Time difference of arrival measurement system

• US 6,201,499 B1
• Filed: 02/03/1998
• Issued: 03/13/2001
• Est. Priority Date: 02/03/1998
• Status: Expired due to Term

• Current Assignee: Authorize Net LLC (Visa, Inc.)
• Original Assignee: Consair Communications
• Inventors: Koehler, Jeffrey L., Hawkes, Kelly D.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/017,864
• Time in Patent Office: 1,134 Days
• Field of Search: 342/387, 342/457, 342/465, 342/463, 342/442, 455/456
• US Class Current: 342/387
• CPC Class Codes: G01S 1/045 Receivers
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method and apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two different sensors where the transmitted signal is generated by a radio frequency transmitter. The apparatus includes a sensor having a receiver which receives a received signal and generates a receiver output signal, a decoder which decodes an encoded signal transferred from another sensor to generate a reconstructed signal representative of the transmitted signal received at the other sensor and a correlator for correlating the reconstructed signal and the receiver output signal to determine a time difference of arrival of the receipt of the transmitted signal at the respective sensors.

Claims

1. An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter, the transmitted signal consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the audio tone having a phase that varies with time, the apparatus comprising;

a remote processor including a decoder and a correlator; and

a first and second sensor where each sensor includes

a receiver for receiving a received signal, the received signal being a time delayed version of the transmitted signal, the receiver operable to generate a receiver output signal including an audio tone and a voice signal;

an encoder for operating on the receiver output signal to generate an encoded signal where the audio tone of the receiver output signal is modeled as having a specific phase at a specific time; and

means for transferring the encoded signal, to a remote processor;

where the remote processor is operable to receive the encoded signal from one of the first and second sensors and where the decoder is operable to decode the encoded signal resulting in a reconstructed version of the received signal, the correlator operable to correlate the reconstructed version of the received signal with the received signal received by the other of the first and second sensors to derive time difference of arrival data associated with the arrival of the transmitted signal at the first and second sensors.

2. The apparatus of claim 1 wherein each sensor further includes

a decoder that operates on the encoded signal received from another sensor to generate a reconstructed signal representative of the received signal received at the another sensor; and

a correlator for measuring the time difference of arrival between the reconstructed signal representative of the received signal received at the another sensor and the received signal at the sensor.

3. The apparatus of claim 1 where the signal correlated with the reconstructed version of the received signal is a reconstructed version of the received signal received at another sensor.

4. The apparatus of claim 1 wherein the remote processor is co-located with one of the first and second sensors.

5. The apparatus of claim 1 wherein each sensor further includes

an analog to digital converter for operating on the receiver output signal to generate a digitized signal including a sequence of samples representative of the receiver output signal, each sample consisting of one or more bits and the digitized signal having a bit rate proportional to a number of bits per sample and a number of samples in a given time interval;

and

a sampling controller for controlling sampling of the receiver output signal by the analog to digital converter;

wherein the encoder operates on the digitized signal to generate the encoded signal which has a bit rate lower than the bit rate of the digitized signal.

6. The apparatus of claim 5 wherein the sampling controller includes time standard;

and

where the remote processor further includes a command-issuing controller operable to issue a tasking command to the time standard indicating a time when the analog to digital converter is to generate a sample of the digitized signal.

7. The apparatus of claim 6 wherein the time standard includes a global positioning system receiver for synchronizing the time standards at each sensor.

8. The apparatus in claim 5 wherein the sampling controller includes a time standard for recording a time when any sample of the digitized signal is generated.

9. The apparatus of claim 1 wherein the encoder includes a signal characteristic monitor for detecting signal characteristics of the received signal;

and wherein the remote processor includes a command issuing controller for issuing a tasking command to the signal characteristic monitor indicating a predefined signal characteristic of the received signal, and upon detecting the predefined signal characteristic, the signal characteristic monitor prompting its respective encoder to generate a time stamp associated with an occurance of the predefined signal characteristic for transfer to the remote processor.

