JP2007306363A - Digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To exactly synchronize the content of digital broadcast which is simulcast. <P>SOLUTION: In this digital broadcast receiver 1A, separation parts 21A, 21B separate a coded bit stream 30 to a first coded bit stream corresponding to first digital broadcast and a second coded bit stream corresponding to second digital broadcast. A first decoder 22A decodes the first coded bit stream to generate a first decoded signal. A second decoder 22B decodes the second coded bit stream to generate a second coded signal. A synchronization shift detection part 28 predicts synchronization shift between the first and second decoded signals based on a transmission parameter 31, sets a retrieval range based on the predicted synchronization shift and compares the first decoded signal with the second decoded signal by unit of a piece of predetermined data in the retrieval range. The synchronization shift detection part 28 detects the synchronization shift based on a comparison result. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for processing a plurality of digital broadcast reception signals, and particularly to a technique for processing a plurality of digital broadcast reception signals transmitted by simulcast.

  Japanese terrestrial digital broadcasting is defined by the ISDB-T (Integrated Services Digital Broadcasting Terrestrial) standard and adopts an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme. The OFDM modulation scheme is a kind of multicarrier modulation scheme capable of hierarchical transmission. According to the ISDB-T standard, as schematically shown in FIG. 1, the transmission bandwidth of one channel (about 5.6 MHz) is divided into 13 subbands, that is, OFDM segments S1 to S13. Segments S1-S13 can be further divided into a maximum of three groups or hierarchies. Transmission characteristics such as carrier modulation scheme, inner code coding rate, and time interleaving depth can be set for each layer, and different broadcast programs can be transmitted for each layer. . For example, 12 OFDM segments S1 to S6, S8 to S13 are used to provide a high-quality high definition broadcast (High Definition Broadcast) for a fixed receiver, or 12 OFDM segments S1 to S6 and S8 to S13 are provided. Divided into two layers to provide standard definition broadcasts for fixed receivers for each layer, or digital broadcasts for mobiles (simple video broadcasts) using only one segment S7 arranged in the center ). As a video compression encoding / decoding standard, MPEG-2 (Moving Picture Experts Group phase 2) standard is adopted for digital broadcasting for fixed receivers, and H.264 is used for digital broadcasting for mobiles. H.264 (MPEG4 AVC) standard is adopted. The prior art relating to the above-described layer division is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-304510.

At the beginning of full-scale digital terrestrial broadcasting, so-called simulcast will be scheduled in which broadcasters will simultaneously provide programs with the same content in both digital broadcasting for fixed receivers and digital broadcasting for mobiles. Has been. Thus, several techniques have been proposed for receiving high-quality digital broadcasting as much as possible using a simulcast in a moving body such as a vehicle. For example, in Patent Document 2 (Japanese Patent Laid-Open No. 2004-312361) and Patent Document 3 (Japanese Patent Laid-Open No. 2004-166173), depending on the reception quality, digital broadcasting for a mobile unit and digital broadcasting for a fixed receiver are used. A receiving device that automatically switches between receiving broadcasts is disclosed.
JP 2003-304510 A Japanese Patent Laid-Open No. 2004-312361 JP 2004-166173 A

  However, even if a digital broadcast for a mobile unit and a digital broadcast for a fixed receiver are provided by simulcast, the contents of both broadcasts are not always accurately synchronized in time. In such a case, when the received broadcast is switched from the digital broadcast for the fixed receiver to the digital broadcast for the mobile body, an unnatural image is displayed, which may give a strange feeling to the viewer of the broadcast program.

  In view of the above, an object of the present invention is to provide a digital broadcast receiving apparatus capable of accurately synchronizing the contents of a simulcast digital broadcast.

