Synchronizing wireless devices using timestamps and relative clock offsets of the wireless devices
First Claim
1. A method of synchronizing a plurality of wireless devices, comprising:
- sending a first set of multiple reference messages from an access point to each of the plurality of wireless devices, each of the multiple reference messages being sent to all of the plurality of wireless devices;
recording, at each of the wireless devices, a timestamp corresponding to each of the reference messages that is received;
in response to a request from the access point, sending from each of the wireless devices a response to the access point that includes the timestamps corresponding to the reference messages received at each of the wireless devices; and
determining, at the access point, relative clock offsets between each of the wireless devices using the timestamps, wherein the relative clock offsets are determined at the access point using only the timestamps corresponding to the reference messages received by the wireless devices that are recorded at each of the wireless devices and included in the responses sent to the access point from the wireless devices, the relative clock offsets between each of the wireless devices being determined independently of any timestamps recorded by the access point.
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Abstract
Wireless communication may be provided between an access point and one or more wireless devices, such as wireless sensors used in avionics applications for sensing, monitoring and control systems. Synchronization of wireless devices may be required so that certain actions, such as data acquisition, are performed at precisely controlled time instances. The system described herein provides for rapid synchronization of wireless devices that does not require the use of prior timing data and that may be performed without communication directly between the wireless devices. Further, techniques are provided for addressing packet losses and packet propagation delays.
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Citations
26 Claims
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1. A method of synchronizing a plurality of wireless devices, comprising:
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sending a first set of multiple reference messages from an access point to each of the plurality of wireless devices, each of the multiple reference messages being sent to all of the plurality of wireless devices; recording, at each of the wireless devices, a timestamp corresponding to each of the reference messages that is received; in response to a request from the access point, sending from each of the wireless devices a response to the access point that includes the timestamps corresponding to the reference messages received at each of the wireless devices; and determining, at the access point, relative clock offsets between each of the wireless devices using the timestamps, wherein the relative clock offsets are determined at the access point using only the timestamps corresponding to the reference messages received by the wireless devices that are recorded at each of the wireless devices and included in the responses sent to the access point from the wireless devices, the relative clock offsets between each of the wireless devices being determined independently of any timestamps recorded by the access point. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A computer readable storage medium storing computer software that synchronizes a plurality of wireless devices, the computer software comprising:
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executable code that sends a set of multiple reference messages from an access point to each of the plurality of wireless devices, each of the multiple reference messages being sent to all of the plurality of wireless devices; executable code that records, at each of the wireless devices, a timestamp corresponding to each of the reference messages that is received; executable code that, in response to a request from the access point, sends from each of the wireless devices a response to the access point with the timestamps corresponding to the reference messages received at each of the wireless devices; and executable code that determines, at the access point, relative clock offsets between each of the wireless devices using the timestamps, wherein the relative clock offsets are determined at the access point using only the timestamps corresponding to the reference messages received by the wireless devices that are recorded at each of the wireless devices and included in the responses sent to the access point from the wireless devices, the relative clock offsets between each of the wireless devices being determined independently of any timestamps recorded by the access point. - View Dependent Claims (11, 12)
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- 13. The computer readable storage medium according to claim, wherein the first set of multiple reference messages are transmitted by the access point to the wireless devices after an expected wake up time of each of the wireless devices from a sleep mode.
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15. A method of synchronizing a first wireless device and a second wireless device, comprising:
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sending a synchronization message from the first wireless device to the second wireless device, wherein the synchronization message includes a first timestamp generated by the first wireless device; receiving the synchronization message at the second wireless device, wherein the second wireless device records a second timestamp corresponding to receipt of the synchronization message; sending a synchronization response from the second wireless device, wherein the synchronization response includes the first timestamp, the second timestamp, and a third timestamp corresponding to the sending of the synchronization response by the second wireless device; receiving the synchronization response at the first wireless device, wherein the first wireless device records a fourth timestamp corresponding to receipt of the synchronization response; and determining a relative clock offset of the first wireless device and the second wireless device using a set of timestamps including the first timestamp, the second timestamp, the third timestamp and the fourth timestamp, wherein the set of timestamps used to determine the relative clock offset of the first and second wireless devices further includes timestamps corresponding to multiple synchronization messages or multiple synchronization responses that are transmitted according to controlled delay times, the controlled delay times being determined and applied to reduce an effect of an operation cycle bias of the wireless devices on the determination of the relative clock offset. - View Dependent Claims (16, 17, 18, 19, 20)
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21. A computer readable storage medium storing computer software that synchronizes a first wireless device and a second wireless device, the computer software comprising:
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executable code that sends a synchronization message from the first wireless device to the second wireless device, wherein the synchronization message includes a first timestamp generated by the first wireless device; executable code that receives the synchronization message at the second wireless device, wherein the second wireless device records a second timestamp corresponding to the synchronization message that is received; executable code that sends a synchronization response from the second wireless device, wherein the synchronization response includes the first timestamp, the second timestamp, and a third timestamp corresponding to the sending of the synchronization response by the second wireless device; executable code that receives the synchronization response at the first wireless device, wherein the first wireless device records a fourth timestamp corresponding to receipt of the synchronization response; and executable code that determines a relative clock offset of the first wireless device and the second wireless device using a set of timestamps including the first timestamp, the second timestamp, the third timestamp and the fourth timestamp, wherein the set of timestamps used to determine the relative clock offset of the first and second wireless devices further includes timestamps corresponding to multiple synchronization messages or multiple synchronization responses that are transmitted according to controlled delay times, the controlled delay times being determined and applied to reduce an effect of a bias of an operation cycle of the wireless devices on the determination of the relative clock offset. - View Dependent Claims (22, 23, 24, 25, 26)
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Specification