10. The apparatus of claim 1 wherein the encoder encodes the receiver output signal by encoding both the audio tone and the voice signal.

11. The apparatus of claim 1 wherein each sensor further includes:

a decoder for decoding the encoded signal generated at the sensor thereby generating a reconstructed signal; and

a correlator for measuring an encoding timing error between the reconstructed signal and the receiver output signal, wherein the encoding timing error may be transferred to the remote processor to be combined with the output of the correlator in the remote processor to generate a more accurate determination of the time difference of arrival for the transmitted signal at the first and second sensors.

12. The apparatus of claim 1 wherein the encoders operate on the receiver output signal to measure a phase of the audio tone at a predetermined time.

13. The apparatus of claim 1 wherein the encoders operate on the receiver output signal to measure the time when the audio tone is at a predetermined phase.

14. The apparatus of claim 1 wherein each receiver includes two or more spatially diverse antennas each coupled to two or more downconverters whose outputs are coupled to a beamformer whose single output constitutes the receiver output signal.

15. An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter, the transmitted signal consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the audio tone having a phase that varies with time, the apparatus comprising:

a sensor which includes;

a receiver which receives a received signal, the received signal being a time delayed version of the transmitted signal, the receiver operable to generate a receiver output signal;

an encoder for operating on the receiver output signal to generate an encoded signal where the audio tone of the receiver output signal is modeled as having a specific phase at a specific time;

a decoder which decodes an encoded signal transferred from another sensor to generate a reconstructed signal representative of the transmitted signal received at the other sensor; and

a correlator for correlating the reconstructed signal and the receiver output signal to determine a time difference of arrival of the receipt of the transmitted signal at the respective sensors.

16. The apparatus of claim 15 wherein the sensor further includes:

an encoder for operating on the receiver output signal to generate an encoded signal where the audio tone of the receiver output signal is modeled as having a specific phase at a specific time; and

a network interface for communicating with a network for transmitting the encoded signal to another sensor.

17. The apparatus of claim 16 wherein the sensor further includes:

an analog to digital converter which operates on the receiver output signal to generate a digitized signal including a sequence of samples representative of the receiver output signal, each sample consisting of one or more bits and the digitized signal having a bit rate proportional to a number of bits per sample and a number of samples in a given time interval; and

a sampling controller which controls sampling of the receiver output signal by the analog to digital converter,

where the encoder operates on the digitized signal to generate the encoded signal which has a bit rate lower than the bit rate of the digitized signal.

18. The apparatus of claim 16 wherein the sensor further includes a signal quality monitor for monitoring the signal quality of the received signal, and wherein the apparatus further includes:

a central processor including a processor controller for receiving signal quality results from the signal quality monitor, for selecting a reference sensor based on the signal quality results and for prompting the reference sensor to transfer its encoded signal to another sensor.

19. The apparatus of claim 18 wherein the signal quality monitor includes:

a decoder for decoding the encoded signal generated by the encoder to synthesize a local reconstructed signal representative of the receiver output signal; and

a correlator for determining signal quality as a measure of similarity between the local reconstructed signal and the receiver output signal.

20. The apparatus of claim 18 where the encoder for the sensor only encodes the receiver output signal if the sensor is selected as the reference sensor.

21. The apparatus of claim 18 wherein the sensor passes to another sensor the encoded signal and determines time difference of arrival data, and wherein the central processor further includes an assignment controller for assigning weights to time difference data determinations made at each sensor so that a more accurate determination of a time difference of arrival for the received signals may be made.

22. The apparatus of claim 18 wherein the processor controller selects the reference sensor based on the highest signal-to-noise power ratio as measured by the signal quality monitor.

23. The apparatus of claim 18 wherein the processor controller selects the reference sensor based on the least amount of co-channel interference as measured by the signal quality monitor.

24. The apparatus of claim 18 wherein the processor controller selects the reference sensor based on the least amount of multi-path interference as measured by the signal quality monitor.