  In order to achieve the above object, according to the present invention, a transmission band is divided into a plurality of layers, and a broadcast transmitted using a multi-carrier modulation method capable of executing interleaving at different depths for each layer. A digital broadcast receiving apparatus for receiving a signal, wherein a demodulated signal is demodulated according to the multi-carrier modulation method to generate an encoded bitstream, and a transmission parameter representing the interleaving depth is extracted from the received signal A circuit, a first encoded bitstream corresponding to a first digital broadcast transmitted through a first layer in the layer, and a second layer in the layer A separation unit that separates the second encoded bit stream corresponding to the second digital broadcast; and the first encoded bit stream A first decoder for generating a first decoded signal, a second decoder for decoding the second encoded bitstream to generate a second decoded signal, the first decoded signal and the second And a synchronization deviation detector for detecting a synchronization deviation between the first decoded signal and the second decoded signal based on the comparison result, and compensating for the synchronization deviation A synchronization control unit for controlling the output timing of the first and second decoded signals, and the synchronization deviation detecting unit is configured to transmit the first decoded signal and the second decoded signal based on the transmission parameter. A synchronization shift between decoded signals is predicted, a search range of at least one of the first and second decoded signals is set based on the predicted synchronization shift, and the first decoding is performed within the search range. Signal and the second decoded signal It is characterized by comparing with the predetermined data units.

  Hereinafter, various embodiments according to the present invention will be described.

  FIG. 2 is a functional block diagram showing a schematic configuration of the digital broadcast receiving apparatus 1A according to the first embodiment of the present invention. The digital broadcast receiving apparatus 1A includes a receiving circuit 2 and a signal processing circuit 3A. The reception circuit 2 includes a tuner 11 and a demodulation circuit 12.

  It is assumed that the digital broadcast receiving apparatus 1A according to the present embodiment receives two digital broadcasts transmitted by simulcast through a transmission band divided into a plurality of layers. For example, as shown in FIG. 1, among 13 OFDM segments S1 to S13, a high-definition broadcast for a fixed receiver is transmitted through 12 OFDM segments S1 to S6 and S8 to S13, and only through 1 segment S7. When a mobile digital broadcast (one-segment broadcast) having the same content as the high-definition broadcast is transmitted, the digital broadcast receiver 1A has a function of receiving the high-definition broadcast and the one-segment broadcast simultaneously. The digital broadcast receiving apparatus 1A has a function of receiving simulcast digital television broadcasts and synchronizing the contents of these digital television broadcasts with each other. However, the present invention is not limited to this, and simulcast digital audio broadcasts are transmitted. It may have a function of receiving and synchronizing the contents of these digital audio broadcasts.

  Referring to FIG. 2, the tuner 11 selects a broadcasting station to be received by the antenna 10 in accordance with an instruction from a system controller (not shown), converts the frequency of the received signal of the broadcast wave, and performs OFDM (Orthogonal Frequency Division). Multiplexing) modulation signal is generated. The demodulation circuit 12 demodulates the OFDM modulation signal from the tuner 11 to generate a TS (Transport Stream) 30 according to the MPEG-2 (ISO / IEC13818-1) standard, and supplies this TS30 to the signal processing circuit 3A. . The tuner 11 may have a function of receiving one or a plurality of broadcasts among terrestrial digital broadcasts, satellite digital broadcasts, and cable digital broadcasts. It may have a function of receiving a digital broadcast transmitted via the computer network.

  FIG. 3 is a functional block diagram showing a schematic configuration of the demodulation circuit 12 shown in FIG. Referring to FIG. 3, the demodulation circuit 12 includes an FFT processing unit 40, a frame decoder 41, a TMCC decoding unit 41A, a demodulation unit 42, a frequency deinterleaver 43, a time deinterleaver 44, a layer division unit 45, and a carrier demodulation unit 46A. , 46B, inner code decoding units 47A, 47A, TS reproduction unit 48, and outer code decoding unit 49.

  The FFT processing unit 40 performs FFT (Fast Fourier Transform) on the OFDM modulation signal from the tuner 11 to convert the signal in the time domain into the signal in the frequency domain. The frame decoder 41 converts the signal from the FFT processing unit 40 into an OFDM segment signal and supplies the signal to the demodulation unit 42. In addition, the frame decoder 41 separates a control signal (TMCC signal; Transmission Multiplexing Configuration Control signal) representing a transmission parameter used in each layer and provides it to the TMCC decoding unit 41A. The TMCC decoding unit 41A decodes the TMCC signal, generates transmission parameters 31 set for each layer in a broadcasting station (not shown), and supplies the transmission parameters 31 to the subsequent processing blocks 42 to 49. ing. Examples of the transmission parameters include the number of OFDM segments, the modulation scheme, and the depth of time interleaving (time interleaving length).

