System and method for locating objects and communicating with the same

• US 7,646,330 B2
• Filed: 12/20/2005
• Issued: 01/12/2010
• Est. Priority Date: 03/14/2005
• Status: Active Grant

• Current Assignee: Santa Mionica Semiconductor
• Original Assignee: Alfred E. Mann Foundation For Scientific Research
• Inventors: Karr, Lawrence J.
• Primary Examiner(s): Gregory; Bernarr E
• Application Number:
  US11/885,843
• Publication Number:
  US 20080165059A1
• Time in Patent Office: 1,484 Days
• Field of Search: 342 29- 51, 342/118, 342/125, 342/145, 342/175, 342192-197, 342450-465, 340901-904, 340933-935, 340/568.1, 340/571, 340 72- 746, 340 101- 106, 340/500, 340/501, 340/514, 340/531, 340/539.1, 340/539.11, 340/539.15, 340/539.3, 340/988, 340/989, 340/993, 340/825, 340/825.36
• US Class Current: 342/44
• CPC Class Codes: G01S 13/765 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence

Abstract

Communication between a remote locator and a transponder is used to determine the relative position of the transponder. The transponder and locator each include a transmitter and a receiver. The locator transmits an inquiry in the form of a relatively powerful cyclically encoded signal with repetitive elements, uniquely associated with a target transponder. Periodically, each transponder correlates its coded ID against a possible inquiry signal, determining frequency, phase and framing in the process. Upon a match, the transponder transmits a synthesized response coherent with the received signal. The locator integrates multiple cyclical response elements, allowing low-power transmissions from the transponder. The locator correlates the integrated response, determines round-trip Doppler shift, time-of-flight, and then computes the distance and angle to the transponder. The transponder can be wearable, bionically implanted, or attached to, or embedded in, some object.

Claims

1. A method for locating a transponder (MT) with a remote locator (RL), the method comprising:

selecting an identification code (ID Code) for transmission from the RL to at least one MT, wherein each of the at least one MT has a specific associated ID Code;

generating a transmission signal for transmission by the RL, the transmission signal comprising;

a first pattern that is repeated over a first transmission sequence, wherein the first transmission sequence contains a first portion of the selected ID code; and

a second pattern that is cyclically shifted over a second transmission sequence such that a first one of the second pattern is cyclically shifted relative to a second one of the second pattern in the second transmission sequence, wherein the second transmission sequence contains a second portion of the selected ID code;

transmitting the transmission signal from the RL for reception by the MT at a first time;

receiving at least a portion of the transmission signal from the RL with the MT to provide a received signal;

correlating at least a first portion of the received signal with at least a first portion of a stored ID Code in the MT to detect the presence of the first portion of the selected ID Code in the first portion of the received signal;

upon detection of the first portion of the selected ID Code in the first portion of the received signal, further correlating at least a second portion of the received signal with at least a second portion of the stored ID Code in the MT to detect the presence of the second portion of the selected ID Code in the second portion of the received signal;

upon detection of the second portion of the selected ID Code in the second portion of the received signal, transmitting an acknowledgement signal from the MT to the RL;

receiving the acknowledgement signal from the MT with the RL at a second time; and

determining a distance between the RL and the MT as a function of an elapsed time between the first time and the second time.

2. The method of claim 1, wherein the first portion of the selected ID code is the same as the second portion of the selected ID code.

3. The method of claim 1, wherein the second pattern that is cyclically shifted over the second transmission sequence such that the first one of the second pattern is cyclically shifted relative to the second one of the second pattern in the second transmission sequence according to a step size, wherein the step size comprises at least one of:

an integer bit shift, a non-integer bit shift, a fractional bit shift, and a pattern timing change.

4. The method of claim 1, wherein the generating the transmission signal further comprises:

combining the first transmission sequence and the second transmission sequence in the transmission signal such that the first transmission sequence and the second transmission sequence overlap one another.

5. The method of claim 1, wherein the generating the transmission signal further comprises:

arranging the first transmission sequence and the second transmission sequence in the transmission signal such that one of the first transmission sequence and the second transmission sequence follows in succession to the other of the first transmission sequence and the second transmission sequence.

