JP2001309273A - Digital broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a degree of signal deterioration of viewer's perception as an indicator of switching when switching to the most suitable layer, in an audio signal and a video signal modulated by a plurality of methods transmitted through layer transmission. SOLUTION: In a receiver for digital broadcasting, an signal error rate considered the degree of signal deterioration of viewer's perception is newly calculated based on the decode error frequency produced at a video decoder and an audio decoder, and at a crossing of the calculated error rate beyond a predetermined threshold level, a demodulation method is switched from a high layer to a low layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcast signal transmitted by a hierarchical transmission system for digitally modulating a video signal and an audio signal constituting one service by a plurality of systems, and receiving one of the modulated signals. The present invention relates to a digital broadcast receiving apparatus that selects a system for video and audio and performs reproduction.

[0002]

2. Description of the Related Art Conventional standard video such as CS broadcasting (SD
When transmitting a high-quality movie (HD video) requiring a bit rate several times higher than that of video (video) transmission, a modulation method called 8PSK, which has a feature of having a large transmission capacity, is adopted. However, when the radio wave condition is deteriorated such as in rainy weather instead of a large transmission capacity, the error resistance is lower than that of the conventional method. On the other hand, conventional QPSK and BP
The SK modulation method has a transmission capacity as small as half or less of 8PSK, but has a higher error tolerance. Therefore, by simultaneously broadcasting the modulation methods corresponding to the case where the radio wave condition is good and the case where the radio wave condition is deteriorated at the receiver, it is possible to select the most suitable system according to the radio wave condition by hierarchical transmission. There is a service called.

[0003] High-layer video can transmit high-resolution video such as HD video, but low-layer video has a low bit rate and is used for transmission of low-resolution video. Instead, if the signal condition is poor, such as when it is raining,
Although the error rate of the high-layer video increases and the rate at which error correction cannot be performed increases, if a low-layer video is selected, the error correction rate is high, so that a video having fewer errors than the high-layer video can be viewed.

[0004] A method generally used as means for switching the hierarchy is to monitor an error rate when receiving an RF signal and demodulating a digitally modulated signal. In the normal case where errors during demodulation are small, a high-layer video is selected, and when the error rate during demodulation increases in rainy weather or the like, switching to a low-layer video is performed (for example, ITE Technical Report: ITE Technical Report). Report vol.21, No.2
5, PP.1-5, BCS'97-12 (Mar, 1997)).

[0005]

The above-described method of monitoring the error rate when demodulating a digitally-modulated signal is as follows.
Regardless of what the final error signal is, for example, whether it is a video signal, an audio signal, subtitle data, or SI data, Will be treated. An HD video signal has a data amount of about 20 Mbps, whereas an audio signal has a data rate of about 72 Kbps / ch. The effect of a signal error depends on whether

Further, even with the same voice data, the influence of a signal error differs depending on the codec system (compression system). For example, MP used in CS broadcasting
In the case of EG1 layer 2, the number of bits constituting one frame is such that 1152 samples of the input signal are treated as one frame, and decoding is performed in frame units. On the other hand, in the case of the MPEG2-AAC method, the number of bits of an input signal per sample is variable, and the sound quality is higher and the bit rate is lower than in the MPEG1 method. Also, A
In the AC system, decoding is performed in units of frames, but overlap processing and the like are performed in the preceding and succeeding frames. Therefore, the influence of one signal error can be considered to be greater than in MPEG1.

[0007] As described above, the influence of a signal error is ultimately related to the degree of deterioration of a signal perceived by the viewer. Even if the signal error rate during demodulation is the same, the signal error is perceived by a signal source or a codec. Depending on the degree of signal degradation, the effect is considerably different. In other words, errors in signal demodulation alone
It is difficult to quantitatively understand the degree of deterioration perceived by the viewer, and even if the viewer does not perceive signal deterioration, switching from high-level video and audio signals to low-level video and audio May be performed. Similarly, the hierarchy may not switch even though the viewer perceives the degradation of the reproduced signal.

