Beacon synchronization in wifi based systems
First Claim
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1. A wireless device comprising:
- a transceiver for transmitting and receiving messages to and from an access point, the wireless device having a sleep mode from which a device application wakes up to perform actions and the transceiver may turn on to listen for beacons from the access point to transmit and receive packets; and
a scheduling system which schedules each application wake up and transceiver turn-on time, the scheduling system comprising a clock drift estimator and wake up adjustment procedure which determines an expected clock drift from a history of synchronization errors calculated with each beacon reception, wherein each synchronization error is computed as the difference between a wireless device actual beacon arrival time and the wakeup time;
wherein the scheduling system schedules the wakeup time such that;
tbIdeal−
tbWakeup=Δ
du+E where tbIdeal is an ideal beacon time, tbWakeup is beacon reception wakeup time, Δ
du is device-up period and E reflects the expected clock drift;
wherein the scheduling system schedules the wakeup time independent of timestamps associated with beacons.
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Abstract
A wireless device comprises a transceiver and a scheduling system. The transceiver transmits and receives messages to and from an access point, and has a sleep mode from which it occasionally wakes at wakeup times to listen for beacons from the access point. The scheduling system schedules wakeup times according to historical beacon synchronization data.
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Citations
12 Claims
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1. A wireless device comprising:
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a transceiver for transmitting and receiving messages to and from an access point, the wireless device having a sleep mode from which a device application wakes up to perform actions and the transceiver may turn on to listen for beacons from the access point to transmit and receive packets; and a scheduling system which schedules each application wake up and transceiver turn-on time, the scheduling system comprising a clock drift estimator and wake up adjustment procedure which determines an expected clock drift from a history of synchronization errors calculated with each beacon reception, wherein each synchronization error is computed as the difference between a wireless device actual beacon arrival time and the wakeup time; wherein the scheduling system schedules the wakeup time such that;
tbIdeal−
tbWakeup=Δ
du+Ewhere tbIdeal is an ideal beacon time, tbWakeup is beacon reception wakeup time, Δ
du is device-up period and E reflects the expected clock drift;wherein the scheduling system schedules the wakeup time independent of timestamps associated with beacons. - View Dependent Claims (2, 3, 4, 5, 6, 7, 11, 12)
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8. A wireless system comprising:
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an access point device which periodically transmits beacons to a network, and which is connected to a device node; and a wireless device in the network, the wireless device comprising; a transceiver with an active mode wherein the transceiver is capable of transmitting and receiving messages, and a sleep mode wherein the transceiver is unpowered; an application system which sends and/or receives data to and/or from the device node periodically via the transceiver and the access point; a timer; and a scheduling system which adjusts a wakeup time on the timer before the transceiver enters the sleep mode, the wakeup time being a time at which the transceiver wakes from the sleep mode to the active mode; wherein the scheduling system comprises a clock drift estimator which determines an expected clock drift from a synchronization error calculated with each beacon reception, wherein the synchronization error is determined from a difference between an actual beacon arrival time and the wakeup time; wherein the scheduling system schedules the wakeup time such that;
tbIdeal−
tbWakeup=Δ
du+Ewhere tbIdeal is an ideal beacon time, tbWakeup is beacon reception wakeup time, Δ
du is device-up period and E reflects the expected clock drift;wherein the scheduling system schedule the wakeup time independent of timestamps associated with beacons. - View Dependent Claims (9, 10)
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Specification