherein said separate data only messages may further contain time tags for send and receive of ranging messages, time tags for arrival of broadcast digital transmissions, and circuit propagation delay and protocol-related delay calibration and correction data.

18. The method according to claim 1, wherein said step of transforming said differential range measurement and said relative range measurement collected at a number of known displacements of at least one of said cooperative devices, further includes the substeps of:

selecting a point of interest at which to determine a location solution for each of said mobile users in a common coordinate frame;

collecting said differential range measurement and relative range measurement at said point of interest;

making at least one displacement by at least one of said mobile users if the number of collected differential and relative range measurements is not sufficient for location solution;

accumulating said differential range measurement and said relative range measurement at each of said displacement point; and

relating said differential range measurement and said relative range measurement collected at said displacements to said point of interest.

19. The method according to claim 18, wherein said step of relating said differential range measurement and said relative range measurement collected at said displacements to said point of interest, further includes the substeps of:

obtaining a displacement vector in terms of distance traveled and orientation changed during said displacement; and

expressing a displacement location in terms of said unknown point of interest and known displacement vector in said common coordinate frame, therein relating said differential range measurement and said relative range measurement collected at said displacements to said point of interest.

20. The method according to claim 19, wherein said displacement vector is selected from a group of sensors consisting of at least an inertial measurement unit mechanized relative to said point of interest, an automotive dead reckoning system, an indoor dead reckoning system, and a personal dead-reckoning system.

21. The method according to claim 1, wherein said step of determining a position location of each of said cooperative devices at said point of interest, further includes the substeps of:

obtaining an initial estimate of said position location of each of said mobile users at said point of interest;

obtaining a prediction error of said differential and relative range measurements of said mobile users to said transmitters;

obtaining a geometry scaling matrix for said differential and relative range measurements;

obtaining an estimate of position location error and an estimate of sensor errors by applying a least-squares fixed-point smoother based on said geometry scaling matrix with said differential and relative range measurements; and

adding said estimate of location error to said initial estimate of position location, therein yielding said position location of each of said mobile users at said point of interest.

22. The method according to claim 21, wherein said initial estimate of said position location is obtained from a group of steps comprising at least directly solving nonlinear range equations, applying an iterative solution to nonlinear range equations, and receiving initialization data from a user interface.

23. The method according to claim 21, wherein said step of obtaining a prediction error of said differential and relative range measurements of said mobile users, further includes the substeps of:

obtaining predicted differential and relative ranges based on said initial estimate of position location of mobile users, said initial estimate of sensor errors, and location of said transmitters; and

subtracting said predicted differential and relative ranges from said measured differential and relative range measurements, therein yielding said prediction error of said differential and relative range measurements, wherein said prediction error is arranged into a vector of range prediction errors.

24. The method according to claim 21, wherein said step of obtaining a geometry scaling matrix for said differential and relative range measurements, further includes the substeps of:

taking partial derivatives of said differential and relative range measurements with respect to each of said position location and sensor error variables; and

arranging said partial derivatives into said geometry scaling matrix.

25. The method according to claim 21, wherein said step of determining a position location of each of said mobile users at said point of interest and said displacement points, further includes the substeps of:

applying said estimate of sensor errors to said displacement measurements, thereby generating error-compensated displacements, and

adding said error-compensated displacements to said estimate of position location at said point of interest, yielding said position location of each of said cooperative devices at said point of interest and said displacement points.

26. A system for determining the position of a plurality of cooperative users, comprising:

a plurality of transmitters that broadcast digital transmissions, wherein each of said digital transmissions embeds at least a known periodic code;

a broadcast digital transmission receiver that keeps a time base and determines a measured time of arrival of said known periodic code in a broadcast digital transmission relative to said time base;

a data link transceiver that keeps a time base, sends and receives ranging messages, determines a send and receive time of said ranging messages relative to said time base, and exchanges said time of arrival;

a displacement sensor that determines a distance travelled and orientation changed during a displacement relative to a common coordinate frame;

a database that holds a location of each of said transmitters in said common coordinate frame, and;

a processor for determining a relative range between said transceivers based on said send and receive time of said ranging messages and a differential range between said cooperative users based on measured time of arrival of each of said transmitters; and

determining a position location of said cooperative users based on said relative range, said differential range, and said displacement.

27. The assembly according to claim 26, wherein said receiver, said transceiver, said displacement sensor, and said processor are integrally formed in a common assembly.