JP2010258670A - Digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a blank time upon mode changeover from 12 segments to 1 segment. <P>SOLUTION: This digital broadcast receiver includes: a first decoding section for decoding 12-segment broadcast data to first video data; a second decoding section for decoding 1-segment broadcast data to second video data; a changeover section for outputting either of the first and second video data to a video display unit; and a control section for controlling the changeover section. When electric field intensity is lowered while the first decoding section decodes the 12-segment broadcast data to the first broadcast data and the changeover section outputs the first video data to the video display unit, the control section causes the second decoding section to start to decode the 1-segment broadcast data to the second video data, and causes the changeover section to changes over the output of the first video data to the output of the second video data when code errors of the first broadcast data increase, whereby a blank time in changing over the 12-segment broadcast to the 1-segment broadcast can be reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a digital broadcast receiver that receives terrestrial digital broadcasts, and more particularly to a digital broadcast receiver that switches between 1-segment and 12-segment broadcasts according to the state of broadcast data.

  In television terrestrial digital broadcasting, broadcast data of a plurality of programs are multiplexed and transmitted by frequency division within one channel. Specifically, the transmission band within 1 channel 6 MHz is divided into 13 segments, and further divided into 12 segments and 1 segment. Here, the larger the number of segments, the larger the data transmission capacity. Therefore, 12-segment broadcasting (hereinafter, 12-segment broadcasting) is used for high-resolution video transmission for a fixed body. On the other hand, 1-segment broadcasting (hereinafter referred to as 1-segment broadcasting) is used for low-resolution video transmission for mobile objects.

  In terrestrial digital broadcasting, broadcast data is modulated by OFDM (Orthogonal Frequency Division Multiplexing). And the accuracy of broadcast data is ensured by the error correction code. Here, the modulation scheme and the coding rate of the error correction code can be set for each segment. Therefore, in the 1-segment broadcasting for mobiles, a modulation scheme and a coding rate that have higher tolerance for code errors than 12-segment broadcasting are used.

  A television device capable of receiving terrestrial digital broadcasting is provided in various modes. For example, it is provided as a fixed body installed in a home or a mobile body mounted on a vehicle such as a portable terminal or an automobile. In recent years, in-vehicle television devices among mobile bodies are required to have entertainment properties. Therefore, there is a strong demand for high-resolution and high-quality images. For this reason, an in-vehicle television device that can watch not only 1-segment broadcasting for mobile bodies but also 12-segment broadcasting originally intended for fixed bodies is provided. Patent Document 1 describes such an in-vehicle television device.

  However, in the case of an in-vehicle television device, the electric field strength varies as the vehicle moves. Generally, when the electric field strength decreases, the C / N ratio (carrier noise ratio) decreases. This leads to an increase in code errors in the broadcast data. As described above, the coding rate and modulation method used in 12-segment broadcasting are not as resistant to code errors as 1-segment broadcasting. Therefore, if code errors occur frequently, the quality of video and audio may deteriorate, and viewing may be hindered. For this reason, when code errors frequently occur during operation in an operation mode for viewing 12-segment broadcasting (hereinafter referred to as 12-segment mode), the mode is switched to an operation mode for viewing 1-segment broadcast (hereinafter referred to as 1-segment mode). A method has been proposed.

JP 2007-336079 A

  By the way, decoding of broadcast data includes decompression processing of compressed data and correction processing of code errors using error correction codes. Therefore, it takes a processing time according to the data transmission amount and the processing capability of the decoding processor. Then, when the mode is switched to the 1 segment mode, a certain delay occurs from the start of decoding to the video output. In particular, since 1-segment broadcasting uses a higher coding rate than 12-segment broadcasting, the processing time becomes longer for a smaller data transmission capacity. Then, the following situation occurs. First, if the code error increases in the 12-segment mode, the video quality deteriorates and viewing becomes difficult. Then, the mode is switched to the 1-segment mode, and a blank time during which no video / audio is output is generated due to the delay time. In particular, since the video has a larger data transmission capacity and requires processing time, the blank time of the video becomes remarkable. For example, the blank time of the video may be over 5 seconds. Then, there is a possibility that the user may feel uncomfortable.