  The demodulator 42 performs differential detection or synchronous detection corresponding to the transmission mode specified by the transmission parameter 31 on the output signal of the frame decoder 41. In a broadcasting station, time interleaving for rearranging TS packets (transport stream packets) to be transmitted in the time direction and frequency interleaving for rearranging time-interleaved TS packets in the frequency direction are performed. The frequency deinterleaver 43 performs deinterleaving that rearranges the frequency interleaved TS packets supplied from the demodulation unit 42 in the original order. In addition, the time deinterleaver 44 performs deinterleaving that rearranges the time-interleaved TS packets supplied from the frequency deinterleaver 43 in the original order.

  Here, the time deinterleaver 44 performs deinterleaving corresponding to the time interleave length specified by the transmission parameter 31. The greater the time interleave length, the higher the degree of data dispersion, so even when digital broadcasts are received by mobiles such as mobile devices and in-vehicle devices, resistance to fading and noise interference is improved. The larger the value, the longer the processing time required for time interleaving and time deinterleaving, and the longer the delay time. Two simulcast digital broadcasts are transmitted through different layers, and frequency interleaving and time interleaving are performed for each layer. Therefore, when transmission parameters related to interleaving differ between layers, the processing time required for interleaving and deinterleaving also differs from layer to layer, so that a delay time difference occurs between layers (that is, between two simulcast digital broadcasts). It becomes.

  Next, the layer division unit 45 divides the data stream supplied from the time deinterleaver 44 into two layers. The data in one layer is demapped and bit deinterleaved by the carrier demodulator 46A, and then depunctured and Viterbi decoded by the inner code decoder 47A. The data of the other layer is subjected to demapping and bit deinterleaving by the carrier demodulation unit 46B, and then subjected to depuncture and Viterbi decoding by the inner code decoding unit 47B. Further, the TS reproduction unit 48 combines the data supplied from the inner code decoding units 47A and 47B to generate a TS packet, and supplies these TS packets to the outer code decoding unit 49. The outer code decoding unit 49 performs energy diffusion and RS decoding (Reed-Solomon decoding) on the output signal of the TS reproducing unit 48, and supplies the TS (encoded bit stream) 30 obtained as a result to the signal processing circuit 3A. To do. In the example of FIG. 3, the hierarchy dividing unit 45 divides the data stream into two hierarchies, but is not limited thereto, and can be divided into a maximum of three hierarchies.

  Next, the operation of the signal processing circuit 3A will be described with reference to FIG. The first separation unit (DeMUX) 21A separates the PES packet (packeted elementary stream packet) corresponding to the first digital broadcast (for example, high-definition broadcast) from the TS 30 supplied via the error monitoring unit 20. The PES packet is supplied to the first decoder 22A. Further, PCR (Program Clock Reference) data is stored in a predetermined area in the TS packet supplied to the first separation unit 21A at regular intervals in a transmitter (not shown) of the broadcasting station. This PCR data is reference time information for generating a reference clock used in the signal processing circuit 3A. The first separation unit 21A supplies the PCR data separated from the TS packet to the clock generation unit 27. The clock generation unit 27 generates a reference clock CLK using PCR data. The clock generation unit 27 includes a first counter 27A that operates according to PCR data, and supplies the count value of the first counter 27A to the first decoder 22A.

  The first decoder 22A extracts elementary streams indicating encoded video data and encoded audio data from the PES packet supplied from the first separation unit 21A, and decodes the encoded video data and encoded audio data. To generate a decoded signal. Here, in the header area of the PES packet, a time stamp is stored as necessary for each PES packet in order to synchronize video and audio. In the case of video, for each picture, a PTS (Presentation Time Stamp) for specifying a reproduction time and a DTS (Decoding Time Stamp) for specifying a decoding time can be stored. The first decoder 22A temporarily stores the elementary stream in a buffer (not shown), and when the time stamp value matches the counter value supplied from the clock generation unit 27, the encoded data is read from the buffer. And decoding of the read encoded data is started, or decoded data is output.

