JP2002135786A - Receiver and digital data decoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver and a digital data decoding method capable of processing error concealment processing at a decoding part without applying viewing stresses to a user. SOLUTION: In the apparatus, the S/N of input signal is detected at an error detecting/correcting part 13. A processing system of error concealment is switched based on the S/N. High-level error concealment is applied if the S/N is excellent, and low-level error concealment is applied if the S/N is not excellent. Therefore, it becomes possible to successively maintain the strength of error concealment of a suitable strength and to conceal errors while suppressing the viewing stresses to the user.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an MPEG (Movi)
ng Picture Coding Experts Group) The present invention relates to a reproducing apparatus having a function of decoding an encoding system stream, a receiving apparatus for decoding and reproducing a moving image encoded by control thereof, and a digital data decoding method.

[0002]

2. Description of the Related Art Recently, CS (Community
Communication satellite (MPEG) -based digital broadcasting services using satellites are becoming widespread. In the near future, the start of an MPEG encoding digital broadcasting service using BS (Broadcast Satellite) satellites, terrestrial waves, cable waves, etc. is planned.

[0003] Generally, the reproduction signal of such a digital broadcasting service is different from the reproduction signal of the terrestrial broadcasting service using a conventional analog signal in that the signal quality is nonlinearly deteriorated due to natural phenomena such as rainfall. For example, in the weather where the rainfall becomes intense, the reception / reproduction signal of the terrestrial broadcasting service by the analog signal gradually deteriorates in image quality almost in proportion to the intensity of the rainfall, and gradually decreases linearly. It becomes difficult to watch.

However, in a similar situation, a received / reproduced signal of a digital broadcasting service by a digital signal can prevent a received / reproduced signal error by an error correction process peculiar to digital processing in order to prevent input signal deterioration to a certain extent. Although it is possible to correct errors non-linearly after a certain deterioration,
An audio signal will be output. The extremely deteriorated reproduced image / audio signal gives an excessive viewing stress to the user, which is not preferable for the receiving / reproducing apparatus.

[0005] As a result, the digital broadcast service receiving / reproducing apparatus performs processing such as turning off the reproduced image / audio signal output when the input modulated signal has deteriorated to some extent, thereby obtaining an extremely degraded image / audio signal. We are trying to prevent users from watching audio signals. Also, MPEG
By performing a specific error concealment process on the encoding stream at the time of decoding, an attempt is made to make errors (noise) on the output reproduced image / audio signal inconspicuous. There are several typical methods for this error concealment process. For example, when an uncorrectable stream error is detected in each image / audio decoding unit, there are a method of continuing to use the result of the latest correct decoding instead, and a method of not updating the reproduction result until the decoding is correctly performed. .

[0006]

However, in the conventional error concealment processing, since the cooperation between the front end unit such as a tuner and each image / audio decoding unit is incomplete, it is detected at the stage of the input modulation signal. It is not possible to dynamically change the error concealment strength in response to a stream error that has occurred.

[0007] Therefore, if the error concealment strength is increased and fixedly set for a rare and extremely deteriorated stream error, a strong error concealment process is performed even for a frequent minor stream error. In some cases, the result is that the viewing stress is accumulated on the user.
For example, when a concealment process is performed so that no decoding result is updated when a decoding error is detected, even if a small decoding error that the user cannot recognize frequently occurs, the reproduced image / audio is It was not updated. This was a result of giving a viewing stress to the user.

Therefore, an ideal error concealment process that does not give a user viewing stress is to grasp the occurrence state of a stream error and to perform concealment processing of a strength appropriate for the situation while sequentially and dynamically changing the concealment process. Think.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a receiving apparatus and a digital data decoding method capable of performing error concealment processing in a decoding unit so as not to give a viewing stress to a user.

[0010]

According to a first aspect of the present invention, there is provided a receiving apparatus for receiving transmitted digital data, comprising: detecting means for detecting a receiving state of digital data; And a decoding means for selecting a decoding error concealment processing method and performing decoding processing of digital data by the decoding error concealment processing method.

According to a sixth aspect of the present invention, in the digital data decoding method, a step of receiving the transmitted digital data, a step of detecting a reception state of the digital data, and a predetermined step based on the reception state of the digital data. Selecting a decoding error concealment processing method and performing digital data decoding processing by the decoding error detection method.

According to the present invention, the error concealment processing method is switched according to a value reflecting an error state of the input signal such as the S / N ratio. For this reason, the error concealment strength can be kept at an appropriate level one by one, and the error can be concealed while suppressing the viewing stress on the user.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a receiving / reproducing apparatus for receiving a digital broadcasting service of an MPEG encoding stream to which the present invention is applied.