  In this regard, there is no problem if a processor dedicated to decoding is provided for each 12-segment or 1-segment broadcast and operated in parallel at all times. On the other hand, space saving and cost reduction are strongly demanded for in-vehicle television devices. Therefore, it is difficult to coexist with processors dedicated to decoding both in terms of device size and cost.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a small and inexpensive digital broadcast receiver capable of shortening the blank time when switching the mode from 12 segments to 1 segment in the in-vehicle television device.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a digital broadcast receiving apparatus mounted on a vehicle for receiving broadcast data multiplexed and transmitted by segments obtained by dividing a predetermined frequency. A first decoding unit for decoding first video data from first broadcast data transmitted by one number of frequency segment groups, and a second number of frequency segment groups less than the first number. A second decoding unit that decodes the second video data from the second broadcast data, a switching unit that outputs one of the first and second video data to the video display unit, and the switching unit. The control unit, wherein the first decoding unit decodes the first broadcast data, and the switching unit outputs the first video data to the video display unit. Sometimes when the electric field strength decreases, When the second decoding unit starts decoding the second video data, and the code error of the first broadcast data increases, the switching unit switches from the first video data to the output of the second video data. A digital broadcast receiving apparatus is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the small and inexpensive vehicle-mounted digital broadcast receiver which can shorten the blank time at the time of mode switching from 12 segments to 1 segment is provided.

It is a figure explaining the external appearance of the vehicle-mounted electronic device in this embodiment. 1 is a diagram illustrating a configuration of an in-vehicle electronic device 10. FIG. 3 is a diagram illustrating a detailed configuration of a decoding unit 16. FIG. 4 is a flowchart illustrating an operation procedure of the in-vehicle electronic device 10. FIG. It is a flowchart figure explaining the operation | movement procedure at the time of mode switching. 6 is a timing chart showing the operation timing of the decoding unit 16. FIG. It is a flowchart figure explaining the operation | movement procedure of a modification. It is a figure explaining the correspondence of the reference value of C / N ratio fall rate and code error occurrence rate. It is a figure explaining the reference value of C / N ratio fall rate and code error occurrence rate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  In the present embodiment, the digital broadcast receiver is used for an in-vehicle television device. The digital broadcast receiving apparatus receives 1-segment broadcast and 12-segment broadcast by terrestrial digital waves, and outputs respective video / audio. The in-vehicle television device is integrated with the car navigation device. Below, it demonstrates as a vehicle-mounted electronic device comprised integrally with car navigation.

  FIG. 1 is a diagram illustrating an overview of an in-vehicle electronic device according to the present embodiment. FIG. 1A shows a front view, and FIG. 1B shows a side view.

  The in-vehicle electronic device 10 includes a display panel 2 and a housing 1. The display panel 2 includes a display unit 3 and operation buttons 4b, and provides a user interface. The housing 1 accommodates an electronic circuit for realizing various functions of the in-vehicle electronic device 10. The in-vehicle electronic device 10 is installed in a state where the housing 1 is embedded in an instrument panel in front of a driver's seat and a passenger seat in a vehicle. The display panel 2 is provided so as to be tiltable with respect to the front surface portion of the housing 1. Thereby, the user can adjust the angle of the display panel 2 appropriately.

  The display unit 3 displays map information and television images. The display unit 3 is constituted by, for example, a liquid crystal display panel or an organic EL panel. Various functions of the in-vehicle electronic device 10 are assigned to the operation button 4b. The display unit 3 includes a touch panel 4a. When the display unit 3 displays the operation menu, the touch panel 4a detects contact of the user's finger with respect to these. Switching between car navigation and television, television channels, and the like are input by the touch panel 4a and the operation buttons 4b. As described above, the touch panel 4 a and the operation buttons 4 b constitute the operation input unit 4.

  The in-vehicle electronic device 10 may be provided with an additional display panel in addition to the display panel 2. In this case, the additional display panel is provided in the front part of the rear seat, for example, apart from the housing 1. An antenna that receives terrestrial digital waves is provided outside the in-vehicle electronic device 10. For example, it is provided as an antenna pattern on a windshield of a vehicle. Furthermore, the television sound and the car navigation sound are output from a speaker installed in the vehicle interior.

  FIG. 2 is a diagram illustrating the configuration of the in-vehicle electronic device 10. The in-vehicle electronic device 10 includes a tuner 12, a demodulator 14, and a decoder 16 as a digital broadcast receiver 10a. The television function is realized by the digital broadcast receiving device 10a and the reproducing unit 20. The in-vehicle electronic device 10 includes a navigation control unit 18 and a storage unit 19 that realize a navigation function. The display unit 3 and the operation input unit 4 are common to each function.