  The first buffer 23A temporarily stores the decoded signal output from the first decoder 22A. The first output control unit 24A reads the decoded signal from the first buffer 23A, and transfers the read decoded signal to the output switching unit 25.

  On the other hand, the second separation unit (DeMUX) 21A separates the PES packet corresponding to the second digital broadcast (for example, one segment broadcast) from the TS 30 supplied via the error monitoring unit 20, and converts the PES packet into the PES packet. This is supplied to the second decoder 22B. Further, PCR data is stored in a predetermined area in the TS packet supplied to the second separation unit 21B at regular intervals in a transmitter (not shown) of the broadcasting station. The second separation unit 21B supplies the PCR data separated from the TS packet to the clock generation unit 27. The clock generation unit 27 includes a second counter 27B that operates in accordance with the PCR data, and supplies the count value of the second counter 27B to the second decoder 22B.

  The first decoder 22A extracts elementary streams indicating encoded video data and encoded audio data from the PES packet supplied from the first separation unit 21A, and decodes the encoded video data and encoded audio data. To generate a decoded signal. Here, in the header area of the PES packet, a time stamp is stored for each PES packet in order to synchronize video and audio. The second decoder 22B temporarily stores the elementary stream in a buffer (not shown), and when the time stamp value matches the count value supplied from the clock generation unit 27, the encoded data is read from the buffer. Reading, decoding of the read encoded data is started, and decoded data is output. The second buffer 23B temporarily stores the decoded signal output from the second decoder 22B. The second output control unit 24B reads the decoded signal from the second buffer 23B and transfers the read decoded signal to the output switching unit 25.

  On the other hand, the synchronization shift detection unit 28 reads out the decoded signals from the first buffer 23A and the second buffer 23B, respectively, and compares the decoded signal of the first digital broadcast and the decoded signal of the second digital broadcast in predetermined data units. In addition, it has a function of detecting a synchronization shift between these decoded signals based on the comparison result. The predetermined data unit may be an image frame unit for video and an audio frame unit for audio.

  Specifically, the synchronization shift detection unit 28 predicts a delay time difference corresponding to the synchronization shift based on the transmission parameter 31 supplied from the demodulation circuit 12, and further searches based on the predicted delay time difference ( A time window is set, and the decoded signals are compared within this search range. An example of the search range setting method will be described below with reference to FIG. FIG. 4 shows a series of image frames M0, M1,..., M10,... Representing a video signal (hereinafter referred to as “first video signal”) among the outputs of the first decoder 22A. A series of image frames H0, H1,..., H5,... Representing a video signal (hereinafter referred to as “second video signal”) among the outputs of 22B are shown. For convenience of explanation, it is assumed that the frame rate of the first video signal output from the first decoder 22A is twice the frame rate of the second video signal output from the second decoder 22B.

The synchronization shift detection unit 28 selects one of the first video signal and the second video signal as a reference frame, and a time window (search range) having a time Tp including the time corresponding to the reference frame. ) Is set. As described above, when the transmission parameters set for interleaving are different between layers, the processing time required for interleaving and deinterleaving varies from layer to layer, so that there is a delay between layers (that is, between two simulcast digital broadcasts). A time difference will occur. The synchronization loss detection unit 28 can predict the delay time difference Δt based on a transmission parameter 31 such as a time interleave length. Synchronization shift detector 28, as shown in FIG. 4, a sequence of image frames M0 of the first video signal, M1, ..., M10, of ..., a predetermined number of image frames M5 close to the reference time t _0, M6 Can be selected as the reference frame. Next, the synchronization shift detection unit 28 sets a time window having a length Tp around the time t ₁ delayed by the predicted value Δt from the reference time t _0, and a series of image frames H 0, Image frames H1, H2, H3 included in the time window are selected from H1,.

