Synchronization-free station locator in wireless network

• US 8,233,457 B1
• Filed: 09/03/2009
• Issued: 07/31/2012
• Est. Priority Date: 09/03/2009
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm Atheros Incorporated (Qualcomm, Inc.)
• Inventors: Chen, Qifan, Zhang, Ning, Cho, James, McFarland, William J.
• Primary Examiner(s): Phan, Tri H
• Application Number:
  US12/553,757
• Time in Patent Office: 1,062 Days
• Field of Search: 370229-239, 370310-350, 370464-468, 370498-519, 455/63.1, 4554221-423, 455445-461
• US Class Current: 370/332
• 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
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864

Abstract

A method of providing synchronization-free station locating in a wireless network is provided. In this method, an AP having a known location sends a unicast packet to the station and notes its time of departure TOD(D). The station receives the unicast packet, notes its time of arrival TOA(D), sends an acknowledgement packet to the AP, and notes its time of departure TOD(D_ACK). The AP receives the acknowledgment packet and notes its time of arrival TOA(D_ACK). Notably, a distance between the AP and the station can be accurately determined using a first difference between the TOA(D_ACK) and the TOD(D) and a second difference between the TOD(D_ACK) and the TOA(D). A plurality of such computed distances between a plurality of APs and the station can be used to determine an accurate location of the station.

Claims

1. A method of providing synchronization-free station locating in a wireless network, the wireless network including a station having an unknown location and a plurality of access points (APs) having known locations, the method comprising:

for each set including one of the plurality of APs and the station,

sending a unicast packet from the AP to the station, the unicast packet having a time of departure TOD(D);

receiving the unicast packet at the station, the unicast packet having a time of arrival TOA(D);

sending an acknowledgement packet from the station to the AP, the acknowledgment packet having a time of departure TOD(D_ACK);

receiving the acknowledgment packet at the AP, the acknowledgment packet having a time of arrival TOA(D_ACK); and

determining a distance between the AP and the station using a first difference between the TOA(D_ACK) and the TOD(D) and a second difference between the TOD(D_ACK) and the TOA(D); and

using a plurality of computed distances between the plurality of APs and the station to determine a location of the station.

2. The method of claim 1, wherein determining the distance between the AP and the station further includes determining a delay T_1,i, a delay T₃, a delay T₁, and a delay T_3,i,

wherein i designates the AP,

wherein the delay T_1,i is a time delay from the TOD(D) to transmission of the unicast packet by an AP antenna,

wherein the delay T₃ is a time delay from receipt of the unicast packet by a station antenna to the TOA(D),

wherein the delay T1 is a time delay from the TOD(D_ACK) to transmission of the acknowledgement packet by the station antenna, and

wherein the delay T_3,i is a time delay from receipt of the acknowledgement packet by the AP antenna to the TOA(D_ACK).

3. The method of claim 2, wherein determining a distance d_i between the AP and the station includes computing:

d_i=((t_4,i−

t_1,i)−

(t₃−

t₂)−

T_1,i−

T_3,1−

T₁−

T₃)/2*SOL

where t_1,i is the TOD of the unicast packet in the AP, t₂ is the TOA of the unicast packet in the station, t₃ is the TOD of the acknowledgement packet in the station, t_4,i is the TOA of the acknowledgement packet in the AP, and SOL is the speed of light.

4. The method of claim 2, further including adjusting at least one of the TOA(D) and the TOA(D_ACK) using a long training field.

5. The method of claim 2, further including adjusting at least one of the TOA(D) and the TOA(D_ACK) using a guard interval and its corresponding OFDM symbol tail.

6. The method of claim 2, further including adjusting at least one of the TOA(D) and the TOA(D_ACK) using a long training field and an inverse fast Fourier transform (IFFT).

7. The method of claim 2, further including calibrating the delay T_1,i and the delay T_3,1 of the AP.

8. The method of claim 2, further including calibrating the delay T₁ and the delay T₃ of the station.

9. The method of claim 1, wherein the second difference between the TOD(D_ACK) and the TOA(D) is one of a constant and an averaged value.