  The navigation control unit 18 controls the overall operation of the in-vehicle electronic device 10 as a whole. The navigation control unit 18 switches between car navigation and television according to the user's selection. When the user selects and inputs one of the functions to the operation input unit 4, a function selection signal corresponding to this is sent to the navigation control unit 18. When the television function is selected, a television activation instruction signal is sent from the navigation control unit 18 to the decoding unit 16. In response to this, the decoding unit 16 sends an activation instruction signal to the tuner 12 and the demodulation unit 14. When the user inputs the received channel to the operation input unit 4, a channel selection signal is sent from the navigation control unit 18 to the decoding unit 16. Then, the decoding unit 16 sends this to the tuner 12. The detailed configuration of the decoding unit 16 will be described later.

  First, the operation when the television is activated will be described.

  When the antenna 11 receives a terrestrial digital wave, the received wave is input to the tuner 12. The tuner 12 is activated in response to the activation instruction signal, and detects the broadcast wave of the channel corresponding to the channel selection signal. In the terrestrial digital wave, the 6 MHz band in the UHF band is assigned as one channel. The tuner 12 down-converts the detected broadcast wave to an intermediate frequency and amplifies it.

  When the demodulator 14 is activated in response to the activation instruction signal, the demodulator 14 demodulates the broadcast wave output from the tuner 12 and extracts broadcast data (digital data). Broadcast data includes video data and audio data. In the OFDM scheme, different modulation schemes are used depending on the segment. In 1-segment broadcasting, QPSK (Quadrature Phase Shift Keying) is used. In 12-segment broadcasting, 16QAM (Quadrature Amplitude Modulation) or 64QAM is used. The demodulator 14 demodulates broadcast data according to each modulation method. The broadcast data obtained here is data encoded before transmission. The demodulator 14 calculates a C / N ratio based on the level of the broadcast wave. At this time, an operation that eliminates the influence of multipath is performed.

  As will be described in detail later, the decoding unit 16 performs a decoding process on the demodulated broadcast data and decodes the broadcast data before encoding.

  Video data of the decoded broadcast data is output to the navigation control unit 18. The navigation control unit 18 performs contrast and color conversion of the video data and outputs a video signal to the display unit 3. Then, the display unit 3 outputs a video corresponding to the video signal. Here, the navigation control unit 18 and the display unit 3 correspond to a “video display unit”.

  Also, audio data among the broadcast data decoded by the decoding unit 16 is input to the reproduction unit 20. The reproducing unit 20 generates an audio signal by digital / analog conversion and performs power amplification. The amplified audio signal is output to a speaker 22 provided in the passenger compartment. The speaker 22 outputs sound corresponding to the sound signal.

Next, an operation when the car navigation is activated will be described.
The navigation control unit 18 performs arithmetic processing for route search / guidance to the input destination based on the map information. The map information is stored in the storage unit 19. The destination is input by the user from the operation input unit 4. The navigation control unit 18 causes the display unit 3 to display a route to the destination and guidance information. Alternatively, the playback unit 20 outputs audio. The navigation control unit 18 is composed of a microcomputer. The storage unit 19 includes a hard disk or a rewritable storage medium.

  FIG. 3 is a diagram illustrating a detailed configuration of the decoding unit 16. The decoding unit 16 includes a 12-segment broadcasting decoding unit (12-segment decoding unit) 30 and a 1-segment broadcasting decoding unit (1-segment decoding unit) 34. Furthermore, it has the switching part 38 which selectively outputs the 1-segment / 12-segment broadcast data decoded by these. The decoding unit 16 includes a control unit 36 that controls the switching unit 38.

  The 12-segment decoding unit 30 is configured by a DSP (Digital Signal Processor) that executes processing to be described later. The 1-segment broadcast decoding unit 34 and the control unit 36 are each configured by a CPU 32 (Central Processing Unit) that executes decoding processing and control processing described later. A program describing the processing operation of the CPU 32 and an OS (Operating System) are stored in a ROM (Read Only Memory) 40 in advance. The CPU 32 executes arithmetic processing in each program using a RAM (Random Access Memory) 42 as a work area. The switching unit 38 is configured with a switching transistor as an example.