  Then, the synchronization shift detection unit 28 compares the reference frames M5 and M6 read from the first buffer 23A with the selected frames H1, H2 and H3 read from the second buffer 23B and has the closest content. Search for frame combinations. That is, combinations (Mx, Hx) of the reference frame and the selection frame are (M5, H1), (M5, H2), (M5, H3), (M6, H1), (M6, H2), (M6, There are six types of H3). Among these combinations, a combination that minimizes the difference in the amount of information between frames can be searched. For example, a luminance difference between frames for each combination is calculated for each pixel, and the sum of these luminance differences is calculated to search for a combination that minimizes the sum. Alternatively, it is possible to search for a combination that maximizes the correlation between frames. In addition, when the resolution differs between the image frames of the first video signal and the second video signal, the resolution of the other image frame is converted in advance so as to match the resolution of the image frame of one video signal. It is desirable.

  The synchronization shift detection unit 28 searches not only a function of searching for a combination of image frames having the closest contents but also a combination of audio frames having the closest contents by executing frequency analysis and correlation calculation processing. It also has a function.

  The synchronization shift detection unit 28 detects a time difference between the combined frames obtained as a result of the search as a synchronization shift. In FIG. 4, when the selected frame H1 has the closest content to the reference frame M5, the time difference between these frames H1 and M5 can be detected as a synchronization shift. The detection result is notified to the synchronization control unit 29.

  The synchronization control unit 29 issues a command to the first output control unit 24A and the second output control unit 24B so as to compensate for the synchronization shift detected by the synchronization shift detection unit 28. In response to the command, the first output control unit 24A and the second output control unit 24B read the decoded signals from the first buffer 23A and the second buffer 23B, respectively, and output the read decoded signals to the output switching unit 25. Forward to. Therefore, the decoded signal of the first digital broadcast and the decoded signal of the second digital broadcast are output to the output switching unit 25 in synchronization with each other accurately.

  The output switching unit 25 selectively selects one of the decoded signals transferred from the first output control unit 24A and the second output control unit 24B according to the switching control signal from the switching control unit 26. This is output to a display device or a speaker device.

  The error monitoring unit 20 constantly monitors the TS 30 from the demodulation circuit 12, detects an uncorrectable bit error in the TS 30, and sends error information indicating the bit error occurrence position and the bit error rate to the switching control unit 26. Supply. Based on the error information from the error monitoring unit 20, the switching control unit 26 determines that an error exists if the bit error rate Ber for the first digital broadcast exceeds an allowable value (threshold), and the bit error rate is If it is less than the allowable value, it can be determined that there is no error. The allowable value can be appropriately set by the user operating an input unit (not shown). Instead of determining the presence or absence of an error based on the bit error rate Ber, for example, when the receiving circuit 2 detects the C / N ratio (carrier power to noise power ratio) of a received signal of digital broadcasting, switching is performed. The control unit 26 can also determine that an error has occurred if the C / N ratio is less than a desired value.

  When it is determined that there is no error, the switching control unit 26 controls the output switching unit 25 so that the decoded signal of the first digital broadcast is output, and when it is determined that there is an error, the first control unit 26 The output switching unit 25 can be controlled so that a decoded signal of the second digital broadcast is output instead of the digital broadcast. For example, when a high-quality first digital broadcast and a low-quality second digital broadcast are simulcast, even if an error occurs in the first digital broadcast due to a change in the reception environment, the switching control unit 26 can output a decoded signal of the second digital broadcast having the same content as the first digital broadcast instead of the first digital broadcast.

  If there is no error, the clock generation unit 27 uses the PCR data supplied from the first separation unit 21A and the count value of the first counter 27A from the viewpoint of the stability of the operation of the system. It is desirable to generate CLK. On the other hand, when the switching control unit 26 determines that there is an error, the clock generation unit 27, while the signal indicating the determination result is supplied from the switching control unit 26, the second separation unit instead of the first separation unit 21A. It is desirable to generate the reference clock CLK using the PCR data supplied from 21B and the count value of the second counter 27B.

