Methods and systems for localization

• US 10,215,837 B1
• Filed: 12/22/2017
• Issued: 02/26/2019
• Est. Priority Date: 12/22/2017
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC), Emirates Telecommunications Corporation
• Original Assignee: British Telecommunications PLC (BT Group PLC), Emirates Telecommunications Corporation, Khalifa University Of Science, Technology & Research
• Inventors: Montuno, Delfin Y., Aweya, James
• Primary Examiner(s): Mizrahi, Diane D
• Application Number:
  US15/852,086
• Time in Patent Office: 431 Days
• CPC Class Codes: G01S 1/0428 Signal details
• CPC Class Codes: G01S 5/02216 Timing or synchronisation of the receivers
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: H04W 4/02 Services making use of location information
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

This invention relates to methods and systems for localization. It is particularly concerned with localization techniques based on time difference of arrival for wireless devices. Embodiments of the invention relate to techniques in which a transmitter transmits periodic distinguishable signals which are relayed upon receipt by the client whose location is sought in a form distinguishable from that of the transmitter. Signals from both the transmitter and the client are received by at least three signal receivers which generate a time difference of arrival based on the difference taken for a signal to reach the receiver directly and via the client. Further embodiments of the invention provide a phase detector in the receivers to determine the time difference of arrival between the signals.

Claims

1. A system configured to track a client device, the system including:

a transmitter station configured to transmit a first wireless signal;

at least three receiver stations; and

a location management station, wherein;

each receiver station is configured to receive the first signal and a second wireless signal transmitted from the client device and triggered by receipt of the first signal by the client device;

the receiver stations and/or the location management station are configured to determine a time difference of arrival between the first signal and second signal for each of the receiver stations;

the location management station is configured to, at multiple times;

compute, based on the corresponding time difference of arrival for each receiver station, a plurality of ellipses each associated with a respective receiver station, each ellipse having a first focal point corresponding to the transmitter station and having a second focal point corresponding to the respective receiver station;

determine a plurality of intersection points between pairs of said ellipses;

estimate the location of the client device using said determined intersection points; and

the location management station is configured to use the locations estimated at the multiple times to track movement of the client device.

2. The system of claim 1, wherein a semi-major axis or a semi-minor axis of each ellipse is calculated based on the corresponding time difference of arrival for that receiver station.

3. The system of claim 1 wherein the receiver stations and/or the location management station are configured to determine a distance, delta(receiver_i), which is the distance corresponding to the time difference between the receipt of the first signal and receipt of the second signal at the i^th receiver station.

4. The system of claim 3, wherein the location management station is configured to calculate, for an i^th ellipse corresponding to an i^th receiver station, a semi-major axis a_i which is half of the sum of:

a) a known distance, distance(f₁, f₂), between the respective receiver station and the transmitter station; and

b) delta (receiver_i).

5. The system of claim 4, wherein the location management station is configured to calculate, for an i^th ellipse corresponding to an i^th receiver station, an eccentricity e_i of the ellipse as:

6. The system of claim 5, wherein the location management station is configured to calculate, for an i^th ellipse corresponding to an i^th receiver station, a semi-minor axis b_i of the ellipse as:

b_i=+a_i√

{square root over (1−

e_i²)}.

7. The system of claim 6, wherein, when determining a plurality of intersection points between pairs of said ellipses, the location management station is configured to solve, for at least two distinct pairs of the computed ellipses, the following simultaneous equations:

8. The system of claim 7, wherein the location management station determines an intersection point in common between the at least two distinct pairs of computed ellipses.

9. The system of claim 1, wherein the receiver stations share a common clock.

10. The system of claim 1, wherein each receiver station includes an independently running clock and wherein the clocks of each receiver station share a nominal frequency.

11. The system of claim 1, wherein the transmitter station and the receiver stations are all transceiver stations, and wherein the transmitter station is chosen from the transceiver stations by determining a smallest round trip delay from each transceiver station to the client.

12. The system of claim 3, wherein the first signal and the second signal are periodic signals which share the same nominal frequency.