  The 12-segment decoding unit 30 extracts 12-segment broadcast data from the broadcast data demodulated by the demodulation unit 14. This broadcast data includes video data and audio data. Video data and audio data are subjected to encoding processing including error correction code encoding, data compression, and data combination before modulation at a broadcasting station. Accordingly, the 12-segment decoding unit 30 decodes the original video data and audio data by performing error correction code decoding, error correction processing using the error correction code, and data expansion processing. In the error correction process, the presence or absence of a code error is notified in response to a request from the control unit 36. The 12-segment decoding unit 30 includes an ASIC (Application Specific Integrated Circuit) or a DSP (Digital Signal Processor) that performs such processing.

  The 1-segment decoding unit 34 extracts 1-segment broadcast data from the demodulated broadcast data. Then, decoding of the error correction code similar to the above, error correction processing using the same, and data expansion processing are performed to decode the original video data and audio data.

  The controller 38 acquires the C / N ratio from the demodulator 14. Here, the C / N ratio is used as a parameter indicating the electric field strength. Then, the control unit 38 determines switching to the 1-segment mode based on the electric field strength and the frequency of code errors during operation in the 12-segment mode. Then, a switching control signal is sent to the switching unit 38 to control the switching operation. This operation will be described in detail later.

  Further, the control unit 36 generates image data such as EPG (Electronic Program Guide) and outputs the image data to the navigation control unit 18. Such image data is synthesized with the display image by the navigation control unit 18. Further, when receiving the activation instruction signal from the navigation control unit 18, the control unit 38 sends it to the tuner 12 and the demodulation unit 14. Further, when receiving a channel selection signal from the navigation control unit 18, the control unit 38 sends it to the tuner 12. In this way, the control unit 38 communicates with the navigation control unit 18 in order to control the television function.

  In this way, the CUP 32 executes the operations of the 1-segment decoding unit 34 and the control unit 36 in a time division manner by multiprogramming. Therefore, the device size and cost can be reduced as compared with the case where the 1-segment decoding unit 34 is configured separately from the CPU 32.

  FIG. 4 is a flowchart for explaining the operation procedure of the in-vehicle electronic device 10 when operating as a television device. The procedure of FIG. 4 is executed when the television is activated. Here, the 12-segment mode is executed as an initial setting.

  The tuner 12 receives the broadcast wave of the selected channel (S2). The demodulator 14 demodulates the broadcast data according to the modulation method for each segment (S4). The decoding unit 16 performs a decoding process to decode 12-segment broadcast data (video data, audio data) (S6). Then, the switching unit 38 outputs video data of the decoded 12-segment broadcast data to the navigation control unit 18 and audio data to the reproduction unit 20 (S8). Then, the navigation control unit 18 outputs video on the display unit 3, and the playback unit 20 causes the speaker 22 to output audio.

  If the electric field strength decreases while the in-vehicle electronic device 10 is operating in the 12-segment mode, broadcast data code errors frequently occur. This will hinder the output of video and audio. On the other hand, in 1-segment broadcasting, a coding rate having higher resistance to code errors than 12-segment broadcasting is used. Therefore, video / audio can be maintained even in a weak electric field. Therefore, if code errors occur frequently in the 12-segment mode, the video / audio can be maintained by switching to the 1-segment mode. By the way, in this case, in the 1-segment mode, it takes time for the decoding process including the correction of the code error for the data transmission capacity. Then, there is a certain delay from the start of decoding to video output. Therefore, in the present embodiment, the mode is switched from 12 segments to 1 segment in a two-step operation as follows. Here, this operation will be described with reference to FIGS.

  FIG. 5 is a flowchart for explaining an operation procedure when mode switching is performed from 12 segments to 1 segment. The procedure in FIG. 5 is executed when video output of 12-segment broadcasting is started in step S10 in FIG. FIG. 6 is a timing chart showing the operation timing of the decoding unit 16. In FIG. 6A, time is shown on the horizontal axis, 1-segment broadcast data decoding processing by the 1-segment decoding unit 34, 1-segment broadcast data output by the 1-segment decoding unit 34, and output switching timing by the switching unit 38 Indicates. Here, in particular, the processing timing of video data having a long processing time among broadcast data is shown.

  The control unit 32 executes the electric field strength monitoring procedure (S20 to S23 in FIG. 5) and the code error monitoring procedure (S30 to S36) in a time division manner by multi-process.

