JP4720157B2 - Digital TV broadcast receiving terminal - Google Patents

Description

  The present invention relates to a digital broadcast receiving terminal, particularly a digital television broadcast receiving terminal in a mobile body, to which a function of receiving is added while reducing adverse effects on broadcast reception due to unnecessary electromagnetic waves radiated by the broadcast receiving terminal itself.

  Terrestrial digital television broadcasts are more resistant to noise and multipath interference than analog television broadcasts. On the other hand, it is known that image quality deteriorates rapidly when the received electric field strength falls below a certain value. This phenomenon of sharply degrading image quality is generally called a cliff effect.

  In particular, terrestrial digital broadcasting services for portable devices are scheduled to start soon and are expected to become widespread. However, in these portable devices, since the devices themselves move, There is a high possibility of being affected by such a cliff effect.

In general, the receiving sensitivity of a broadcast receiving terminal depends on the received electric field strength of the radio wave transmitted from the broadcasting station, but unnecessary electromagnetic waves radiated by the receiving terminal itself deteriorate the own receiving sensitivity. Sensitivity is greatly affected by electromagnetic waves radiated by the receiving terminal itself.
Such unnecessary electromagnetic wave deterioration of reception sensitivity is generally called sensitivity suppression.

As a conventional method for preventing such sensitivity suppression, for example, in Patent Document 1, in a wireless device having a reception unit and a control unit that intermittently receive a signal, the reception unit is in a reception operation state. In addition, there is disclosed a method in which the operation of the control unit is partially stopped to reduce unnecessary electromagnetic wave radiation from a wireless device and to reduce deterioration of reception sensitivity.
JP 2001-332994 A

  However, in wireless devices and mobile phones, the intermittent operation as described above is effective because transmission and reception and waiting are executed in a time-sharing manner. Because the data is transmitted seamlessly, if you try to alternately receive broadcast radio waves and play and display the received video data by time-division by intermittent operation, the video data will always be interrupted and the display screen will be distorted In addition, since the content of the reproduced image cannot be confirmed, and the image data of the digital television broadcast is transmitted using an image compression technique such as MPEG, for example, the P frame or the B frame in the MPEG image compressed data is transmitted. As such, there is a frame that cannot be decoded by its own single frame and that decodes based on the information of other frames. Therefore, it is not always possible to reproduce all image frames transmitted within the time allotted to the reproduction and display of video data, and as a result, the display screen is disturbed and the content of the reproduced image cannot be confirmed. Had.

  In order to solve the above problems, the digital television broadcast receiving terminal of the present invention has a function of constantly monitoring the electric field intensity of the received broadcast radio wave, and the electric field intensity of the received broadcast radio wave is below a predetermined value In this case, the operation of receiving broadcast radio waves and further storing the received image data and the operation of decoding (reproducing) the stored image data and displaying the data on a display or the like are performed alternately. A specific frame of received image data, for example, an I frame in MPEG image compressed data is limited to a frame that can reproduce one image as a single frame, and the stored image data of the specific frame is Decodes the stored image data within the time allotted to the operation for decoding and displaying it, and displays it on a display etc. It is intended to.

  The digital broadcast receiving terminal of the present invention performs the reception and storage operation of broadcast radio waves and the playback operation of the stored image data alternately in a weak electric field in which the image quality of the reproduced video is unacceptably degraded. During broadcast radio wave reception operation, it is possible to suppress the radiation of unwanted electromagnetic waves emitted by itself and suppress the decrease in broadcast radio wave reception sensitivity, and the reproduction of image data can be performed only by a specific frame within the received image data. For example, by limiting to only I frames in MPEG image compressed data, and by receiving broadcast radio waves and storing received image data at other times, within the time allotted for playback, It is possible to reliably reproduce and display a specific frame present in the received and accumulated image data. Therefore, even in a weak electric field that deteriorates the image quality of the reproduced video to an unacceptable level, or in a weak electric field that disturbs the displayed image, the broadcast image is reproduced and displayed reliably but intermittently. can do.

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

(Embodiment 1)
FIG. 1 is a block diagram showing an example of the configuration of a digital television broadcast receiving terminal in Embodiment 1 of the present invention.

