Patent EA-002748-B1 (EA)
Title: Method and apparatus for fine frequency synchronization in multi-carrier demodulation
Inventor: EBERLEIN ERNST
IPC: H04L27/26
Filed: 1998-04-14
Abstract: 1. A method of performing a fine frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency in a multi-carrier demodulation system (130) of the type capable of carrying out a differential phase decoding of multi-carrier modulated signals, said signals comprising a plurality of symbols (200), each symbol being defined by phase differences between simultaneous carriers (202) having different frequencies, said method comprising the steps of: a). determining a phase difference between phases of the same carrier in different symbols; b). determining a frequency offset by eliminating phase shift uncertainties corresponding to codeable phase shifts from said phase difference; and c). performing a feedback correction of said carrier frequency deviation based on said determined frequency offset. 2. The method of performing a fine frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency in a multi-carrier demodulation system (130) of the type capable of carrying out a differential phase decoding of multi-carrier modulated signals, said signals comprising a plurality of symbols (200), each symbol being defined by phase differences between simultaneous carriers (202) having different frequencies, said method comprising the steps of: a). determining respective phase of the same carrier in different symbols; b). eliminating phase shift uncertainties corresponding to codeable phase shifts from said phases to determine respective phase deviations; c). determining a frequency offset by determining a phase difference between said phase deviations; performing a feedback correction of said carrier frequency deviation based on said determined frequency offset. 3. The method according to claim 1, wherein steps (a) and (b) are performed for a plurality of carriers (202) in said symbols (200), determining an averaged frequency offset by averaging said determined frequency offsets of said plurality of carriers; performing a feedback correction of said frequency deviation in step (c) based on said averaged frequency offset. 4. The method according to claim 1, wherein steps (a), (b) and (c)are performed for a plurality of carriers (202) in said symbols (200), determining an averaged frequency offset by averaging said determined frequency offsets of said plurality of carriers; performing a feedback correction of said frequency deviation based on said averaged frequency offset. 5. The method according to claim 1, wherein said step (a) of determining a phase difference comprises the step of determining a phase difference between phases of the same carrier (202) in symbols (200) which are adjacent in the time axis direction. 6. The method according to claim 1, wherein said step (b) of determining a frequency offset comprises the step of eliminating phase shift uncertainties corresponding to M-ary phase shifts. 7. The method according to claim 2, wherein said step (a) of determining respective phases comprises the step of determining respective phases of the same carrier (202) in symbols (200) which are adjacent in the time axis direction. 8. The method according to claim 2, wherein said step (b) of eliminating phase shift uncertainties comprises the step of eliminating M-ary phase shifts. 9. An apparatus for performing a fine frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency, for a multi-carrier demodulation system (130) of the type capable of carrying out a differential phase decoding of multi-carrier modulated signals, said signals comprising a plurality of symbols (200), each symbol being defined by phase differences between simultaneous carriers (202) having different frequencies, said apparatus comprising: means (330) for determining a phase difference between phases of the same carrier (202) in different symbols (200); M-ary phase shift keying decision device connected to the output of said means for determining a phase difference, for determining a frequency offset by eliminating phase shift uncertainties corresponding to codeable phase shifts from said phase difference; and means connected to the output of said M-ary phase shift keying decision device for performing a feedback correction of said frequency deviation based on said determined frequency offset. 10. The apparatus for performing a fine frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency, for a multi-carrier demodulation system (130) of the type capable of carrying out a differential phase decoding of multi-carrier modulated signals, said signals comprising a plurality of symbols (200), each symbol being defined by phase differences between simultaneous carriers (202) having different frequencies, said apparatus comprising: means for determining respective phases of the same carrier in different symbols; M-ary phase shift keying decision device connected to the output of said means for determining a phase difference for eliminating phase shift uncertainties corresponding to codeable phase shifts from said phases to determine respective phase deviations; means connected to the output of said M-ary phase shift keying decision device for determining a frequency offset by determining a phase difference between said phase deviations; means connected to the output of said for performing a feedback correction of said frequency deviation based on said determined frequency offset. 11. The apparatus according to claim 9, wherein further comprising: means (344) for determining an averaged frequency offset by averaging determined frequency offsets of a plurality of carriers; and means for performing a feedback correction of said frequency deviation based on said averaged frequency offset. 12. The apparatus according to claim 10, wherein further comprising: means (344) for determining an averaged frequency offset by averaging determined frequency offsets of a plurality of carriers; and means for performing a feedback correction of said frequency deviation based on said averaged frequency offset. 13. The apparatus according to claim 9, wherein said means (330) for determining a phase difference comprises means for determining a phase difference between phases of the same carrier in symbols which are adjacent in the time axis direction. 14. The apparatus according to claim 10, wherein said means for determining respective phases comprises means for determining respective phases of the same carrier in symbols which are adjacent in the time axis direction. 15. The apparatus according to one of claim 9, wherein said means for performing a feedback correction of said frequency deviation comprises a numerical controlled oscillator (322) and a complex multiplier (326). 16. The apparatus according to claim 15, wherein said means for performing a feedback correction of said frequency deviation further comprises a low path filter (324) preceding said numerical controlled oscillator (322).