As described above, in the digital broadcast receiving apparatus 1A according to the first embodiment, the synchronization deviation detection unit 28 predicts the synchronization deviation based on the transmission parameter 31 supplied from the demodulation circuit 12, and based on the predicted synchronization deviation. A search range is set, and within the search range, the decoded signal of the first digital broadcast and the decoded signal of the second digital broadcast are compared in frame units (image frame units or audio frame units). Therefore, since the search range can be limited, the closest combination of frames can be searched in a short time. In addition, the amount of calculation required for the search process can be reduced. Furthermore, it is possible to accurately detect the synchronization shift. For example, when the predicted value Δt is not taken into account in FIG. 4, a time window (search range) having a length Tn with respect to the reference time t ₀ is set. Since the number of selected frames H1, H2, H3, H4, and H5 included in this time window is large, the time required for the search process is long and the amount of calculation increases.

  In addition, the digital broadcast receiving apparatus 1A of the first embodiment can accurately synchronize the contents of the first digital broadcast and the contents of the second digital broadcast. As a result, even when an error occurs in the first digital broadcast and the decoded signal of the second digital broadcast is output instead of the first digital broadcast, it is possible to provide a visually natural video as much as possible. is there.

  Next, a second embodiment according to the present invention will be described. FIG. 5 is a functional block diagram showing a schematic configuration of the digital broadcast receiving apparatus 1B of the second embodiment. The digital broadcast receiving apparatus 1B includes a receiving circuit 2 and a signal processing circuit 3B. Components denoted by the same reference numerals in FIGS. 2 and 5 are assumed to have substantially the same function, and detailed description thereof is omitted.

  As shown in FIG. 5, the configuration of the signal processing circuit 3B includes a first separation unit 21A including a first time stamp adjustment unit 50A and a second separation unit 21B including a second time stamp adjustment unit 50B. The configuration of the signal processing circuit 3A according to the first embodiment is different from the configuration of the signal processing circuit 3A of the first embodiment in that it includes a synchronization control unit 51 that controls the first time stamp adjustment unit 50A and the second time stamp adjustment unit 50B.

  The signal processing circuit 3A of the first embodiment controls the read timing of the decoded signals from the first buffer 23A and the second buffer 23B to control the output timing of the decoded signals of the first and second digital broadcasts, thereby It compensated for the synchronization loss. On the other hand, the signal processing circuit 3B of the second embodiment changes the time stamp value in the header area of the PES packet to control the output timing of the decoded signals of the first and second digital broadcasts, thereby This is to compensate for the synchronization error.

  Specifically, the synchronization error detection unit 28 detects the synchronization error between the decoded signal of the first digital broadcast and the decoded signal of the second digital broadcast using the transmission parameter 31 as described above. The detection result is notified to the synchronization control unit 51. The synchronization control unit 51 sets a first offset value and a second offset value that can compensate for the detected synchronization deviation, and supplies the first offset value to the first time stamp adjustment unit 50A of the first separation unit 21A. The second offset value is supplied to the second time stamp adjustment unit 50B of the second separation unit 21B. The first time stamp adjustment unit 50A reads the time stamp (PTS) from the header area of the PES packet, adds the first offset value to the time stamp value, and determines the time stamp value in the header area of the PES packet. Rewrite to addition value. On the other hand, the second time stamp adjustment unit 50B reads the time stamp from the header area of the PES packet, adds the second offset value to the time stamp value, and adds the time stamp value in the header area of the PES packet. Rewrite the value.

  As a result, the first decoder 22A reads the encoded data from its own buffer (not shown) when the time stamp value matches the count value supplied from the clock generation unit 27, and the read code The decoding of the encrypted data is started or the decoded data is output. The second decoder 22B performs the same process. Therefore, the signal processing circuit 3B can compensate for the synchronization shift by controlling the output timing of the decoded signals of the first and second digital broadcasts.

  In the second embodiment, the time stamp adjusters 50A and 50B are incorporated in both the first separator 21A and the second separator 21B. However, the present invention is not limited to this, and the first separator 21A and the second separator are not limited thereto. The time stamp adjustment unit may be incorporated in only one of the units 21B.

  The various embodiments according to the present invention have been described above. The configuration of the signal processing circuits 3A and 3B in the above embodiment may be realized by hardware, or may be realized by using a program that causes a processor such as a CPU to execute processing.

