JP4336248B2 - Transmission control signal receiver and digital terrestrial television broadcast receiver using the same - Google Patents

Description

  The present invention relates to a transmission control signal receiver and a terrestrial digital television broadcast receiver using the transmission control signal receiver, and a transmission control signal receiver for receiving a transmission control signal of terrestrial digital television broadcast, and a terrestrial digital television broadcast using the same. Regarding the receiver.

  FIG. 1 shows a block diagram of an example of an analog television broadcast receiver that receives a conventional emergency alert broadcast. An antenna reception signal output from the reception antenna 1 is input to the analog television broadcast tuner 2. The video signal and audio signal output from the analog television broadcast tuner 2 are input to the receiver 3. The analog television broadcast tuner 2 is fed from a power source 4 through a feeder line 5.

  In order to receive the emergency alert broadcast, the demodulation system of the analog television broadcast tuner 2 needs to be in an operating state. On the other hand, the receiver 3 is supplied with power from the power source 4 through the power supply line 6 and through the switch 7. In the standby state, the power source of the receiver 3 is turned off by the switch 7.

  When the analog television broadcast tuner 2 receives the emergency warning broadcast start flag, the switch-on signal 8 is output from the analog television broadcast tuner 2 to the switch 7, the switch 7 is turned on, and the receiver 3 is supplied with power and operates. It becomes.

As an emergency alert broadcast receiving system that receives an emergency alert broadcast that is broadcast superimposed on a BS television broadcast, for example, there is a system described in Patent Document 1.
JP 2004-23591 A

  As with analog television broadcasting, in order to activate a receiver by emergency warning broadcasting in terrestrial digital television broadcasting, the demodulation system of the digital terrestrial television broadcasting receiver can receive the emergency warning broadcasting activation flag of the transmission control signal. Must be kept in a powered state.

  FIG. 2 is a block diagram showing an example of a demodulation system of the terrestrial digital television broadcast receiver. The antenna reception signal received by the reception antenna is supplied to the channel selection unit 10 and an intermediate frequency signal of an OFDM (Orthogonal Frequency Division Multiplexing) signal of a designated channel is output. This intermediate frequency signal is digitized and then orthogonally demodulated by the orthogonal demodulator 11 and supplied to the synchronous reproduction unit 12 and the FFT processor 13.

  The synchronous reproduction unit 12 reproduces the OFDM symbol synchronization and the FFT sample frequency according to the mode and the guard interval length. The FFT processor 13 performs an FFT (Fast Fourier Transform) operation on the effective symbol period of the OFDM symbol. The frame extraction unit 14 extracts a frame synchronization signal from a TMCC (Transmission and Multiplexing Configuration Control: transmission control signal) signal output from the FFT processing unit 13. The TMCC decoding unit 15 extracts various control information including an emergency warning broadcast activation flag from the TMCC signal.

  The carrier demodulation unit 16 performs carrier demodulation according to the TMCC information and detects amplitude and phase information. The demapping section 17 performs QPSK, 16QAM and 64QAM demapping from the carrier demodulated information to extract bit information. The TS playback unit 18 performs processing for transport stream playback. The RS decoding unit 19 decodes the shortened Reed-Solomon code, and decodes baseband MPEG-TS (Transport Stream).

  In order to keep the demodulation system of the terrestrial digital television broadcast receiver in an energized state, power consumption of at least several hundred mW or more is necessary. In portable receivers that operate on batteries due to battery capacity restrictions, There is a problem that activation of a receiver by emergency alert broadcasting is not practical and difficult to implement.

  The present invention has been made in view of the above points, and provides a transmission control signal receiver capable of reducing standby power for receiving a transmission control signal and a terrestrial digital television broadcast receiver using the same. For the purpose.

The invention according to claim 1 is a preliminarily obtained filter that passes a carrier having a predetermined frequency among a plurality of carriers constituting an OFDM signal that is a terrestrial digital television broadcast signal, and is configured by a digital filter. by replacing the coefficients, and the band filter means Ru switches the carrier of the desired frequency to pass among the plurality of carriers includes a transmission control signal,
Quadrature detection means for obtaining quadrature detection output of the carrier by quadrature detection of the output signal of the bandpass filter means;
A sampling rate converting means for thinning out the quadrature detection output is signal samples the orthogonal detection means outputs to an integral fraction is one order of 2 ¹⁰ minutes,
Low-pass filter means that passes the low-frequency component of the quadrature detection output from the sampling rate conversion means and supplies the low-frequency component to the delay detection means;
Delay detection means for obtaining a transmission control signal transmitted by the carrier by delay detection of quadrature detection output from the low-pass filter means ;
Detecting means for detecting an emergency warning broadcast activation flag from a transmission control signal output from the delay detection means;
Means for supplying a signal supplied to the band filter means to an FFT processing section of a digital terrestrial television broadcast tuner;
By preparing,
Some circuits such as AD conversion means of the transmission control signal receiver can be shared with the digital terrestrial television broadcast tuner, and standby power for receiving the transmission control signal can be reduced.

