JP2014053864A - Receiver and automatic starting method for the same - Google Patents

Abstract

A receiving apparatus capable of reducing power consumption for monitoring the presence of an emergency broadcast in a standby state is provided.
A receiving apparatus performs an FFT process of a partial band including at least one AC carrier on which emergency broadcast presence / absence information is multiplexed, and acquires a subcarrier of the partial band; A pilot data symbol demodulation processing unit 50 that performs FFT processing of the entire band of the signal to obtain subcarriers of the entire band, and demodulates broadcast content included in the OFDM signal based on the obtained subcarriers; For the signal, the switch 20 for switching between the FFT processing in the FFT circuit 23 and the FFT processing in the FFT circuit 25 and the FFT circuit 23 in the standby state perform the FFT processing. When the broadcast is indicated, the switch 20 is controlled so that the FFT circuit 25 performs the FFT process. And a that controller 28.
[Selection] Figure 1

Description

  The present invention relates to a receiving apparatus that automatically starts based on an emergency broadcast presence / absence signal included in an OFDM signal, and an automatic starting method thereof.

  In the terrestrial digital broadcasting systems such as ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) and ISDB-TSB (Integrated Services Digital Broadcasting-Terrestrial Sound Broadcasting), emergency warning broadcasting (EWS) occurs when an emergency disaster such as an earthquake or tsunami occurs. : Emergency Warning System) has been standardized (see ARIB STD-B10 / B29 / B31 etc.).

  In this standard, in the event of a disaster, an emergency information descriptor is multiplexed with a PMT (Program Map Table) among control signals used for OFDM (Orthogonal Frequency Division Multiplexing) transmission, and an emergency alert broadcast is transmitted to TMCC (Transmission Multiplexing Configuration Control). By multiplexing the activation flag, the receiving apparatus side is notified of the presence or absence of emergency broadcasting. Further, as another control signal, the transmission of emergency earthquake early warning using AC (Auxiliary Channel) is also studied in Non-Patent Document 1, for example.

  Emergency broadcasts such as EWS and earthquake early warnings are received by a receiving device that can output video and audio, but the emergency broadcasts contained evacuation information and so on, so what the state of the receiving device was However, it is necessary to be able to reliably detect the receiving device as soon as possible after delivery (for example, within 10 seconds). For this reason, even if the receiving apparatus is in a standby state (that is, a state in which the receiving apparatus is not used and no video or audio is output), an emergency broadcast is detected and triggered automatically. It is desirable to have an automatic activation function that activates automatically and outputs emergency broadcast video and audio.

  As a prior art that realizes such an automatic activation function, there is a digital broadcast receiving apparatus described in Patent Document 1. FIG. 13 is a block diagram illustrating a configuration of a digital broadcast receiving device described in Patent Document 1. In FIG. The digital broadcast receiving apparatus 121 includes a broadcast receiving unit 119, an emergency earthquake information receiving unit 120, and a control unit 118 that performs operation control and power control of the broadcast receiving unit 119 and the emergency earthquake information receiving unit 120.

  The broadcast receiving unit 119 is a mainstream block for reproducing a video signal and an audio signal, and includes a channel selection unit 102, an orthogonal demodulation unit 103, a fast Fourier transform (FFT) unit 104, an FFT unit 104 and subsequent ISDB-T system TS output. Demodulation / decoding unit 105 that performs demodulation / decoding operation, descrambling unit 106, demux unit 107, video signal and audio signal decoding unit 108, video display unit 109 that displays the decoded video signal, and decoded audio signal An audio output unit 110 that performs output, a synchronous playback unit 111, and a frame extraction unit 112 are provided. The broadcast receiving unit 119 further includes a TMCC decoding unit 113 that performs synchronization signal reproduction for performing the operation of the demodulation decoding unit 105 and obtains information such as transmission parameters. The emergency earthquake information reception unit 120 includes a flag detection unit 114, a data extraction unit 115, a determination unit 116, and an emergency earthquake early warning output unit 117.

  The digital broadcast receiver 121 receives emergency earthquake information transmitted using an AC signal included in the segment number # 0 in the ISDB-T system. When the emergency broadcast is not broadcast, the digital broadcast receiving apparatus 121 only receives the AC carrier in the first power consumption state, does not output video or audio, and sets an emergency start flag on the AC carrier. If it is detected, it immediately shifts to the second power consumption state and outputs emergency broadcast video and audio.

  Specifically, in the standby state, the digital broadcast receiving apparatus 121 uses the configuration A shown in FIG. 13 in order to monitor the presence / absence of the earthquake early warning multiplexed on the AC carrier. When the digital broadcast receiving apparatus 121 detects the earthquake early warning according to the configuration A, it further outputs the earthquake early warning using the configuration B. In the case of monitoring the earthquake early warning while receiving and outputting normal broadcast content (video and audio), the configuration C is used in addition to the configuration A. This digital broadcast receiving device 121 automatically monitors the presence of an emergency earthquake warning in a standby state and automatically starts outputting emergency broadcast video and audio when it detects that an emergency earthquake warning is being broadcast. Startup can be realized.

JP 2011-114593 A

"Survey Report on Prompt Transmission of Earthquake Early Warning (Details)" Radio Industry Association Digital Broadcasting System Development Group Digital Receiver Working Group Emergency Information Transmission TG, September 4, 2009

  However, in order to realize the automatic activation function, as described above, since it is necessary to monitor whether or not the receiving device has always received a control signal indicating the presence or absence of emergency broadcast even in the standby state, Therefore, there is a problem that power consumption is accelerated, which is disadvantageous from the viewpoint of energy saving. In particular, in the case of a receiver that is carried during a disaster, it is required to be driven for a long time in a situation where supplies such as dry batteries are limited, so the power consumption problem is directly related to the available time of the receiver, It will be a big challenge.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a receiving apparatus that can reduce power consumption for monitoring the presence or absence of emergency broadcasting in a standby state and an automatic activation method thereof.