  In FIG. 1, 101 is an antenna, 102 is a channel selection unit, 103 is an OFDM demodulation unit, 104 is a demultiplexing unit, 105 is a sensitivity determination unit, 106 is a selector, 107 is a frame extraction unit, 108 is a storage unit, and 109 is an image. Decoding means, 110 is a display means, 111 is an audio decoding means, and 112 is an audio output means.

  The operation of the digital television broadcast receiving terminal configured as described above will be described below.

  The antenna 101 receives a digital television broadcast wave and outputs the received broadband signal to the channel selection unit 102 as a received signal.

  The channel selection means 102 extracts the signal band of the channel that the user wants to view from the wideband received signal received by the antenna 101, and outputs the extracted signal to the OFDM demodulation means 103 as the channel selection signal.

  The OFDM demodulation means 103 performs OFDM demodulation and error correction processing on the input channel selection signal, and then outputs the processed signal to the demultiplexing means 104 as a transport stream signal. The OFDM demodulator 103 further outputs sensitivity information representing the quality of the input channel selection signal to the sensitivity determination unit 105. Here, as the sensitivity information, it is possible to use a bit error rate that is generally used for evaluating the reception characteristics (quality of received signals) of digital television broadcasting. That is, since the value of the reception sensitivity can be associated based on the value of the bit error rate that represents the quality of the channel selection signal, the value of the bit error rate can be used as an example of sensitivity information. However, the sensitivity information need not be limited to the bit error rate, and may be another value corresponding to the bit error rate.

  The demultiplexing unit 104 extracts a video signal included in the transport stream signal input from the OFDM demodulation unit 103, and outputs the extracted video signal to the selector 106 and the frame extraction unit 107 as a video elementary stream signal. Further, an audio signal included in the transport stream signal is extracted, and the extracted audio signal is output to the audio decoding unit 111 as an audio elementary stream signal.

When the value provided by the sensitivity information input from the OFDM demodulating unit 103 is lower than a preset value, the sensitivity determination unit 105 enables the intermittent operation enable signal that is an output signal, and the sensitivity information If the resulting value is greater than or equal to a preset value, the intermittent operation enable signal, which is an output signal, is disabled and output. As described above, the bit error rate is often used to evaluate the reception characteristics of digital television broadcasts. If this bit error rate is 2 × 10 ^-4 or less, the signal is restored by error correction. Therefore, the bit error rate value of 2 × 10 ⁻⁴ can be used as a preset value. Further, if a slight image quality deterioration is allowed, a value larger than this value may be used as a preset value. However, the preset value need not be limited to this bit error rate value, and may be another value corresponding to the bit error rate.

  When the intermittent operation enable signal input from the sensitivity determination unit 105 indicates enable, that is, when receiving an intermittent operation instruction, the selector 106 outputs a frame output signal input from the storage unit 108 described later as a selector output signal. When the intermittent operation enable signal input from the sensitivity determination means 105 indicates disable, that is, when an instruction for normal operation is received, the video elementary stream signal is output as a selector output signal.

  When the intermittent operation enable signal input from the sensitivity determination unit 105 indicates enable, that is, when an instruction for intermittent operation is received, the frame extraction unit 107 receives a specific video from the video elementary stream signal input from the demultiplexing unit 104. Remove the frame. Here, the specific video frame is a frame in which one image can be reproduced by a single frame, such as an I frame in MPEG image compressed data. When a digital television broadcast video signal is transmitted after being compressed into an MPEG image, the extracted I video frame, which is a specific video frame, is output from the frame extraction means 107 to the storage means 108 as a frame video signal. At the same time, an accumulation enable signal indicating whether or not this frame video signal is valid is output from the frame extraction means 107 to the accumulation means 108.

  The storage means 108 determines that the frame video signal input from the frame extraction means 107 is valid when the storage enable signal input from the frame extraction means 107 indicates enable, and stores the input frame video signal. I do. When the accumulation of the frame video signal is completed, the accumulated frame video signal is output to the selector 106 as a frame output signal. At the same time, a decode enable signal is output to the video decoding means 109, and this decode enable signal indicates whether or not the simultaneously output frame output signal is valid.

  The video decoding means 109 decodes the selector output signal input from the selector 106 at any time when the intermittent operation enable signal input from the sensitivity determination means 105 is disabled, and stores it when the intermittent operation enable signal is enabled. Only when the decode enable signal input from the means 108 is enabled, the selector output signal input from the selector 106 is decoded, and the reproduction operation is stopped at other times, and the decoded signal is displayed as a display signal. Output to.

