Self-calibrating position location using periodic codes in broadcast digital transmissions

• US 7,388,541 B1
• Filed: 11/27/2006
• Issued: 06/17/2008
• Est. Priority Date: 07/25/2005
• Status: Expired due to Fees

• Current Assignee: Chun Yang
• Original Assignee: Chun Yang
• Inventors: Yang, Chun
• Primary Examiner(s): Tarcza; Thomas H.
• Assistant Examiner(s): Mull; Fred H.
• Application Number:
  US11/604,151
• Time in Patent Office: 568 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.12, 342/357.15, 342463-464
• US Class Current: 342/464
• CPC Class Codes: G01C 21/206 specially adapted for indoor navigation
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence

Abstract

A broadcast digital transmission (BDT) receiver, computer-readable media, and associated method for receiving and processing of BDT signals from a plurality of transmitters. A BDT receiver includes an antenna to intercept broadcast radio signals and an analog front-end to down-convert it to a suitable frequency for digitization. A baseband signal processor acquires and tracks designated codes in BDT signals using a generalized correlator to produce time of arrival measurements thereof. A data processor, coupled to the baseband signal processor and with input from an auxiliary sensor and a digital database, first calibrates time offsets of said transmitters relative to the BDT receiver'"'"'s time base and then operates on offset-adjusted time of arrival measurements to produce a position solution.

Claims

1. In a self-calibrating position location system utilizing a plurality of transmitters that broadcast digital multimedia signals, a method of obtaining a position solution for a user receiver, comprising the steps of:

receiving broadcast digital transmissions from at least some of said transmitters, wherein each of said broadcast digital transmissions embeds at least one known periodic code, and wherein each of said transmitters has a transmitter phase center;

providing a user receiver that generates a time base;

determining a measured time of arrival of said known periodic code at said user receiver relative to said time base of said user receiver;

estimating a phase center of said antenna of said user receiver, therein producing a receiver phase center;

calculating, at said user receiver, self-calibrating time offsets from said transmitter phase center and said receiver phase center

calculating a predicted time of arrival of said known periodic code for said transmitters based on said self-calibrating time offsets; and

determining a position of said user receiver based on said measured time of arrival and said predicted time of arrival of each of said transmitters.

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

3. The method according to claim 1, wherein each said broadcast digital transmission is a broadcast digital television signal and each said known periodic code is a combination of a synchronization code embedded in said broadcast digital transmission signal and a modulated pseudonoise sequence superimposed onto said broadcast digital television signal.

4. The method according to claim 3, wherein said broadcast digital transmission signal is an advanced television systems committee signal;

and said synchronization code is a combination of a field synchronization segment and a segment synchronization code within an advanced television systems committee signal frame.

5. The method according to claim 1, wherein said step of receiving broadcast digital transmissions further includes the substeps of:

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

turning a local oscillator to 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 incoming signal time samples.

6. The method according to claim 1, 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;

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

7. The method according to claim 6, wherein said step of maintaining lock onto said known periodic code of said transmitters, further includes the substeps of:

generating an integrated delay-Doppler map of complex spectrum filtering correlations;

processing said integrated delay-Doppler map of complex spectrum filtering correlations through a joint code delay, carrier phase and frequency error discriminator, yielding a joint code delay, carrier phase and frequency error;

processing said joint code delay, carrier phase and frequency error through a joint code and carrier tracking filter, yielding a predicted code delay, carrier phase and frequency for a next data window; and

sending said predicted code delay and carrier phase and frequency as code and carrier feedbacks to a spectrum filtering correlator, therein closing a code feedback loop and a carrier feedback loop.

8. The method according to claim 7, wherein said joint code and carrier tracking filter is a Kalman filter based on a coupled kinematic model of code delay, carrier phase and frequency.

9. The method according to claim 7, wherein said step of generating an integrated delay-Doppler map of complex spectrum filtering correlations, further includes the substeps of:

selecting a number of search intervals to be used as a decision block;

partitioning the number of search intervals into coherent integration intervals and incoherent integration intervals within each said decision block;

obtaining a coherently integrated delay-Doppler map of complex generalized correlations up to said coherent integration intervals; and

making an incoherent integration up to said incoherent integration intervals, yielding said integrated delay-Doppler map of complex spectrum filtering correlations.

10. The method according to claim 9, wherein said step of obtaining a coherently integrated delay-Doppler map of complex spectrum filtering correlations, further includes the substeps of:

obtaining incoming signal samples of several search intervals within said coherent integration interval;

applying an adjustment to said incoming signal samples, yielding frequency-adjusted samples;

summing up said frequency-adjusted samples per search interval on a sample-to-sample basis, therein yielding a pre-correlation coherent integration samples;

performing a spectrum filtering correlation between said pre-correlation coherent integration samples, therein yielding an coherently integrated generalized correlation as a function of delay; and

repeating said spectrum filtering correlation for a range of frequency feedback values, yielding said coherently integrated delay-Doppler map of complex spectrum filtering correlations.