  The receiving apparatus of the present invention includes receiving means for receiving an OFDM signal including emergency broadcast presence / absence information indicating presence / absence of an emergency broadcast, and at least one control carrier on which the emergency broadcast presence / absence information of the OFDM signal is multiplexed. Narrowband FFT means for performing partial band FFT processing to obtain subcarriers in the partial band, and presence / absence of emergency broadcast multiplexed on the at least one control carrier included in the partial band subcarriers Based on control signal decoding means for extracting information, full-band FFT means for performing full-band FFT processing on the OFDM signal to obtain sub-carriers for the full band, and subcarriers obtained by the full-band FFT means In a standby state where the demodulation means for demodulating the broadcast content included in the OFDM signal and the demodulation means are not activated, When the narrowband FFT means performs FFT processing of the OFDM signal, and the emergency broadcast presence / absence information extracted by the control signal decoding means indicates that there is an emergency broadcast, the full-band FFT means And a control means for performing FFT processing of the OFDM signal.

  According to this configuration, in the standby state, the narrowband FFT means performs a partial band FFT process, and when it is detected that there is an emergency broadcast based on the FFT process, the fullband FFT means and the demodulation are performed. Since the broadcast content is demodulated by the means, it is possible to reduce the processing load on the FFT processing for monitoring the presence or absence of the emergency broadcast in the standby state, and to reduce the power consumption.

  The OFDM signal may include a plurality of control carriers in which the emergency broadcast presence / absence information of the same content is multiplexed, and the narrowband FFT means determines the partial band according to the reception quality of the OFDM signal. You may change it.

  According to this configuration, FFT processing can be performed in an appropriate partial band according to reception quality.

  The narrowband FFT means may change the bandwidth of the partial band according to the reception quality of the OFDM signal.

  According to this configuration, when the reception quality is poor, the emergency broadcast presence / absence information can be reliably detected by performing FFT processing in a partial band including a plurality of control carriers.

  The narrowband FFT means may change the position of the partial band according to the reception quality of the OFDM signal.

  According to this configuration, when the reception quality is poor due to the influence of frequency selective fading or the like, the emergency broadcast presence / absence information is reliably detected by performing FFT processing on a part of the band including the control carrier with good reception quality. it can.

  The reception quality may be obtained based on a demodulation result of the broadcast content by the demodulation unit.

  According to this configuration, reception quality can be easily obtained.

  The demodulating means may be periodically activated even in the standby state to obtain the reception quality.

  According to this configuration, newer reception quality information can be obtained.

  The reception quality may be obtained based on a decoding result of the control carrier by the control signal decoding unit.

  According to this configuration, the latest reception quality information can be obtained without activating the demodulation means.

  The OFDM signal may include a plurality of control carriers in which the emergency broadcast presence / absence information having the same content is multiplexed, and the narrowband FFT means sequentially performs a plurality of different partial band FFT processes. Good.

  According to this configuration, emergency broadcast presence / absence information can be reliably detected even when there is frequency selective fading.

  The narrow-band FFT means includes a band-pass filter that passes only the partial band, a sampling rate converter that changes a sampling rate according to the bandwidth of the partial band, and the sampling rate converter that is sampled It may have a configuration including an FFT circuit that performs FFT processing on a signal and acquires subcarriers in the partial band.

  According to this configuration, the window of the FFT process by the narrowband FFT unit can be reduced.

  The control carrier may be a TMCC carrier or an AC carrier.

  According to this configuration, the emergency broadcast presence / absence information can be transmitted to the receiving terminal using the control carrier.

  A receiving apparatus according to another aspect of the present invention includes a receiving unit that receives an OFDM signal including emergency broadcast presence / absence information indicating whether or not an emergency broadcast is present, a control signal decoding unit that extracts the emergency broadcast presence / absence information from the OFDM signal, Demodulation means for demodulating broadcast content included in the OFDM signal based on subcarriers of the OFDM signal, and in the standby state in which the demodulation means is not activated, the emergency broadcast presence / absence information includes an emergency broadcast In the case shown, it has a configuration including a control means for enabling or disabling the automatic start function for starting the demodulation means.

  According to this configuration, when the automatic start function for automatically activating the demodulation means by monitoring the emergency broadcast presence / absence information in the standby state is not required, the automatic start function is disabled and the standby state is set. By stopping the monitoring of emergency broadcast presence / absence information, various power consumption can be reduced.

  An automatic activation method for a receiving apparatus of the present invention includes a reception step of receiving an emergency broadcast presence / absence information indicating presence / absence of an emergency broadcast, and a standby state in which the broadcast content included in the OFDM signal is not demodulated, A narrowband FFT step of obtaining a subcarrier of the partial band by performing an FFT process of a partial band including at least one control carrier multiplexed with the emergency broadcast presence / absence information of the OFDM signal; A control signal decoding step for extracting the emergency broadcast presence / absence information multiplexed on the at least one control carrier included in the subcarrier of the subband, and the emergency broadcast presence / absence information extracted in the control signal decoding step is an emergency broadcast If the signal indicates that there is a subcarrier of the entire band, the FFT processing of the entire band of the OFDM signal is performed. A full band FFT step of acquiring, on the basis of the subcarriers obtained in the full band FFT step, and a demodulation step of demodulating the broadcast content included in the OFDM signal.

  Even in this configuration, in the standby state, when the FFT processing of a part of the band is performed, and it is detected that there is an emergency broadcast based on the FFT processing, the broadcast content is processed by the FFT processing and demodulation processing of the entire band Since it is demodulated, it is possible to reduce the processing load on the FFT processing for monitoring the presence or absence of emergency broadcasting in the standby state, and to reduce power consumption.

  The above-described automatic activation method of the receiving device further includes a second control signal decoding step of extracting the emergency broadcast presence / absence information included in the subcarriers of the full band obtained in the full band FFT step; A switching step of stopping the demodulation step and switching to the narrowband FFT step when the emergency broadcast presence / absence information extracted in the control signal decoding step 2 indicates that there is no emergency broadcast. May be.

  According to this configuration, it is possible to automatically start from the standby state, output an emergency broadcast, and then return to the standby state again when the emergency broadcast ends.

