Digital broadcast receiver, mobile terminal and channel search method
A tuner selects a channel in a designated frequency band. An FFT circuit converts a received signal in the selected channel into a plurality of carrier signals. A carrier shift detection circuit calculates the correlation between the phase information of each carrier signal and reference phase information prepared in advance. If the correlation is larger than a given threshold, it is determined that an OFDM signal is present in the search target channel. A TMCC extraction circuit analyzes the TMCC of the received signal and determines whether or not digital broadcasts of the search target channel can be received.
1. A digital broadcast receiver for receiving digital broadcasts using OFDM, comprising:
a Fourier transformation circuit to perform Fourier transformation of a received signal to obtain a plurality of carrier signals including a plurality of DBPSK carrier signals respectively carrying a DBPSK signal;
a phase difference calculation unit to detect a phase difference between adjacent symbols in each of the plurality of carrier signals;
a correlation calculation unit to calculate a correlation value representing the correlation between the phase difference detected by the phase difference calculation unit and zero or π; and
a determination unit to determine whether an OFDM signal is present, wherein
the plurality of DBPSK carrier signals are allocated in a predetermined allocation pattern,
the phase difference calculation unit sequentially detects the phase differences for a plurality of carrier signals in the allocation pattern while sweeping frequency,
the correlation calculation unit respectively calculates sums of the correlation values for the plurality of carrier signals in the allocation pattern in the sweeping, and detects a maximum sum of the correlation values,
the determination unit determines that the OFDM signal is present if the maximum sum of the correlation values is larger than a predetermined threshold.
2. The digital broadcast receiver according to claim 1 , wherein
the OFDM signal of the digital broadcast comprises a data carrier signal, an AC carrier signal, and a TMCC carrier signal, and
the DBPSK carrier signal is the AC carrier signal or the TMCC carrier signal.
3. The digital broadcast receiver according to claim 1 , wherein
the correlation calculation unit cumulatively adds the correlation value for a certain time period, and
the determination unit determines that the OFDM signal is present if the cumulatively added correlation value is larger than a threshold.
4. The digital broadcast receiver according to claim 1 , further comprising:
an equalization circuit to equalize the data carrier signal comprised in the OFDM signal of digital broadcast; and
an error correction circuit to perform error correction of an output signal of the equalization circuit.
5. A mobile terminal for receiving 1-segment and 3-segment digital broadcasts using OFDM, comprising:
a Fourier transformation circuit for performing Fourier transformation of a received signal;
a phase difference calculation unit for detecting the phase information of a plurality of carrier signals obtained by said Fourier transformation circuit;
a correlation calculation unit for calculating a correlation value representing the correlation between the phase information detected by said phase difference calculation unit and prescribed phase information prepared in advance;
a TMCC extraction circuit for detecting whether or not the received signal is a 13-segment broadcast signal on the basis of TMCC data comprised in the received signal; and
a determination unit for determining that an OFDM signal can be received if the correlation value obtained by said correlation calculation unit is larger than a predetermined threshold and that the received signal is not a 13-segment broadcast signal.
6. The mobile terminal according to claim 5 , wherein
said correlation calculation unit recalculates the correlation value in parallel with the processing of said TMCC extraction circuit to analyze TMCC data, and
said determination unit determines that the OFDM signal can be received only when the correlation value is larger than the threshold in the recalculation.
7. A channel search method in a digital broadcast receiver for receiving digital broadcast using OFDM, comprising:
performing the Fourier transformation of a received signal by using a Fourier transformation circuit to obtain a plurality of carrier signals including a plurality of DBPSK carrier signals respectively carrying a DBPSK signal;
detecting a phase difference between adjacent symbols in each of the plurality of carrier signals;
calculating a correlation value representing the correlation between the detected phase difference and zero or π; and
determining whether an OFDM signal is present, wherein
the plurality of DBPSK carrier signals are allocated in a predetermined allocation pattern,
the phase differences for a plurality of carrier signals in the allocation pattern is detected while sweeping frequency,
sums of the correlation values for the plurality of carrier signals in the allocation pattern are respectively calculated in the sweeping, and a maximum sum of the correlation values is detected,
it is determined that the OFDM signal is present if the maximum sum of the correlation values is larger than a predetermined threshold.