6. The method of claim 1, wherein transmitting the transmission signal from the RL to the MT comprises:

transmitting the transmission signal during a first time period; and

wherein receiving at least the portion of the transmission signal from the RL with the MT comprises;

receiving the at least the portion of the transmission signal during a second time period that is substantially less than the first time period, and wherein the second time period overlaps with at least a portion of the first time period.

7. The method of claim 1, further comprising:

receiving at least a portion of the acknowledgement signal from the MT with the RL during a third time period; and

wherein transmitting the acknowledgement signal from the MT to the RL comprises;

transmitting the acknowledgement during the third time period with the MT.

8. The method of claim 1, wherein transmitting the transmission signal from the RL to the MT comprises:

transmitting the transmission signal at a first power level during a first time period with the RL; and

wherein transmitting the acknowledgement signal from the MT to the RL comprises transmitting the acknowledgement at a second power level during a third time period with the MT, wherein the first power level is at least an order of magnitude greater than the second power level.

9. The method of claim 1, further comprising:

adjusting a synthesized frequency associated with the MT, wherein the synthesized frequency is adjusted according to at least one of a frequency, timing, phase, frequency offset, and cadence associated with the transmitter in the MT based upon the received signal, and wherein transmitting the acknowledgement signal from the MT to the RL comprises transmitting the acknowledgement signal with the synthesized frequency in the MT.

10. The method of claim 9, wherein the received signal is Doppler shifted relative to the transmitted signal from the RL such that the synthesized frequency corresponds to synthesized version of the Doppler shifted signal.

11. The method of claim 10, wherein the received acknowledgment signal is Doppler shifted relative to the transmitted acknowledgement signal from the MT such that the received acknowledgement signal corresponds to a synthetic round-trip Doppler shifted signal.

12. The method of claim 9, wherein the internal clocking mechanisms of both the RL and the MT each have a sufficient short-term stability to permit the MT to reply to the RL with an exactly synthesized frequency with negligible error.

13. The method of claim 1, wherein generating a transmission signal further comprises:

generating a third pattern that is repeated over a third transmission sequence, wherein the third transmission sequence contains a third portion of the selected ID Code, and wherein the third transmission sequence is encoded with a message for the MT.

14. The method of claim 13, further comprising:

partitioning the selected ID Code into at least one of;

equally sized first, second, and third portions;

differently sized first, second, and third portions;

equally sized first and second portions where the third portion is different in size from the first and second portions;

equally sized first and third portion where the second portion is different in size from the first and third portions, and equally sized second and third portion where the first portion is different in size from the second and third portions.

15. The method of claim 13, wherein encoding the third portion of the message for the MT comprises encoding the message in the third transmission frame with an error correction code.

16. The method of claim 13, wherein the message for the MT comprises a command and control message.

17. The method of claim 13, further comprising:

transmitting the first transmission sequence, the second transmission sequence, and the third transmission sequence in succession to one another.

18. The method of claim 1, wherein transmitting the transmission signal from the RL comprises modulating the transmission signal for at least one of:

a multi-phase shift keying (MPSK) pattern, a binary-phase shift keying (BPSK) pattern, a quadrature phase shift keying (QPSK) pattern, a differential phase shift keyed (DPSK) pattern, a continuous phase modulation (CPM) pattern, and a multiple amplitude and phase shift keying (MAPSK) pattern.

19. The method of claim 1, wherein transmitting the transmission signal comprises transmitting the transmission signal with a transmitter in the RL, and wherein receiving at least the portion of the transmission signal comprises receiving the at least the portion of the transmission signal with a receiver in the RL, and wherein the transmitter in the RL and the receiver in the MT are phase and frequency coherent with one another.

20. The method of claim 1, wherein transmitting the acknowledgement signal comprises transmitting the acknowledgement signal with a transmitter in the MT, and wherein receiving the acknowledgement signal comprises receiving the acknowledgement signal with a receiver in the RL, and wherein the transmitter in the MT and the receiver in the RL are phase and frequency coherent with one another.

