Methods and system for multi-path mitigation in tracking objects using reduced attenuation RF technology

• US 7,872,583 B1
• Filed: 07/14/2009
• Issued: 01/18/2011
• Est. Priority Date: 12/15/2005
• Status: Active Grant

• Current Assignee: Qualcomm Technologies Incorporated (Qualcomm, Inc.)
• Original Assignee: InvisiTrack, Inc.
• Inventors: Markhovsky, Felix, Prevatt, Truman, Yushkov, Andrey, Weill, Lawrence, Zhulanov, Vladimir
• Primary Examiner(s): Bugg; George A
• Assistant Examiner(s): Labbees; Edny
• Application Number:
  US12/502,809
• Time in Patent Office: 553 Days
• Field of Search: 3405721-5729, 340/539.13, 340/825.49, 340/568.1, 340/541, 340/573.1, 342/47, 342/204, 702/158, 235375-385, 455/425, 455/560
• US Class Current: 340/572.1
• CPC Class Codes: G01S 13/767 Responders; Transponders teaching or practice apparatus for gun-aiming or gun-laying using reflecting targets or active targets F41G3/26
• CPC Class Codes: G01S 2013/466 by Trilateration, i.e. two antennas or two sensors determine separately the distance to a target, whereby with the knowledge of the baseline length, i.e. the distance between the antennas or sensors, the position data of the target is determined
• CPC Class Codes: G01S 2013/468 by Triangulation, i.e. two antennas or two sensors determine separately the bearing, direction or angle to a target, whereby with the knowledge of the baseline length, the position data of the target is determined

Abstract

A method and system for a long range Radio Frequency (RF)-based identification, tracking and locating of objects. The method and system use a narrow bandwidth ranging signal(s), including VHF of lower frequency bands, which minimizes propagation loss and loss of accuracy of the RF locating signals. The method and system includes narrow bandwidth ranging signal multi-path mitigations processor, which further improves the track-locate accuracy. The signal is sent from a Master Unit(s) to a Tag. The signal traveling time is recorded and the distance between the Master(s) and the Tag is calculated. The method and system allow achieving a longer distance of the RF narrow bandwidth ranging signal penetration and an increased accuracy by using VHF bands in conjunction with the narrow bandwidth ranging signal multi-path mitigations processor. The techniques of Digital Signal Processing and Software-Defined Radio are used. The actual waveforms transmitted and received by the radios are defined by the software. The roles of the Master Unit(s) and the Tag can be reversed.

Claims

1. A system for RF-based tracking and locating objects, comprising:

a Master Unit having an RF transceiver and adapted to interface to a Tag to measure distance to the Tag;

the Master Unit having an RF transceiver and adapted to interface to one or more Masters to measure distance to between Masters; and

the Tag having an RF transceiver and adapted to interface to the Master Unit; and

the Master Unit having an RF transceiver and adapted to interface to one or more Master Units,

wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal;

the RF transceiver of the Master Unit and the RF transceiver(s) of one or more Master Units are configured to transmit and receive a ranging signal,

wherein the RF transceivers of all Master Units are configured to transmit a ranging signal,

wherein the RF transceiver of the Tag is configured to receive a ranging signal;

wherein the RF transceivers of all Master Units are configured to receive a ranging signal

wherein the ranging signal includes multiple pulses at different frequencies,

wherein the ranging signal is used for measuring the distance between the Master Unit and the Tag, and all Master Units; and

wherein a high-resolution spectrum estimation analysis is used to reduce spatial ambiguity in the distance measurement, including estimating a model size for a number of (GB) frequency components, and calculating the distance based on a distribution of the frequency components.

2. The system of claim 1, wherein the ranging signal is a widebandwidth signal.

3. The system of claim 1, wherein the system uses different individual frequency components to generate a ranging signal and a base-band ranging signal.

4. The system of claim 1, wherein system clocks synchronization between one or more master Unit(s) and one or more Tag Unit(s) is periodically performed remotely by adjusting each Unit clocks frequency, wherein each Master Unit calculates and stores the difference between its system clocks frequency and other Unit(s) clocks frequencies, and wherein each master Unit and/or Tag adjusts complex amplitude measurements for the difference between its system clocks frequency and other Unit(s) system clocks frequencies.

5. The system of claim 1, wherein the ranging signal is a narrow bandwidth signal.

6. The system of claim 1, wherein different frequency components of the ranging signal and a base-band ranging signal are pseudorandomly selected, the components are contiguous and/or spaced apart in frequency and/or time.