25. An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the apparatus comprising:

first and second sensors where each sensor includes

a receiver for receiving a received signal, the received signal being a time delayed version of the transmitted signal, the receiver operable to generate a receiver output signal including an audio tone and a voice signal;

an analog to digital converter for operating on the receiver output signal to generate a digitized signal including a sequence of samples representative of the receiver output signal, each sample consisting of one or more bits and the digitized signal having a bit rate proportional to a number of bits per sample and a number of samples in a given time interval;

an encoder for operating on the digitized signal to generate an encoded signal which has a bit rate lower than the bit rate of the digitized signal; and

a central processor that includes

a decoder that operates on encoded signals received from each sensor to generate reconstructed signals representative of the received signals; and

a correlator for measuring the time difference of arrival between the reconstructed signals.

26. The apparatus of claim 25 wherein the transmitted signal consists of a digital communication signal consisting of a sequence of symbols, and where the receiver output signal is encoded according to an occurrence of a symbol of the receiver output signal at a specific time.

27. The apparatus of claim 26 wherein the encoder models the receiver output signal according to recovered symbols, carrier phase and frequency.

28. The apparatus of claim 25 wherein each sensor further includes:

a sampling controller for controlling sampling of the receiver output signal by the analog to digital converter; and

where the encoder operates on the digitized signal to generate the encoded signal which has a bit rate lower than the bit rate of the digitized signal.

29. The apparatus of claim 28 wherein the sampling controller includes:

a time standard; and

wherein the central processor further includes;

a command-issuing controller for issuing a tasking command to each time standard indicating a time when the analog to digital converter is to generate a sample of the digitized signal.

30. The apparatus of claim 29 wherein the time standard includes a global positioning system receiver for synchronizing the time standards at each sensor.

31. The apparatus of claim 28 wherein the sampling controller includes a time standard for recording a time when any sample of the digitized signal is generated.

32. The apparatus of claim 25 wherein the encoder includes a signal characteristic monitor for detecting signal characteristics of a received signal and the central processor includes a command issuing controller for issuing a tasking command to the signal characteristic monitor of each encoder indicating a predefined signal characteristic of the received signal, and upon detecting the predefined signal characteristic, the signal characteristic monitor prompting its respective encoder to generate a time stamp associated with an occurrence of the predefined signal characteristic for transfer to the remote processor.

33. The apparatus of claim 25 wherein each receiver includes two or more spatially diverse antennas each coupled to two or more downconverters whose outputs are coupled to a beamformer whose single output constitutes the receiver output signal.

34. An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the apparatus comprising:

two sensors each including

a receiver for receiving a received signal including an audio tone and a voice signal, the received signal having a first bit rate associated therewith and being a time delayed version of the transmitted signal;

an encoder for operating on the received signal to generate an encoded signal having a second bit rate, where the first bit rate is greater than the second bit rate;

a signal quality monitor for monitoring the signal quality of the received signal;

means for transferring the encoded signal to another sensor;

a decoder for decoding an encoded signal received from another sensor to generate a reconstructed signal representative of the received signal at the other sensor; and

a correlator for correlating the reconstructed signal and the received signal for a given sensor to determine a time difference of arrival for receiving the received signals at the respective sensors; and

a central processor including a controller for receiving signal quality results from the signal quality monitor in each sensor, for selecting a reference sensor based on the signal quality results and for prompting the reference sensor to transfer an encoded signal to another sensor.

35. A method for reducing network bandwidth in a cellular communication system having a plurality of remote cells each including a sensor for determining time difference of arrival measurements between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two remote sensors in a cellular communication system, the transmitted signal being generated by a cellular telephone and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the method comprising:

receiving a received signal from a cellular telephone at two remote sensors;

generating an arrival signal at each remote sensor including arrival information associated with the received signals including an audio tone and a voice signal, wherein the arrival signal has a first bit rate associated therewith;

modeling the arrival signal based on one or more signal characteristics to produce an encoded arrival signal, the encoded arrival signal having a second bit rate, where the first bit rate is greater than the second bit rate;

transmitting the encoded arrival signal to the central processing facility;

decoding encoded arrival signals from the two remote sensors to reconstruct the arrival signals;

correlating the reconstructed arrival signals to determine time difference of arrival data.