21. The method of claim 1, wherein receiving the acknowledgement signal from the MT with the RL further comprises:

capturing at (east portion of the acknowledgment signal with the RL, and coherently accumulating the captured portion to provide an accumulated captured portion such that the signal-to-noise ratio associated with the captured acknowledgement signal is increased.

22. The method of claim 21, wherein the coherent accumulation is provided by at least one of:

a digital accumulator and an analog accumulator.

23. The method of claim 1, wherein transmitting the transmission signal from the RL for reception by the MT comprises:

operating a transmitter in the RL with a frequency reference to provide a transmitted signal;

wherein receiving at least a portion of the transmission signal from the RL with the MT comprises;

operating a receiver in the MT to capture at least a portion of the transmission signal, wherein the operating frequency and sampling clock associated with the receiver are phase locked to the frequency reference used in the transmitted signal; and

wherein transmitting an acknowledgement signal from the MT to the RL comprises;

operating a transmitter in the MT such that the receiver in the MT is frequency and phase coherent with the transmitter in the MT.

24. The method of claim 23, further comprising:

retrieving a second identification code (second ID Code) for transmission from the MT to the RL, wherein the second ID Code is associated with the MT; and

generating the acknowledgement signal for transmission by the MT, the acknowledgement signal comprising;

a fourth pattern that is repeated over a fourth sequence, wherein the fourth sequence contains a first portion of the second ID code; and

a fifth pattern that is cyclically shifted over a fifth sequence such that a first instance of the fifth pattern is cyclically shifted relative to a second instance of the fifth pattern in the fifth sequence, wherein the fifth sequence contains a second portion of the second ID code.

25. The method of claim 24, wherein the second ID is at least one of:

matched to the ID code, and different from the ID Code.

26. The method of claim 24, wherein the fourth pattern is at least one of:

matched to the first pattern, and different from the first pattern.

27. The method of claim 24, wherein the fifth pattern is at least one of:

matched to the second pattern, and different from the second pattern.

28. The method of claim 23, further comprising:

capturing portions of the acknowledgement signal with the RL;

correlating the capture portions of the acknowledgement signal with the RL,

summing the correlations associated with captured portions of the acknowledgement signal in the RL to provide an accumulated correlation, and

identifying a correlation match in the RL when the accumulated correlation indicates that the acknowledgement transmission is matched to at least a portion of the second ID Code that is associated with the MT.

29. The method of claim 23, further comprising:

capturing portions of the acknowledgement signal with the RL;

summing the captured portions of the acknowledgement signal to provide an accumulated signal; and

correlating the accumulated signal to provide an accumulated correlation, and

identifying a correlation match in the RL when the accumulated correlation indicates that the acknowledgement transmission is matched to at least a portion of the second ID Code that is associated with the MT.

30. The method of claim 29, further comprising:

cyclically selecting a different capture buffer in the RL for each subsequent captured portion of the acknowledgement signal when the captured portion of the acknowledgement signal corresponds to the fifth pattern, and coherently accumulating each cyclically rotated captured portion with the cyclically selected capture buffers to provide a coherently accumulated received pattern such that signal-to-noise ratio associated with reception in the RL is increased.

31. The method of claim 23, further comprising:

determining at least one of fine timing, phase, starting time, and cadence of the transmission associated with the MT by evaluating at least one correlation associated with the stored captured portions of the acknowledgement signal.

32. The method of claim 1, further comprising:

receiving a first portion of the transmission signal that is associated with the first transmission sequence at a first time in the MT;

correlating the received first portion of the transmission signal with the first portion of the ID Code in the MT;

receiving a second portion of the transmission signal at a second time with the MT; and

identifying a fine timing and a phase associated with a frame timing of the transmission signal from the RL when the received portions of the transmission signal in the MT correlate with the first portion of the ID Code.

33. The method of claim 32, further comprising:

refining frequency and timing estimates associated with the first frame timing with a subsequently received portion of the transmission signal that is associated with the first transmission sequence.