The invention according to claim 2 is a digital terrestrial television broadcast receiver having the transmission control signal receiver according to claim 1 ,
By supplying power to the demodulation / decoding unit of the tuner of the terrestrial digital television broadcast receiver when the transmission control signal receiving device detects an emergency warning broadcast activation flag in the transmission control signal. ,
Standby power in the digital terrestrial television broadcast receiver can be reduced.

  According to the present invention, standby power for receiving a transmission control signal can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Here, as a signal format of the OFDM signal, for example, a recommendation of the International Telecommunications Union (ITU-R Rec. BT-1306: Error-correction, data framing, modulation and emission methods for digital terrestrial terrestrial broadcasting BS, BS-1306). for terrestrial digital sound broadcasting to vehicular, portable and fixed receivers in the frequency range 30-3000 MHz), etc. Assuming signals standardized as a standard (ARIB STD-B29) and a transmission standard for digital terrestrial television broadcasting (ARIB STD-B31), the frequencies are orthogonal as shown in FIG. A plurality of carriers 1 to k are multiplexed.

  FIG. 4 shows a block diagram of an embodiment of the transmission control signal receiver of the present invention. In the figure, an intermediate frequency signal of the received OFDM signal (for example, a center frequency of 8.127 MHz in the case of terrestrial digital television broadcasting ISDB-T) is supplied to an AD converter 22 in the transmission control signal receiving device 20, For example, it is digitized by sampling using a sampling frequency of 32.508 MHz. In addition, by sampling at a frequency of 4 × n (n is an integer) of the center frequency of the intermediate frequency signal (for example, center frequency of 8.127 MHz), the output of the AD converter 22 becomes a quadrature detection output and is orthogonal to the in-phase detection output I. The detection output Q is separated.

  The digital received signal is supplied to the guard correlation circuit 24, and the guard interval of the OFDM signal is delayed by the effective symbol length to correlate with the data after the effective symbol period, thereby detecting the start timing of the guard interval and reproducing the timing. This is supplied to the circuit 26 and the carrier reproduction circuit 28. The timing reproduction circuit 26 reproduces the symbol timing and supplies it to the carrier reproduction circuit 28, and the carrier reproduction circuit 28 reproduces the carrier of the intermediate frequency signal.

  As for the method of symbol timing recovery of the OFDM signal and carrier recovery of the intermediate frequency signal, for example, as described in Japanese Patent No. 3074103, Japanese Patent No. 2774961, etc., the I and Q signals are delayed by the effective symbol length. There is a method for controlling the timing of the clock of the AD converter 22 and controlling the frequency of the local oscillator using a correlation output signal with the I ′ and Q ′ signals.

  The OFDM signal subjected to timing recovery and carrier recovery is supplied to a band-pass filter circuit (BPF) 30 having a passband characteristic indicated by a broken line in FIG. 5A, and a carrier component shown in FIG. 5B is extracted.

The band filter 30 can be realized by setting a coefficient using an FIR (finite impulse response) filter shown in FIG. In FIG. 6, the FIR filter includes delay elements 50 ₁ to 50 _k that sequentially delay an input signal at a symbol period, and multipliers 52 _{1 to} 52 that multiply the outputs of the delay elements 50 ₁ to 50 _k by coefficients C ₁ to C _k, respectively. _k and adders 54 _{1 to} 54 _k for adding the outputs of the multipliers 52 _{1 to} 52 _k .

Here, the frequency band in the case of sampling the entire band of the input OFDM signal is divided by k (for example, 8192 = 2 ¹³ ) that is a power of two. However, k needs an integer greater than or equal to the number of OFDM carriers (for example, 5616). For each divided area, a k-row data string is prepared in which 1 is assigned to the divided area through which the bandpass filter 30 passes and 0 is assigned to the other divided areas. By applying inverse discrete Fourier transform to the k rows of data strings, coefficients C1 to Ck of the FIR filter for obtaining an impulse response that passes only the desired carrier are obtained.