  According to the present invention, in the standby state, a partial band FFT process is performed, and when it is detected that there is an emergency broadcast based on the FFT process, the broadcast content is processed by the full band FFT process and demodulation process. Therefore, it is possible to reduce power consumption by reducing the processing load on the FFT processing for monitoring the presence or absence of emergency broadcasting in the standby state.

The block diagram which shows the structure of the receiver in the 1st Embodiment of this invention The figure which shows the OFDM signal of the baseband output from the orthogonal demodulator 19 in the 1st Embodiment of this invention The figure explaining the FFT process of all the bands in the 1st Embodiment of this invention The figure explaining the FFT processing of the narrow band in the 1st Embodiment of this invention Operation flow diagram of receiving apparatus in standby state (state A) in the first exemplary embodiment of the present invention Operation flow diagram of receiving apparatus when pilot / data symbol demodulation processing section according to first embodiment of the present invention is automatically activated by emergency broadcast presence / absence information (state B) The block diagram which shows the structure of the receiver of the 2nd Embodiment of this invention The figure for demonstrating switching of the window size in the FFT circuit of the 2nd Embodiment of this invention Operation flow diagram of receiving apparatus in standby state (state A) in the second exemplary embodiment of the present invention Flowchart of operation of receiving apparatus when pilot / data symbol demodulation processing unit in the second embodiment of the present invention is automatically activated by emergency broadcast presence / absence information (state B) The block diagram which shows the structure of the receiver of the 3rd Embodiment of this invention The figure for demonstrating the FFT window in the FFT circuit of the 3rd Embodiment of this invention Block diagram showing the configuration of a conventional digital broadcast receiving apparatus

  The inventor of the present application has paid attention to the fact that the power consumption of the FFT processing for the received OFDM signal is particularly large when the presence or absence of the emergency broadcast is monitored in the conventional receiving apparatus having the automatic activation function. That is, in the configuration of FIG. 13, it is necessary to operate the configuration A in the standby state in which the presence or absence of emergency broadcasting is monitored, but the power consumption in the processing in the FFT 104 in this case is relatively large. Therefore, in the receiving apparatus according to the embodiment of the present invention, the amount of FFT calculation in a standby state for monitoring the presence or absence of emergency broadcasting is reduced to reduce the power consumption of the receiving apparatus. In the following description, the standby state refers to a state in which power from a power source such as a battery is supplied to the receiving apparatus, but broadcast content is not reproduced.

(First embodiment)
Hereinafter, a receiving apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the receiving apparatus of this embodiment. The receiving apparatus 100 includes an antenna 11, a channel selection unit 12, an oscillator 13, a multiplier 14, an IF circuit 15, an oscillator 16, a multiplier 17, an A / D converter 18, an orthogonal demodulation circuit 19, a switch 20, a bandpass filter ( BPF) 21, sampling rate converter (decimation) unit 22, fast Fourier transform (FFT) circuit 23, control information decoder 24, fast Fourier transform (FFT) circuit 25, control information decoder 26, power supply control unit 27, and control A portion 28 is provided.

  A transmission wave on which a signal modulated by the OFDM method (OFDM signal) is superimposed is transmitted from the transmission device. The antenna 11 of the receiving apparatus 100 receives this transmission wave as an RF signal. This antenna 11 corresponds to the receiving means of the present invention. The channel selection unit 14 outputs a channel selection signal corresponding to the channel selected by the user to the oscillator 13. The oscillator 13 transmits an oscillation frequency according to the channel selection signal. The multiplier 14 outputs an RF signal having an oscillation frequency according to the channel selection signal to the IF circuit 15. The IF circuit 15 converts the frequency of the RF signal and outputs an IF signal.

  The oscillator 16 outputs the carrier frequency to the multiplier 17. The multiplier 17 outputs an IF signal having a carrier frequency to the A / D converter 18. The A / D converter 18 performs A / D conversion on the IF signal and outputs it to the quadrature demodulation circuit 19. The orthogonal demodulation circuit 19 performs orthogonal demodulation on the digitized IF signal and outputs a baseband OFDM signal sampled in the time domain.

  Connected to the output side of the quadrature demodulation circuit 19 is a switch 20 for switching whether the quadrature demodulation circuit 19 is connected to the BPF 21 or whether the quadrature demodulation circuit 19 is connected to the FFT circuit 25. Switching of the switch 20 is controlled by the control unit 28. The control unit 28 connects the switch 20 to the BPF 22 side when the receiving apparatus 100 is in a standby state and monitors the presence or absence of an emergency broadcast, and the receiving apparatus 100 receives a video signal or an audio signal and reproduces it. In the case of performing, the switch 20 is connected to the FTT circuit 25. The control unit 28 corresponds to the control means of the present invention.

  During standby, the control unit 28 connects the switch 20 to the BPF 21. At this time, the BPF 21 is connected to the orthogonal demodulation circuit 19 via the switch 20. The BPF 21 outputs only a part of the frequency band signals among the OFDM signals input from the orthogonal demodulation circuit 19. The sampling rate converter 22 thins out (decimates) the signal output from the BPF 21 at intervals according to the filtering in the BPF 21. Specifically, when the BPF 21 outputs only 1 / N frequency bands of the entire frequency band, the sampling rate converter 22 also extracts subcarriers every N lines.

  The FFT circuit 23 applies narrow band FFT processing corresponding to the band passed by the BPF 21 to the subcarriers output from the sampling rate converter 22. The configuration comprising the BPF 21, the sampling rate converter 22 and the FFT circuit 23 corresponds to the narrowband FFT means of the present invention. The control information decoder 24 extracts the control information by decoding the OFDM signal output from the FFT circuit 23, that is, the OFDM signal after FFT processing sampled in the frequency domain. In particular, the control information decoder 24 extracts emergency broadcast presence / absence information in the AC carrier included in the control information. That is, in this embodiment, the emergency broadcast presence / absence information is multiplexed on the AC carrier as an emergency broadcast flag. The control information decoder 24 notifies the power supply control unit 27 and the control unit 28 of emergency broadcast presence / absence information, that is, whether the emergency broadcast flag is ON or OFF.