11. The method according to claim 10, wherein said step of applying an adjustment to said incoming signal samples, further includes the substeps of:

obtaining an initial phase and a frequency offset estimate from a carrier frequency feedback;

generating a complex carrier replica with said initial phase and said frequency offset plus a nominal frequency; and

multiplying said complex carrier replica to incoming signal samples, yielding a phase-rotation adjustment to said incoming signal samples.

12. The method according to claim 10, wherein said step of obtaining incoming signal samples of several search intervals within said coherent integration interval, further includes the substep of windowing signal sampling and buffering operation in sync with a duty cycle of known periodic code within a repetition interval in a tracking mode.

13. The method according to claim 9, wherein said step of generating a coherently integrated delay-Doppler map of complex spectrum filtering correlations up to coherent integration interval, for a received signal subject to large frequency error, further includes the substeps of:

generating a delay-Doppler map of complex spectrum filtering correlations for each code repetition interval within said coherent integration interval;

padding zeros before and behind each delay-Doppler map point so as to maintain a uniform timely order relative other repetition intervals within said coherent integration interval, therein producing a zero-padded delay-Doppler map;

taking a fast Fourier transform of said zero-padded delay-Doppler map; and

adding a fast Fourier transform of a repetition interval to a partial sum of an earlier repetition interval, therein yielding said coherently integrated delay-Doppler map.

14. The method according to claim 13, wherein said step of generating a delay-Doppler map of complex spectrum filtering correlations, further includes the substeps of:

filling an incoming signal time samples buffer of double code length, wherein said samples buffer includes a half buffer of oldest samples and a half buffer of newest samples;

shifting out said half buffer of oldest when subsequent samples are shifted in;

preparing a replica code time samples buffer wherein a known periodic code is appended with zeros of the same amount, yielding a zero-padded replica code sequence of double code length; and

applying spectrum filtering correlation between samples in said incoming signal time samples buffer and said replica code time samples buffer, yielding said delay-Doppler map of complex spectrum filtering correlations.

15. The method according to claim 14, wherein said step of filling an incoming signal time samples buffer of double code length, further includes the substep of windowing signal sampling and buffering operation in sync with a duty cycle of known periodic code within a repetition interval in a tracking mode.

16. The method according to claim 14, wherein said spectrum filtering correlation is a generalized frequency-domain correlation, wherein frequency feedback is used to remove residual frequency error by spectrum shifting and code feedback is used to select correlations around main lobe and to place a sample on peak.

17. The method according to claim 6, wherein said step of determining a direct correlation peak, further includes the substeps of:

obtaining an integrated delay-Doppler map of complex spectrum filtering correlations for each of said transmitters; and

detecting a first peak in said integrated delay-Doppler map that exceeds a pre-defined threshold, therein yielding said direct correlation peak.

18. The method according to claim 1, wherein said step of calculating a predicted time of arrival of said known periodic code, further includes the substeps of:

calculating a line of sight distance between said location of each of said transmitters and said approximate location of said user receiver;

dividing an adjusted line of sight distance by a tropospheric propagation velocity of light, yielding an approximate time of flight from each of said transmitters to said user receiver; and

applying said self-calibrating time offsets for each of said transmitters to said approximate time of flight, yielding said predicted time of arrival of each of said transmitters.

19. The method according to claim 18, wherein said step of calculating a line of sight distance between said location of each of said transmitters and said approximate location of said user receiver, further includes the substeps of:

obtaining said location of each of said transmitters from at least one digital database; and

obtaining said approximate location of said user receiver in a general geographic area through a combination of an input from a user, a supply from at least an auxiliary sensor, a digital database, an estimate from measured signal strength plus propagation loss versus transmitter power, and a previous position location.

20. The method according to claim 18, wherein said step of dividing an adjusted line of sight distance by a tropospheric propagation velocity of light, further includes the substeps of:

adjusting said line of sight distance for topographic distortion caused by terrain elevation in a vicinity of said user receiver when a two-dimensional position solution is sought, yielding an adjusted line of sight distance; and

obtaining a tropospheric propagation velocity of light according to weather conditions in a vicinity of said user receiver.

21. The method according to claim 18, wherein said step of applying said self-calibrating time offsets for each of said transmitters, in a point calibration procedure, further includes the substep of:

obtaining a measured time of arrival for each of said transmitters relative to said user receiver time base;

obtaining a time of flight from each of said transmitters to said user receiver;

subtracting said time of arrival from said time of flight, yielding a time of transmission relative to said time base; and

averaging said time of transmission relative to said time base at least at one time and at least at one location, yielding said self-calibration time offsets for each of said transmitters.