By loading the coefficients C1 to Ck into the multipliers 52 _{1 to} 52 _k and inputting the OFDM signal samples to the FIR filter, the FIR filter has a passband characteristic indicated by a broken line in FIG. Can be output.

  By matching the number of band divisions k for obtaining the coefficients C1 to Ck of the band filter 30 and the FFT size used for the demodulation processing of the normal OFDM signal, the band filter 30 for extracting an arbitrary carrier from the OFDM signal can be realized. When OFDM is set to mode 3 of digital terrestrial television broadcasting ISDB-T, there are four carriers including TMCC in one segment, and coefficients C1 to Ck corresponding to the four carriers are obtained in advance. Thus, by selecting the coefficients C1 to Ck corresponding to any one of the carriers and setting them in the bandpass filter 30, the carrier in which TMCC is included can be switched.

  Next, the portion where the guard interval is inserted is removed by the effective symbol interval extraction circuit 32 shown in FIG. 4, and only the effective symbol interval is continuously output. After that, the quadrature detection circuit 34 converts the output signal of the band filter 30 into baseband. The quadrature detection circuit 34 mixes the output signal of the effective symbol section extraction circuit 32 with each of an oscillation signal that is the center frequency of the desired carrier and a signal obtained by shifting the oscillation signal by π / 2, whereby I, Q Obtain quadrature detection output consisting of components.

Next, the sampling rate conversion circuit 36 thins out the signal samples to 1 / integer while maintaining the quality of the sampling signal. The quadrature detection output is a signal having a narrower band than the sampling frequency. For example, in the case of digital terrestrial television broadcasting ISDB-T, for example, sampling is performed at a sampling frequency of 32 MHz, whereas the frequency of the TMCC signal is about 1 kHz. Therefore, the sampling rate conversion circuit 36 maintains the quality of the sampling signal. Mom decimating a signal sample to an integral fraction of 1 (eg 1 about 2 ¹⁰ minutes). Thereby, the operation speed of the subsequent circuit can be reduced, that is, the power consumption can be reduced.

  Since the output signal of the quadrature detection circuit 34 includes the band of the symbol to be processed and the interference component from the adjacent carrier as shown by the oblique line in FIG. 5B, the low-pass filter (LPF) 38 Reduce the interference component and pass the desired signal.

  When quadrature synchronous detection is performed on a received carrier, it is necessary that the discrimination determination timing is the maximum eye opening time before the input of the symbol determiner, and the carrier phase is the symbol identification determination output with the minimum determination error. The waveform equalizer 40 realizes the above function and operates to cancel the linear distortion and minimize the symbol identification determination error.

  However, when the received carrier is a differential phase modulation (DBPSK) signal, the desired carrier signal can be demodulated by the delay detection circuit 42 without reproducing the carrier wave. After the delay detection circuit 42, the demodulated output is a TMCC signal in the terrestrial digital television broadcast ISDB-T.

  In the terrestrial digital television broadcast transmission apparatus shown in FIG. 7, the TMCC signal is supplied to the OFDM frame configuration unit 56 without performing the interleaving process, and is converted into an OFDM frame together with the interleaved TS signal. As shown in FIG. 8, this means that the TMCC signal is always transmitted by a carrier having a predetermined frequency. FIG. 8 is a structural diagram of an OFDM frame in mode 3, 1 segment of terrestrial digital television broadcasting ISDB-T.

Since the output signal of the quadrature detection circuit 34 is a DBPSK signal, it can be demodulated by the delay detection circuit 42 shown in FIG. Each of the I and Q components of the complex signal output from the quadrature detection circuit 34 of FIG. 4 is directly and in FIG. 9 delayed by one symbol period by the delay element 60 and supplied to the multiplier 62, and the phase difference Δθ obtained here is obtained. = Tan ⁻¹ (Q _n / I _n ) −tan ⁻¹ (Q _n−1 / I _n−1 ) is supplied to the determiner 64. The determiner 64 makes a determination by comparing the phase difference Δθ with a predetermined threshold value, and outputs a TMCC signal subjected to delay detection.

  In the TMCC signal, as shown in FIG. 10, the first bit B0 is a reference for differential demodulation, bits B1 to B16 are frame synchronization signals, bits B17 to B19 are segment format identification, bits B20 to B121 are TMCC information, Bits B122 to B203 are parity bits for error correction. Of these bits, bit B26 is an emergency warning broadcast activation flag, and bit B26 is “1” indicating “with activation control”.