10. A method of providing synchronization-free device locating in a wireless network, the wireless network including a device having an unknown location (DUL) and a plurality of devices having known locations (DKLs), the method comprising:

for each set including one of the plurality of DKLs and the DUL,

sending a unicast packet from the DKL to the DUL, the unicast packet having a time of departure TOD(D);

receiving the unicast packet at the DUL, the unicast packet having a time of arrival TOA(D);

sending an acknowledgement packet from the DUL to the DKL, the acknowledgment packet having a time of departure TOD(D_ACK);

receiving the acknowledgment packet at the DKL, the acknowledgment packet having a time of arrival TOA(D_ACK); and

determining a distance between the DKL and the DUL using a first difference between the TOA(D_ACK) and the TOD(D) and a second difference between the TOD(D_ACK) and the TOA(D); and

using a plurality of computed distances between the plurality of DKLs and the DUL to determine a location of the station.

11. The method of claim 10, wherein determining the distance between the DKL and the DUL further includes determining a delay T_1,i, a delay T₃, a delay T₁, and a delay T_3,i,

wherein i designates the DKL,

wherein the delay T_1,i is a time delay from the TOD(D) to transmission of the unicast packet by a DKL antenna,

wherein the delay T₃ is a time delay from receipt of the unicast packet by a DUL antenna to the TOA(D),

wherein the delay T1 is a time delay from the TOD(D_ACK) to transmission of the acknowledgement packet by the DUL antenna, and

wherein the delay T_3,i is a time delay from receipt of the acknowledgement packet by the DKL antenna to the TOA(D_ACK).

12. The method of claim 11, wherein determining a distance d_i between the DKL and the DUL includes computing:

d_i=((t_4,i−

t_1,i)−

(t₃−

t₂)−

T_1,i−

T_3,1−

T₁−

T₃)/2*SOL

where t_1,i is the TOD of the unicast packet in the DKL, t₂ is the TOA of the unicast packet in the DUL, t₃ is the TOD of the acknowledgement packet in the DUL, t_4,i is the TOA of the acknowledgement packet in the DKL, and SOL is the speed of light.

13. The method of claim 11, further including adjusting at least one of the TOA(D) and the TOA(D_ACK) using long training fields.

14. The method of claim 11, further including adjusting at least one of the TOA(D) and the TOA(D_ACK) using guard intervals.

15. The method of claim 11, further including adjusting at least one of the TOA(D) and the TOA(D_ACK) using long training fields and inverse fast Fourier transform (IFFT).

16. The method of claim 11, further including calibrating the delay T_1,i and the delay T_3,1 of the DKL.

17. The method of claim 11, further including calibrating the delay T₁ and the delay T₃ of the DUL.

18. The method of claim 10, wherein the second difference between the TOD(D_ACK) and the TOA(D) is one of a constant and an averaged value.

19. A method of providing synchronization-free device locating in a wireless network, the wireless network including a device having an unknown location (DUL) and a plurality of devices having known locations (DKLs), the method comprising:

for each set including one of the plurality of DKLs and the DUL,

sending a unicast packet from the DKL to the DUL, the unicast packet having a time of departure TOD(D);

receiving the unicast packet at the DUL, the unicast packet having a time of arrival TOA(D);

sending an acknowledgement packet from the DUL to the DKL, the acknowledgment packet having a time of departure TOD(D_ACK);

receiving the acknowledgment packet at the DKL, the acknowledgment packet having a time of arrival TOA(D_ACK); and

determining a distance between the DKL and the DUL using a first difference between the TOA(D_ACK) and the TOD(D) and a predetermined value representing a second difference between the TOD(D_ACK) and the TOA(D), wherein the predetermined value is one of a constant and an averaged value; and

using a plurality of computed distances between the plurality of DKLs and the DUL to determine a location of the station.

20. A method of providing synchronization-free device locating in a wireless network, the wireless network including a device having an unknown location (DUL) and a plurality of devices having known locations (DKLs), the method comprising:

for each set including one of the plurality of DKLs and the DUL,

sending a unicast packet from the DKL to the DUL, the unicast packet having a time of departure TOD(D);

receiving the unicast packet at the DUL, the unicast packet having a time of arrival TOA(D);

sending an acknowledgement packet from the DUL to the DKL, the acknowledgment packet having a time of departure TOD(D_ACK);

receiving the acknowledgment packet at the DKL, the acknowledgment packet having a time of arrival TOA(D_ACK); and

determining a distance between the DKL and the DUL using a first difference between the TOA(D_ACK) and the TOD(D), wherein a second difference between the TOD(D_ACK) and the TOA(D), wherein the predetermined value is one of a constant and an averaged value; and

using a plurality of computed distances between the plurality of DKLs and the DUL to determine a location of the station.