Beacon frame monitoring

Patent metadata

Field	Value
Publication number	US-9398519-B2
Application number	US-201213539237-A
Country	US
Kind code	B2
Filing date	Jun 29, 2012
Priority date	Jun 22, 2012
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

Techniques are disclosed relating to reception of beacon frames. In one embodiment, an apparatus is disclosed that includes a radio circuit. The radio circuit is configured to determine an estimated time period during which the radio circuit will receive a next beacon frame from a wireless access point associated with a wireless channel. The estimated time period is determined relative to a clock of the radio circuit. The radio circuit is further configured to begin monitoring the wireless channel for the next beacon frame during the estimated time period.

First claim

What is claimed is:

1. A device, comprising:
a radio circuit configured to:
receive an initial frame specifying a beacon interval and a timestamp corresponding to a clock of a first wireless access point, wherein the clock of the first wireless access point has a different local time than a clock of a second wireless access point;
determine an estimated time period during which the radio circuit will receive a next beacon frame from the first wireless access point associated with a wireless channel, wherein the radio circuit is configured to determine the estimated time period by:
performing a modulo operation with the timestamp as a dividend and the beacon interval as a divisor;
subtracting a result of the modulo operation from a value of a local clock of the radio circuit; and
adding a multiple of the beacon interval to a result of the subtracting to determine the estimated time period;

wherein the radio circuit is further configured to determine the estimated time period while the value of the local clock is synchronized with the clock of the second wireless access point, and wherein the radio circuit is configured to further determine the estimated time period without synchronizing the value of the local clock with the timestamp; and
begin monitoring the wireless channel for the next beacon frame during the estimated time period.

2. The device of claim 1 , wherein the radio circuit is further configured to send a probe request to the first wireless access point to initiate transmission of the initial frame.

3. The device of claim 1 , wherein the radio circuit is further configured to:
monitor, based on the estimated time period, the wireless channel for additional beacon frames broadcasted periodically by the first wireless access point;
detect a failure to receive one of the additional beacon frames;
in response to detecting the failure, send a probe request to the first wireless access point to receive a probe response; and
determine another estimated time period based on the probe response.

4. The device of claim 1 , wherein the radio circuit is further configured to enter and exit a low power state before beginning the monitoring of the wireless channel for the next beacon frame.

5. A non-transitory computer readable medium having program instructions stored thereon, wherein the program instructions are executable by a device to cause the device to perform operations comprising:
receiving an initial frame over a wireless channel from a wireless access point, wherein the initial frame includes a timestamp of the wireless access point and a beacon interval;
determining an estimated time period during which the device will receive a beacon frame from the wireless access point, wherein the estimated time period is determined based on the timestamp, the beacon interval, and a current time value for a clock of the device, wherein determining the estimated time period includes:
performing a modulo operation with the timestamp as a dividend and the beacon interval as a divisor;
subtracting a result of the modulo operation from the current time value; and
adding a multiple of the beacon interval to a result of the subtracting, wherein the estimated time period is a result of the adding.

6. The computer readable medium of claim 5 , wherein the operations further comprise:
beginning monitoring for the beacon frame within three milliseconds of the estimated time period.

7. The computer readable medium of claim 5 , wherein receiving the initial frame includes submitting a probe request to the wireless access point to cause transmission of a probe response, and wherein the probe response is the initial frame.

8. The computer readable medium of claim 5 , wherein receiving the initial frame includes monitoring the wireless channel for a periodic broadcast of a beacon frame by the wireless access point.

9. A device, comprising:
a clock configured to maintain a local time value;
a radio circuit configured to:
determine an estimated time period during which the radio circuit will receive a next beacon frame from a first wireless access point associated with a wireless channel, wherein the radio circuit is further configured to determine the estimated time period based on the local time value, a timestamp specified in a frame from the first wireless access point, and a beacon interval specified in the frame by:
performing a modulo operation with the timestamp as a dividend and the beacon interval as a divisor;
subtracting a result of the modulo operation from the local time value; and
adding a multiple of the beacon interval to a result of the subtracting to determine the estimated time period;

wherein the radio circuit is configured to further determine the estimated time period while the local time value is synchronized with a clock of a second wireless access point that has a different local time than a clock of the first wireless access point; and
wait until the estimated time period to monitor the wireless channel for the next beacon frame.

10. The device of claim 9 , wherein the frame is a previous beacon frame specifying a timestamp of the first wireless access point and a beacon interval.

11. The device of claim 9 , wherein the radio circuit is further configured to determine, for each of a plurality of wireless access points, a respective estimated time period during which the radio circuit will receive a next beacon frame from each wireless access point.

12. The device of claim 11 , wherein the radio circuit is further configured to:
receive, from a first of the plurality of wireless access points, timing information indicative of local time values of clocks associated with other ones of the wireless access points; and
determine an estimated time period for a second wireless access point based on the received timing information, wherein the estimated time period for the second wireless access point is an estimated time period during which the radio circuit will receive a next beacon frame from the second wireless access point.

13. The device of claim 9 , wherein the radio circuit is further configured to:
communicate with another wireless access point while waiting until the estimated time period; and
resume communication with the other wireless access point after monitoring the wireless channel for the next beacon frame.

Assignees

• Chhabra Kapil
• Thomas Tito
• Apple Inc

Inventors

• Chhabra Kapil
• Thomas Tito

Classifications

• H04W48/12 Primary

  using downlink control channel · CPC title