HIGH-RESOLUTION RANGING AND LOCATION FINDING USING MULTICARRIER SIGNALS

• US 20120032855A1
• Filed: 02/03/2011
• Published: 02/09/2012
• Est. Priority Date: 10/05/2006
• Status: Active Grant

• Current Assignee: AmeriSys Inc. (Brown & Brown Inc.)
• Original Assignee: Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Industry, Through The Communications Research Centre Canada
• Inventors: Reede, Ivan, Chouinard, Gerald
• Granted Patent: US 8,711,038 B2
• Time in Patent Office: Days
• US Class Current: 342/458
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 13/82 wherein continuous-type signals are transmitted
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement
• CPC Class Codes: G01S 13/876 Combination of several spaced transponders or reflectors of known location for determining the position of a receiver G01S13/874 takes precedence
• CPC Class Codes: G01S 5/0289 of multiple transceivers, e.g. in ad hoc networks

Abstract

The invention relates to methods and systems for accurate ranging and geo-locationing using coherent multicarrier (CM) signals and based on a high-resolution estimation of a receiver timing offset in a signal receiver that receives ranging CM signals. A transmitter transmits a ranging CM signal having a known subcarrier modulation pattern. The receiver samples the ranging CM signal it receives reflected back from an object or from the remote transmitter, and processes the sampled signal that preserves relative subcarrier phases using a high-resolution model channel response function to determine the receiver timing offset with resolution much better than the receiver sampling period. The receiver timing offset is used to determine a flight time for the ranging CM signal with high accuracy.

Claims

1. A method for determining a receiver timing offset, comprising:

a) receiving a coherent multicarrier (CM) signal by a receiver, the CM signal comprising a plurality of frequency multiplexed subcarriers characterized by subcarrier phases and subcarrier amplitudes and generated by a CM transmitter using a known subcarrier modulation pattern or a known absence of subcarrier modulation;

b) transforming the CM signal at the receiver into a sampled signal preserving relative subcarrier phase information, wherein the sampled signal has a sample rate R satisfying a Nyquist criterion R>

2F, wherein F is a modulation bandwidth of the CM signal; and

,

c) computing a discrete complex channel impulse response (CCIR) from the sampled signal;

d) processing the discrete CCIR to obtain a high-resolution channel function defined on a high-resolution time grid spaced by a time step dt that is at least 2 times smaller than a sample time period of the sampled signal; and

,

e) identifying a peak location in the high-resolution channel function to determine the timing offset in the receiver.

2. The method according to claim 1, wherein step d) comprises correlating the discrete CCIR with a high-resolution model function defined on the high-resolution time grid, wherein the high-resolution model function represents a pre-determined model CCIR.

3. The method according to claim 1, further comprising:

obtaining the sampled signal in the form of one of;

two quadrature sequences of signal samples, or a sequence of real-valued signal samples;

transforming the sampled signal to a frequency domain to obtain subcarrier coefficients comprising amplitude and phase information for the plurality of subcarriers;

obtaining the discrete CCIR from the subcarrier coefficients for the plurality of subcarriers using the known subcarrier modulation pattern.

4. The method according to claim 1, wherein the CM signal comprises a signal generated using orthogonal frequency division multiplexing (OFDM).

5. The method according to claim 4, wherein the receiver comprises an OFDM receiver.

6. The method of claim 1, wherein step e) comprises selecting a peak from a plurality of peaks in the high-resolution channel function.

7. The method of claim 6, wherein the selected peak is a first peak that satisfies a pre-determined condition.

8. A method for determining a distance to an object from a first communication device comprising a first coherent multicarrier (CM) transmitter and a first receiver, comprising:

directing the first CM transmitter to transmit a first ranging CM signal for impinging upon an object, and recording a first transmission start time indicative of a time instance when the first ranging CM signal leaves the first CM transmitter;

upon receiving by the first receiver a return CM signal from the object, performing the steps of;

applying the method of claim 1 to the return CM signal to determine a first receiver timing offset in the first receiver;

recording a first coarse time of arrival for the return CM signal at the first receiver; and

,

determining the distance between the object and the first communication device based on at least the first transmission start time, the first sampling start time, and the first timing offset at the first receiver.

