Claims
- 1. A method of timing synchronization to a symbol boundary of a packet comprising:
performing an auto-correlation on samples of an incoming packet to identify the symbol and a first approximation of a trailing boundary of the symbol; and performing a cross-correlation between samples of the incoming packet and standard symbol values to more precisely identify the symbol trailing boundary near the first approximation.
- 2. A method of claim 1, wherein the symbol is the last symbol in a preamble.
- 3. A method of claim 2, wherein performing a cross-correlation further includes processing the result of the cross-correlation to discard a number of the most recent cross-correlation values and identify the symbol trailing boundary from the remaining cross-correlation values.
- 4. A method of claim 3, wherein identifying the symbol timing boundary includes locating a number of maximum peaks in the remaining cross-correlation values and determining the symbol trailing boundary depending on the distance between the maximum peaks.
- 5. A method of claim 4, wherein identifying the symbol timing boundary further includes repeatedly selecting a maximum peak occurring earliest in time as the symbol timing boundary unless any of the remaining maximum peaks occurs a certain distance of cross-correlation values or more away, until a maximum peak has been identified as a symbol timing boundary.
- 6. A method of claim 5 wherein the number of maximum peaks is 3.
- 7. A method of claim 5 wherein the certain distance of cross-correlation values is 10.
- 8. A method of claim 1 wherein the packet and standard symbol values conform to the IEEE 802.11a standard.
- 9. A method of claim 1 wherein the packet and standard symbol values conform to the IEEE 802.11g standard.
- 10. A method of claim 1 further comprising:
detecting a rise in short power, where a rise is determined when the incoming power of a packet is above a set threshold for a set number of consecutive clock cycles; and in response to detection of a rise in short power performing the auto-correlation.
- 11. A method of claim 10 wherein the set threshold is four consecutive clock cycles.
- 12. A method of claim 1 wherein the timing synchronization occurs at a network access point.
- 13. A method of claim 1 where in the timing synchronization occurs at a individual mobile stations.
- 14. A method of timing synchronization to a symbol boundary of a packet conforming to an IEEE 802.11 standard occurring at a network access point comprising:
detecting a rise in short power, wherein the incoming power of a signal is above a set threshold for a set number of consecutive clock cycles; in response to detection of a rise in short power, performing an auto-correlation on samples of an incoming packet to identify the preamble and a first approximation of a trailing boundary of the preamble; and performing a cross-correlation between samples of an incoming packet and a standard preamble and processing the results by discarding a number of the most recent cross-correlation values, locating a number of maximum peaks in the remaining cross-correlation values, then repeatedly selecting a maximum peak occurring earliest in time as the symbol timing boundary unless any of the remaining maximum peaks occurs a certain distance of cross-correlation values or more away, until a maximum peak has been identified as a symbol timing boundary near the first approximation.
- 15. An apparatus for timing synchronization to a symbol boundary of a packet comprising:
an auto-correlator that performs an auto-correlation on samples of an incoming packet; a cross-correlator that performs a cross-correlation between samples of the incoming packet and standard symbol values; and a processor with inputs from both the auto-correlator and the cross-correlator, wherein the processor first identifies a first approximation of a trailing boundary of the symbol using the input from the auto-correlator, and subsequently more precisely identifies the symbol timing boundary near the first approximation using the input from the cross-correlator.
- 16. An apparatus of claim 15 further comprising:
a delay line, the delay line having a plurality of pipelined registers for receiving samples of an incoming packet, and having outputs to provide sample values to the auto-correlator and cross-correlator.
- 17. An apparatus of claim 16 wherein the cross-correlator includes a peak processing module for discarding a number of the most recent cross-correlation values and identifying the symbol timing boundary from the remaining cross-correlation values.
- 18. An apparatus of claim 17 wherein the peak processing module identifies the symbol timing boundary by locating a number of maximum peaks in the remaining cross-correlation values and determining the symbol trailing boundary depending on the distance between the maximum peaks.
- 19. An apparatus of claim 18 wherein the peak processing module further identifies the symbol timing boundary by repeatedly selecting a maximum peak occurring earliest in time as the symbol timing boundary unless any of the remaining maximum peaks occurs a certain distance of cross-correlation values or more away, until a maximum peak has been identified as a symbol timing boundary.
- 20. An apparatus of claim 19 wherein the number of maximum peaks is 3.
- 21. An apparatus of claim 19 wherein the distance of cross-correlation values is 10.
- 22. An apparatus of claim 15 wherein the packet and standard preamble conform to the IEEE 802.11a standard.
- 23. An apparatus of claim 15 wherein the packet and standard preamble conform to the IEEE 802.11g standard.
- 24. An apparatus of claim 15 further comprising:
a short power circuit connected to the registers of the delay line that detects a rise in short power, where a rise is determined when the incoming power of a packet is above a set threshold for a set number of consecutive data samples; and wherein the processor further comprises an input from the short power circuit, and initiates the performance of the auto-correlation circuit when prompted by the short power circuit.
- 25. An apparatus of claim 24 wherein the set threshold is four consecutive data samples.
- 26. An apparatus of claim 15 wherein the apparatus is located in a network access point.
- 27. An apparatus located in network access point for timing synchronization to a symbol boundary of a packet conforming to an IEEE 802.11 standard comprising:
a delay line, the delay line having a plurality of pipelined registers for receiving samples of an incoming packet; an auto-correlator connected to registers of the delay line that performs an auto-correlation on samples of an incoming packet; a cross-correlator connected to registers of the delay line that performs a cross-correlation between samples of the incoming packet and standard preamble values, and includes a peak processing module for discarding a number of the most recent cross-correlation values, locating a number of maximum peaks in the remaining cross-correlation values and determining the symbol trailing boundary depending on the distance between the maximum peaks, and then repeatedly selecting a maximum peak occurring earliest in time as the symbol timing boundary unless any of the remaining maximum peaks occurs a certain distance of cross-correlation values or more away, until a maximum peak has been identified as a symbol timing boundary; a short power circuit connected to the registers of the delay line that detects a rise in short power, where a rise is determined when the incoming power of a packet is above a set threshold for a set number of consecutive data samples; and a processor with inputs from the auto-correlation circuit, the cross-correlation circuit, and the short power circuit, wherein the processor initiates the performance of the auto-correlation circuit when prompted by the short power circuit, then identifies a first approximation of a trailing boundary of the preamble using the input from the auto-correlation circuit, and subsequently more precisely identifies the symbol timing boundary near the first approximation using the input from the cross-correlation circuit.
- 28. An apparatus for timing synchronization to a symbol boundary of a packet comprising:
means for performing an auto-correlation on samples of an incoming packet to identify the preamble and a first approximation of a trailing boundary of the preamble; and means for performing a cross-correlation between samples of the incoming packet and standard preamble values to more precisely identify the symbol timing boundary near the first approximation.
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application No. 60/426,214, filed Nov. 14, 2002. The entire teachings of the above application are incorporated herein by reference.
Provisional Applications (1)
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Number |
Date |
Country |
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60426214 |
Nov 2002 |
US |