7. The system of claim 6, wherein the Master and Tag receivers determine complex amplitude of the received ranging signal and the base-band ranging signal, and

wherein complex amplitude samples of the multiple received ranging signal/base-band ranging signal individual frequency components samples are averaged to improve the complex amplitude determination accuracy by increasing the Signal to Noise Ratio.

8. The system of claim 7, wherein multiple received ranging signals'"'"' complex amplitude values are determined using matched filtering techniques.

9. The system of claim 7, wherein multiple received ranging signal complex amplitude values are calculated from the received ranging signal/base-band ranging signal individual frequency components RSSI values and from phase values of the received ranging signal and the base-band ranging signal individual frequency components.

10. The system of claim 9, wherein the received ranging signal and the base-band ranging signal individual frequency components phase values are calculated via comparison of the received ranging signal individual frequency components phase values with the transmitted (original) ranging signal individual frequency components phase values.

11. The system of claim 6, wherein multiple received ranging signal complex amplitude phase values are calculated from differences in phase values of two or more of the returned ranging signal and the base-band ranging signal individual frequency components.

12. The system of claim 6, wherein complex amplitude values of the multiple received ranging signal/base-band ranging signal individual frequency components are transformed from the roundtrip values to one-way complex amplitude values.

13. The system of claim 6, wherein multiple received ranging signal/base-band ranging signal individual frequency components complex amplitude values are obtained by sampling the received base band signal individual component frequency with a corresponding outgoing base band signal individual component frequency and integrating the resulting signal over period of time that is less than or equal to the time duration of the base band signal individual component frequency.

14. The system of claim 6, wherein the multiple received ranging signal/base-band ranging signal individual frequency components complex amplitude values are assembled into a synthetic ranging signal with a larger bandwidth.

15. The system of claim 14, wherein the synthetic ranging signal has a sinusoidal waveform pre-cursor of the synthetic ranging signal cancelled out by constructing a waveform that closely approximates the signal on a selected interval, and then subtracting it from the original synthetic ranging signal.

16. The system of claim 8, wherein the received ranging signal and the base-band ranging signal individual frequency components are filtered by only two digital filters, wherein one filter is always tuned for first frequency component and the other filter is dynamically tuned for all other frequencies components, and wherein multiple instances of ranging signal are sent by the Master Unit and each instance consists of only two frequencies, a first frequency f₁ and a second frequency f_i, where i∈

2;

n.

17. The system of claim 8, wherein the received ranging signal and the base-band ranging signal individual frequency components are filtered with two or more digital filters without dynamic filter tuning by generating the rest of the frequency components by adjusting the Master Unit and the Tag Unit RF transceivers'"'"' frequency synthesizers/operating frequency.

18. The system of claim 9, wherein two measurements at the same frequency are made in order to cancel a phase offset that might develop after changing a synthesizer'"'"'s frequency.

19. The system of claim 1, wherein the received ranging signal and the base-band ranging signal individual frequency components are determined via Fourier transforms.

20. The system of claim 1, wherein the transmitted ranging signal and a base-band ranging signal is determined by using Fourier transforms.

21. The system of claim 1, wherein the high-resolution spectrum estimation analysis uses MUSIC/rootMUSIC and ESPRIT algorithms.

22. The system of claim 1, wherein high-resolution spectrum estimation analysis uses the F-statistics to estimate the number of ranging signal reflections.

23. The system of claim 22, wherein the high-resolution spectrum estimation analysis combines two or more algorithms that estimate individual frequencies by using different eigenstructure properties to further reduce the direct path delay and other path delay determination ambiguity.

24. The system of claim 23, wherein the high-resolution spectrum analysis adjusts the model size for each model using an F-statistic and depending upon the high-resolution spectrum estimation algorithm properties.

25. The system of claim 23, wherein the high-resolution spectrum estimation analysis uses a window of model sizes in order to maximize a probability of detecting the direct path signal.

26. The system of claim 25, wherein the high-resolution spectrum estimation analysis uses multiple measurements of the received signal and data generated from windows multiple model sizes from two or more spectrum estimation algorithms, and performs cluster analysis on the multiple measurements and data to generate the distance estimate.

27. The system of claim 26, wherein the cluster analysis includes multimodal cluster analysis that estimates an equivalent range of the received multipath components.

28. The system of claim 27, wherein the high-resolution spectrum analysis operates on the data returned by the multimodal analysis of the range estimates and combines statistically identical estimates to achieve a higher range estimate accuracy.