[0008]

It is difficult for a receiver to quantitatively measure the state of deterioration of a signal perceived by a viewer, but the perceived state of deterioration is determined by one frame of audio or video as one unit. Can be estimated to some extent by handling. Considering the reproduction of an audio signal as an example, in the case of the MPEG2-AAC method, the decoding unit is one frame, and the decoding result is 1024.
Be a sample. When the sampling frequency is 48 kHz, the minimum unit of decoding is about 21 msec. A
As a function for correctly decoding the AC encoded data, a method of finding a synchronization byte in a header of a decoding unit frame and a CR attached to each frame are provided.
Based on the C data, it is possible to determine whether an error exists in the frame. In other words, if the output cannot be performed due to the decoding error, the output is not performed for the time of the frame. Therefore, the receiver knows the proportion of the time that is correctly output by measuring the frequency of the decoding error. be able to. As a result, if the frequency of the decoding error is low, the perceived degree of deterioration is low, and if the frequency is high, the degree of deterioration is high. By using the frequency of this decoding error as an index of layer switching, it is possible to control according to the deterioration state perceived by the viewer.

[0009]

(Embodiment 1) FIG. 1 is a block diagram showing a digital broadcast receiving apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 100 denotes an IF signal input from an antenna or the like. Signal demodulation means for receiving and demodulating the digitally modulated signal and performing error correction processing. The signal output from the signal demodulation unit 100 is sent to the signal separation unit 101 as a transport packet. The signal separating means 101 filters the transport packets having the corresponding packet IDs by setting the packet IDs of the video and audio constituting the program, and outputs the result. The audio and video PES packets output from the signal separating unit 101 are output to the video signal reproducing unit 102 and the audio signal reproducing unit 103, respectively. In addition, MPEG-2 SI / PSI (Service Informatio
Additional data other than video and audio such as (n / Program Specific Information) information is sent to the additional information processing unit 104.

The signal input to the video signal reproducing means 102 is an encoded video signal.
At 03, decoding is performed and the video signal is output to an external device such as a television or a display unit of a display. The encoded audio signal input to the audio signal reproducing means 103 is also decoded and output to an external speaker or the like, like the video. The data input to the additional information processing means 104 includes channel selection information such as packet IDs of video and audio signals, and the signal separation instructing means 105 uses the data to transmit packet IDs to the signal separation means 101. By specifying
Instructs signal filtering. Further, the signal separation instructing means 105 outputs information necessary for demodulating a signal, such as a transport stream ID (TS-ID) including a video or audio to be reproduced, to the signal demodulating means 100. The basic operation of outputting video and audio can be realized by the above processing means.

In the present invention, a case where an IF signal modulated by hierarchical transmission is input to the signal demodulation means 100 is considered. As a modulation method used in a higher hierarchy, a modulation method having a large transmission capacity such as 8PSK is employed, and is used for transmission of HD video. On the other hand, the modulation method used in the lower hierarchy is a modulation method having a relatively small transmission capacity such as QPSK, and is used for transmitting SD video having a low resolution. When the audio is transmitted in both layers, it is conceivable that a 5.1-channel multi-channel audio is transmitted to the higher layer, and the lower layer is mixed down to output the audio with a reduced bit rate. Hierarchical transmission usually consists of two types of video signals and two types of audio signals for one program, and it is assumed that a high-level video / audio signal is selected when the radio wave condition is good.

In the audio signal reproducing means 103 for decoding the high-level audio signal separated by the signal separating means 101,
The input coded data is decoded, and audio data is constructed for each frame. In the case of the MPEG2-AAC audio system, one frame of audio to be output is decoded in a decoding unit called ADTS. FIG. 2 is a block diagram showing an example of the configuration of the audio signal reproducing means 103. In the audio signal reproducing unit 103, an error check of the ADTS is performed by the error detecting unit 207 before performing the decoding process.

As a method of error checking, ADTS
Check of the synchronization byte of the data and CRC code. The synchronization byte check is based on the first SY of the ADTS.
If the NC data does not match, the frame is treated as an error frame. Also, CRC check is ADTS
It is checked whether or not a signal error exists in the ADTS using the CRC code provided for each, and if it does not match the CRC data, it is treated as an error frame. As a result of the above-mentioned SYNC byte check and CRC check, if the frame is determined to be an error frame, the frame is not decoded and a signal error occurrence signal is output to the hierarchy switching instruction means 106.