It is a figure which shows several OFDM segments. It is a functional block diagram which shows schematic structure of the digital broadcast receiver of 1st Example which concerns on this invention. It is a functional block diagram which shows schematic structure of a demodulation circuit. It is a figure for demonstrating an example of the setting method of a search range. It is a functional block diagram which shows schematic structure of the digital broadcast receiver of 2nd Example which concerns on this invention.

Explanation of symbols

1A, 1B Digital broadcast receiver 2 Receiving circuit 3A, 3B Signal processing circuit 20 Error monitoring unit 21A, 21B Separating unit (DeMUX)
22A, 22B Decoder 23A, 23B Buffer 24A, 24B Output control unit 25 Output switching unit 26 Switching control unit 28 Synchronization deviation detection unit 29, 51 Synchronization control unit 50A, 50B Time stamp adjustment unit

Claims (8)

A digital broadcast receiving device that receives a broadcast signal transmitted using a multicarrier modulation method in which a transmission band is divided into a plurality of layers and interleaving at different depths can be performed for each layer,
A demodulation circuit that generates a coded bitstream by demodulating the received signal according to the multi-carrier modulation scheme, and that extracts a transmission parameter representing the depth of the interleaving from the received signal;
A first encoded bitstream corresponding to a first digital broadcast transmitted through the first layer in the layer, and a second encoded signal transmitted through the second layer in the layer. A separation unit that separates the second encoded bit stream corresponding to digital broadcasting;
A first decoder that decodes the first encoded bitstream to generate a first decoded signal;
A second decoder for decoding the second encoded bitstream to generate a second decoded signal;
Synchronization for comparing the first decoded signal and the second decoded signal in a predetermined data unit and detecting a synchronization shift between the first decoded signal and the second decoded signal based on the comparison result A deviation detection unit;
A synchronization control unit for controlling the output timing of the first and second decoded signals so as to compensate for the synchronization shift,
The synchronization shift detection unit predicts a synchronization shift between the first decoded signal and the second decoded signal based on the transmission parameter, and the first and second synchronization shifts based on the predicted synchronization shift. A digital broadcast reception characterized in that a search range of at least one of decoded signals is set, and the first decoded signal and the second decoded signal are compared in the predetermined data unit within the search range. apparatus.   The digital broadcast receiving apparatus according to claim 1, wherein the synchronization deviation detection unit compares the first decoded signal and the second decoded signal within the search range and has a data unit having the closest content. A digital broadcast receiving apparatus that searches for a combination and detects a time difference between data units of the combination as the synchronization shift. The digital broadcast receiver according to claim 1 or 2,
A first buffer for temporarily storing the first decoded signal;
A second buffer for temporarily storing the second decoded signal;
The digital broadcast receiving apparatus, wherein the synchronization control unit controls the output timing of the first and second decoded signals by controlling reading of signals from the first buffer and the second buffer. The digital broadcast receiver according to claim 1 or 2,
The first encoded bit stream and the second encoded bit stream each include a time stamp that specifies a reproduction time of the first decoded signal and the second decoded signal;
The separation unit includes a time stamp adjustment unit that adds an offset value to at least one of time stamps included in the first encoded bit stream and the second encoded bit stream,
The digital broadcast receiving apparatus, wherein the synchronization control unit controls the output timing of the first and second decoded signals by determining the offset value so as to compensate for the synchronization shift. The digital broadcast receiving device according to any one of claims 1 to 4,
An error monitoring unit for detecting an error in the first encoded bitstream;
An output switching unit that outputs the first decoded signal when the error is not detected, and outputs the second decoded signal instead of the first decoded signal when the error is detected;
A digital broadcast receiving apparatus, further comprising:   6. The digital broadcast receiving apparatus according to claim 1, wherein the interleaving is a time direction interleaving. 7.   7. The digital broadcast receiving apparatus according to claim 1, wherein the predetermined data unit is an image frame of a video signal or an audio frame of an audio signal. Receiver device.   8. The digital broadcast receiving apparatus according to claim 1, wherein the encoded bit stream is a transport stream compliant with the MPEG-2 standard. apparatus.

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