Wireless communication apparatus for synchronizing a frame cycle's beginning position in relation to other devices
A communication station needs to autonomously and synchronously operate by maintaining an equal frame interval. A clock error is measured from a received packet in a wireless communication system where a beacon is transmitted periodically. This clock error is used to synchronize a counter to count the beacon's transmission/reception time and adjust a clock cycle deviation for synchronization. The synchronization is possible even in the case of restoration from a sleep state when the reference clock accuracy is poor. A period to maintain the sleep state can be extended irrespectively of the clock accuracy. It is possible to prevent desynchronization due to incorrect synchronization with an abnormal value.
1. A wireless communication apparatus operating in a wireless communication environment where communication stations communicate with each other at specified frame cycles, said apparatus comprising:
communication means for sending and receiving wireless data on a communication channel;
notification signal generation means for generating a notification signal containing time information about a frame cycle;
notification signal analysis means for analyzing a notification signal received from a peripheral station; and
synchronization means for, based on time information obtained from a notification signal received from a peripheral station, synchronizing a frame cycle beginning position in relation to said peripheral station and adjusting frame cycle synchronization.
2. The wireless communication apparatus according to claim 1 further comprising:
a clock generator and means for counting clocks output from said clock generator to measure a frame cycle,
wherein, if time information is obtained from a notification signal received from a peripheral station, said synchronization means measures a frame cycle beginning position error obtained based on the time information as clock count error α, subtracts α from a count value to synchronize the frame cycle beginning position, and extends the count value per frame by α to synchronize the frame cycle.
3. The wireless communication apparatus according to claim 1 , wherein, if a frame cycle beginning position error with respect to a peripheral station exceeds a specified threshold, said synchronization means synchronizes the frame cycle beginning position with said peripheral station but does not synchronize the frame cycle.
4. The wireless communication apparatus according to claim 1 , further comprising:
scan operation means for receiving said notification signal at a specified scan cycle,
wherein said synchronization means detects a frame cycle beginning position error based on a received notification signal and said scan operation means increases said scan cycle if the frame cycle beginning position error is smaller than a specified threshold.
5. The wireless communication apparatus according to claim 4 , wherein said scan operation means shortens a scan cycle if a frame beginning position error with reference to a peripheral station exceeds a specified threshold.
6. The wireless communication apparatus according to claim 1 , wherein said notification signal generation means provides a notification signal, including a flag, immediately after synchronization, and said synchronization means, upon reception of said notification signal, synchronizes a frame cycle beginning position with said first communication station but does not synchronize the frame cycle if a frame cycle beginning position error exceeds a specified threshold.
7. The wireless communication apparatus according to claim 1 , wherein said synchronization means, upon reception of a notification signal from a newly entered station, synchronizes a frame cycle beginning position but does not synchronize the frame cycle.
8. A wireless communication method employed by a wireless communication apparatus in a wireless communication environment where notification signals are transmitted periodically, the method comprising:
generating a notification signal, at the apparatus, containing clock cycle time information;
analyzing a notification signal, at the apparatus, received from a peripheral station; and
synchronizing, at the apparatus, a frame cycle beginning position in relation to a peripheral station, the synchronization being based on time information obtained from the notification signal received from said peripheral station; and
adjusting frame cycle synchronization at the apparatus.
9. A computer-readable medium storing computer-readable instructions thereon, the computer-readable instructions when executed by a computer cause the computer to perform the steps comprising:
generating a notification signal containing clock cycle time information;
analyzing a notification signal received from a peripheral station; and
synchronizing a frame cycle beginning position in relation to the peripheral station based on the clock cycle time information obtained from the notification signal received from said peripheral station; and
adjusting frame cycle synchronization.