29. The system of claim 1, wherein in addition to the high-resolution spectrum analysis is a parameter estimation analysis is employed to distinguish a signal Direct Line Of Sight (DLOS) path from other multi-paths with high accuracy using individual frequency components complex amplitude values.

30. The system of claim 1, wherein modulation of the ranging signal includes any of Spread Spectrum, Chirp Spread Spectrum and Frequency Hopping.

31. The system of claim 1, wherein the ranging signal is a discrete or continuous chirp, and wherein each chirp is started at the same phase, and one or more chirps are transmitted and received by the Master Unit.

32. The system of claim 31, wherein the processor aligns each received individual chirp so that the returned chirp is from the middle of an area of interest and then “

deramps”

each individual returned chirp.

33. The system of claim 32, wherein the processor assembles results of individually “

deramped”

chirps and produces complex amplitude samples/values.

34. The system of claim 1, wherein the ranging signal is processed using Digital Signal Processing (DSP) and Software-Defined Radio (SDR).

35. The system of claim 1, wherein the ranging signal is in no higher than VHF band.

36. The system of claim 1, wherein the ranging signal is in the UHF band and higher frequencies.

37. The system of claim 1, wherein one of the Master Units operates in a single originating reader mode and the other Master Units operate in a satellite mode and Master-to-Master distance measurement mode.

38. The system of claim 37, wherein each Tag receives a first and second ranging signals sequences, the first ranging signal sequence being generated by the originating Master Unit and the second ranging signal sequence is re-transmitted by the satellite Master Unit, and

wherein each ranging signal sequence is processed separately by the Tag to determine a time delay during distance measurement and each Tag calculates the time of flight for each of the ranging signals.

39. The system of claim 38, wherein a difference between the times of flight of the first and second ranging signals is used to determine position of the Tag relative to the Master Units,

wherein Master-Tag and Master-Master distance measurements are performed using any of Differential Time of Arrival (DTOA) and a combination of DTOA, Virtual triangulation and Reverse Virtual Triangulation.

40. The system of claim 1, wherein Master-Tag or Master-Master distance measurements are performed using any of Time of Arrival (TOA) and a combination of TOA, Virtual triangulation and Reverse Virtual Triangulation.

41. The system of claim 1, wherein the high-resolution spectrum estimation analysis utilizes eigenvalues of the covariance matrix of baseband ranging signal samples,

wherein the covariance matrix provides an estimation of individual frequencies that are representative of path delays, and

wherein the eigenvalues are separated into orthogonal noise and signal eigenvectors (subspaces) and the individual frequencies are determined by projecting the observable return signal onto the noise subspace and minimizing an energy of the projection,

wherein a rotation operator is determined from a rotation-invariant signal subspace property, and individual frequencies are estimated from the rotation operator.

42. The system of claim 1, wherein communications between Master and Master and/or Master and Tag(s) are full-duplex or half duplex.

43. The system of claim 1, wherein communications between Master and Master and/or Master and Tag(s) are simplex.

44. The system of claim 1, wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal in full-duplex or half duplex and,

the RF transceiver of the Master and the RF transceiver(s) of one or more Master Units are configured to transmit and receive a ranging signal, in full-duplex or half duplex.

45. The system of claim 1, wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal in simplex and,

the RF transceiver of the Master Unit and the RF transceiver(s) of one or more Master Units are configured to transmit and receive a ranging signal in simplex.

46. A system for RF-based tracking and locating objects, comprising:

a Master Unit having an RF transceiver and adapted to interface to a Tag to measure distance to the Tag, and adapted to interface to one or more Masters to measure distance to between Masters; and

the Tag having an RF transceiver and adapted to interface to at least one Master Unit; and

the Master Unit having an RF transceiver and adapted to interface to one or more Master Units,

wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal;

the RF transceiver of the Master Unit and the RF transceiver(s) of one or more Master Units are configured to transmit and receive a ranging signal,

wherein the RF transceivers of all Master Units are configured to transmit a ranging signal,

wherein the RF transceiver of the Tag is configured to receive a ranging signal;

wherein the RF transceivers of all Master Units are configured to receive a ranging signal,

wherein the ranging signal includes multiple pulses at different frequencies,

wherein different frequency components of the ranging signal and a base-band ranging signal are pseudorandomly selected, the components are contiguous and/or spaced apart in frequency and/or time,

wherein the ranging signal is used for measuring the distance between the Master Unit and the Tag, and all Master Units; and

wherein the system calculates the complex amplitude of the received ranging signal.