34. The method of claim 32, wherein identifying the fine timing and phase associated with the frame timing comprises:

estimating a frequency associated with the transmission signal from the RL, measuring a first phase associated with the received first portion of the transmission signal, measuring a second phase associated with the received second portion of the transmission signal, determining a difference between the first phase and the second phase, identifying a frequency offset associated with the frequency from the difference between the first phase and the second phase.

35. The method of claim 34, further comprising:

estimating a phase associated with the second portion of the transmission signal, and scheduling the reception of the first and second portions of the transmission signal at the first and second times such that a magnitude associated with a difference between the estimated phase and the second phase is in a range from 0 to 90 degrees.

36. The method of claim 32, further comprising:

receiving a third portion of the transmission signal at a third time in the MT, wherein the third portion of the transmission signal is associated with the first transmission sequence;

correlating the third portion of the transmission signal with the first portion of the ID Code in the MT; and

refining at least one of the frequency, frequency offset, timing, and phase estimates associated with the first frame timing with information determined from the received third portion of the transmission signal in the MT.

37. The method of claim 1, further comprising:

receiving a fourth portion of the transmission signal at a fourth time in the MT, wherein the fourth portion of the transmission signal is associated with the second transmission sequence;

correlating the received fourth portion of the transmission signal with the second portion of the ID Code in the MT; and

identifying a position within the second frame when the received fourth portion of the transmission signal correlates with the second portion of the ID Code in the MT.

38. The method of claim 37, further comprising:

completing a coarse timing acquisition base on the recovered correlated peak associated with the received portion of the transmission signal with the MT.

39. The method of claim 1, further comprising:

correlating the received signal with a third portion of the ID Code, wherein generating the transmission signal for transmission by the RL further comprises generating a third pattern that is repeated over a third transmission sequence, wherein the third transmission sequence contains the third portion of the selected ID code, and wherein a message is encoded in the third transmission sequence; and

extracting at least a portion of the message from the received signal when the received signal correlates with the third portion of the ID code in the MT.

40. The method of claim 1, further comprising:

sensing a direction of travel associated with the RL relative to the MT, determining a location of the MT relative to the RL with at least the sensed direction of travel and the determined distance.

41. The method of claim 40, wherein determining the location of the MT further comprises at least one of:

evaluating a Doppler shift, evaluating a Double Doppler shift, evaluating a synthetic round-trip Doppler shift, evaluating an acceleration vector, evaluating a velocity vector, evaluating a direction vector, and evaluating successive distance measurements.

42. The method of claim 40, further comprising:

identifying a first portion of the acknowledgement signal with the RL, wherein the first portion of the acknowledgement signal is associated with a first antenna when the RL is traveling in a first direction;

identifying a second portion of the acknowledgement signal with the RL, wherein the second portion of the acknowledgement signal is associated with the first antenna when the RL is traveling in a second direction that is different from the first direction; and

wherein determining a location of the MT further comprises;

evaluating arrival times for the receipt of the first portion and the second portion of the acknowledgement signal; and

resolving a direction of travel ambiguity relative to the RL and the MT based on the evaluation of the arrival times.

43. The method of claim 40,

wherein identifying arrival times further comprises:

identifying a first portion of the acknowledgement signal with the RL, wherein the first portion of the acknowledgement signal is associated with a first antenna;

identifying a second portion of the acknowledgement signal with the RL, wherein the second portion of the acknowledgement signal is associated with the second antenna, and wherein the first antenna and the second antenna are located apart from one another in the RL; and

wherein determining a location of the MT further comprises;

evaluating the arrival times for the receipt of the first portion and the second portion of the acknowledgement signal; and

resolving a direction of travel ambiguity relative to the RL and the MT based on the evaluation of the arrival times.

44. The method of claim I, further comprising:

identifying a first portion of the acknowledgement signal with the RL, wherein the first portion of the acknowledgement signal is associated with a first antenna;

identifying a second portion of the acknowledgement signal with the RL, wherein the second portion of the acknowledgement signal is associated with a second antenna;

identifying a third portion of the acknowledgement signal with the RL, wherein the third portion of the acknowledgement signal is associated with a third antenna, and wherein the first antenna, the second antenna, and the third antenna are each located apart from one another;

evaluating the arrival times for the receipt of the first, second, and third portions of the acknowledgement signals; and

resolving a direction of travel ambiguity relative to the RL and the MT based on the evaluation of the arrival times.

