Measuring distance using wireless communication

• US 20060197704A1
• Filed: 02/21/2006
• Published: 09/07/2006
• Est. Priority Date: 08/21/2003
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Luzzatto, Ariel, Serfaty, Salomon
• Granted Patent: US 7,515,103 B2
• Time in Patent Office: Days
• US Class Current: 342/458
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 11/06 using intensity measurements
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

A method of estimating the distance between a first wireless communication terminal and a second wireless communication terminal includes: receiving a signal at the first terminal, processing the received signal including performing a demodulation operation to produce a demodulated signal; and resolving the demodulated signal into a plurality of components corresponding to different path length components included in the received signal; identifying which of the resolved components corresponds to a shortest path length; and for the identified component, computing a time of travel from the second terminal to the first terminal.

Claims

1. A method of estimating the distance between a first wireless communication terminal and a second wireless communication terminal including:

(i) receiving at the first terminal a received signal comprising a composite multipath derivative of a RF transmission signal transmitted by a second terminal which transmission signal comprises an OFDM signal; and

(ii) processing the received signal including performing a demodulation operation to produce a demodulated signal;

(iii) resolving the demodulated signal into a plurality of components corresponding to different path length components included in the received signal by producing a composite vector C of phasors from the demodulated signal, constructing a special set {Ck} of vectors, wherein each component cf the set {Ck} corresponds to a different particular path length travelled by the received signal, and carrying out a mathematical functional operation to find the absolute value of the inner product |<

C,Ck>

| of the composite vector C with each of the components of the constructed set {Ck};

(iv) identifying which of the resolved components corresponds to a shortest path length; and

(v) for the identified component, computing a time of travel from the second terminal to the first terminal.

2. A method according to claim 1 including determining by the first terminal a strength value for each of the components resolved in step (iii).

3. A method according to claim 2 wherein the strength value is compared with a threshold value to determine if the strength value is to be considered as non-zero, and in step (iv) only components having non-zero strength values are included to find the component having the shortest path length.

4. A method according to claim 3 wherein the signal received and processed by the first terminal is a multipath derivative of the PLCP (Physical Layer Convergence Procedure) Training Signal defined in the 802.11 standard.

5. A method according to claim 4 wherein information produced as an output by the demodulation operation in step (ii) is stored in a memory.

6. A method according to claim 5 wherein the information stored in the memory comprises time samples and the method includes applying to the information a processing function to locate a time corresponding to a start of a training symbol within the stored time samples.

7. A method according to claim 6 wherein the processing function is operable to locate within the stored time samples a time T2 corresponding to the start of a second transmission of a training symbol.

8. A method according to claim 7 including applying by the first terminal a correction factor to the stored time samples to compensate for frequency offset.

9. A method according to claim 8 including performing a fast fourier transform (FFT) operation on the time samples to produce the composite vector C of phasors.

10. A first wireless communication terminal operable to measure the distance between itself and second wireless communication terminal, the first terminal including:

(i) a receiver for receiving a received signal comprising a composite multipath derivative of a RF transmission signal transmitted by a second terminal which transmission signal comprises an OFDM signal; and

(ii) a demodulator for performing a demodulation operation on the received signal to produce a demodulated signal; and

iii) one or more processors operable to;

(a) resolve the demodulated signal into a plurality of components corresponding to different path length components included in the received signal by producing a composite vector C of phasors from the demodulated signal, constructing a special set {Ck} of vectors, wherein each component of the set {Ck} corresponds to a different particular path length travelled by the received signal, and carrying out a mathematical functional operation to find the absolute value of the inner product |<

C,Ck>

| of the composite vector C with each of the components of the constructed set {Ck};

(b) identify which of the resolved components corresponds to a shortest path length; and

(c) for the identified component, compute a time of travel from the second terminal to the first terminal.

11. A terminal according to claim 10 which is operable to determine a strength value for each of the resolved components.

12. A terminal according to claim 11 which is operable to compare the strength value for each of the resolved components with a threshold value to determine if the strength value is to be considered as non-zero, whereby the component having that strength value is to be included to find the component having the shortest path length.

13. A terminal according to claim 12, wherein the first terminal is operable to receive and process as the received signal a multipath derivative of the PLCP (Physical Layer Convergence Procedure) Training Signal defined in the 802.11 standard.

14. A terminal according to claim 13, including a memory to store information produced as an output by the demodulator.

15. A terminal according to claim 14, wherein the memory is operable to store complex time samples of the signal demodulated by the demodulator.

16. A terminal according to claim 15 wherein the first terminal further includes a processing function which is operable to locate a time corresponding to a start of a training symbol within the stored time samples.

17. A terminal according to claim 16 wherein the processing function is operable to locate within the stored time samples a time T2 corresponding to the start of a second transmission of a training symbol.

18. A terminal according to claim 17 wherein the first terminal further includes a processing function operable to apply a correction factor to the time samples to compensate for frequency offset.

19. A terminal according to claim 18 wherein the first terminal includes a processor operable to perform a FFT operation on the time samples to produce a composite vector C of phasors.

20. A terminal according to claim 19 which further includes a processor operable to perform a LAN system operation using the estimated distance result.

21. A terminal according to claim 20 which comprises a LAN Access Point and the terminal includes a processor operable to participate in an assisted handoff procedure of a second terminal, the second terminal being a Remote Unit (RU) of the LAN.

22. A terminal according to claim 20 operable to determine, with the assistance of other Access Point terminals, using the estimated distance result the location of a Remote Unit terminal.

23. A method of estimating the distance between a first wireless communication terminal and a second wireless communication terminal including:

at the second (transmitting) terminal;

(i) generating an OFDM training symbol comprising phasors in the frequency domain;

(ii) processing the generated signal by applying an inverse FFT operation to the phasors of the generated signal in the frequency domain to generate I and Q components of a complex signal in the time domain;

(iii) combining the I and Q components to produce a transmission signal; and

(iv) transmitting the transmission signal; and

at the first (receiving) terminal;

(v) receiving a received signal comprising a composite multipath derivative of the transmission signal transmitted by the second terminal; and

(vi) processing the received signal including performing a demodulation operation to produce a demodulated signal;

(vii) resolving the demodulated signal into a plurality of components corresponding to different path length components included in the received signal by producing a composite vector C of phasors from the demodulated signal, constructing a special set {Ck} of vectors, wherein each component of the set {Ck} corresponds to a different particular path length travelled by the received signal, and carrying out a mathematical functional operation to find the absolute value of the inner product |<

C,Ck>

| of the composite vector C with each of the components of the constructed set {Ck};

(viii) identifying which of the resolved components corresponds to a shortest path length; and

(ix) for the identified component, computing a time of travel from the second terminal to the first terminal.

24. A method according to claim 23 wherein the second terminal is a standard unmodified RU terminal.

25. A method according to claim 24 wherein the method operates using a one-way communication path from the second terminal to the first terminal without loopback.