FIG. 3 shows a block diagram of the hierarchy switching instruction means 106. The signal error occurrence signal output from the audio signal reproducing means 103 is input to the audio decoding error rate calculation means 309 shown in FIG. In addition, the parameters of the audio being decoded are also sent. The contents of the parameters include the encoding method of the stream to be reproduced, the number of channels, and the sampling frequency. MPEG2-A
In the case of AC, one frame is composed of 1024 samples. For example, in the case of 2-channel data at 48 kHz sampling, there are approximately 94 audio frames per second. If this is 32 kHz sampling, about 6
There are three frames.

The speech decoding error rate calculation means 309
An audio decoding error rate is calculated from the number of audio frames per unit time and the number of signal error occurrence signals input for each error frame. Voice decoding error rate calculation means 309
Requests the switching instruction means 311 to output an audio layer switching instruction signal when the threshold value exceeds a preset threshold value.

The video signal reproducing means 102 also checks the coded video data before performing the decoding process in the same manner as the audio signal processing. An MPEG2 video signal has a hierarchical structure including a sequence layer, a GOP layer, a picture layer, and a slice layer. The video signal decoded by the video signal reproducing unit 102 is input to the video decoding error rate calculation unit 310. When an error occurs in the picture layer of the input video signal, the video decoding error rate calculation means 310 sends out a decoding error occurrence signal and the total number of pictures per unit time. The video decoding error calculation means 310 counts the number of errors,
The decoding error rate of the video is calculated by comparing with the number of pictures successfully decoded. The video decoding error rate calculation unit 310 requests the switching instruction unit to output a video layer switching instruction signal when the threshold value exceeds a preset threshold value.

When the signal for requesting switching of the hierarchy is input from the hierarchy switching instructing means 106, the signal separation instructing means 105 of FIG. 1 determines that the program is a hierarchical transmission program and that the high hierarchy signal is decoded. In this case, an instruction signal is sent to the signal demodulation unit 100 to demodulate the low-layer signal and output it to the signal separation unit 101, and to the signal separation unit 101, a video signal or an audio signal flowing in the low layer Set the packet ID of

The setting of the decoding error rate threshold for determining whether or not to issue the layer switching request set by the layer switching instructing means 106 is performed based on the video or audio that has been transmitted and degraded in the higher layer and the error transmitted in the lower layer. The decoding error rate is set when the viewer switches between low-resolution but low-resolution video and audio with a small amount of information.

As described above, in the digital broadcast receiving apparatus according to the present embodiment, the index of hierarchy switching is calculated based on a decoding error in the video / audio reproducing means that finally generates data for outputting to the viewer. As a result, when switching from a higher hierarchy to a lower hierarchy, it is possible to match the deterioration state of the video and audio with the deterioration criterion felt by the viewer, and it is possible to suppress the variation.

(Embodiment 2) FIG. 4 shows a second embodiment of the present invention.
5 is a block diagram showing a digital broadcast receiving device described in FIG. 5. In FIG. 5, the difference from the block diagram showing the digital broadcast receiving device described in (Embodiment 1) is a signal demodulating means 400, and FIG. An example of the configuration of the signal decoding means 400 and its processing will be described. 5 in FIG.
12 is digital demodulation means for digitally demodulating the IF signal,
Numeral 513 denotes a signal error state monitoring means.
At 14, error correction of the digital data demodulated by the digital demodulation means 512 is performed.

The operation of the signal demodulating means 400 will be described below. In FIG. 5, the IF signal input to the signal demodulation means 400 is demodulated into a digital signal by a digital demodulation means 512, and the signal error state monitoring means 513
Is output to The signal error state monitoring means 513 stores the input data in a memory (for example, the signal error state monitoring means 51).
3) and output to the error correction means 514. The error correction unit 514 performs an error correction process on the data encoded by convolutional coding or the like, and outputs the data to the signal error state monitoring unit 513. The signal error state monitoring means 513 stores the error correction means 514 stored in the memory.
Is compared with the data after error correction processing is performed by the error correction means, the error rate of the signal is calculated, and the value is output to the hierarchy switching instruction means 406.