22. The method according to claim 21, wherein said step of obtaining a time of flight from each of said transmitters to said user receiver, further includes the substeps of:

obtaining a location of each of said transmitters from at least one digital database;

obtaining a precise location of said user receiver in a general geographic area from a list of location input choices;

calculating a line of sight distance between said location of each of said transmitters and said location of said user receiver;

adjusting said line of sight distance for topographic distortion caused by terrain elevation in a vicinity of said user receiver when a two-dimensional position solution is sought, therein yielding an adjusted line of sight distance; and

dividing said adjusted line of sight distance by a tropospheric propagation velocity of light, yielding said time of flight from each of said transmitters to user receiver.

23. The method according to claim 22, wherein said list of location input choices is selected from a group consisting of at least location input from a user, location referenced to from a digital map, location on a known landmark, location at a street intersection, location at a check point, location at an entrance/exit of a building, location read from barcodes and RF tags, location from a GPS receiver, location from a dead-reckoning device, self-positioning via integer ambiguity resolution for multi-wavelength measurements, and a combination of the above and alike.

24. The method according to claim 1, wherein said step of determining a position of said user receiver, further includes the substeps of:

subtracting said predicted time of arrival from said measured time of arrival, yielding a time of arrival prediction error for each of said transmitters, wherein said time of arrival prediction error is arranged into a vector of time of arrival prediction errors for ensemble of said transmitters;

obtaining a line of sight vector from said user receiver to each of said transmitters, wherein said line of sight vector is arranged into a geometry scaling matrix of line of sight vectors for ensemble of said transmitters;

applying a least-square estimator based on said vector of time of arrival prediction errors and said geometry scaling matrix of line of sight vectors, yielding an estimate of location error of said user receiver; and

adding said estimate of location error to said approximate location, yielding said position of said user receiver.

25. The method according to claim 1, wherein said step of determining a position of said user receiver, further includes the substeps of:

subtracting said predicted time of arrival from said measured time of arrival, yielding a time of arrival prediction error for each of said transmitters at each of said calibration points, wherein said time of arrival prediction error is arranged into a vector of time of arrival prediction errors;

obtaining an augmented line of sight vector from said user receiver to each of said transmitters at each of said calibration points, wherein said augmented line of sight vector is arranged into a geometry scaling matrix of augmented line of sight vectors;

applying a least-square estimator based on said vector of time of arrival prediction errors and said geometry scaling matrix of line of sight vectors, yielding an estimate of location error of said user receiver; and

adding said estimate of location error to said approximate location, yielding said position of said user receiver.

26. The method according to claim 25, wherein said step of obtaining a predicted time of arrival for calibration points, further includes the substeps of:

determining a minimal number of calibration points for said displacement calibration procedure based on a number of transmitters available;

obtaining a displacement vector to each of said calibration points within said displacement calibration procedure from a list of input choices;

adding to said approximate location said displacement vectors successively, yielding an approximate location at each of said calibration points; and

obtaining a predicted time of arrival for each of calibration points based on said approximate location at each of said calibration points and a location of each of said transmitters.

27. The method according to claim 26, wherein said list of input choices is selected from a group consisting of at least an inertial measurement unit mechanized relative to said approximate user location, an automotive dead reckoning system, and an indoor dead reckoning system.

28. The method according to claim 25, wherein said step of obtaining an augmented line of sight vector from said user receiver to each of said transmitters at each of said calibration points, further includes the substeps of:

obtaining a line of sight vector from said user receiver to each of said transmitters at each of said calibration points; and

increasing the dimension of said line of sight vector by one wherein an unit entry is inserted for each of said transmitters, yielding said augmented line of sight vector.

29. The method according to claim 1, wherein said step of determining a position of said user receiver, further includes the substeps of:

obtaining a predicted time of arrival based on a predicted position of said user receiver from an auxiliary sensor, an initial estimate of time offset of each of said transmitters, and a location of each of said transmitters;

subtracting said predicted time of arrival from said measured time of arrival, yielding a time of arrival prediction error, wherein said time of arrival prediction error is arranged into a vector of time of arrival prediction errors for ensemble of said transmitters;

updating an error state estimate of an integration Kalman filter with said vector of time of arrival prediction errors, yielding an updated error state estimate, wherein said error state includes at least position errors, time offset errors, and auxiliary sensor parameter errors; and

adding said updated error state estimate to said predicted position, yielding said position of said user receiver.

30. The method according to claim 29, wherein said auxiliary sensor is a combination of an inertial navigation system, an automotive dead reckoning system, an indoor dead reckoning system, and a GPS receiver when GPS signal is available.