9. The method according to claim 8, wherein the return CM signal comprises the first ranging CM signal reflected from the object.

10. The method according to claim 8, wherein the first ranging CM signal is an OFDM signal comprising a plurality of OFDM subcarriers modulated with a pseudo-random subcarrier modulation pattern.

11. The method according to claim 8, wherein the object comprises a second communication device comprising a second receiver and a second CM transmitter, the method further comprising:

recording a second coarse time of arrival of the first ranging signal at the second communication device;

generating the return CM signal by the second communication device using a subcarrier modulation pattern that is known to the first receiver;

transmitting the return CM signal by the second CM transmitter for receiving at the first communication device; and

,

recording a second transmission start time at which the return signal leaves the second transmitter.

12. The method according to claim 11, further comprising:

applying the method of claim 1 to the first ranging CM signal received at the second receiver to determine a second timing offset at the second receiver;

determining a time-of-flight value for CM signal propagation between the first and second communication device accounting for at least the first receiver timing offset and the second receiver timing offset.

13. The method according to claim 11, wherein the ranging signal is an OFDM signal comprising a plurality of OFDM subcarriers modulated with a pseudo-random subcarrier modulation pattern.

18. A method of ranging between two wireless transceivers, each wireless transceiver comprising a coherent multicarrier (CM) transmitter and a receiver, comprising:

directing the transceivers to exchange ranging CM signals, while recording at each of the transceivers a transmission start time for the ranging CM signal generated at the transceiver, and a sampling start time for the ranging CM signal received at the transceiver;

applying the method of claim 1 to the ranging CM signals received at each of the two transceivers to determine receiver timing offset values therefor; and

,

determining a time-of-flight value for CM signal propagation between the two transceivers based on the transmission start times, the sampling start times, and the receiver timing offset values.

19. In a system comprising a first wireless transceiver comprising a first CM transmitter and a first receiver at a first known location, a second wireless transceiver comprising a second CM transmitter and a second receiver at a second known location, and a third wireless transceiver comprising a third CM transmitter and a third receiver, a method to determine a location of the third transceiver, comprising:

directing the first transmitter to transmit a first ranging signal at a first reference time instant Tref₁ for reception by the second and third transceivers, and directing the second and third transmitters to transmit second and third ranging signals, respectively, for reception at the first transceiver, and using the first, second and third CM ranging signals for ranging according to the method of claim 18 between the first transceiver and the second transceiver, and between the first transceiver and the third transceiver, for determining;

a first time-of-flight value ToF₁₂ between the first transceiver and the second transceiver and a second timing offset δ

t₂ for the first ranging signal received at the second receiver;

a second time-of-flight value ToF₁₃ between the first transceiver and the third transceiver and a third timing offset δ

t₃ for the first ranging signal received at the third receiver;

determining a second reference time instant Tref₂ at the second transceiver relative to the first reference time instant Tref₁ at the first transceiver according to an equation Tref₂=Tref₁+ToF₁₂−

δ

t₂;

determining a third reference time instant Tref₃ at the third transceiver relative to the first reference time instant Tref₁ at the first transceiver according to an equation Tref₃=Tref₁+ToF₁₃−

δ

t₃;

directing the second transceiver to transmit a forth ranging CM signal at a first time delay Tdelay₂ after the second reference time instance Tref₂;

directing the third transceiver to receive the forth ranging CM signal at a second time delay Tdelay₃ after the third reference time instance Tref₃;

determining a forth receiver timing offset δ

t₄ for the forth ranging signal received at the third receiver;

computing a third time-of-flight value ToF₂₃ between the second transceiver and the third transceiver according to an equation

ToF₂₃=ToF₁₃−

ToF₁₂−

δ

t₃+δ

t₂+Tdelay₃−

Tdelay₂+δ

t₄; and

,

determining the location of the third transceiver based on the time of flight values ToF₁₃, ToF₁₂, ToF₂₃, and the known location of the first and second transceivers by triangulation.