  First, in the electric field strength monitoring procedure, the control unit 32 acquires the C / N ratio periodically (for example, every 100 milliseconds) (S20). Then, when the C / N ratio is equal to or less than a predetermined reference value (Yes in S21), a ratio (hereinafter referred to as a C / N ratio decrease rate) where the C / N ratio falls below the reference value is calculated (S22). . The reference value referenced in step S21 is the electric field strength at which code errors frequently occur in 12-segment broadcasting. For example, an arbitrary value can be used in the range of 19 to 21 dB. In step S22, the C / N ratio decrease rate is obtained as a ratio within a predetermined monitoring time by integrating the time when the C / N ratio falls below the reference value. Here, as the monitoring time, an arbitrary time longer than 100 milliseconds, which is the processing cycle of this procedure, for example, in the range of several hundred milliseconds to 2 seconds is used.

  Then, when the C / N ratio reduction rate is equal to or higher than the reference value (Yes in S23), the control unit 32 causes the 1-segment decoding unit 34 to start decoding 1-segment broadcast data (S24, FIG. 6A). ) Time t1). At this time, the reference value is a C / N ratio reduction rate at which coding errors frequently occur, and an arbitrary value (for example, 30%) is used. Then, the 1-segment decoding unit 34 outputs the broadcast data that has been decoded to the switching unit 38 (time t2).

  On the other hand, in the code error monitoring procedure, the control unit 32 acquires the presence / absence of a code error from the 12-segment decoding unit 30 periodically (for example, every 100 milliseconds) (S30 in FIG. 5). When a code error is detected (YES in S32), a code error occurrence rate is calculated (S36). The code error occurrence rate is obtained as a ratio within a predetermined monitoring time by accumulating times when code errors occur. Here, as the monitoring time, an arbitrary time longer than 100 milliseconds, which is the processing cycle of this procedure, for example, in the range of several hundred milliseconds to 2 seconds is used. When the code error occurrence rate becomes equal to or higher than the reference value (Yes in S38), switching to the output of 1-segment broadcast data (S40, time t3 in FIG. 6A). Here, as the reference value of the code error occurrence rate, a value that hinders viewing of video and is set arbitrarily (for example, 10%) is used.

  After starting the decoding of 1-segment broadcasting data according to the above procedure, the code error of 12-segment broadcasting data may decrease after entering the strong electric field region. In such a case, the determination result in step S38 of FIG. 5 is “No”. Therefore, at this time, the control unit 32 causes the 1-segment decoding unit 34 to stop decoding the 1-segment broadcast data (S42). Then, the switching unit 38 is switched to output 12-segment broadcast data (S44).

  As in the above procedure, the in-vehicle electronic device 10 starts decoding of 1-segment broadcast data prior to switching based on the code error occurrence rate. By doing so, even if it takes time from when the 1-segment decoding unit 34 starts decoding 1-segment broadcast data (time t1 in FIG. 6) to when the decoded broadcast data is output (time t2), The switching of the output from the 12-segment broadcast data to the 1-segment broadcast data by the switching unit 38 can be delayed (time t3). Therefore, the blank time of the video can be eliminated. This is shown by comparison with FIG.

  FIG. 6B shows the timing of 1-segment broadcast data decoding processing by the 1-segment decoding section 34 and output of 1-segment broadcast data from the 1-segment decoding section 34 and switching processing of the switching section 38 in the prior art. . Conventionally, when the code error occurrence rate becomes equal to or higher than a reference value, decoding of 1-segment broadcasting data is started, and the output of the switching unit 38 is switched at the same time (time t3). Then, broadcast data was output after the elapse of the decoding processing time (time t4). Then, a blank time of video occurs from time t3 to time t4. In this regard, as shown in FIG. 6A, according to the present embodiment, such a blank time can be eliminated. Alternatively, even when the output timing of 1 segment video data (time t2) is delayed from the timing of switching video data (time t3), the start of decoding 1 segment broadcast data is advanced (time t1), thereby reducing the blank time. it can. Therefore, the possibility that the user may feel uncomfortable can be reduced.

  Further, as shown in FIGS. 5 and 6A, while the C / N ratio reduction rate is lower than the reference value, that is, while in the strong electric field region, the control unit 36 sets the 1-segment decoding unit 34. Do not decode 1-segment broadcast data. Even after switching to the 12-segment mode, decoding of 1-segment broadcast data is stopped when the strong electric field is restored. Therefore, when the 1-segment broadcast data is not decoded, the CPU 32 can execute other operations. Thus, since the processing capability of the CPU 32 can be effectively utilized, the circuit scale and cost can be minimized.

