Claims
- 1. A method for determining a local oscillator carrier offset frequency in a communication system, said method comprising the steps of:
receiving a signal having at least one spectral null inserted therein; locating a position of said spectral null in said signal; and using said position of said spectral null to estimate said local oscillator carrier offset frequency if one or more predefined conditions are satisfied.
- 2. The method according to claim 1, wherein said signal is an OFDM signal.
- 3. The method according to claim 1, wherein said signal is a DMT signal.
- 4. The method according to claim 1, wherein said predefined conditions ensure that a signal-to-noise ratio satisfies predefined conditions.
- 5. The method according to claim 1, wherein said predefined conditions evaluate a ratio of the powers of the carriers to determine if their averaged difference is less than some predefined threshold.
- 6. The method according to claim 5, wherein an acquisition mode is complete if said averaged difference is less than said predefined threshold.
- 7. The method according to claim 1, wherein said predefined conditions evaluate a ratio of the powers of the carriers during a tracking mode to determine if their averaged difference are consistently greater than a threshold indicating a that a loss of tracking has occurred.
- 8. The method according to claim 1, wherein said local oscillator carrier offset frequency is determined by said position of said spectral null in a tracking mode and is zero in an acquisition mode.
- 9. The method according to claim 1, further comprising the steps of:
extracting a plurality of sub-carriers of said signal after a fast fourier transform (FFT) operation; determining a minimum energy sub-carrier of said plurality of sub-carriers; calculating at least one average energy of said plurality of sub-carriers, excluding an energy of said minimum energy sub-carrier; comparing a ratio of said average energy and said energy of said minimum energy sub-carrier to a predefined threshold; and multiplying an index of said minimum energy sub-carrier by an inter-carrier spacing to generate said local oscillator carrier offset frequency.
- 10. A system for determining a local oscillator carrier offset frequency in a communication system, comprising:
a memory that stores computer-readable code and information relating to local oscillator carrier offset calculations; and a processor operatively coupled to said memory, said processor configured to implement said computer-readable code, said computer-readable code configured to: receive a signal having at least one spectral null inserted therein; locate a position of said spectral null in said signal; and use said position of said spectral null to estimate said local oscillator carrier offset frequency if one or more predefined conditions are satisfied.
- 11. The system according to claim 10, wherein said signal is an OFDM signal.
- 12. The system according to claim 10, wherein said signal is a DMT signal.
- 13. The system according to claim 10, wherein said predefined conditions ensure that a signal-to-noise ratio satisfies predefined conditions.
- 14. The system according to claim 10, wherein said predefined conditions evaluate a ratio of the powers of the carriers to determine if their averaged difference is less than some predefined threshold.
- 15. The system according to claim 14, wherein an acquisition mode is complete if said averaged difference is less than said predefined threshold.
- 16. The system according to claim 10, wherein said predefined conditions evaluate a ratio of the powers of the carriers during a tracking mode to determine if their averaged difference are consistently greater than a threshold indicating a that a loss of tracking has occurred.
- 17. The system according to claim 10, wherein said local oscillator carrier offset frequency is determined by said position of said spectral null in a tracking mode and is zero in an acquisition mode.
- 18. The system according to claim 10, wherein said processor is further configured to:
extract a plurality of sub-carriers of said signal after a fast fourier transform (FFT) operation; determine a minimum energy sub-carrier of said plurality of sub-carriers; calculate at least one average energy of said plurality of sub-carriers, excluding an energy of said minimum energy sub-carrier; compare a ratio of said average energy and said energy of said minimum energy sub-carrier to a predefined threshold; and multiply an index of said minimum energy sub-carrier by an inter-carrier spacing to generate said local oscillator carrier offset frequency.
- 19. A communication system, comprising:
a receiver for receiving a signal having at least one spectral null inserted therein; means for locating a position of said spectral null in said signal; and means for using said position of said spectral null to estimate said local oscillator carrier offset frequency if one or more predefined conditions are satisfied.
- 20. The communication system according to claim 19, wherein said signal is an OFDM signal.
- 21. The communication system according to claim 19, wherein said signal is a DMT signal.
- 22. The communication system according to claim 19, wherein said predefined conditions ensure that a signal-to-noise ratio satisfies predefined conditions.
- 23. The communication system according to claim 19, wherein said predefined conditions evaluate a ratio of the powers of the carriers to determine if their averaged difference is less than some predefined threshold.
- 24. The communication system according to claim 23, wherein an acquisition mode is complete if said averaged difference is less than said predefined threshold.
- 25. The communication system according to claim 19, wherein said predefined conditions evaluate a ratio of the powers of the carriers during a tracking mode to determine if their averaged difference are consistently greater than a threshold indicating a that a loss of tracking has occurred.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention is related to U.S. patent application Ser. No. 09/382,847, filed Aug. 25, 1999, entitled “Orthogonal Frequency Division Multiplexed (OFDM) Carrier Acquisition Method,” (Attorney Docket Number Sayeed 9) and U.S. patent application Ser. No. 09/398,502, filed Sep. 17, 1999, entitled “Method and Apparatus for Performing Differential Modulation Over Frequency in an Orthogonal Frequency Division Multiplexing (OFDM) Communication System,” (Attorney Docket Number Riazi 3-11-3), each assigned to the assignee of the present invention and incorporated by reference herein.