Synchronization within wireless devices
View Patent ↗Synchronizing a wireless sensor includes receiving a first command at the wireless sensor, noting a first timestamp value indicating when the first reply is sent, responding to the first command with a first reply, receiving a second command at the wireless sensor that contains a second timestamp value indicating when the first reply was received and a third timestamp value indicating when the second command was sent to the wireless sensor, noting a fourth timestamp value indicating when the second command was received by the wireless sensor, and determining an offset at the wireless sensor using the first, second, third, and fourth timestamp values. The presence of the first timestamp value may be interpreted as a request to provide timestamp information for synchronization. An access point may communicate with the wireless sensor.
1. A method for synchronizing a wireless sensor, comprising:
receiving a first command at the wireless sensor from an access point;
responding to the first command with a first reply sent from the wireless sensor to the access point;
noting, at the wireless sensor, a first timestamp value indicating when the first reply is sent;
receiving a second command at the wireless sensor from the access point that contains a second timestamp value indicating when the first reply was received at the access point and a third timestamp value indicating when the second command was sent from the access point to the wireless sensor;
noting, at the wireless sensor, a fourth timestamp value indicating when the second command was received by the wireless sensor;
determining an offset at the wireless sensor using the first, second, third, and fourth timestamp values, wherein the offset determined at the wireless sensor enables self-synchronization of the wireless sensor with a clock of the access point, and wherein the access point attaches the second and third timestamp values to the second command independently of any timestamp values noted at the wireless sensor; and
compensating for the offset by determining a latest start time for collecting timestamp data by the sensor and an earliest end time for collecting the timestamp data by the sensor, and discarding at least one of a portion of the timestamp data collected prior to the latest start time and a portion of the timestamp data collected after the earliest end time.
2. A method, according to claim 1 , wherein the offset is determined using the formula:
Offset=((the second timestamp value minus the first timestamp value)−(the fourth timestamp value minus the third timestamp value))/2.
3. A method, according to claim 1 , wherein the first timestamp value is provided with the first reply.
4. A method, according to claim 3 , wherein the presence of the first timestamp value is interpreted as a request to provide timestamp information for synchronization.
5. A method, according to claim 1 , wherein the first command is a request to collect data.
6. A method according to claim 5 , wherein the wireless sensor is one of a plurality of wireless sensors, and wherein each of the wireless sensors collects data in synchronization with other ones of the wireless sensors.
7. A method, according to claim 6 , wherein exchanges for synchronizing the wireless sensors overlap.
8. A method, according to claim 1 , wherein the first reply indicates a requested number of exchanges.
9. A method, according to claim 1 , wherein substantially all commands received by the wireless sensor include timestamp values.
10. A non-transitory computer-readable medium storing software that synchronizes a wireless sensor, the software comprising:
executable code that receives a first command at the wireless sensor from an access point;
executable code that responds to the first command with a first reply from the wireless sensor to the access point;
executable code that notes, at the wireless sensor, a first timestamp value indicating when the first reply is sent;
executable code that receives a second command at the wireless sensor from the access point that contains a second timestamp value indicating when the first reply was received at the access point and a third timestamp value indicating when the second command was sent from the access point to the wireless sensor;
executable code that notes, at the wireless sensor, a fourth timestamp value indicating when the second command was received by the wireless sensor;
executable code that determines an offset at the wireless sensor using the first, second, third and fourth timestamp values, wherein the offset determined at the wireless sensor enables self-synchronization of the wireless sensor with a clock of the access point, and wherein the access point attaches the second and third timestamp values to the second command independently of any timestamp values noted at the wireless sensor; and
executable code that compensates for the offset by determining a latest start time for collecting timestamp data by the sensor and an earliest end time for collecting the timestamp data by the sensor, and discarding at least one of a portion of the timestamp data collected prior to the latest start time and a portion of the timestamp data collected after the earliest end time.
11. The non-transitory computer-readable medium according to claim 10 , wherein the offset is determined using the formula:
Offset=((the second timestamp value minus the first timestamp value)−(the fourth timestamp value minus the third timestamp value))/2.
12. The non-transitory computer-readable medium according to claim 10 , wherein the first timestamp value is provided with the first reply.
13. The non-transitory computer-readable medium according to claim 10 , wherein the wireless sensor is one of a plurality of wireless sensors and wherein exchanges for synchronizing the wireless sensors overlap.
14. The non-transitory computer-readable medium according to claim 10 , wherein the first reply indicates a requested number of exchanges.
15. The non-transitory computer-readable medium according to claim 10 , wherein substantially all commands received by the wireless sensor include timestamp values.