Frequency offset compensation for WiFi ranging

Patent metadata

Field	Value
Publication number	US-9955446-B2
Application number	US-201614987264-A
Country	US
Kind code	B2
Filing date	Jan 4, 2016
Priority date	Jan 31, 2013
Publication date	Apr 24, 2018
Grant date	Apr 24, 2018

Abstract

Methods, systems, and apparatus are disclosed for determining accurate ranging measurements between communication devices. Various embodiments are described for recording timestamps associated with when transmissions are sent and received between the communication devices. The communication devices are configured to determine a difference in their clock frequencies and to communicate this difference with one another. Furthermore, each of the communication devices is configured to compensate for these differences before or after the timestamps are exchanged and to send a compensation indicator of whether the compensation has been performed. If the compensation has not been performed, either of the communication devices can compensate for the clock frequency differences after receiving the timestamps based on the compensation indicator. By using compensated clock frequencies based on a single clock reference, highly accurate ranging measurements are obtained using round trip propagation time calculations.

First claim

What is claimed:

1. A method, comprising:
determining, at a first communication device that utilizes a first clock having a first clock frequency, a first timestamp corresponding to when a first transmission is transmitted by a second communication device that utilizes a second clock having a second clock frequency;
determining, at the first communication device, a second timestamp corresponding to when a second transmission is received at the second communication device; and
determining, at the first communication device, whether the first communication device requested a signal exchange that includes the first transmission and the second transmission;
determining, at the first communication device, whether the first communication device is to generate a compensated first timestamp and a compensated second timestamp to compensate for a difference between the first clock frequency and the second clock frequency, wherein the determining is based on whether the first communication device requested the signal exchange; and
generating, at the first communication device, the compensated first timestamp and the compensated second timestamp in response to determining that the first communication device is to generate the compensated first timestamp and the compensated second timestamp to compensate for the difference between the first clock frequency and the second clock frequency;
wherein a wireless communication protocol determines whether the first communication device or the second communication device is to generate the compensated first timestamp and the compensated second timestamp to compensate for the difference between the first clock frequency and the second clock frequency based on which of the first communication device or the second communication device requested the signal exchange that includes the first transmission and the second transmission.

2. The method of claim 1 , further comprising:
determining, at the first communication device, a third timestamp corresponding to when the first transmission is received at the first communication device based on the first clock frequency; and
determining, at the first communication device, a fourth timestamp corresponding to when the second transmission is transmitted by the first communication device based on the first clock frequency.

3. The method of claim 2 , further comprising:
when the first communication device determines that the first communication device is to generate the compensated first timestamp and the compensated second timestamp to compensate for the difference between the first clock frequency and the second clock frequency, calculating, at the first communication device, a round trip time using the compensated first timestamp, the compensated second timestamp, the third timestamp, and the fourth timestamp; and
when the first communication device determines that the first communication device is not to generate the compensated first timestamp and the compensated second timestamp to compensate for the difference between the first clock frequency and the second clock frequency:
generating, at the first communication device, a compensated third timestamp and a compensated fourth timestamp to compensate for the difference between the first clock frequency and the second clock frequency, and
calculating, at the first communication device, the round trip time using the first timestamp, the second timestamp, the compensated third timestamp, and the compensated fourth timestamp.

4. The method of claim 1 , wherein the act of generating comprises:
evaluating a first equation:

[

t
1

(
2
)

=

(

t
1

(
2
)

)

(

1
+

ppm

1
-
2

)

]

⁢
for
⁢

⁢

t
1

(
2
)

;

and
evaluating a second equation:

[

t
2

(
2
)

=

(

t
2

(
2
)

)

(

1
+

ppm

2
-
2

)

]

⁢
for
⁢

⁢

t
2

(
2
)

,

wherein:
t 1 (1) and t 2 (1) represent the first timestamp and the second timestamp, respectively;
ppm 1-2 represents a difference between the first clock frequency and the second clock frequency in parts-per-million; and
t 1 (2) and t 2 (2) represent the compensated first timestamp and the compensated second timestamp, respectively.

5. The method of claim 1 , wherein the first transmission includes a fine timing measurement packet, and
wherein the second transmission includes an acknowledgement of the fine timing measurement packet.

6. The method of claim 1 , wherein the wireless communication protocol specifies that the communication device that requested the signal exchange is to generate the compensated first tim

Assignees

• Marvell World Trade Ltd

Inventors

• Zhang Hongyuan
• Yu Mao
• Yong Su Khiong
• Srinivasa Sudhir

Classifications

• H04W56/004 Primary

  compensating for timing error of reception due to propagation delay · CPC title

• G01S11/02

  using radio waves (G01S19/00 takes precedence) · CPC title

• G01S13/767

  Responders; Transponders (teaching or practice apparatus for gun-aiming or gun-laying using reflecting targets or active targets F41G3/26) · CPC title

• H04W56/002

  Mutual synchronization · CPC title

• H04W64/003

  locating network equipment · CPC title