Demodulation apparatus, broadcasting system and broadcast receiving apparatus
View Patent ↗A demodulation apparatus that shortens demodulation time and performs efficient high-quality demodulation control. A digital signal generating section generates digital signals corresponding to phase axes from a modulated input signal. A frequency correction value outputting section outputs a frequency correction value. A frequency correcting section gives a frequency offset to digital signals on the basis of a frequency correction value to generate frequency-corrected signals. A timing recovering section performs timing recovery by extracting symbol timing for frequency-corrected signals. A C/N detecting section detecting C/N from a symbol. An optimum frequency correction value determining section treats a frequency correction value corresponding to the maximum C/N value as an optimum frequency correction value. A carrier recovering section performs carrier recovery by correcting finally a shift in the frequency of a signal on which a frequency correction by the use of an optimum frequency correction value and timing recovery have been made. A synchronization detecting section makes an error correction on a symbol and detects a unique word.
1. A demodulation apparatus for demodulating modulated signals, the apparatus comprising:
a digital signal generator for performing synchronous detection of a modulated input signal and for making an A/D conversion to generate digital signals corresponding to phase axes;
a frequency correction value outputting unit for outputting a frequency correction value set on the basis of a symbol rate;
a frequency corrector for giving a frequency offset to the digital signals on the basis of the frequency correction value to generate frequency-corrected signals;
a timing recovering unit for performing timing recovery by extracting symbol timing for the frequency-corrected signals;
a C/N detector for detecting C/N from a symbol obtained by the timing recovering unit;
an optimum frequency correction value determining unit for treating a frequency correction value corresponding to the maximum value of the C/N as an optimum frequency correction value;
a carrier recovering unit for performing carrier recovery by correcting finally a shift in the frequency of a signal on which a frequency correction by the use of the optimum frequency correction value and timing recovery have been made; and
a synchronization detector for making an error correction on a symbol after carrier recovery and for detecting a unique word.
2. The demodulation apparatus according to claim 1 , wherein the C/N detector detects C/N, in the case of performing carrier pull-in control, from a symbol which depends on the shift in frequency, and detects C/N, after carrier pull-in, from a symbol which does not depend on the shift in frequency.
3. The demodulation apparatus according to claim 1 , wherein the C/N detector detects the C/N on the basis of dispersion in the direction of symbol amplitude.
4. The demodulation apparatus according to claim 1 , wherein the frequency correction value outputting unit updates a frequency correction value by a frequency value being smaller than the pull-in range of the carrier recovering unit.
5. The demodulation apparatus according to claim 1 , wherein the frequency correction value outputting unit updates a frequency correction value by a frequency value being greater than the pull-in range of the carrier recovering unit.
6. The demodulation apparatus according to claim 5 , further comprising a shift detector for detecting the shift between a signal on which a frequency correction by the use of an optimum frequency correction value determined on the basis of the frequency correction value greater than pull-in range and timing recovery have been made and the pull-in range of the carrier recovering unit.
7. The demodulation apparatus according to claim 1 , wherein the frequency correction value outputting unit outputs a frequency correction value being greater than the pull-in range of the carrier recovering unit before determination of the optimum frequency correction value and outputs, on the basis of a synchronization detection signal, a frequency correction value being smaller than the pull-in range after determination of the optimum frequency correction value.
8. A broadcasting system for communicating digital satellite broadcasts, the system comprising:
a broadcast sending apparatus including:
a modulator for modulating a signal to be sent to generate a modulated signal,
an up converter for converting the modulated signal to a radio signal, and
a sending unit for sending the radio signal to a satellite via an antenna; and
a broadcast receiving apparatus including:
a receiving unit for receiving a signal sent from the satellite to the ground,
a down converter for converting the frequency of a signal received to generate a signal to be demodulated,
a digital signal generator for performing synchronous detection of a signal output from the down converter which was modulated on the sending side and for making an A/D conversion to generate digital signals corresponding to phase axes,
a frequency correction value outputting unit for outputting a frequency correction value set on the basis of a symbol rate,
a frequency corrector for giving a frequency offset to the digital signals on the basis of the frequency correction value to generate frequency-corrected signals,
a timing recovering unit for performing timing recovery by extracting symbol timing for the frequency-corrected signals,
a C/N detector for detecting C/N from a symbol obtained by the timing recovering unit,
an optimum frequency correction value determining unit for treating a frequency correction value corresponding to the maximum value of the C/N as an optimum frequency correction value,
a carrier recovering unit for performing carrier recovery by correcting finally a shift in the frequency of a signal on which a frequency correction by the use of the optimum frequency correction value and timing recovery have been made, and
a synchronization detector for making an error correction on a symbol after carrier recovery and for detecting a unique word.
9. A broadcast receiving apparatus for demodulating modulated signals for a digital satellite broadcast, the apparatus comprising:
a receiving unit for receiving a signal sent from a satellite to the ground;
a down converter for converting the frequency of a signal received to generate a signal to be demodulated;
a digital signal generator for performing synchronous detection of a signal output from the down converter which was modulated on the sending side and for making an A/D conversion to generate digital signals corresponding to phase axes;
a frequency correction value outputting unit for outputting a frequency correction value set on the basis of a symbol rate;
a frequency corrector for giving a frequency offset to the digital signals on the basis of the frequency correction value to generate frequency-corrected signals;
a timing recovering unit for performing timing recovery by extracting symbol timing for the frequency-corrected signals;
a C/N detector for detecting C/N from a symbol obtained by the timing recovering unit;
an optimum frequency correction value determining unit for treating a frequency correction value corresponding to the maximum value of the C/N as an optimum frequency correction value;
a carrier recovering unit for performing carrier recovery by correcting finally a shift in the frequency of a signal on which a frequency correction by the use of the optimum frequency correction value and timing recovery have been made; and
a synchronization detector for making an error correction on a symbol after carrier recovery and for detecting a unique word.