  On the other hand, when outputting broadcast content such as video and audio (including emergency broadcast content) based on the received OFDM signal, the control unit 28 switches the switch 20 to the FFT circuit 25, and the FFT circuit 25 20 is connected to the quadrature demodulator 19. The FFT circuit 25 performs FFT processing on the subcarriers input from the quadrature demodulation circuit 19. At this time, unlike the FFT circuit 23, the FFT circuit 25 applies the FFT processing to all the frequency bands of the subcarriers. The FFT circuit 25 corresponds to the full-band FFT means of the present invention. The control information decoder 26 decodes the OFDM signal output from the FFT circuit 25, that is, the OFDM signal after FFT processing sampled in the frequency domain, and extracts control information including the TMCC carrier and the AC carrier.

  Hereinafter, the FFT processing by the FFT circuit 23 and the FFT circuit 25 will be described in detail. FIG. 2 is a diagram illustrating an output after FFT processing with the horizontal axis as a frequency. FIG. 2 shows an example in the case of mode 3 of 1-segment transmission of ISDB-T. In FIG. 2, a solid line arrow indicates a data carrier, and a broken line arrow indicates an AC carrier. As shown in FIG. 2, the OFDM signal includes 432 subcarriers. The 432 subcarriers include 8 AC carriers, and their positions are known.

  The same emergency broadcast presence / absence information is multiplexed on each AC carrier. This means that if the reception quality is poor, the S / N ratio can be improved by analog synthesis of reception results transmitted by a plurality of AC carriers, while not receiving all AC carriers. Also means that emergency broadcast presence / absence information can be detected. On the other hand, when reproducing broadcast content (including emergency broadcast content), it is naturally necessary to extract all data carriers.

  FIG. 3 is a diagram for explaining the FFT processing in the FFT circuit 25, and FIG. 4 is a diagram for explaining the FFT processing in the FFT circuit 23. When reproducing broadcast content, the switch 20 connects the quadrature demodulator 19 to the FFT circuit 25. All subcarriers demodulated by the orthogonal demodulator 19 are input to the FFT circuit 25. As shown in FIG. 3, the FFT circuit 25 performs full-size (1024 points) FFT processing on this subcarrier. By this processing, a control carrier including a data carrier, a TMCC carrier, and an AC carrier is extracted.

  In contrast, in the standby state, it is sufficient that only the AC carrier can be extracted. As described above, 432 subcarriers include 8 AC carriers, and the same emergency broadcast presence / absence information is multiplexed on each AC carrier. Therefore, the FFT circuit 23 does not need to perform FFT processing in a window that covers all 432 subcarriers. Therefore, the FFT circuit 23 performs FFT processing with a window size smaller than all the subcarriers.

  At this time, the FFT circuit 23 sets the size and position of the window so as to include at least one subcarrier on which emergency broadcast presence / absence information is multiplexed. In the present embodiment, the FFT circuit 25 that performs normal processing performs 1024-point FFT processing, whereas the FFT circuit 23 performs 64-point FFT processing. That is, the FFT circuit 23 performs the FFT process in a window having a size 1/16 of the full size.

  For this reason, the BPF 21 passes only the band necessary for the narrowband FFT processing performed by the FFT circuit 23. That is, when the number of FFT points in the FFT processing in the FFT circuit 23 is 1 / N of the whole, the BPF 21 passes only the 1 / N band. Also, the sampling rate converter 22 performs a thinning process so that every N subcarriers sampled from there when the bandwidth passed by the BPF 21 becomes 1 / N (the sampling rate is 1 / N). N). In this embodiment, since the window size is 1/16, the BPF 21 passes a band of 1/16 width corresponding to the window, and the sampling rate converter 22 also sets the sampling rate to 1/16. To do.

  Returning to FIG. 1, receiving apparatus 100 further includes pilot / data symbol demodulation processing section 50. The pilot / data symbol demodulation processing unit 50 receives the data carrier output from the FFT circuit 25 and demodulates the data carrier to acquire data symbols in order to reproduce the broadcast content. Further, when reproducing the broadcast content, the pilot data symbol demodulation processing unit 50 receives the control signal decoded by the control signal decoder 26 and demodulates the broadcast content according to the control signal. The pilot data symbol demodulation processing unit 50 corresponds to the demodulation means of the present invention.

  The pilot / data symbol demodulation processing unit 50 includes a data carrier demodulation unit 29, a frequency deinterleaving unit 30, a time deinterleaving unit 31, a demapping unit 32, a bit deinterleaving unit 33, a depuncturing unit 34, a Viterbi decoding unit 35, a byte decoding unit. An interleaving unit 36, a despreading unit 37, and a Reed-Solomon decoding unit 38 are provided.

  The data carrier demodulator 29 demodulates the data carrier among the frequency components output from the FFT circuit 25. The frequency deinterleaving unit 30 rearranges the order of the carrier-demodulated subcarriers. Time deinterleaving section 31 further changes the order of subcarriers. The demapping unit 32 performs data reassignment processing (demapping processing) on the carrier signal to restore the transmission data sequence. The bit deinterleaving unit 33 rearranges the transmission data series in units of bits by deinterleaving processing corresponding to interleaving processing for error dispersion of multilevel symbols.

  The depuncturing unit 34 inserts a provisional value in the signal area by depuncturing processing corresponding to puncturing processing for transmission bit reduction. The Viterbi decoding unit 35 decodes the folded and decoded bit string. The byte deinterleave unit 36 performs interleave processing in units of bytes. The despreading unit 37 reversely multiplies the pseudo-noise sequence multiplied on the transmission side in order to eliminate the bias of the signal polarity and to provide randomness. The Reed-Solomon decoding unit 38 performs error correction detection and error correction decoding as block error correction decoding. The data symbols are demodulated by the above-described series of processing of the pilot data symbol demodulation processing unit 50. The pilot symbols multiplexed on the data carrier are also demodulated in the same manner as described above.

