Synchronizing pulse generating method and method of receiving OFDM signal
First Claim
1. A method of generating a synchronisation pulse representing a symbol boundary in an OFDM signal comprising useful symbol periods separated by guard spaces, with data in each guard space corresponding to part of the data in a respective useful period, the method comprisingproviding a signal representing the degree of correlation between samples of a received signal which are separated by a period corresponding to the useful part of the symbol, the signal thus providing an output representing for each symbol an interval during which significant correlation is found, the method comprisingdetermining respective degrees of correlation in each of plural sub-intervals within said interval,detecting a sub-interval within which a maximum degree of correlation occurs, andproviding a synchronisation pulse within the detected sub-interval.
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Abstract
In an OFDM receiver, a synchronisation pulse for defining a Fast Fourier Transform window is generated by examining the output of a correlator to find a sub-interval within which there is maximum correlation between samples of the symbol separated by the length of the useful part of the symbol. The synchronisation pulse is generated during this sub-interval (102). Adjustments to the timing of the synchronisation pulse are made only if the current error is significant and persistent. A signal representing the amount of adjustment is used to determine phase rotations applied to the output of the FFT circuit.
35 Citations
25 Claims
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1. A method of generating a synchronisation pulse representing a symbol boundary in an OFDM signal comprising useful symbol periods separated by guard spaces, with data in each guard space corresponding to part of the data in a respective useful period, the method comprising
providing a signal representing the degree of correlation between samples of a received signal which are separated by a period corresponding to the useful part of the symbol, the signal thus providing an output representing for each symbol an interval during which significant correlation is found, the method comprising determining respective degrees of correlation in each of plural sub-intervals within said interval, detecting a sub-interval within which a maximum degree of correlation occurs, and providing a synchronisation pulse within the detected sub-interval.
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12. A method of generating a synchronisation pulse representing a symbol boundary in an OFDM signal comprising useful symbol periods separated by guard spaces, with data in each guard space corresponding to part of the data in a respective useful period, the method including:
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calculating an error in the current timing; comparing the magnitude of the calculated error with a predetermined threshold; and adjusting the timing of the synchronisation pulse when the magnitude of the calculated error in the current timing exceeds said predetermined threshold. - View Dependent Claims (16)
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- 13. A method of generating a synchronisation pulse representing a symbol boundary in an OFDM signal comprising useful symbol periods separated by guard spaces, with data in each guard space corresponding to part of the data in a respective useful period, the method including the step of (i) counting the number of symbol periods over which the current timing is determined to be in error, and (ii) adjusting the timing of the synchronisation pulse in response to the counted symbol periods exceeding a predetermined number greater than one, wherein the error in the current timing is calculated by comparing a timing signal with a range of values corresponding to a sub-interval, said sub-interval being detected by determining respective degrees of correlation in each of plural sub-intervals within a correlation interval within which significant correlation occurs, and detecting said sub-interval within which a maximum degree of correlation occurs.
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15. A method of generating a synchronisation pulse representing a symbol boundary in an OFDM signal, said signal comprising symbols, each symbol being formed of successive complex samples, each of said successive complex samples having a sample period, and each symbol including useful symbol periods, said useful symbol periods being separated by guard spaces, with data in each guard space corresponding to part of the data in a respective useful symbol period, the method including:
changing the timing of the synchronisation pulse by a predetermined adjustment quantity, said predetermined adjustment quantity being calculated by a rounding operation so that said predetermined adjustment quantity is equal to a plurality of sample periods.
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20. A method of receiving an OFDM signal, the method including:
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generating a synchronisation pulse and using the synchronisation pulse in order to apply, in a FFT unit, a Fast Fourier Transform to complex samples derived from the OFDM signal; providing, once the timing of the synchronisation pulse is altered, a signal representing the degree of alteration to a phase rotation unit; and applying, to the transformed samples received from the FFT, phase rotations determined based on the signal. - View Dependent Claims (21)
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24. A method of generating a synchronisation pulse representing a symbol boundary in an OFDM signal comprising useful symbol periods separated by guard spaces, with data in each guard space corresponding to part of the data in a respective useful period, the method including the steps of:
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adjusting the timing of the synchronisation pulse in predetermined quantities corresponding to a plurality of sample periods, receiving an OFDM signal, by generating the synchronisation pulse, using the synchronisation pulse in order to apply a Fast Fourier Transform to complex samples derived from the OFDM signal in a FFT unit, providing to a phase rotation unit, once the timing of the synchronisation pulse is altered, a signal representing the degree of alteration, and applying, to the transformed samples received from the FFT unit, phase rotations determined based on the signal. - View Dependent Claims (25)
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Specification