In FIG. 1, an input modulated (RF) signal output from a parabolic antenna, a cable line, or the like is supplied from an input terminal 10 to a tuner section 11 in the front end section 1.
, And the demodulation unit 12 outputs, for example, QPSK (Qu
adrature Phase Shift Keying) Demodulated. Demodulation unit 1
The output from 2 is supplied to the error detection / correction unit 13. The error detection / correction unit 13 performs error correction as much as possible upon detecting an error.

At this time, the S / N ratio information of the input modulation signal detected in the front end unit 1 is sent from the error detection / correction unit 13 to the control microcomputer unit 14 via the system bus 3, for example. .

The control microcomputer unit 14, the ROM unit 15, and the R
In the AM unit 16 and the like, a key required to decrypt the encryption is stored together with the decryption program. When the transmitted digital signal is encrypted, a key for decrypting the encrypted signal and a decryption process are required. Therefore, a key to be decrypted is read out from the control microcomputer unit 14, the ROM unit 15, the RAM unit 16, and the like, and this key is supplied to the demultiplexer unit 17.

The demultiplexer 17 uses this key to decrypt the encrypted digital signal.
In addition to the key required for the decryption, the decryption program and the billing information are stored together in the memory.

The demultiplexer 17 detects an error.
The output signal from the correction unit 13 is received, and is temporarily stored in an appropriate memory area of the RAM unit 16 for the data buffer memory or a memory area inside the demultiplexer unit 17. Then, this is read out as appropriate, and the decoded image signal is supplied to the image decoding unit 18 and the audio signal is supplied to the audio decoding unit 19. At this time, from the multiplexed encoded data,
Information necessary for re-creating the system clock is extracted by the clock generator 20 and used for processing by the image decoder 18 and the audio decoder 19.

The processing of the demultiplexer 17 is based on the ISO
(International Organization for Standardization)
/ IEC (International Electrotechnical Commissio
n) It is specified in detail in the specification of 13818-1 (Geneva 1995).

The image decoding unit 18 stores the input coded data in the RAM unit 16 as appropriate, and executes a decoding process of an image signal that has been compression-encoded by the MPEG system.
The decoded image signal is supplied to the display image forming unit 21, where, for example, a luminance signal (Y) of the NTSC system,
It is converted into a chroma signal (C) and a composite signal (CV). This signal is supplied to the D / A converter 22
Is converted to analog and output. From the output terminal 23, a video signal is output in the S-video signal format, for example.

The processing of the image decoding unit 18 is based on the ISO (Intern
ational Organization for Standardization) / IEC
(International Electrotechnical Commission) 13818-
2 (Geneva 1995) is specified in detail.

The audio decoding unit 19 includes a demultiplexer 1
The encoded audio signal supplied from 7 is stored in the RAM section 16 as appropriate, and a decoding process of the audio signal compressed and encoded by the MPEG method is executed. The decoded digital audio signal is supplied to the D / A converter unit 24 and is converted into an analog signal. At this time, the audio signals of the left and right channels are properly processed, and as the audio output of the left and right channels,
Output from the output terminal 25.

The processing of the audio decoding unit 19 is performed according to the ISO Internet
tional Organization for Standardization) / IEC
(International Electrotechnical Commission) 13818
-3 (Geneva 1995).

The control microcomputer section 14 executes various processes according to a program stored in the ROM section 15. For example, the tuner unit 1 via the system bus 3
1, the processing in the demodulation unit 12, the error detection / correction unit 13 and the like is controlled. Also, the processing blocks of the demultiplexer unit 17, the image decoding unit 18, the audio decoding unit 18, and the display image forming unit 21 are controlled via the system bus 3, and the ROM unit 15,
It controls read / write processing of each memory address with respect to the RAM section 16 and the decoded data memory section 26 and the like.

On the other hand, a predetermined command from the user interface unit 27 that has received input information from a remote commander or the like can be directly input to the control microcomputer unit 14.

Further, the demultiplexer unit 17 includes, besides the coded digital image / audio signal supplied from the error detection / correction unit 13, SI (Speci?
fication Information) Information is also supplied in a multiplexed state. This SI information is stored and processed in a buffer memory in the RAM unit 16 or the demultiplexer unit 17 as appropriate.

Next, an outline of the error concealment processing at the time of the video / audio decoding processing used in the present invention will be described.

Representative examples of the error concealment processing at the time of image decoding processing include a mute method, an intra error concealment method,
SNR scalability / data partitioning method, small slice method, and the like. Representative examples of the error concealment processing at the time of the audio decoding processing include a mute method, a fade-out method, a previous value hold method, an average value interpolation method, and the like.