45. A method for adjusting an internal timing and frequency in a transponder (MT) by receiving a transmission from a remote locator (RL), the method comprising:

capturing a first portion of a first transmission sequence from the transmission during a first capture interval;

correlating the captured first portion with a first portion of an identification code (ID Code) that is associated with the MT;

identifying a first received time associated with the correlated captured first portion;

extracting initial timing and phase from the correlated captured first portion;

scheduling a second capture interval with an expected phase;

capturing a second portion of the first transmission sequence from the transmission during the second capture interval;

correlating the captured second portion with the first portion of the ID Code that is associated with the MT;

identifying a second receive time associated with the correlated captured second portion;

extracting a second timing and phase from the correlated captured second portion;

determining a phase difference between the expected phase and the extracted second phase, and a time different between the first capture interval and the second capture interval; and

adjusting a fine timing and phase associated with the receiver when the captured portions correlate, with the determined phase difference and the determined time difference.

46. The method of claim 45, wherein the determined phase difference is in a range from 0 to 90 degrees.

47. The method of claim 45, further comprising synthesizing a frequency for the MT by synthesizing an in-phase clock signal and synthesizing a quadrature phase clock signal with a reference clock signal.

48. The method of claim 45, further comprising:

capturing a third portion of a second transmission sequence from the transmission during a third capture interval;

circularly correlating the captured third portion with a second portion of the ID Code that is associated with the MT;

identifying a position in a transmission frame when the captured third portion correlates with the second portion of the ID code; and

adjusting a coarse timing associated with the transmission frame from the identified position.

49. The method of claim 48, further comprising:

scheduling a capture time interval for a third transmission sequence based upon;

the identified position associated with the second transmission sequence, and the adjusted fine timing and phase associated with the receiver timing from the first transmission sequence;

capturing a portion of a third transmission sequence from the transmission at the scheduled capture time interval;

correlating the captured portion of the third transmission sequence with a third portion of the selected ID Code; and

extracting at least a portion of an encoded message from the captured portion of the third transmission sequence when the captured portion of the third transmission sequence correlates with the third portion of the selected ID Code.

50. The method of claim 49, further comprising:

partitioning the selected ID Code into at least one of;

equally sized first, second, and third portions;

differently sized first, second, and third portions;

equally sized first and second portions where the third portion is different in size from the first and second portions;

equally sized first and third portion where the second portion is different in size from the first and third portions, and equally sized second and third portion where the first portion is different in size from the second and third portions.

51. The method of claim 49, further comprising:

evaluating the third transmission sequence to improve the reliability of the message with an error correcting code.

52. The method of claim 49, wherein extracting the encoded message comprises:

decoding a modulated message in the third transmission frame, wherein the modulated message was encoded with at least one of;

a multi-phase shift keying (MPSK) pattern, a binary-phase shift keying (BPSK) pattern, a quadrature phase shift keying (QPSK) pattern, a differential phase shift keyed (DPSK) pattern, a continuous phase modulation (CPM) pattern, and a multiple amplitude and phase shift keying (MAPSK) pattern.

53. The method of claim 49, further comprising:

identifying a command and control message from the extracted message.

54. The method of claim 48, further comprising:

transmitting an acknowledgement signal to the RL using at least one of the frequency, timing, phase, position, and cadence information determined from the received portions of the transmission associated with the first transmission sequence and the second transmission sequence.

55. The method of claim 45, further comprising:

activating a sleep mode in the MT when the first portion of the first transmission sequence fails to correlate to the first portion of the selected ID Code.

