Time stamp replication within a wireless network using error calculation
Time stamp replication within wireless networks is described. In an embodiment, a wireless station receives an input time stamp and uses this input time stamp to generate an output time stamp. The wireless station transmits the output time stamp to wireless stations in one of a number of groups which make up the wireless network. The output time stamp is generated to compensate for delays between receiving the input time stamp and transmitting the output time stamp such that output time stamp which is transmitted at a time T corresponds to the value that the input time stamp would have had if it had been received at time T (and not at a time earlier than T). This may, therefore, reduce or eliminate independent time stamp errors and jitter caused by multiple disparate systems and processes.
1. A method comprising:
receiving an input time stamp at a wireless station in a wireless network, the wireless network comprising a plurality of groups of wireless stations, each group running with a different timing clock;
extracting the input time stamp;
calculating an error between a value of the input time stamp and a value of a local counter driven by a local oscillator;
adjusting a rate of the local counter based on the calculated error;
using the input time stamp to overwrite the local counter;
generating an output time stamp based on the value of the local counter at a time a frame comprising the output time stamp is predicted to be transmitted; and
transmitting the frame comprising the output time stamp to wireless stations within one of the plurality of groups.
2. The method according to claim 1 , wherein receiving an input time stamp comprises:
receiving a frame comprising an input time stamp; and
extracting the input time stamp from the received frame.
3. The method according to claim 1 , further comprising determining an amount of drift between the rate of the local counter and a master time stamp based on the elapsed time since a previous adjustment.
4. The method according to claim 1 , further comprising repeating adjusting the rate of the local counter each time an input stamp is received.
5. The method according to claim 1 , wherein the frame comprising an input time stamp is received via a first communication interface and the frame comprising the output time stamp is transmitted via a second communication interface.
6. The method according to claim 1 , wherein the frame comprising an input time stamp is received via a first communication interface and the frame comprising the output time stamp is transmitted via a second communication interface, and
wherein the wireless station comprises a single communication interface which operates as both the first and second communication interfaces.
7. The method according to claim 1 , wherein the frame comprising an input time stamp is received via a first communication interface and the frame comprising the output time stamp is transmitted via a second communication interface, and
wherein the second communication interface is a wireless interface.
8. The method according to claim 1 , wherein the frame comprising an input time stamp is received via a first communication interface and the frame comprising the output time stamp is transmitted via a second communication interface, and
wherein the first communication interface is a wireless interface.
9. The method according to claim 1 , wherein the frame comprising an input time stamp is received via a first communication interface and the frame comprising the output time stamp is transmitted via a second communication interface, and wherein the first communication interface is a wired interface.
10. The method according to claim 1 , wherein the input time stamp is an original time stamp generated by an access point in the wireless network.
11. The method according to claim 1 , wherein the input time stamp is a time stamp received from a master station in another group and generated by the master station based on an input time stamp received by the master station.
12. The method according to claim 1 , wherein the input time stamp is a time stamp received from a master station in another group and generated by the master station based on an input time stamp received by the master station, and
wherein the input time stamp received by the master station is an original time stamp generated by an access point in the wireless network.
13. The method according to claim 1 , wherein the frames are beacon frames.
14. The method according to claim 1 , wherein the wireless station is a Wi-Fi™ station.
15. The method according to claim 1 , wherein the wireless station is a wireless speaker.
16. A wireless station comprising:
a local counter driven by a local oscillator;
a first communication interface arranged to receive an input time stamp; and
a second communication interface arranged to transmit an output time stamp to wireless stations in one of a plurality of groups in a wireless network, each group running with a different timing clock,
wherein the output time stamp is generated by overwriting the local counter and generating the output time stamp based on a value of the local counter at a time the output time stamp is predicted to be transmitted; and
wherein the wireless station further comprises a rate adjustment unit arranged to calculate an error between a value of the input time stamp and the value of the local counter and adjust a rate of the local counter based on the error, prior to overwriting the local counter.
17. The wireless station according to claim 16 , wherein the input time stamp is received in a frame and the first communication interface is arranged to extract the input time stamp from the received frame.
18. The wireless station according to claim 16 , wherein the rate adjustment unit is arranged to determining an amount of drift between the rate of the local counter and a master time stamp based on the elapsed time since a previous adjustment.
19. The wireless station according to claim 16 , wherein the rate adjustment unit is arranged to repeat adjusting the rate of the local counter each time an input stamp is received.
20. A non-transitory computer readable storage medium having stored thereon a computer readable dataset description of an integrated circuit that, when processed, causes a layout processing system to generate a circuit layout description used in an integrated circuit manufacturing system to manufacture a device comprising:
a local counter driven by a local oscillator;
a first communication interface arranged to receive an input time stamp; and
a second communication interface arranged to transmit an output time stamp to wireless stations in one of a plurality of groups in a wireless network, each group running with a different timing clock,
wherein the output time stamp is generated by overwriting the local counter and generating the output time stamp based on a value of the local counter at a time the output time stamp is predicted to be transmitted; and
wherein the device further comprises a rate adjustment unit arranged to calculate an error between a value of the input time stamp and the value of the local counter and adjust a rate of the local counter based on the error, prior to overwriting the local counter.