36. The method of claim 35 further including determining a reference arrival signal from the encoded arrival signals and correlating an arrival signal associated with the remote sensor that did not produce the reference arrival signal and the reference arrival signal to compute time difference of arrival data.

37. The method of claim 36 wherein the reference arrival signal is selected based on quality data gathered at the remote sensor.

38. The method of claim 37 wherein the quality data is selected from the group of signal-to-noise power ratio, co-channel interference, multi-path interference, and a correlation coefficient derived from a correlation of the arrival signal and a reconstructed arrival signal.

39. The method of claim 36 wherein the reference arrival signal is distributed to the other remote sensor for correlation with an arrival signal.

40. The method of claim 39 wherein each remote sensor calculates time difference of arrival data based on the reference arrival signal and the received signal.

41. The method of claim 40 wherein each calculated time measurement is weighted based on signal quality to more accurately determine the time difference of arrival for the received signals.

42. The method of claim 35 wherein the transmitted signal consists of a frequency modulated voice signal plus audio tone and the arrival signal is modeled based on the voice signal and the phase, frequency and amplitude of the audio tone.

43. The method of claim 35 wherein the received signal is a digital communication signal received from a digital cellular telephone and where the received signal is encoded based on a measured symbol epoch for the received signal.

44. The method of claim 35 wherein the correlating step is accomplished remotely at one of the remote sensors and wherein the process further includes selecting a reference encoded signal from the encoded signals and transmitting the reference encoded signal to each remote sensor prior to correlating.

45. A method for reducing network bandwidth while determining time difference of arrival measurements between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two remote sensors in a cellular communication system, the transmitted signal being generated by a cellular transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the method comprising:

receiving a received signal from a cellular telephone at two remote sensors;

generating an arrival signal at each remote sensor including arrival information associated with the received signal;

encoding the arrival signal;

transmitting the encoded arrival signal to a central processing facility;

selecting the encoded arrival signal from one of the two remote sensors as a reference signal;

distributing the reference signal to all of the remote sensors;

at each remote sensor

decoding the reference signal;

correlating an arrival signal from one of the remote sensors with the reference signal to determine time difference of arrival data; and

transmitting the time difference of arrival data to the central processing facility.

46. A method for reducing network bandwidth while determining time difference of arrival measurements between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two remote sensors in a cellular communication system, the transmitted signal being generated by a cellular telephone and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the method comprising:

receiving a received signal from the cellular telephone at two remote sensors;

selecting one of the remote sensors as a reference remote sensor based on a predetermined signal characteristic of the received signal;

generating a reference signal at the reference remote sensor including arrival information associated with the received signal at the reference remote sensor;

transmitting the reference signal to the other remote sensor;

decoding the reference signal at the other remote sensor to reconstruct the received signal received at the reference remote sensor;

correlating the received signal at the other remote sensor and the reconstructed received signal to determine time difference of arrival data.

47. An apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal, the transmitted signal being generated by a radio frequency transmitter and consisting of a continuous transmission on a reverse voice channel of a frequency modulated analog voice signal plus audio tone, the apparatus comprising:

a first and second sensor where each sensor includes

a receiver for receiving a received signal and generating an receiver output signal,

a demodulator for demodulating the receiver output signal and generating a demodulator output signal including an audio tone and a voice signal,

a filter for limiting the bandwidth of the demodulator output signal and generating a filter output signal,

an analog to digital converter operating on the filter output signal for generating a digitized signal consisting of a sequence of samples,

a time standard to control when the analog to digital converter generates samples, and

network interface for communicating with a network to transmit a representation of the digitized signal to a remote processor, where the representation of the digitized signal is modeled as having a specific phase at a specific time; and

the remote processor including a correlator which operates on the two digitized signals to measure the time difference of arrival between the two received signals.