13. The system of claim 12, wherein each receiver station includes a signal phase detector circuit, the circuit counting at a frequency f_os a number of counts C_i between receiving the first signal and receiving the second signal at the respective receiver station, and the distance delta(receiver_i) is calculated as:

14. The system of claim 1 further including the client device, wherein the client device is configured to transmit the second signal, the transmission of the second signal being triggered by receipt of the first signal at the client.

15. A method of tracking a client device using a wireless network, the method having the steps of:

transmitting, from a transmitter station, a first signal;

receiving, at a client device, the first signal;

transmitting, from the client device, a second signal which corresponds to the first signal and whose transmission is triggered by receipt of the first signal;

receiving, at each of at least three receiver stations, the first signal and the second signal;

determining, for each of the receiver stations, a time difference of arrival between the first signal and second signal;

computing, for each of the receiver stations and based on the corresponding time difference of arrival, an ellipse having a first focal point corresponding to the transmitter station and having a second focal point corresponding to the respective receiver station;

determining a plurality of intersection points between pairs of said ellipses;

estimating the location of the client device using said determined intersection points;

repeating the above steps to obtain a plurality of estimated locations of the client device; and

using the plurality of estimated locations to track the client device.

16. The method of claim 15, wherein a semi-major axis or a semi-minor axis of each ellipse is calculated based on the corresponding time difference of arrival for that receiver station.

17. The method of claim 15, including a step of determining a distance, delta(receiver_i), which is the distance corresponding to the time difference between the receipt of the first signal and receipt of the second signal at the i^th receiver station.

18. The method of claim 17, including a step of calculating, for an i^th ellipse corresponding to an i^th receiver station, a semi-major axis a_i which is half of the sum of:

a) a known distance, distance(f₁, f₂) between the respective receiver station and the transmitter station; and

b) delta(receiver_i).

19. The method of claim 18, including a step of calculating, for an i^th ellipse corresponding to an i^th receiver station, an eccentricity e_i of the ellipse as:

20. The method of claim 19, including a step of calculating, for an i^th ellipse corresponding to an i^th receiver station, a semi-minor axis b_i, of the ellipse as:

b_i=+a_i√

{square root over (1−

e_i²)}.

21. The method of claim 20, including a step of solving, for at least two distinct pairs of the computed ellipses, the following simultaneous equations:

22. The method of claim 15, wherein the receiver stations share a common clock.

23. The method of claim 15, wherein each receiver station includes an independently running clock and wherein the clocks of each receiver station share a nominal frequency.

24. The method of claim 15, wherein the transmitter station and the receiver stations are all transceiver stations, and the method includes a step of:

choosing the transmitter station from the transceiver stations by determining a smallest round trip delay from each transceiver station to the client.

25. The method of claim 17, wherein the first signal and the second signal are periodic signals which share the same nominal frequency.

26. The method of claim 25, wherein a signal phase detector circuit, within each receiver station, counts at a frequency f_os a number of counts C_i between receiving the first signal and receiving the second signal at the respective receiver station, and calculates the distance delta(receiver_i) as:

27. A location tracking management station, connected to a wireless network, and having a processor, wherein the processor is configured to:

receive, from each of at least three receiver stations connected to the wireless network, a time difference of arrival measurement, the time difference of arrival measurement being the time difference between the arrival of a first signal and a second signal at the respective received stations, wherein;

the first signal is a signal transmitted from a transmitter station; and

the second signal is a signal corresponding to the first signal and transmitted from a client device, the transmission of which is triggered by receipt, at the client device, of the first signal;

compute, for each of the receiver stations and based on the corresponding time difference of arrival, an ellipse having a first focal point corresponding to the transmitter station and having a second focal point corresponding to the respective receiver station;

determine a plurality of intersection points between pairs of said ellipses; and

estimate the location of the client device using said determined intersection points;

repeat the above steps to obtain a plurality of estimated locations of the client device; and

use the plurality of estimated locations to track the client device.