  The display unit 110 is a device that displays the display signal input from the video decoding unit 109.

  The audio decoding unit 111 decodes the audio elementary stream signal input from the demultiplexing unit 104 and outputs the output signal to the audio output unit 112 as an audio signal.

  The audio output unit 112 is a unit that reproduces the audio signal input from the audio decoding unit 111 into audio, and is a device such as a speaker or headphones.

  When the digital broadcast receiving terminal is configured as described above, the reception and storage of broadcast radio waves and the received video will occur when the electric field strength of the received broadcast radio waves falls below a certain value and the image quality deteriorates rapidly. By alternately performing data playback, stopping the video data playback operation when receiving broadcast radio waves to reduce the occurrence of unnecessary radiation at the receiving terminal itself, improving the reception sensitivity, and further playing back video data Is limited to a specific video frame in the video data (for example, an I frame in the MPEG image compression data), so that a specific frame in the video data received and stored within the time allocated for decoding (playback) Can be reproduced reliably, even in weak electric fields where the image quality of the reproduced video is degraded to an unacceptable level visually. There can be performed a stable image display.

(Embodiment 2)
FIG. 2 is a block diagram showing an example of the configuration of a digital television broadcast receiving terminal according to Embodiment 2 of the present invention.

  In FIG. 2, 101 is an antenna, 102 is a channel selection means, 103 is an OFDM demodulation means, 204 is a demultiplexing means with a voice stop function, 105 is a sensitivity determination means, 106 is a selector, 107 is a frame extraction means, and 108 is an accumulation means. 109 is a video decoding means, 110 is a display means, 111 is an audio decoding means, and 112 is an audio output means.

  The operation of the digital television broadcast receiving terminal configured as described above will be described below. However, in the digital television broadcast receiving terminal of the second embodiment, the demultiplexing means 104 in the digital TV broadcast receiving terminal of the first embodiment shown in FIG. 1 is replaced with a demultiplexing means 204 with a voice stop function. Therefore, each component other than the demultiplexing unit 204 with the voice stop function is assigned the same number as each component in the first embodiment, and the description thereof is omitted here.

  The multiplexing / demultiplexing means 204 with an audio stop function extracts a video signal included in the transport stream signal input from the OFDM demodulating means 103, and the selector 106 and the frame extracting means as the extracted video signal as a video elementary stream signal. In addition, when the intermittent operation enable signal input from the sensitivity determination unit 105 indicates enable, that is, when the intermittent operation is instructed, the output of the audio signal to the audio decoding unit 111 is stopped. When the intermittent operation enable signal indicates disable, that is, when the intermittent operation is not instructed, an audio signal included in the transport stream signal input from the OFDM demodulating means 103 is extracted, and the audio Audio data as an elementary stream signal And it outputs the over de means 111.

  By configuring the digital broadcast receiving terminal as described above, when the electric field strength of the received broadcast radio wave falls below a certain value and the image quality deteriorates rapidly, the reception of the broadcast radio wave and the received video data The reproduction is performed alternately, and the reproduction of the video data is performed by decoding (reproducing) only a specific video frame in the video data (for example, an I frame in the MPEG image compression data). Since reception and accumulation of received data are performed, certain frames in the received data can be reliably played back within the time allotted to decoding, and the reproduced video can be displayed intermittently. Further, since the output of the audio signal from the demultiplexing means 204 with the audio stop function is also stopped when the broadcast radio wave is received, compared with the first embodiment. Since the radiation noise signal terminal itself generates can be further reduced, it is possible to receive field intensity for displaying intermittently while playing a video even more weaker situation.

In the second embodiment, when the intermittent operation enable signal input from the sensitivity determination unit 105 indicates enable, that is, when the intermittent operation is instructed, the demultiplexing unit 204 with the voice stop function is used. Although the output of the audio signal to the audio decoding unit 111 is stopped, the intermittent operation enable signal which is the output signal of the sensitivity determination unit 105 is also input to the audio decoding unit 111, and the sensitivity determination unit When the intermittent operation enable signal input from 105 indicates enable, by configuring so that the audio reproduction operation in the audio decoding unit 111 is stopped, the same effect as described in the second embodiment can be obtained. it can.