56. A system for locating a transponder with a remote locator, the system comprising:

a remote locator (RL) comprising;

means for selecting an identification code (ID Code) for transmission from the RL, wherein the selected ID Code is associated with the MT;

means for generating a first transmission sequence with a first pattern, wherein the first transmission sequence is arranged for transmission in a first frame such that the first pattern is repeated in the first transmission sequence over the first frame;

means for generating a second transmission sequence with a second pattern, wherein the second transmission sequence is arranged for transmission in a second frame such that each subsequent pattern in the second transmission sequence is cyclically shifted relative to the preceding pattern over the second frame;

means for generating a third transmission sequence with a third pattern, wherein the third transmission sequence is arranged for transmission in a third frame;

means for encoding a first portion of the selected ID Code into the first transmission sequence;

means for encoding a second portion of the selected ID Code into the second transmission sequence;

means for encoding a third portion of the selected ID Code and a message for the MT into the third transmission sequence;

means for transmitting the first, second, and third transmission frames;

means for receiving an acknowledgement signal from an MI; and

means for determining a distance between the RL and the MT as a function of an elapsed time between the transmission of the first, second, and third transmission frames and the receipt of the acknowledgement signal from the MT; and

a transponder (MT) comprising;

means for capturing at least a first portion and a second portion of the first transmission sequence;

means for correlating the captured first and second portions of the first transmission sequence with the first portion of the ID Code;

means for adjusting a fine timing, phase, and frequency associated with the MT frequency when the captured first and second portions of the first transmission sequence is correlated to the first portion of the ID Code;

means for capturing a portion of the second transmission sequence;

means for correlating the captured portion of the second transmission sequence with a second portion of the ID Code;

means for identifying a position with the second transmission frame when the captured portion of the second transmission sequence is correlated to the second portion of the ID Code;

means for scheduling a capture time interval for receiving the third transmission sequence based upon;

the identified position associated with the second transmission frame, and the adjusted frequency, fine timing, and phase associated with the receiver timing from the first transmission frame;

means for capturing the third transmission sequence at the scheduled capture time interval;

means for correlating the captured third transmission sequence with the third portion of the ID Code;

means for extracting the encoded message from the third transmission sequence when the captured third transmission sequence is correlated to the third portion of the selected ID Code; and

means for transmitting an acknowledgement signal to the RL from the MT.

57. The system of claim 56, wherein the MT transmitted acknowledgement signal is arranged to match a corresponding Doppler shifted RL signal.

58. A remote locator (RL) that is arranged to locate a transponder (MT), the RL comprising:

a means for selecting an identification code (ID Code) that is associated with the MT;

a means for generating sequences, wherein the means for generating sequences is arranged provide;

a first transmission sequence with a first pattern, wherein the first transmission sequence is arranged for transmission in a first frame such that the first pattern is repeated in the first transmission sequence over the first frame; and

a second transmission sequence with a second pattern, wherein the second transmission sequence is arranged for transmission in a second frame such that each subsequent second pattern in the second transmission sequence is cyclically processed relative to the preceding second pattern over the second frame;

a means for encoding, wherein the means for encoding is arranged to encode;

a first portion of the selected ID Code into the first transmission sequence; and

a second portion of the selected ID Code into the second transmission sequence.

59. The RL of claim 58, further comprising:

a means for transmitting the first and second transmission frames in succession to one another.

60. The RL of claim 58, wherein the second transmission sequence is cyclically processed such that a first pattern in the second transmission sequence is related to a second pattern in the second transmission sequence according to at least one of:

an integer bit shift, a non-integer bit shift, a fractional bit shift, and a pattern timing change, and a carrier phase change.

61. The RL of claim 58, wherein the means for generating sequences is further arranged to provide a third transmission sequence with a third pattern, wherein the third transmission sequence is arranged for transmission in a third frame;

and wherein the means for encoding is further arranged to encode a third portion of the selected ID Code and a message for the MT into the third transmission sequence.

62. The RL of claim 58, further comprising:

a means for receiving a reply transmission from the MT, and a means for evaluating a round-trip time associated with the transmissions and receptions between the apparatus and the MT.

63. The RL of claim 62, further comprising:

a means for resolving a direction of travel ambiguity relative to the RL and the MT based on the evaluation of the arrival times.

