Ofdm demodulation apparatus
First Claim
1. An OFDM demodulator for demodulating an orthogonal frequency division multiplex (OFDM) signal using, as a unit of transmission, a transmission symbol including an effective symbol generated by making time division of an information series and modulating the information into a plurality of sub-carriers and a guard interval generated by copying the signal waveform of a part of the effective symbol, the apparatus comprising:
- a reference time generating circuit for generating a reference time on the basis of a reference clock;
a guard correlation peak time detecting circuit for detecting a timing in which the autocorrelation of the guard interval portion of the OFDM signal attains to its peak and generating the timing (peak time) synchronous with the reference time; and
a symbol-boundary time calculating circuit for calculating, on the basis of the peak time, a symbol-boundary time that is a boundary time of the transmission symbol synchronous with the reference time, the symbol-boundary time calculating circuit including;
a symbol-boundary time generator for generating a symbol-boundary time synchronous with the reference time;
a time difference detector for detecting a difference between the symbol-boundary time and peak time; and
an averaging unit for calculating a mean time difference by low-pass filtering of the time difference, the symbol-boundary time generator calculating the symbol-boundary time on the basis of the mean time difference.
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Accused Products
Abstract
An OFDM demodulation (1) is provided which includes a guard correlation/peak time detection circuit (12) to generate a peak timing Np of a guard interval correlation value, and a timing synchronization circuit (13) to estimate a symbol-boundary time Nx from the peak timing Np. The timing synchronization circuit (13) calculates the symbol-boundary time Nx by filtering the peak time Np by a DLL (delay locked loop) filter (43). Further, the DLL filter (43) includes a limiter (52) to limit the range of phase-error component and an asymmetric gain circuit (53) to change the magnitude of the gain correspondingly to the polarity of the phase error to prevent the timing from being pulled out due to a fading or multipath.
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Citations
33 Claims
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1. An OFDM demodulator for demodulating an orthogonal frequency division multiplex (OFDM) signal using, as a unit of transmission, a transmission symbol including an effective symbol generated by making time division of an information series and modulating the information into a plurality of sub-carriers and a guard interval generated by copying the signal waveform of a part of the effective symbol, the apparatus comprising:
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a reference time generating circuit for generating a reference time on the basis of a reference clock;
a guard correlation peak time detecting circuit for detecting a timing in which the autocorrelation of the guard interval portion of the OFDM signal attains to its peak and generating the timing (peak time) synchronous with the reference time; and
a symbol-boundary time calculating circuit for calculating, on the basis of the peak time, a symbol-boundary time that is a boundary time of the transmission symbol synchronous with the reference time, the symbol-boundary time calculating circuit including;
a symbol-boundary time generator for generating a symbol-boundary time synchronous with the reference time;
a time difference detector for detecting a difference between the symbol-boundary time and peak time; and
an averaging unit for calculating a mean time difference by low-pass filtering of the time difference, the symbol-boundary time generator calculating the symbol-boundary time on the basis of the mean time difference. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. An OFDM demodulator for demodulating an orthogonal frequency division multiplex (OFDM) signal using, as a unit of transmission, a transmission symbol including an effective symbol generated by making time division of an information series and modulating the information into a plurality of sub-carriers and a guard interval generated by copying the signal waveform of a part of the effective symbol, the apparatus including:
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a reference time generating circuit for generating a reference time on the basis of a reference clock;
a guard correlation peak time detecting circuit for detecting a timing in which the autocorrelation of the guard interval portion of the OFDM signal attains to its peak and generating the timing (peak time) synchronous with the reference time; and
a symbol-boundary time calculating circuit for calculating, on the basis of the peak time, a symbol-boundary time that is a boundary time of the transmission symbol synchronous with the reference time, the symbol-boundary time calculating circuit including;
an asymmetric gain unit that makes discrimination between when the peak time is earlier than the symbol-boundary time and when the peak time is later than the symbol-boundary time, makes the gain when the peak time is later than the symbol-boundary time larger than that when the peak time is earlier than the symbol-boundary time, and multiplies the peak time by the gain; and
an averaging unit for calculating a symbol-boundary time by low-pass filtering of the peak time multiplied by the gain by the asymmetric gain unit. - View Dependent Claims (32, 33)
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Specification