Method and apparatus for clock synchronization in a wireless network
First Claim
1. A method of synchronizing a local clock value in a wireless receiver receiving a data unit containing synchronization information, the method comprising:
- receiving a first data unit containing synchronization information transmitted by a first transmitter having a local clock value;
copying a local free-running clock at a known reference point in time relative to the time the first data unit was received to generate a local timestamp;
extracting the synchronization information from the received first data unit; and
calculating an offset to the free-running clock using the extracted synchronization information and the local timestamp, the calculating in non real-time,such that the sum of the calculated offset and the value of the free-running clock provides a local clock value for the receiver, and such that the receiver'"'"'s local clock value is approximately synchronized in time to the local clock value of the first transmitter.
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Accused Products
Abstract
A method and apparatus for synchronizing a local clock value in a wireless receiver receiving a data unit containing synchronization information. The method includes receiving a first data unit containing synchronization information, extracting the synchronization information from the received first data unit, copying a local free-running clock at a known reference point in time relative to the time the first data unit was received to generate a local timestamp; and calculating an offset to the free-running clock using the extracted synchronization information and the local timestamp, the calculating in non real-time, such that the sum of the calculated offset and the value of the free-running clock provides a local clock value that is approximately synchronized in time. The apparatus implementing the method is part of a node of a wireless station, and provides a time synchronization function, typically at the MAC layer.
110 Citations
51 Claims
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1. A method of synchronizing a local clock value in a wireless receiver receiving a data unit containing synchronization information, the method comprising:
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receiving a first data unit containing synchronization information transmitted by a first transmitter having a local clock value; copying a local free-running clock at a known reference point in time relative to the time the first data unit was received to generate a local timestamp; extracting the synchronization information from the received first data unit; and calculating an offset to the free-running clock using the extracted synchronization information and the local timestamp, the calculating in non real-time, such that the sum of the calculated offset and the value of the free-running clock provides a local clock value for the receiver, and such that the receiver'"'"'s local clock value is approximately synchronized in time to the local clock value of the first transmitter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
such that the receiver'"'"'s local clock value is approximately synchronized in time to the local clock value of the second transmitter.
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8. A method as recited in claim 7, wherein the receiver is part of a station in an infrastructure network, wherein the extracted synchronization information from the received second data unit is a second received timestamp value, and wherein re-calculating the offset includes:
forming the re-calculated offset as the second received timestamp less the copied free running clock value and less the difference between the second known reference point in time and the location in the received second data unit of the extracted synchronization information.
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9. A method as recited in claim 8, wherein the difference between the second known reference point and the location in the received second data unit of the extracted synchronization information is a function of the data rate.
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10. A method as recited in claim 7, wherein the receiver is part of a station in an ad hoc network and wherein the updating is carried out only if the receiver'"'"'s local clock value lags the time using the re-calculated offset.
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11. A method as recited in claim 10, further comprising:
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the station cancelling any outstanding beacon transmission; wherein the re-calculating the offset includes; forming the re-calculated offset as the second received timestamp value less the copied free running clock value and less the difference between the known reference point in time relative to the time the second data unit was received and the location in the received second data unit of the extracted synchronization information.
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12. A clock synchronization method in a wireless node of a wireless network, the wireless node including a receiver, the method comprising:
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generating an offset to the value of a free-running clock such that a local time reference determined as the sum of the value of the free-running clock and the generated offset is approximately synchronized to a previous timestamp in a previously received data unit containing a previous timestamp, the generating forming a determined offset; and receiving a new data unit containing a new timestamp at the receiver; extracting the new timestamp from the received new data unit containing the new timestamp; updating the determined offset after the receipt of the new data unit using the extracted new timestamp and the value of the free-running clock at a known reference point in time relative to the time the new data unit was received. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A method of transmitting a data unit containing synchronization information from a wireless node of a wireless network, the wireless node including a transmitter, the method comprising:
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determining an offset to the value of a local free-running clock at a known reference point in time relative to the time a data unit for transmission is to be transmitted; generating a timestamp corresponding to the sum of the value of the local free-running clock at the known reference point and the determined offset; inserting the generated timestamp into the data unit for transmission at a known point in the data unit; and transmitting the data unit for transmission containing the inserted time stamp, wherein the wireless node includes a receiver to receive at least one data unit containing synchronization information, wherein the synchronization information in a received data unit is used to calculate an adjustment factor to the value of the free-running clock, and wherein determining the offset includes forming the sum of a previously determined adjustment factor and the difference between the known reference point in time relative to the time the data unit is transmitted and the location in the data unit of the inserted timestamp. - View Dependent Claims (29)
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30. An apparatus to synchronize a clock in a wireless receiver, the apparatus comprising:
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a free-running clock; means for receiving a first data unit containing synchronization information; means for copying the free-running clock contents at a known reference point in time relative to the time the data unit was received to generate a local timestamp, the copying means coupled to the free-running clock; means for extracting the synchronization information from the received first data unit to form an extracted timestamp, the extracting means coupled to the receiving means; means for calculating an offset to the free-running clock using the extracted timestamp and the local timestamp, the calculating means coupled to the extracting means and the copying means, such that the sum of the calculated offset and the value of the free-running clock provides a local clock value that is approximately synchronized in time. - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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47. An apparatus for transmitting a data unit containing synchronization information from a wireless node of a wireless network, the wireless node including a transmitter, the apparatus comprising:
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a local free-running clock; means for copying the value of the free-running clock at a known reference point in time relative to the time a data unit for transmission is to be transmitted, the means for copying coupled to the local free-running clock, the copying providing a local timestamp; means for generating a timestamp, the generating means including means for determining an offset to the local timestamp, the timestamp corresponding to the sum of the local timestamp and the determined offset, the generating means coupled to the copying means; means for inserting the generated timestamp into the data unit for transmission at a known point in the data unit, the inserting means coupled to the timestamp generating means; and means for transmitting the data unit for transmission containing the inserted timestamp, the transmitting means coupled to the timestamp insertion means. - View Dependent Claims (48, 49, 50, 51)
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Specification