64. The RL of claim 58, further comprising an output means, wherein the output means comprises at least one of:

an electronic compass display, a graphic display, a compass row-type display, a photo-ID display, a graphical indicator superimposed on the display indicating a location on a map, a vector-type display, a raster-type display, a LCD-type display, a discrete LED display, a distance indicator, a compass indicator, a directional indicator, an audio indicator, and a synthesized voice indicator.

65. The RL of claim 58, further comprising an input means, wherein the input means comprises at least one of:

an electronic keypad, a touch-panel, a mouse, a joystick, a keyboard, a voice recognition mechanism, and a microphone.

66. A transponder (MT) that is arranged to receive transmission from a remote locator (RL), the MT comprising:

a means for synthesizing a receiver frequency;

a means for associating an ID Code with the apparatus;

a means for capturing transmissions;

a means for scheduling that is arranged in cooperation with the means for capturing transmissions to selectively capture at least a portion of at least one of a first transmission frame and at least a portion of a second transmission frame;

a means for correlating captured transmissions with the ID Code;

a means for evaluating the correlation of the captured transmissions;

a means for adjusting a fine timing and a phase associated with the receiver frequency when the selective evaluation of the correlation of the captured transmission yields a match with a first portion of the Code; and

a means for identifying a position with the second transmission frame when the selective evaluation of the correlation of the captured transmission yields a match with a second portion of the ID Code.

67. The MT of claim 66, further comprising:

a means for authenticating captured transmissions when the captured transmissions correlated to the ID Code.

68. The MT of claim 66, further comprising:

a means for capturing at least a portion of a third transmission frame, and a means for extracting information from captured portions of the third transmission frame when the captured portion of the third transmission frame correlate to a third portion of the ID Code.

69. The MT of claim 68, wherein the information extracted from the captured portions for the third transmission comprise at least one of:

an encoded message, an error correction coded message, a command message, and a control message.

70. The MT of claim 66, further comprising:

a means for transmitting a reply message, wherein the reply message is transmitted using the timing, phase, cadence, and frequency that is determined from;

the adjusted fine timing and phase, and identified position from the second transmission frame.

71. The MT of claim 66, further comprising:

a means for logging at least one of physiological information and sensory information associated with a user of the MT.

72. The MT of claim 71, further comprising a means for encoding the logged information into a reply transmission for the RL.

73. The MT of claim 71, wherein the logged information comprises at least one of:

a physiological condition associated with the user, a blood pressure associated with the user, a body temperature associated with the user, a heart rate associated with the user, a blood-sugar level associated with the user, and a heart rhythm associated with the user.

74. A transponder (MT) that is arranged to communicate with a remote locator (RL), the RL adapted to provide a signal transmission that is coded with a transmit identification code (transmit ID Code) that is associated with the MT, the MT comprising:

a means for synthesizing a transmit frequency for the MT;

a means for receiving at least a portion of the transmission from the RL;

a means for correlating received portions of the transmission;

a means for extracting first timing and first phase information from a first captured portion of the transmission that correlates with the transmit ID Code;

a means for extracting second timing and second phase information from a second captured portion of the transmission that correlates with the transmit ID Code;

a means for determining a frequency offset for the transmit frequency from the first timing information, first phase information, second timing information, and second phase information;

a means for adjusting at least one of the frequency, timing, phase, and cadence associated with the transmit frequency in response to the determined frequency offset; and

a means for transmitting an acknowledgement signal to the RL using the adjusted frequency, timing, phase, and cadence that is recovered from the received signals from the RL.

75. The MT of claim 74, further comprising a sensing means for providing sensory information, wherein the sensing means comprises at least one of:

a physiological condition sensor, a blood pressure sensor, a body temperature sensor, a heart rate sensor, a blood-sugar level sensor, and a heart rhythm sensor.

76. The MT of claim 75, the means for transmitting the acknowledgement signal further comprising:

a means for encoding the sensory information in a reply message, and a means for encoding the reply message with a reply ID Code.

77. The MT of claim 76, wherein the reply ID Code corresponds to at least one of:

the transmit ID Code, and another ID Code that is different from the transmit ID Code.