20. A method according to claim 19, wherein the system further comprises a fourth wireless transceiver comprising a fourth CM transmitter and a fourth receiver at a third known location, and wherein the first, second and third known locations include altitude information, the method further comprising:

directing the fourth transmitter to transmit a fifth ranging signal for reception at the first transceiver, and using the fifth ranging signal and the first ranging signal received at the fourth transceiver for ranging according to the method of claim 18 between the first transceiver and the fourth transceiver, for;

determining a third time-of-flight value ToF₁₄ between the first transceiver and the fourth transceiver and a fifth timing offset δ

t₅ for the first ranging signal received at the fourth receiver;

determining a fourth reference time instant Tref₄ at the fourth transceiver relative to the first reference time instant Tref₁ at the first transceiver according to an equation Tref₄=Tref₁+ToF₁₄−

δ

t₅;

directing the fourth transceiver to receive the fourth ranging CM signal at a third time delay Tdelay₄ after the fourth reference time instance Tref₄;

determining a sixth receiver timing offset δ

t₆ for the fifth ranging signal received at the fourth receiver;

computing a fourth time-of-flight value ToF₂₄ between the second transceiver and the fourth transceiver according to an equation

ToF₂₄=ToF₁₄−

ToF₁₂−

δ

t₅+δ

t₂+Tdelay₄−

Tdelay₂+δ

t₆; and

,

determining three spatial coordinates of the third transceiver based on the time of flight values ToF₁₂, ToF₁₃, ToF₁₄, ToF₂₃, ToF₂₄ and the known locations of the first, second and fourth transceivers using a triangulation method.

21. The method of claim 1, wherein step b) is performed so as to preserve relative subcarrier amplitude information.

22. The method of claim 2, wherein the high-resolution model function is obtained by combining a set of discrete time-shifted CCIR functions of a model communication channel.

14. A communication device, comprising:

receiver front-end circuitry for transforming a received signal into a sampled signal having a sample rate R satisfying a Nyquist criterion R>

2F, wherein F is a modulation bandwidth of the signal;

a channel estimator for generating a discrete complex channel impulse response (CCIR) function from the sampled signal when the received signal comprises a plurality of coherently multiplexed subcarriers, wherein the channel estimator uses a known subcarrier modulation pattern, or a known absence of the subcarrier modulation for generating the CCIR function;

a correlator coupled to the channel estimator for correlating the discrete CCIR and a higher-resolution model function defined on a high-resolution time grid spaced at a time interval that is at least two times smaller than a sample time period of the sampled signal, and for outputting a high-resolution channel function defined on the high-resolution time grid; and

a peak processor for identifying a peak location in the high-resolution channel function for determining a timing offset in the receiver with a time resolution of a fraction of the sample time period.

15. The communication devices of claim 14, further comprising a model function memory for storing the higher-resolution model function.

16. An apparatus for determining a distance between a first transceiver comprising a first CM transmitter and a first receiver, and a second transceiver comprising a second receiver and a second CM transmitter, comprising:

an input port for receiving information signals comprising information defining first and second discrete complex channel impulse responses (CCIRs) from the first and second receivers, and for receiving coarse timing information from at least one of the first and second transceivers;

a model function memory for storing at least one higher-resolution model function defined at time intervals that are at least 2 times smaller than a sampling time period used for determining the first and second discrete CCIRs at the first and second receivers, respectively;

a ranging processor comprising;

a CCIR processor for processing the first and second discrete CCIRs using at least one discrete high-resolution model function to obtain first and second high-resolution channel functions;

a peak locator for identifying peak locations in the first and second high-resolution channel functions to determine first and second receiver timing offsets in the first and second receivers with a time resolution of a fraction of the sampling time period; and

,

a flight time computer for determining a flight time estimate between the first and second communication devices based on at least the coarse timing information, and the first and second receiver timing offsets.

17. The apparatus of claim 16, wherein the information defining the first and second discrete CCIRs comprises a first sequence of signal samples obtained by sampling, at the second receiver, a first ranging signal received by the second receiver from the first CM transmitter, and a second sequence of signal samples obtained by sampling, at the first receiver, a second ranging signal received by the first receiver from the second CM transmitter, the apparatus further comprising:

a modulation pattern memory for storing at least one modulation pattern used to modulate at least one of the first and second modulation signals;

a channel estimator coupled to the input port and the modulation pattern memory for processing the first and second sequences of signal samples using the at least one modulation pattern, and for outputting first and second discrete CCIRs for providing thereof to the distance processor.