  The TMCC frame synchronization unit 44 detects the beginning of the TMCC frame based on the correlation between the bits B0 to B19 of the TMCC signal having a 204 symbol period and a known frame synchronization signal, and outputs a 204-bit TMCC frame. When frame synchronization is not established, the performance as a TMCC receiver can be improved by switching the coefficients C1 to Ck of the band filter 30 and switching and receiving other TMCCs in the same segment.

  The TMCC frame is supplied to an EWS (emergency warning broadcast activation flag) detection circuit 46, where the presence or absence of the 26th bit emergency warning broadcast activation flag of the 204-bit TMCC frame is constantly monitored. When the EWS detection circuit 46 detects that the value of the emergency warning broadcast activation flag is “1: with activation control”, it outputs an EWS detection signal of value 1. Note that the EWS detection circuit 46 outputs an EWS detection signal having a value of 1 only when a frame having an emergency warning broadcast activation flag value of “1” continues for a predetermined number of frames, and the emergency warning broadcast activation flag It is good also as a structure which improves detection accuracy.

  Here, in terrestrial digital television broadcasting ISDB-T, simulation results when only the carrier of the TMCC signal including the emergency warning broadcast activation flag is extracted by the band filter 30 are shown in FIGS. As simulation conditions, when the input OFDM intermediate frequency signal is a terrestrial digital television broadcast ISDB-T mode 3, 1 segment signal, the frequency spectrum of the output signal of the carrier reproduction circuit 28 is as shown in FIG. In this case, there are four carriers including TMCC. A frequency spectrum of a signal obtained by extracting one carrier by the bandpass filter 30 is as shown in FIG. Furthermore, the constellation after quadrature detection is as shown in FIG.

  As described above, since the transmission control signal receiver demodulates only the carrier of the TMCC signal, it is considerably smaller than the circuit of the terrestrial digital television broadcast tuner, and further, the sampling rate of the quadrature detection output is thinned out, and the subsequent stage. The operating power is further reduced. Therefore, it can be expected that the power consumption is significantly reduced as compared with the conventional terrestrial digital television broadcast tuner.

  FIG. 14 is a block diagram showing an embodiment of a digital terrestrial television broadcast receiver to which the transmission control signal receiver of the present invention is applied. In the figure, an antenna reception signal from a reception antenna 70 is supplied to a channel selection unit 72 of a terrestrial digital television broadcast tuner 71, and an intermediate frequency signal of an OFDM signal of a designated channel is output. The intermediate frequency signal of the OFDM signal is supplied to the transmission control signal receiving device 74 and the demodulation / decoding unit 76 of the digital terrestrial television broadcast tuner 71. The transmission control signal receiving device 74 has the configuration shown in FIG.

  The demodulating / decoding unit 76 has a configuration in which, for example, the channel selection unit 10 is excluded from the configuration in FIG. 2, and the output video signal and audio signal are supplied to the receiver 78. The demodulator / decoder 76 is supplied with power from the power supply 80 via the switch 82. The receiver 78 is supplied with power from a power source 80 via a switch 84. In the standby state, the power supply of the demodulation / decoding unit 76 is turned off by the switch 82, and the power supply of the receiver 78 is turned off by the switch 84.

  The transmission control signal receiver 74 is supplied with power from the power supply 80 and is always in an operating state. When the emergency warning broadcast activation flag included in the TMCC signal of the terrestrial digital television broadcast wave has a value of 1, the transmission control signal receiving device 74 supplies the EWS detection signal having the value of 1 to the switch 82 and turns it on. The demodulation / decoding unit 76 of the television broadcast tuner 71 is activated. The demodulator / decoder 76 is ready to receive an emergency alert broadcast for the first time. When the demodulation / decoding unit 76 receives the emergency warning broadcast activation flag, a switch-on signal is supplied from the demodulation / decoding unit 76 to the switch 84 and the switch 84 is turned on, and the receiver 78 is supplied with power from the power supply 80 and is in an operating state. It becomes. Note that both the switches 82 and 84 may be turned on by an EWS detection signal of value 1.

  FIG. 15 shows a block diagram of a modification of the transmission control signal receiving apparatus of the present invention. 15 is different from FIG. 4 in that the output signal of the carrier reproduction circuit 28 is supplied to the FFT processing unit 90. The FFT processing unit 90 constitutes a part of the terrestrial digital television broadcast tuner, and corresponds to the FFT processing unit 13 in FIG. Again, the demodulation / decoding unit of the digital terrestrial television broadcast tuner including the FFT processing unit 90 is supplied with power by outputting an EWS detection signal having a value of 1 from the EWS detection circuit 46.