  By the way, in the above procedure, mode switching between 1 seg and 12 seg may occur frequently when in the boundary region of the electric field strength, that is, when the C / N ratio decrease rate fluctuates near the reference value. Then, video and audio are frequently switched, which may cause the user to feel uncomfortable. Therefore, in the boundary region of the electric field strength, the code error occurrence rate reference value is increased after switching to the 1-segment mode once. By doing so, it can prevent that a screen switches frequently.

  FIG. 7 is a flowchart in which such a procedure is added. The procedure S39 is added to FIG. That is, after switching the output of the switching unit 38 in step S38, the control unit 36 increases the reference value of the code error occurrence rate from 10% to a larger value, for example, 20%. By doing so, in the next processing cycle, the incidence of code errors is less likely to be below the reference value. Therefore, the 1-segment mode is maintained, and frequent switching can be prevented.

  Furthermore, at this time, the reference value of the code error occurrence rate can be changed based on the C / N ratio decrease rate. An example of the correspondence between the C / N ratio reduction rate and the reference value of the code error occurrence rate at this time is shown in FIG. For example, as shown in FIG. 8A, when the C / N ratio reduction rate is below 30%, it means that the vehicle is in the strong electric field region. Then, the probability that the code error occurrence rate will increase is small. In such a case, the code error occurrence rate reference value is not changed. On the other hand, when the C / N ratio reduction rate is 30% or more, it means a weak electric field region. Then, there is a high probability that the code error occurrence rate will increase. In such a case, the reference value of the code error occurrence rate is increased (for example, 20%). By doing so, the 1-segment mode is maintained and frequent switching can be prevented.

  Also, map data as shown in FIG. 8B may be used so that the code error occurrence rate changes linearly with a C / N ratio reduction rate of 30% as a boundary. The correspondence relationships shown in FIGS. 8A and 8B are stored in the ROM 40 in advance. Further, such correspondence is not limited to the specific numerical values shown here.

  Furthermore, it is possible to allow the user to set which of the 1-segment and 12-segment modes is important. In a modification described below, a mode that is important for the user can be set. Specifically, a mode that emphasizes the image quality of the image (a mode that emphasizes 12 segments) and a mode that avoids image blanking (a mode that emphasizes 1 segment) are displayed on the display unit 3 as options. Then, the user selects and inputs either one by the operation input unit 4. Then, the ratio of operating in the selected mode of either 1 segment or 12 segments is increased. Such setting is made possible by the control unit 36 changing the reference value of the C / N ratio reduction rate and the reference value of the code error occurrence rate.

  FIG. 9 is a diagram for explaining the reference values for the C / N ratio decrease rate and the code error occurrence rate. In the above embodiment, the reference value of the C / N ratio reduction rate for starting decoding of 1-segment broadcast data is 30%, and the reference value of the code error occurrence rate for changing the output of broadcast data is 10%. Showed the case. In contrast, in the 12-segment mode, both the C / N ratio reduction rate reference value and the code error occurrence rate reference value are increased. For example, the reference value for the C / N ratio reduction rate is 50%, and the reference value for the code error occurrence rate is 20%. By doing so, the in-vehicle electronic device 10 can maintain the 12-segment mode as long as both the C / N ratio decrease rate and the code error occurrence rate do not increase significantly. On the other hand, in the 1-segment priority mode, both the reference value for the C / N ratio reduction rate and the reference value for the code error occurrence rate are reduced. For example, the reference value for the C / N ratio reduction rate is 10%, and the reference value for the code error occurrence rate is 5%. By doing so, decoding of 1-segment broadcasting data can be started with only a slight increase in the C / N ratio reduction rate, and switching to output of 1-segment broadcasting data with only a slight increase in the code error occurrence rate. 10 can shift to 1 segment mode. The 1-segment mode can be maintained unless both the reference value for the C / N ratio reduction rate and the reference value for the code error occurrence rate are significantly improved.

  Note that the reference values shown here are merely examples, and the present modification is not limited to these numerical values. These reference values are stored in the ROM 40 in advance. Then, the change of the reference value is performed at an arbitrary position in the procedure of FIG. 4 (for example, before step S2) when the television is activated when the mode switching is focused on 1 segment or 12 segments. By doing so, it is possible to operate in the mode selected by the user when the electric field strength changes.

