Timing synchronization in a receiver employing orthogonal frequency division multiplexing
First Claim
1. A method of determining the boundaries of symbols in a stream of data being transmitted through a channel and having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a replication of a portion of said active interval, the method comprising the steps of:
- sampling first portions of said stream, wherein said first portions are separated by said active interval to form a first comparison block of data;
measuring a first dispersion of said first comparison block;
sampling second portions of said stream, wherein said second portions are separated by said active interval to form a second comparison block of data;
measuring a second dispersion of said second comparison block; and
calculating a statistic of said first dispersion and said second dispersion; and
synchronizing said stream based on said statistic, for signal reconstruction by a fast Fourier transform.
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Accused Products
Abstract
A method and apparatus are disclosed for determining the boundaries of guard intervals of data symbols being received in a coded orthogonal frequency division multiplexed signal. Temporal samples separated by an interval of an active interval of a data symbol are associated in pairs, and difference signals obtained. The dispersion of a first comparison block of difference signals is determined, and compared to the dispersion of a second comparison block of difference signals, the second comparison block being displaced from the first comparison block by n samples. An F ratio is calculated for the dispersions of the two blocks. F ratios are iterated in a succession of comparison blocks, and a signal representing the F ratios subjected to peak detection. The peaks represent the boundaries of the symbol'"'"'s guard interval. This information is utilized in synchronizing an FFT window for subsequent signal reconstruction.
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Citations
42 Claims
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1. A method of determining the boundaries of symbols in a stream of data being transmitted through a channel and having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a replication of a portion of said active interval, the method comprising the steps of:
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sampling first portions of said stream, wherein said first portions are separated by said active interval to form a first comparison block of data; measuring a first dispersion of said first comparison block; sampling second portions of said stream, wherein said second portions are separated by said active interval to form a second comparison block of data; measuring a second dispersion of said second comparison block; and calculating a statistic of said first dispersion and said second dispersion; and synchronizing said stream based on said statistic, for signal reconstruction by a fast Fourier transform. - View Dependent Claims (2, 3)
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4. A method of decoding a stream of data symbols having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a replication of a portion of said active interval, the method comprising the steps of:
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sampling said stream at a sampling interval during an evaluation interval of said symbol period Ts ; associating samples in a plurality of pairs, each said pair having a first member and a second member, each said first member being separated in said stream from said second member by said active interval, wherein said first members and said second members lie in a first block and a second block respectively, and said first block and said second block are no larger than said guard interval; for each said pair, determining a function of said first member and said second member of each said pair, and outputting a first output signal that is representative of said function; measuring a dispersion of said first output signal; outputting a second output signal representative of said dispersion; displacing said first block and said second block relative said stream, and repeating said steps of associating samples, determining a function, measuring a dispersion and outputting a third output signal; comparing said second output signal with said third output signal and outputting a fourth output signal that is representative of said comparison; and detecting a predetermined criterion in said fourth output signal, wherein said criterion indicates boundaries of said guard interval and said active interval; and synchronizing an FFT window using said predetermined criterion for signal reconstruction. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of decoding a stream of data symbols having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a cyclic extension of a portion of said active interval, the method comprising the steps of:
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sampling said stream at a sampling interval during an evaluation interval of said symbol period Ts ; associating samples in a plurality of pairs, each said pair having a first member and a second member, each said first member being separated in said stream from said second member by said active interval, wherein said first members and said second members lie in a first block and a second block respectively, and said first block and said second block are no larger than said guard interval; for each said pair, determining a function of said first member and said second member of each said pair, and outputting a first output signal that is representative of said function; measuring a dispersion of said first output signal; outputting a second output signal representative of said dispersion; displacing said first block and said second block relative said stream, and repeating said steps of associating samples, determining a function, measuring a dispersion and outputting a third output signal; comparing said second output signal with said third output signal and outputting a fourth output signal that is representative of said comparison; and detecting a predetermined criterion in said fourth output signal, wherein said criterion indicates boundaries of said guard interval and said active interval; and synchronizing an FFT window using said predetermined criterion for signal reconstruction. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method of decoding a stream of data symbols having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a cyclic extension of a terminal portion of said active interval, the method comprising the steps of:
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sampling said stream at a sampling interval for an evaluation interval of said symbol period Ts ; associating samples in a plurality of pairs, each said pair having a first member and a second member, each said first member being separated in said stream from said second member by said active interval, wherein said first members and said second members lie in a first block and a second block respectively, and said first block and said second block are no larger than said guard interval; for each said pair, determining a difference of said first member and said second member of each said pair, and outputting a first output signal that is representative of said difference; measuring the dispersion of the magnitudes of said first output signal; outputting a second output signal representative of said dispersion; displacing said first block and said second block relative said stream, and repeating said steps of associating samples, determining a difference, measuring a dispersion and outputting a third output signal; determining an F ratio of a magnitude of said second output signal and a magnitude of said third output signal and outputting a fourth output signal that is representative of said F ratio; and detecting a predetermined magnitude in said fourth output signal, wherein said magnitude indicates boundaries of said guard interval and said active interval; and synchronizing an FFT window using said predetermined criterion for signal reconstruction. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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31. A method of timing synchronization for demodulating a signal that is modulated according to frequency division multiplexing, the signal comprising a stream of data symbols having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a replication of a portion of said active interval, the method comprising the steps of:
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temporally sampling said stream at a sampling interval for at least said symbol period Ts ; associating samples in a plurality of pairs, each said pair having a first member and a second member, each said first member being separated in said stream from said second member by said active interval, wherein said first members and said second members lie in a first block and a second block respectively, and said first block and said second block are no larger than said guard interval; for each said pair, determining a difference of said first member and said second member of each said pair, and outputting a first output signal that is representative of said difference; measuring the dispersion of the magnitudes of said first output signal; outputting a second output signal representative of said dispersion; displacing said first block and said second block relative said stream, and repeating said steps of associating samples, determining a difference, measuring a dispersion and outputting a third output signal; determining an F ratio of a magnitude of said second output signal and a magnitude of said third output signal and outputting a fourth output signal that is representative of said F ratio; and detecting a predetermined magnitude in said fourth output signal, wherein said magnitude indicates boundaries of said guard interval and said active interval; and synchronizing an FFT window using said predetermined criterion for signal reconstruction. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38)
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39. A demodulator for a frequency division multiplexed signal, the signal comprising a stream of data symbols having a symbol period Ts, wherein the symbols comprise an active interval and a guard interval, said guard interval being a replication of a portion of said active interval, wherein the improvement comprises a timing synchronization circuit for locating a boundary of said guard interval, the circuit comprising:
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a first delay circuit, providing a delay for a first predetermined interval, and accepting a sampled input signal; a first subtracter, for subtracting an output of said first delay circuit from said input signal; a first circuit coupled to said first subtracter for producing a signal having an unipolar magnitude that is proportional to an input thereof; a second delay circuit coupled to an output of said first circuit; an adder/subtracter circuit, having a first input coupled said output of said first circuit, a second input connected to an output of said second delay circuit, and a third input; a register for accumulating the output of said adder/subtracter circuit, wherein said register is connected to said third input; a lookup memory, addressed according to said output of said adder/subtracter circuit, for accessing a logarithm of said output of said adder; a third delay circuit, providing a delay for a second predetermined interval, and having an input connected to said lookup memory; a second subtracter having a first input connected to said lookup memory, and a second input connected to an output of said third delay circuit; and a comparison circuit, connected to an output of said second subtracter, for comparison thereof with a threshold value. - View Dependent Claims (40, 41, 42)
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Specification