  In this modification, the AD converter 22, the guard correlation circuit 24, the timing recovery circuit 26, and the carrier recovery circuit 28 in the transmission control signal receiver 20 can be shared with the digital terrestrial television broadcast tuner, and the circuit scale can be increased. Can be reduced.

  In the above-described embodiment, the case where the emergency warning broadcast activation flag is received has been described as an example. However, in the transmission control signal receiving apparatus that receives AC (Auxiliary Channel) that transmits additional information related to transmission control of a modulated wave and the like. It may be applied and is not limited to the above embodiment. Further, the present invention can be applied to obtaining the probability of normal reception of a total of 20 bits including the TMCC differential demodulation reference 1 bit, the synchronization signal 16 bits, and the segment format identification 3 bits, and evaluating the reception state from the probability.

  The band filter 30 corresponds to the band filter means described in the claims, the quadrature detection circuit 34 corresponds to the quadrature detection means, the delay detection circuit 44 corresponds to the delay detection means, and the AD converter 22 serves as the AD conversion means. Correspondingly, the sampling rate conversion circuit 36 corresponds to sampling rate conversion means, the low-pass filter 38 corresponds to low-pass filter means, and the EWS detection circuit 46 corresponds to detection means.

It is a block diagram of an example of the analog television broadcast receiver which receives the conventional emergency alert broadcast. It is a block diagram of an example of a demodulation system of a terrestrial digital television broadcast receiver. It is a figure for demonstrating an OFDM signal. It is a block diagram of one Embodiment of the transmission control signal receiver of this invention. It is a frequency spectrum for demonstrating a band-pass filter circuit. It is a block diagram of a FIR filter. It is a block diagram of the transmission apparatus of terrestrial digital television broadcasting. It is a structural diagram of an OFDM frame. It is a block diagram of a delay detection circuit. It is a figure which shows the bit structure of a TMCC signal. It is a figure which shows the simulation result of a carrier reproduction circuit output. It is a figure which shows the simulation result of a bandpass filter output. It is a figure which shows the simulation result of the constellation after quadrature detection. 1 is a block diagram of an embodiment of a digital terrestrial television broadcast receiver to which a transmission control signal receiver of the present invention is applied. It is a block diagram of the modification of the transmission control signal receiver of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Transmission control signal receiver 22 AD converter 24 Guard correlation circuit 26 Timing recovery circuit 28 Carrier recovery circuit 30 Band filter 32 Effective symbol area extraction circuit 34 Orthogonal detection circuit 36 Sampling rate conversion circuit 38 Low-pass filter 40 Waveform equalizer 42 Delay detection circuit 44 TMCC frame synchronization unit 46 EWS detection circuit 50 ₁ to 50 _k , 60 delay element 52 _{1 to} 52 _k multiplier 54 _{1 to} 54 _k adder 56 OFDM frame configuration unit 62 multiplier 64 decision unit 70 receiving antenna 71 Terrestrial digital television broadcast tuner 72 Channel selection unit 74 Transmission control signal receiver 76 Demodulation / decoding unit 78 Receiver 80 Power source 82, 84 Switch 90 FFT processing unit

Claims (2)

A transmission control signal is generated by passing a carrier having a predetermined frequency among a plurality of carriers constituting an OFDM signal which is a terrestrial digital television broadcast signal , and comprising a digital filter, replacing a previously obtained filter coefficient. a bandpass filter means Ru switch between multiple carrier of a desired frequency to pass out of the carrier included,
Quadrature detection means for obtaining quadrature detection output of the carrier by quadrature detection of the output signal of the bandpass filter means;
A sampling rate converting means for thinning out the quadrature detection output is signal samples the orthogonal detection means outputs to an integral fraction is one order of 2 ¹⁰ minutes,
Low-pass filter means that passes the low-frequency component of the quadrature detection output from the sampling rate conversion means and supplies the low-frequency component to the delay detection means;
Delay detection means for obtaining a transmission control signal transmitted by the carrier by delay detection of quadrature detection output from the low-pass filter means ;
Detecting means for detecting an emergency warning broadcast activation flag from a transmission control signal output from the delay detection means;
Means for supplying a signal supplied to the band filter means to an FFT processing section of a digital terrestrial television broadcast tuner;
Transmission control signal receiving apparatus characterized by comprising. A terrestrial digital television broadcast receiver comprising the transmission control signal receiver according to claim 1 ,
Terrestrial digital, wherein the transmission control signal receiving device supplies power to a demodulator / decoder of a tuner of a terrestrial digital television broadcast receiver when detecting an emergency warning broadcast activation flag in the transmission control signal Television broadcast receiver.

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