  As described above, in the standby state, the control information decoder 24 extracts the AC carrier, and outputs the emergency broadcast presence / absence information multiplexed there to the power supply control unit 27, so that the emergency broadcast is transmitted. The presence or absence is notified to the power supply control unit 27. The power supply control unit 27 activates the pilot / data symbol demodulation processing unit 50 when the emergency broadcast flag is ON in the emergency broadcast presence / absence information. That is, in the standby state, power is not supplied to the pilot / data symbol demodulation processing unit 50, and the pilot / data symbol demodulation processing unit 50 is in a pause state, and the pilot / data symbol demodulation processing unit 50 detects that the emergency broadcast flag is ON. Then, power is supplied by the power control unit 27 to start up.

  The control information decoder 24 also outputs emergency broadcast presence / absence information to the control unit 28 to notify the presence / absence of the emergency broadcast. When the emergency broadcast flag is ON in the emergency broadcast presence / absence information, the control unit 28 controls the switch 20 to connect the quadrature demodulator 19 and the FFT circuit 25. The data carrier is output from the FFT circuit 25 to the pilot / data symbol demodulation processing unit 50, and the pilot / data symbol demodulation processing unit 50 starts demodulating the pilot symbols and data symbols.

  On the other hand, in the standby state, when the emergency broadcast flag is OFF, the power supply control unit 27 maintains a state in which no power is supplied to the pilot / data symbol demodulation processing unit 50, and the pilot / data symbol demodulation processing unit Leave 50 paused. Further, when the emergency broadcast flag is OFF in the standby state, the control unit 28 maintains the switch 20 as it is connected to the BPF 21. In addition, when the pilot data symbol demodulation processing unit 50 is automatically activated by the emergency broadcast presence / absence information as described above, the emergency broadcast flag is turned OFF in the control information received from the control signal decoder 26. In the case (when the emergency broadcast ends), the operation is suspended.

  FIG. 5 is an operation flowchart of the receiving apparatus 100 in the standby state (state A), and FIG. 6 is a diagram when the pilot / data symbol demodulation processing unit 50 is automatically activated by the emergency broadcast presence / absence information (state B). 6 is an operation flowchart of the receiving apparatus 100. FIG. In the standby state (state A), the switch 20 connects the quadrature demodulation circuit 19 to the BPF 21. As shown in FIG. 5, the BPF 21 performs a band pass filter process that passes a narrow band corresponding to the narrow band FFT process in the FFT circuit 23 (step S <b> 51). The sampling rate converter 22 performs sampling rate conversion processing on the output of the BPF 21 at a sampling rate corresponding to the narrowband FFT processing in the FFT circuit 23 (step S52). Next, the FFT circuit 23 performs N (N = 64) point narrow band FFT processing on the subcarrier thinned out by the sampling rate converter 22 (step S53).

  The control signal decoder 24 extracts an AC carrier (step S54). The power supply control unit 27 determines whether or not the emergency broadcast flag is ON in the extracted AC carrier (step S55). If the emergency broadcast flag is ON (YES in step S55), the pilot The power is supplied to the data symbol demodulation processing unit 50 and activated (step S56). When the pilot / data symbol demodulation processing unit 50 is activated, the state shifts to the state B (step S57).

  In the state where the pilot / data symbol demodulation processing unit 50 is activated (state B), the switch 20 connects the orthogonal demodulation circuit 19 to the FFT circuit 25. As shown in FIG. 6, the FFT circuit 25 performs full-size (1024 points) FFT processing on the plurality of subcarriers output from the orthogonal demodulation circuit 19 (step S61). The control signal decoder 26 extracts the TMCC and the AC carrier (step S62), and controls the demodulation processing in the pilot / data symbol demodulation processing unit 50 based on this.

  The control signal decoder 26 determines whether or not the emergency broadcast flag is ON in the extracted AC carrier (step S63). If the emergency broadcast flag is ON (YES in step S63), that is, if there is still an emergency broadcast, pilot / data symbol demodulation processing unit 50 inputs the Fourier transform coefficient output from FFT circuit 25. The pilot symbol and data symbol are demodulated (step S64), and the process returns to step S61. Here, since there is an emergency broadcast, the pilot / data symbol demodulation processing unit 50 performs a demodulation process on the emergency broadcast content. When the emergency broadcast is completed and the emergency broadcast flag is turned OFF (NO in step S63), power supply control unit 27 stops supplying power to pilot / data symbol demodulation processing unit 50 and is in a standby state. The process proceeds to (state A) (step S65).

  As described above, according to receiving apparatus 100 of the present embodiment, the data in the standby state can be obtained using the fact that the emergency broadcast flag indicating the presence or absence of emergency broadcast is multiplexed on a plurality of AC carriers. Since a narrow window including at least one AC carrier among a plurality of subcarriers including carriers is set and FFT processing is performed, and AC carriers are extracted, as compared with the case where FFT processing is performed on all subcarriers. Thus, the amount of FFT processing for detecting the emergency broadcast flag can be reduced, and the power consumption in the standby state can be suppressed.

  In addition, when the emergency broadcast flag is turned on, power is immediately supplied to the pilot / data symbol demodulation processing unit 50, so that the pilot / data symbol processor can be automatically started immediately in accordance with the emergency broadcast flag, and from the standby state. Emergency broadcast content can be played automatically.

(Second Embodiment)
FIG. 7 is a block diagram illustrating a configuration of the receiving apparatus according to the second embodiment. In the receiving apparatus 200 of the present embodiment, the same components as those of the receiving apparatus 100 of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In reception apparatus 200 of the present embodiment, reception quality information is given from pilot / data symbol demodulation processing unit 50 to control unit 28, and BPF 21, sampling rate converter 22, and FFT circuit 23 are supplied from control unit 28. On the other hand, it differs from the receiving apparatus 100 of the first embodiment in that a control signal is given.