FIG. 6 shows an example of the configuration of the hierarchy switching instruction means 406. The layer switching instructing unit 106 described in (Embodiment 1) is replaced with an audio decoding error rate calculating unit 609.
The video decoding error rate calculation means 610 performs the same function, but the switching instruction means 611 receives the error rate of the signal output from the signal error state monitoring means 513 of the signal demodulation means 400.

The function newly added in the present embodiment is that, when an IF signal modulated by hierarchical transmission is input to the signal demodulation means 400, the radio wave condition deteriorates, the decoding error rate increases, and the image of the lower hierarchy is reduced. It is assumed that the voice has been switched to a voice or voice. When switching from high-level video and audio to low-level,
The layer switching instructing unit 406 counts the number of decoding error occurrence instruction signals output from the video signal reproducing unit 402 and the audio signal reproducing unit 403 to calculate the decoding error rate, which is used as an index of the layer switching instruction. When a hierarchical signal is being reproduced, the audio / video of the higher hierarchy is not decoded by the signal reproducing means, so that the switching cannot be determined. On the other hand, the signal demodulation means 400 always performs demodulation and error correction processing of both layers. A demodulation signal error state monitoring means 513 is provided between the digital demodulation means 512 and the error correction means 514, and the error is corrected by the above-described method. By monitoring the rate, it is possible to output the signal state of the higher hierarchy during the reproduction of the lower hierarchy to the hierarchy switching instruction means 406.

The hierarchy switching instructing means 406 determines that the state of the hierarchy has deteriorated when the input error rate exceeds a preset threshold value, and determines that the state is good when the error rate is lower than the threshold value. , A request to switch to a higher hierarchy is issued to the signal separation instructing means 405. Switching from a low hierarchy to a high hierarchy is the above operation, and for other operations,
This is the same as the digital broadcast receiving apparatus according to the first embodiment.

As described above, the digital broadcast receiving apparatus according to the present embodiment monitors the signal state of the higher hierarchy based on the error correction processing performed after demodulating the digitally modulated signal, and recovers the signal state. In order to perform switching to a higher layer at a point in time, in addition to switching from a higher layer of video and audio to a lower layer by the configuration described in (Embodiment 1), Switching to audio / video signals can also be realized without discomfort for the viewer.

(Embodiment 3) FIG. 7 shows a third embodiment of the present invention.
Is a block diagram related to the digital broadcast receiving apparatus described in FIG. 2, and is different from the block diagram showing the digital receiving apparatus described in (Embodiment 2) in FIG. And a layer switching threshold setting means 715 for outputting a layer switching threshold setting signal.

(Embodiment 1) and (Embodiment 2)
In each configuration of the digital broadcast receiving apparatus described in the above, in the case of automatically switching between the high hierarchy and the low hierarchy, there is a desire to continue to watch high-resolution video even if the video is disturbed, It cannot respond to the user's desire to keep watching low-resolution images with few errors. Therefore, the digital broadcast receiving apparatus according to the present embodiment is provided with a hierarchy switching threshold setting unit 715 so that a user can set a threshold of a decoding error rate when issuing a hierarchy switching request. 71
The threshold value set in the hierarchy switching instructing means 706 can be changed by the output signal from No. 5. The functions and operations of the other components are the same as those described in (Embodiment 1) and (Embodiment 2).

[0028]

According to the method of switching the hierarchy when the signal is degraded when the hierarchical transmission is performed, from the standpoint of the viewer, the switching to the lower hierarchy is performed only when the state of the video or audio is uncomfortable. There is a demand to reproduce a high-layer signal having as much information as possible. In addition, it is necessary to avoid the variation of the degradation state at the time of switching depending on the stream. In the present invention, the index of the hierarchy switching is calculated based on the decoding error in the video / audio reproducing means that finally generates the data to be output to the viewer. If a decoding error occurs in the video / audio reproduction means, the frame is not output and, as a result, 0 data is output to the viewer. Conversely, if no decoding error occurs, it can be considered that correct data is output. That is, the frequency at which correct data is output to the viewer can be calculated, and the index can be considered as an index having a considerably high correlation with the deterioration state felt by the viewer. As a result, when switching from a high hierarchy to a low hierarchy, it is possible to match the deterioration state of the video and audio with the deterioration criterion felt by the viewer, and it is possible to suppress the variation.