  Further, in the configuration of the second embodiment, an intermittent operation enable signal that is an output signal of the sensitivity determination unit 105 is also input to the audio decoding unit 111 so that the intermittent operation enable input from the sensitivity determination unit 105 is performed. Needless to say, even when the configuration in which the audio reproduction operation in the audio decoding unit 111 is stopped when the signal indicates enable, the same or higher effect as that shown in the second embodiment can be obtained.

  In the above description, terrestrial digital television broadcasting has been described as an example, but the same effect can be obtained even in digital television broadcasting using a broadcasting satellite such as BS broadcasting or CS broadcasting. .

  Since the digital television broadcast receiving terminal of the present invention can display a reproduced video intermittently even in a weak electric field where the image quality deteriorates to an unacceptable level visually, there is a possibility that reception conditions are not particularly constant. This is effective in mobile digital TV broadcast receiving terminals such as high-definition car TVs and portable terminals.

1 is a block diagram showing an example of the configuration of a digital television broadcast receiving terminal in Embodiment 1 of the present invention. The block diagram which shows an example of a structure of the digital television broadcast receiving terminal in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Antenna 102 Channel selection means 103 OFDM demodulation means 104 Demultiplexing means 105 Sensitivity judgment means 106 Selector 107 Frame extraction means 108 Storage means 109 Video decoding means 110 Display means 111 Audio decoding means 112 Audio output means 204 Audio multiplexing means with audio stop function

Claims (3)

An antenna that receives broadcast radio waves and outputs a received signal;
Channel selection means for extracting a signal of a channel desired to be viewed from the received signal input from the antenna, and outputting the extracted signal as a channel selection signal;
OFDM that performs OFDM demodulation processing and error correction processing on the channel selection signal input from the channel selection means and outputs it as a transport stream signal, while outputting the quality state of the channel selection signal as sensitivity information Demodulation means;
When the sensitivity information input from the OFDM demodulator is lower than a preset value, an intermittent operation enable signal for instructing an intermittent operation is output. In other cases, an intermittent operation enable signal for instructing a normal operation is output. Sensitivity judgment means for outputting
Demultiplexing means for separating and outputting a video elementary stream signal and an audio elementary stream signal from the transport stream signal input from the OFDM demodulating means;
When the intermittent operation enable signal input from the sensitivity determination means is a signal for instructing intermittent operation, an I frame is extracted from the video elementary stream signal input from the demultiplexing means and is extracted as a frame image. frame sampling means for outputting a signal, and outputs the accumulation enable signal indicating whether or not storing the frame video signal in further,
When the storage enable signal input from said frame extracting means is enabled, accumulate previous SL frame video signal, the accumulation of said frame video signal is completed, and outputs the stored said frame video signal as a frame output signal, a storage means for outputting a decode enable signal indicating whether or not to decode the output and the frame output signal,
When the intermittent operation enable signal input from the sensitivity determination means is a signal for instructing intermittent operation, the frame output signal input from the storage means is output as a selector output signal, and the intermittent operation enable signal is In the case of a signal for instructing normal operation, a selector that outputs the video elementary stream signal input from the demultiplexing means as a selector output signal;
When the intermittent operation enable signal input from the sensitivity determination means is a signal for instructing intermittent operation, the input from the selector is performed only when the decode enable signal input from the storage means is enabled. Decodes the selector output signal and stops decoding at other times. If the intermittent operation enable signal is a signal for instructing normal operation, the selector output signal is decoded as needed and output as a display signal. Video decoding means,
Display means for displaying the display signal input from the video decoding means;
Audio decoding means for decoding the audio elementary stream signal input from the demultiplexing means and outputting as an audio signal;
With
The operation of accumulating the frame video signal and the operation of decoding the selector output signal are alternately performed,
The selector output signal is decoded within the time allotted to the operation of decoding the selector output signal.
A digital television broadcast receiving terminal characterized by the above. Said demultiplexing means, said from the transport stream signal video elementary stream signal and the audio elementary stream signal and the separated output, and the intermittent operation enable signal input from the sensitivity decision unit intermittent operation 2. The digital television broadcast receiving terminal according to claim 1, wherein the signal is a demultiplexing means with an audio stop function for stopping output of the audio elementary stream signal when the signal is an instruction signal. It said audio decoding means, and if the previous SL intermittent operation enable signal indicates a signal for instructing the intermittent operation, claim 1, characterized by being configured to stop the audio reproduction operation in the audio decoding means The digital TV broadcast receiving terminal described.

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