  Receiving apparatus 200 of the present embodiment can change the window size (FFT size) in the FFT processing in the standby state. As described above, since a plurality of subcarriers include a plurality of AC carriers having the same contents, it is only necessary to detect the emergency broadcast flag from only a part of them, but if the band is limited in this way, When the reception quality in the receiving apparatus 200 is poor, there is a case where the AC carrier in the narrow band cannot be received due to frequency selective fading. Therefore, when the reception quality is low, it is advantageous to receive the AC carrier in a wider band. Therefore, receiving apparatus 200 of the present embodiment changes the FFT size according to the reception quality.

  The pilot data symbol demodulation processing unit 50 calculates a reception quality value as reception quality information when demodulating broadcast content. The reception quality value uses BER (Bit Error Rate), but is not limited to this, and any value that represents reception quality is sufficient, FER (Frame Error Rate), received electric field strength (RSSI: Received Signal Strength Indicator), The moving speed of the receiving terminal can also be suitably used. The reception quality information is not limited to a specific value representing the reception quality as described above, and may be information indicating whether the reception quality value is below a predetermined threshold.

  The pilot data symbol demodulation processing unit 50 outputs the calculated reception quality value to the control unit 28. In the standby state, the control unit 28 connects the switch 20 to the BPF 21 as in the first embodiment. At this time, if the reception quality value is lower than a predetermined threshold value, the FFT circuit 23 is more connected. The BPF 21, the sampling rate converter 22, and the FFT circuit 23 are controlled so that the FFT process is performed with a wide window.

  FIG. 8 is a diagram for explaining switching of the window size in the FFT circuit 23. When the reception quality is higher than the threshold, the FFT circuit 23 performs (1) 64-point FFT processing in a window including two AC carriers as shown in FIG. 8, and the reception quality is lower than the threshold. In this case, (2) 512-point FFT processing is performed in a wider window including four AC carriers.

  Therefore, when the reception quality is higher than the threshold, the control unit 28 controls the BPF 21 to pass the subcarriers of the 64-point window and sets the sampling rate to (64/1024 =) 1/16. Thus, the sampling rate converter 22 is controlled, and the FFT circuit 23 is controlled so as to perform 64-point FFT processing. In addition, when the reception quality is lower than the threshold, the control unit 28 controls the BPF 21 to pass the subcarriers of the 512-point window and sets the sampling rate to (512/1024 =) 1/2. Then, the sampling rate converter 22 is controlled, and the FFT circuit 23 is controlled to perform 512-point FFT processing.

  FIG. 9 is an operation flow diagram of receiving apparatus 200 in the standby state (state A), and FIG. 10 is a diagram when pilot / data symbol demodulation processing unit 50 is automatically activated by emergency broadcast presence / absence information (state B). 6 is an operation flowchart of the receiving apparatus 200. FIG. In the standby state (state A), the switch 20 connects the quadrature demodulation circuit 19 to the BPF 21. As shown in FIG. 9, in the standby state, the control unit 28 determines the FFT size N based on the immediately preceding reception quality information (step S91). In the present embodiment, the FFT size N is either 64 points or 512 points.

  Subsequently, the control unit 28 controls the BPF 21 and the sampling rate converter 22 according to the FFT size N (step S92). Specifically, the control unit 28 sets the frequency band that the BPF 21 passes according to the FFT size, and sets the sampling rate in the sampling rate converter 22.

  The BPF 21 performs a band pass filter process when the frequency band to be passed is set by the control unit 28 (step S93). The sampling rate converter 22 performs sampling rate conversion processing on the output of the BPF 21 at the sampling rate set by the control unit 28 (step S94). Next, the FFT circuit 23 performs N (N = 64 or 512) point narrow band FFT processing on the subcarriers thinned out by the sampling rate converter 22 (step S95).

  The control signal decoder 24 extracts an AC carrier (step S96). The power supply control unit 27 determines whether or not the emergency broadcast flag is ON in the extracted AC carrier (step S97). If the emergency broadcast flag is ON (YES in step S97), the pilot is determined. The power is supplied to the data symbol demodulation processing unit 50 and activated (step S98). When the pilot / data symbol demodulation processing unit 50 is activated, the state shifts to the state B (step S99).

  In the state where the pilot / data symbol demodulation processing unit 50 is activated (state B), the switch 20 connects the orthogonal demodulation circuit 19 to the FFT circuit 25. As shown in FIG. 10, the FFT circuit 25 performs full-size (1024 points) FFT processing on a plurality of subcarriers output from the orthogonal demodulation circuit 19 (step S101). The control signal decoder 26 extracts the TMCC and the AC carrier (step S102), and controls the demodulation processing in the pilot data symbol demodulation processing unit 50 based on this.

  The control signal decoder 26 determines whether or not the emergency broadcast flag is ON in the extracted AC carrier (step S103). If the emergency broadcast flag is ON (YES in step S103), that is, if there is still an emergency broadcast, pilot / data symbol demodulation processing unit 50 inputs the Fourier transform coefficient output from FFT circuit 25. The pilot symbol and data symbol are demodulated (step S104). Then, the pilot / data symbol demodulation processing unit 50 calculates reception quality and outputs it to the control unit 28 (step S105), and returns to step S101. Here, since there is an emergency broadcast, the pilot / data symbol demodulation processing unit 50 performs a demodulation process on the emergency broadcast content. When the emergency broadcast is completed and the emergency broadcast flag is turned off (NO in step S103), power supply control unit 27 stops supplying power to pilot / data symbol demodulation processing unit 50 and is in a standby state. The process proceeds to (state A) (step S105).

  The pilot / data symbol demodulation processing unit 50 also calculates reception quality and outputs it to the control unit 28 as reception quality information even when performing demodulation processing on normal broadcast content that is not emergency broadcast. Whenever the reception quality information is received, the control unit 28 updates the old reception quality information and always stores the latest reception quality information. When in the standby state, the control unit 28 refers to the latest reception quality information and determines the FFT size.

  As described above, according to receiving apparatus 200 of the present embodiment, the window size in the narrowband FFT process for detecting the emergency broadcast flag in the standby state is determined according to the reception quality. This can reduce the possibility that the emergency broadcast flag cannot be received.