For switching from a lower hierarchy to a higher hierarchy,
Since the audio / video reproducing means is not reproducing, it is not possible to calculate a decoding error. In this case, based on the error correction processing performed after demodulating the digitally modulated signal, the signal state of the higher layer is monitored, and when the signal state is recovered, switching to the higher layer is performed. If no signal error occurs in the error correction processing after demodulation, it is considered that there is little possibility that an error due to deterioration of the transmission path will occur in the signal input to the audio / video signal reproducing means. It is unlikely that a person will feel uncomfortable.

Further, by providing a layer switching threshold value setting means for setting the threshold value of the signal deterioration state when the viewer switches between the high layer and the low layer, the deterioration state at the time of the switching intended by the viewer is provided. As a result, it is possible to cope with a deterioration state at the time of layer switching different for each viewer.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital broadcast receiving apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an audio signal reproducing unit of the digital broadcast receiving apparatus.

FIG. 3 is a block diagram showing a configuration of a hierarchy switching instruction unit of the digital broadcast receiving apparatus.

FIG. 4 is a block diagram illustrating a configuration of a digital broadcast receiving apparatus according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a signal demodulating unit of the digital broadcast receiving apparatus.

FIG. 6 is a block diagram showing a configuration of a hierarchy switching instruction unit of the digital broadcast receiving apparatus.

FIG. 7 is a block diagram illustrating a configuration of a digital broadcast receiving apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 100, 400, 500, 700 Signal demodulation means 101, 401, 701 Signal separation means 102, 402, 702 Video signal reproduction means 103, 403, 703 Audio signal reproduction means 104, 404, 704 Additional information processing means 105, 405, 705 Signal separation instructing means 106, 406, 706 Hierarchical switching instructing means 207 Error detecting means 208 Decoding means 309, 609 Audio decoding error rate calculating means 310, 610 Video decoding error rate calculating means 311, 611 Switching instructing means 512 Digital demodulating means 513 Signal Error state monitoring means 514 Error correction means 715 Hierarchical switching threshold setting means

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Claims (3)

[Claims] 1. A digital broadcast receiving apparatus for digitizing main information including video and audio signals and additional information including channel selection information and receiving a packetized and multiplexed broadcast signal for digital broadcasting, When the audio signal and the video signal of information are digitally modulated by different methods, respectively, and a hierarchical transmission signal that constitutes one program is input, the digital broadcast signal is received and digital demodulation and error correction are performed. Signal demodulation means, signal separation means for filtering an audio signal, a video signal, and an additional information signal specified by a signal separation instruction means from a signal input from the demodulation means, and decoding of the video signal separated by the signal separation means A video signal that reproduces and outputs a decoded video signal and a video decoding error occurrence signal. Means, audio signal reproduction means for decoding and reproducing the audio signal separated by the signal separation means, and outputting a decoded audio signal and an audio decoding error occurrence signal; and additional information separated by the signal separation means. Additional information processing means for decoding;
Layer switching instructing means for receiving a video decoding error occurrence signal output from the video signal reproducing means and a video decoding error generating signal output from the audio signal reproducing means and issuing a layer switching request; And a program separation signal output from the additional information processing means, and a setting signal for hierarchical switching is output to the signal demodulation means and the signal separation means. For receiving device. 2. The digital broadcast receiving apparatus for receiving a digital broadcast signal in which the video / audio signal of the main information is multiplexed as hierarchical transmission is calculated by an error correction process in a digital demodulation process. 2. The digital broadcast receiving apparatus according to claim 1, further comprising a signal demodulating unit that outputs an error rate of the demodulated signal to the hierarchical switching instruction unit. 3. The digital broadcast receiving apparatus further comprises: a hierarchy switching threshold setting unit that receives an instruction signal from a user and outputs a decoding error threshold setting signal to the hierarchy switching instruction unit. Claim 2
The receiving device for digital broadcasting according to the above.