  In the digital terrestrial broadcasting of television, there are a simultaneous broadcasting in which the same program is broadcast in the 12-segment mode and the 1-segment mode, and a non-simal broadcasting in which different programs are broadcast. If the 12-segment mode is switched to the 1-segment mode during simulcast, the same program can be viewed. On the other hand, when switching from the 12-segment mode to the 1-segment mode during non-simultaneous broadcasting, a different program is displayed. Then, the user may feel inconvenience.

  A further modification of the present embodiment for solving this problem will be described. The control unit 36 acquires the EPG from the 12-segment decoding unit 30, and determines simulcast / non-simultaneous broadcasting. The mode switching described above is executed for simulcasting, and mode switching is not performed for non-simultaneous broadcasting. Alternatively, the control unit 36 may determine the simultaneous / non-simultaneous broadcasting by obtaining the audio data decoded from the 12-segment decoding unit 30 and comparing it with the audio data decoded by the 1-segment decoding unit 34. Also in that case, whether or not to perform mode switching is controlled according to the determination result. By doing so, it is possible to prevent the user from feeling inconvenience.

  In the above-described embodiment, the C / N ratio decrease rate, that is, the time ratio at which the C / N ratio becomes equal to or less than the reference value within the monitoring time is used as a method for detecting the decrease in electric field strength. However, the method for detecting the decrease in electric field strength is not limited to this. For example, the number of times that the C / N ratio becomes less than or equal to the reference value within the monitoring time may be used. Alternatively, the electric field intensity itself may be measured and compared with a predetermined reference value, and a time ratio or number of times that is less than or equal to the reference value within the monitoring time may be used. In the above-described embodiment, the code error occurrence rate, that is, the time ratio at which a code error occurs within the monitoring time is used as a method for detecting an increase in code error. However, other than this, for example, the number of times a code error has occurred within the monitoring time may be used.

  In the above description, the digital broadcast receiving apparatus integrated with the car navigation in the in-vehicle electronic device is shown as an example. However, the digital broadcast receiving apparatus in this embodiment can also be applied to a configuration in which a television apparatus alone is mounted on a vehicle. Even in that case, it is possible to reduce the blank time when switching from 12-segment broadcasting to 1-segment broadcasting.

  As described above, according to the digital broadcast receiving apparatus of the present embodiment, it is possible to reduce the blank time when switching from 12-segment broadcasting to 1-segment broadcasting with a small and inexpensive configuration.

3: display unit, 4: operation input unit, 10: in-vehicle electronic device, 10a: digital broadcast receiver, 11: antenna, 12: tuner, 14: demodulation unit, 16: decoding unit, 18: navigation control unit, 30: 12 segment decoding unit, 34: 1 segment decoding unit, 36: control unit, 38: switching unit

Claims (5)

A digital broadcast receiving device for receiving broadcast data that is mounted on a vehicle and multiplexed and transmitted by a segment obtained by dividing a predetermined frequency,
A first decoding unit for decoding first video data from first broadcast data transmitted by a first number of frequency segments;
A second decoding unit for decoding second video data from second broadcast data transmitted by a second number of frequency segments less than the first number;
A switching unit for outputting either the first or second video data to a video display unit;
A control unit for controlling the switching unit,
When the electric field strength decreases when the first decoding unit decodes the first broadcast data and the switching unit outputs the first video data to the video display unit, the control unit When the second decoding unit starts decoding the second video data and the code error of the first broadcast data increases, the switching unit outputs the second video data from the first video data. A digital broadcast receiver characterized by switching to In claim 1,
The control unit detects a decrease in the electric field strength when the ratio of the time when the C / N ratio is equal to or lower than a reference value is equal to or higher than a first reference value, and the occurrence rate of the code error is a second reference value. A digital broadcast receiving apparatus that detects an increase in the code error at the time described above. In claim 2,
The digital broadcast receiving apparatus, wherein the control unit increases the second reference value after switching to the output of the second video data. In claim 2,
The digital broadcast receiver according to claim 1, wherein the controller changes the first and second reference values based on a selection input. In any one of Claims 1 thru | or 4,
The digital broadcast receiving apparatus, wherein the second broadcast data includes data encoded at a higher encoding rate than the first broadcast data.

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