  In the second embodiment, the FFT circuit 23 performs the FFT processing by switching between two types of FFT sizes. However, the number of FFT sizes that can be switched according to reception quality is three or more. Good. In addition, when the FFT circuit 23 is mounted by a field-programmable gate array (FPGA) or an application specific integrated circuit (ASIC), a plurality of FFT circuits having different sizes are provided, and the FFT size is changed by switching the FFT circuit to be used. You may switch. However, if a plurality of FFT circuits are provided, a corresponding amount of space is required. Therefore, it is determined whether the FFT size is switched by one FFT circuit or a plurality of FFT circuits having different sizes are provided according to the allowable space. That's fine.

  In the second embodiment, the FFT size is determined based on the previous reception quality information in the standby state. That is, the FFT size in the subsequent standby state is determined based on the final reception quality when the broadcast content is reproduced before entering the standby state. However, if the standby state continues for a relatively long time, the reception state may change, and the reception quality information may become outdated. Therefore, in the standby state, the power supply control unit 27 periodically starts the pilot / data symbol demodulation processing unit 50 even when the emergency activation flag is OFF (that is, shifts to the state B). The control unit 28 may acquire the latest reception quality information.

  Further, instead of or in addition to the periodic forced activation of the pilot / data symbol demodulation processing unit 50 described above, the control signal decoder 24 calculates reception quality information and outputs it to the control unit 28 in a standby state. Also good. In this case, the control signal decoder 24 decodes the TMCC carrier, and receives the reception quality based on the reception status of the symbol indicating the fixed value included in the TMCC carrier and the reception status of the synchronization word for each frame. Information may be calculated.

(Third embodiment)
FIG. 11 is a block diagram illustrating a configuration of a receiving apparatus according to the third embodiment. In the receiving apparatus 300 of this embodiment, the same components as those of the receiving apparatus 100 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. Receiving apparatus 300 of this embodiment reduces power consumption for detecting an emergency broadcast flag in a standby state, and reception degradation due to fading occurs in a specific frequency band due to the influence of frequency selective fading and the like. The possibility that the emergency broadcast flag cannot be detected is reduced.

  FIG. 12 is a diagram for explaining an FFT window in the FFT circuit 23 of the receiving apparatus 300 according to the present embodiment. The receiving apparatus 300 changes the position of the FFT window for each OFDM frame. Specifically, as shown in FIG. 12, the FFT circuit 23 performs FFT processing on the k-th (k is a natural number) OFDM frame using a 64-point FFT window (1) including the first AC carrier. The k + 2th OFDM frame is subjected to FFT processing in a 128-point FFT window (2) including the second and third AC carriers, and the k + 3th OFDM frame is fourth. FFT processing is performed in a 64-point FFT window (3) including AC carriers. That is, for each OFDM frame, the windows are changed in the order of different FFT windows (1), (2), and (3), and this is repeated.

  The control unit 28 controls the BPF 21, the sampling rate converter 22, and the FFT circuit 23 to realize the above window size switching. Specifically, the control unit 28 controls the BPF 21 to pass a band corresponding to the position and size of the FFT window, and sets a sampling rate corresponding to the size of the FFT window in the sampling rate converter 22. The FFT circuit 23 is controlled so as to perform the FFT processing in the FFT window as described above.

  As described above, according to receiving apparatus 300 of the present embodiment, in an idle state, narrow band FFT windows having different frequencies are set for different OFDM frames, and FFT processing is performed to detect an emergency broadcast flag. Therefore, power saving in the standby state can be realized, and frequency selective fading resistance can be increased.

  In the present embodiment, the sizes of the FFT window (1) and the FFT window (3) are the same, and the size of the FFT window (2) is different, but the size of each FFT window is the same. Or different. In the present embodiment, a plurality of FFT windows do not overlap each other, but some may overlap with other FFT windows. Furthermore, in the present embodiment, the FFT window is switched for each OFDM frame, but it is only necessary to switch with the passage of time without switching for each OFDM frame. Further, the switching period of the FFT window may be dynamically changed. For example, the FFT window switching period may be dynamically determined according to the fading speed.

  Further, the FFT window may be shifted as described above, and the control signal decoder 24 may evaluate the reception quality for each FFT window and thereafter fix the FFT window with a good reception quality. Further, when the reception quality of a certain FFT window is poor, it may be shifted to another FFT window.

  Although the first to third embodiments of the present invention have been described above, the receiving apparatuses of the first to third embodiments described above are all FFT processing for detecting an emergency broadcast flag in a standby state. In order to reduce power consumption, only the necessary symbols are extracted intermittently in time to detect the emergency broadcast flag. It is possible to reduce processing on the time axis. However, the reduction of processing on the time axis has a demerit that reception quality cannot be ensured because error correction becomes impossible and frame synchronization becomes impossible. On the other hand, in the embodiment of the present invention, since processing on the frequency axis is reduced, it is more advantageous than reduction on processing on the time axis in that error correction and frame synchronization are possible. However, the present invention does not exclude the case where the processing reduction on the time axis is performed together with the processing reduction on the frequency axis.

  In the above embodiment, an example in which emergency broadcast presence / absence information is multiplexed on an AC carrier has been described. However, emergency broadcast presence / absence information may be multiplexed on a TMCC carrier. In this case, the control signal decoder 24 extracts the TMCC carrier and detects the emergency broadcast flag therefrom.

  In addition, when the receiving device of the first to third embodiments confirms the difference between the time given to the control information and the time on the receiving terminal side, and the difference does not exceed a predetermined threshold A time check function for determining that the information is significant may be provided. Moreover, the receiving device may have a GPS function, and may have an area check function for determining whether the emergency broadcast is for an area to which the receiving device belongs. By these time check function and area check function, it is possible to avoid receiving and reproducing an emergency broadcast of wrong contents broadcast maliciously.

  In addition, the receiving apparatus according to the first to third embodiments performs full-size FFT processing in the FFT circuit 25 when reproducing broadcast content, while performing narrow-band FFT processing in the FFT circuit 23 in a standby state. By doing so, the power consumed in the standby state was suppressed. Depending on the situation, the receiving device may not need to monitor whether there is an emergency broadcast in a standby state. For example, when in a refuge at the time of a disaster, it is assumed that there is another device that monitors the presence of an emergency broadcast nearby.