47. A system for RF-based tracking and locating objects, comprising:

a Master Unit having an RF transceiver and adapted to interface to a Tag to measure distance to the Tag;

the Tag having an RF transceiver and adapted to interface to the Master Unit;

the RF transceiver of the Master Unit and the RF transceiver of the Tag being configured to transmit and receive a narrow bandwidth ranging signal in a UHF band; and

the RF transceiver of the Master Unit being configured to transmit a narrow bandwidth ranging signal in a UHF band;

the RF transceiver of the Tag being configured to receive a narrow bandwidth ranging signal in the UHF band,

wherein the narrow bandwidth ranging signal includes one or more multiple pulses at different frequencies,

wherein the narrow bandwidth ranging signal includes one or more multiple pulses at the same frequency,

wherein the ranging signal includes any of (a) one pulse at multiple frequencies, (b) multiple pulses at a single frequency, and (c) multiple pulses at different frequencies,

wherein different frequency components of the ranging signal and a base-band ranging signal are pseudorandomly selected, the components are contiguous and/or spaced apart in frequency and/or time.

48. A system for RF-based tracking and locating objects, comprising:

a Master Unit having an RF transceiver and adapted to interface to a Tag to measure distance to the tag;

a Master Unit having an RF transceiver and adapted to interface to one or more Master Units to measure distance between the Master Units; and

the Tag having an RF transceiver and adapted to interface to the Master Unit; and

the Master Unit having an RF transceiver and adapted to interface to one or more Master Units,

wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal;

the RF transceiver of the Master Unit and the RF transceiver(s) of one or more Master Units are configured to transmit and receive a ranging signal,

wherein the RF transceivers of all Master Units are configured to transmit a ranging signal,

wherein the RF transceiver of the Tag is configured to receive a ranging signal;

wherein the RF transceivers of all Master Units are configured to receive a ranging signal,

wherein the ranging signal includes any of (a) one pulse at multiple frequencies, (b) multiple pulses at a single frequency, and (c) multiple pulses at different frequencies,

wherein different frequency components of the ranging signal and a base-band ranging signal are pseudorandomly selected, the components are contiguous and/or spaced apart in frequency and/or time, and

wherein a high-resolution spectrum estimation analysis is used to reduce spatial ambiguity in the distance measurement, including estimating a model size for a number of multi-path frequency components, and calculating the distance based on a distribution of the frequency components.

49. A system for RF-based tracking and locating objects, comprising:

a Master Unit having an RF transceiver and adapted to interface to a Tag and/or another master unit to measure distance to the Tag and/or another master unit; and

the Tag and or another master unit having an RF transceiver and adapted to interface to the Master Unit,

wherein Master unit having an RF transceiver and adapted to interface to the another Master Unit,

wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal,

wherein the RF transceiver of the Master Unit is configured to transmit a ranging signal, wherein the RF transceiver the Tag is configured to receive a ranging signal,

wherein the ranging signal includes any of (a) one pulse at multiple frequencies, (b) multiple pulses at a single frequency, and (c) multiple pulses at different frequencies,

wherein the ranging signal is used for measuring the distance between the Master Unit and the Tag,

wherein the ranging signal is used for measuring the distance between multiple Master Units and

wherein the system calculates the complex amplitude of the received ranging signal to determine Master-Tag distance and/or Master Unit to Master Unit distance.

50. A system for RF-based tracking and locating objects, comprising:

a Master Unit having an RF transceiver and adapted to interface to a Tag to measure distance to the Tag;

a Master Unit having an RF transceiver and adapted to interface to one or more Master Units to measure distance to between the Master Units; and

the Tag having an RF transceiver and adapted to interface to the Master Unit; and

Master having an RF transceiver and adapted to interface to one or more Master Units,

wherein the RF transceiver of the Master Unit and the RF transceiver of the Tag are configured to transmit and receive a ranging signal;

the RF transceiver of the Master Unit and the RF transceiver(s) of one or more Master Units are configured to transmit and receive a ranging signal,

wherein the RF transceivers of all Master Units are configured to transmit a ranging signal,

wherein the RF transceiver of the Tag is configured to receive a ranging signal;

wherein the RF transceivers of all Master Units are configured to receive a ranging signal, wherein different frequency components of the ranging signal and a base-band ranging signal are pseudorandomly selected, wherein (a) the components are contiguous or spaced apart in frequency, (b) the components are generated at the same time and/or spaced apart in time, or (c) a combination of (a) and (b) and

wherein different frequency components of the ranging signal and a base-band ranging signal are pseudorandomly selected, the components are contiguous and/or spaced apart in frequency and/or time.