  Therefore, the receiving apparatuses according to the first to third embodiments have a function of turning on / off monitoring of the presence / absence of an emergency broadcast in the standby state described above from the viewpoint of saving power consumption. It is desirable. If there is another device that monitors whether there is an emergency broadcast in the surrounding area, the user can turn off the emergency broadcast monitoring function in the standby state of the user's receiving device, thereby reducing the power consumption of the receiving device. Can be suppressed.

  The present invention has the effect of reducing the processing load on the FFT processing for monitoring the presence or absence of emergency broadcasts in a standby state and suppressing power consumption. It is useful as a receiving device that automatically starts based on the above.

DESCRIPTION OF SYMBOLS 11 Antenna 12 Channel selection part 13 Oscillator 14 Multiplier 15 IF circuit 16 Oscillator 17 Multiplier 18 A / D converter 19 Orthogonal demodulation circuit 20 Switch 21 Band pass filter (BPF)
Reference Signs List 22 sampling rate converter (decimation) 23 fast Fourier transform (FFT) circuit 24 control signal decoder 25 fast Fourier transform (FFT) circuit 26 control signal decoder 27 power supply control unit 28 control unit 29 data carrier demodulation unit 30 frequency deinterleave Section 31 Time deinterleaving section 32 Demapping section 33 Bit deinterleaving section 34 Depuncture section 35 Viterbi decoding section 36 Byte deinterleaving section 37 Despreading section 38 Reed-Solomon decoding section 50 Pilot data symbol demodulation processing section 100, 200, 300 Reception apparatus

Claims (13)

Receiving means for receiving an OFDM signal including emergency broadcast presence / absence information indicating presence / absence of emergency broadcast;
Narrowband FFT means for performing FFT processing of a partial band including at least one control carrier on which the emergency broadcast presence / absence information of the OFDM signal is multiplexed, and acquiring the subcarrier of the partial band;
Control signal decoding means for extracting the emergency broadcast presence / absence information multiplexed on the at least one control carrier included in the subcarrier of the partial band;
A full-band FFT means for performing FFT processing of the full band of the OFDM signal to obtain sub-carriers of the full band;
Demodulating means for demodulating broadcast content included in the OFDM signal based on subcarriers obtained by the full-band FFT means;
In a standby state where the demodulation means is not activated, the narrowband FFT means performs FFT processing of the OFDM signal, and the emergency broadcast presence / absence information extracted by the control signal decoding means indicates that there is an emergency broadcast. Control means for causing the full-band FFT means to perform FFT processing of the OFDM signal,
A receiving apparatus comprising: The OFDM signal includes a plurality of control carriers in which the emergency broadcast presence / absence information of the same content is multiplexed,
The receiving apparatus according to claim 1, wherein the narrowband FFT unit changes the partial band according to reception quality of the OFDM signal.   The receiving apparatus according to claim 2, wherein the narrowband FFT unit changes the bandwidth of the partial band in accordance with the reception quality of the OFDM signal.   The receiving apparatus according to claim 2 or 3, wherein the narrowband FFT means changes the position of the partial band according to the reception quality of the OFDM signal.   The receiving apparatus according to any one of claims 2 to 4, wherein the reception quality is obtained based on a demodulation result of the broadcast content by the demodulation means.   6. The receiving apparatus according to claim 5, wherein the demodulating unit is periodically activated even in the standby state to obtain the reception quality.   The receiving apparatus according to claim 2, wherein the reception quality is obtained based on a decoding result of the control carrier by the control signal decoding unit. The OFDM signal includes a plurality of control carriers in which the emergency broadcast presence / absence information of the same content is multiplexed,
The receiving apparatus according to claim 1, wherein the narrowband FFT means sequentially performs a plurality of different partial band FFT processes.   The narrow-band FFT means includes a band-pass filter that passes only the partial band, a sampling rate converter that changes a sampling rate according to the bandwidth of the partial band, and the sampling rate converter that is sampled The receiving apparatus according to claim 1, further comprising: an FFT circuit that performs FFT processing on a signal and acquires the subcarriers of the partial band.   The receiving apparatus according to claim 1, wherein the control carrier is a TMCC carrier or an AC carrier. Receiving means for receiving an OFDM signal including emergency broadcast presence / absence information indicating presence / absence of emergency broadcast;
Control signal decoding means for extracting the emergency broadcast presence / absence information from the OFDM signal;
Demodulation means for demodulating broadcast content included in the OFDM signal based on subcarriers of the OFDM signal;
Control means for enabling or disabling an automatic activation function for activating the demodulation means when the emergency broadcast presence / absence information indicates that there is an emergency broadcast in a standby state where the demodulation means is not activated When,
A receiving apparatus comprising: A receiving step of receiving an OFDM signal including emergency broadcast presence / absence information indicating presence / absence of emergency broadcast;
In a standby state where the broadcast content included in the OFDM signal is not demodulated, FFT processing of a partial band including at least one control carrier multiplexed with the emergency broadcast presence / absence information of the OFDM signal is performed, A narrowband FFT step of acquiring the subcarriers of the partial band;
A control signal decoding step of extracting the emergency broadcast presence / absence information multiplexed on the at least one control carrier included in the subcarriers of the partial band;
When the emergency broadcast presence / absence information extracted in the control signal decoding step indicates that there is an emergency broadcast, the entire bandwidth of the OFDM signal is obtained by performing FFT processing of the entire band. A band FFT step;
A demodulation step of demodulating the broadcast content included in the OFDM signal based on the subcarrier obtained in the full-band FFT step;
A method for automatically starting a receiving apparatus. A second control signal decoding step of extracting the emergency broadcast presence / absence information contained in the subcarriers of the full band obtained in the full band FFT step;
A switching step of stopping the demodulation step and switching to the narrowband FFT step when the emergency broadcast presence / absence information extracted in the second control signal decoding step indicates that there is no emergency broadcast;
The method for automatically starting a receiving apparatus according to claim 12, further comprising:

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