FIG. 2 is a schematic diagram showing an example of the error concealment processing at the time of the image decoding processing. FIG. 2A is a technique commonly called “intra concealment”, and FIG.
Is an example of a technique called “intra-concealment vector”.

An encoding system using predictive encoding between images, such as an MPEG encoding system, is generally vulnerable to errors. This is because predictive coding is performed from a previously decoded image. Therefore, once an error occurs, the error propagates in the time axis direction.

In the MPEG encoding system, an I (Intra) picture exists to converge this error propagation in a certain section.

That is, in the MPEG2 system, I (Intra
) Picture, P (Predicti) picture, and B (Bidir)
Three types of screens called "sectionally predictive" pictures are sent. In an I picture, DCT (Discrete Cosine Transform) coding is performed using pixels of the same frame. In a P picture, the already encoded I
DCT coding using motion compensation prediction is performed with reference to a picture or a P picture. In a B picture, DCT coding using motion prediction is performed with reference to an I picture or a P picture before and after the B picture.

In P-pictures and B-pictures, errors are propagated because of predictive encoding between frames, but in I-pictures, intra-frame encoding is performed, so that error propagation can be prevented. However, conversely, if an error occurs during transmission of an I picture, the contents of the GOP following the I picture are all destroyed, resulting in an error in the decoded image signal. For this reason, the principle of error resilience is protection of I pictures.

The intra-concealment vector method is a method according to this principle.

Among the methods having the highest error concealment processing strength, when an error exists in a P picture or a B picture, the decoding of that picture image is abandoned, and the picture image that could be decoded immediately without error is continuously output. That is.
Then, the decoding result is not updated until an I-picture without a decoding error following the sequence header code can be decoded.

One example of a method with a low strength of the error concealment processing is to remove a block lost due to an error existing in each picture from a reference image for prediction without considering motion as shown in FIG. 2A. It is a method of fitting as it is. In FIG. 2A, a pixel P2 located at the same position in a previous picture (t + 1) with respect to a pixel P2 on a line x of a picture t
1 is fitted.

A method of slightly increasing the strength of this method is a method of concealing by performing motion compensation from a reference image using a motion vector as shown in FIG. 2B. This motion compensation value is added to each macroblock of the I picture. At this time, the added motion vector is a motion vector of a block located under its own block. The image decoding unit stores the vector of each transmitted macroblock in units of one horizontal row. If a block is lost due to an error, the vector of this block is 1
Since it has already been transmitted and stored on the column, it is used to conceal errors.

As described above, there are a plurality of methods for error concealment processing. In the embodiment of the present invention, the method of the error concealment processing is switched according to the S / N ratio.

FIG. 3 shows a control method in which the decoding error concealment processing of the video and audio decoding units can be switched independently using the S / N ratio detected in the demodulation processing of the input modulation signal. It is a processing flow of.

As for the error concealment method during the processing and the difference in the concealment strength, no particular method or limited strength is specified. The present invention does not specify a specific concealment method or intensity value.

First, when the system is started, step S
By the process of T1, the control microcomputer unit 14 receives the S / N ratio of the input modulation signal from the front end unit 1. This S
In accordance with the value of the / N ratio, the strength of the error concealment processing in the image decoding unit 18 and the audio decoding unit 19 is sequentially changed.

As the initial value of the system, the error concealment strength value variable p is set to (p = 1) by the processing of step ST2. As a result, the threshold value for a certain S / N ratio, threshold-
p is determined.

In the process of step ST3, this threshold value is compared with the S / N ratio of the input modulation signal detected by the front end unit 1.

In the process of step ST3, the threshold thre
If the S / N ratio is smaller than shold-p, step ST
In 4, the error concealment strength value variable p is incremented by 1, and the process returns to step ST3.

By repeating the processing of steps ST3 and ST4, the threshold value gradually decreases. By comparing this threshold value with the S / N ratio, the S / N ratio of the input signal is detected. .

In step ST3, S / S is more than the threshold.
When the N ratio increases, an error concealment strength variable p is determined in the process of step ST5.

The error concealment processing for video and audio corresponding to the error concealment strength variable p is predetermined as shown in FIGS. Then, in step ST6, each of the image decoding unit 18 and the audio decoding unit 19 executes an error concealment process corresponding to the error concealment strength variable ECp.

FIGS. 4 and 5 show an example of video and audio error concealment processing corresponding to the error concealment strength variable p.

As shown in FIG. 4, in the video error concealment process, when the S / N ratio of the input signal is large, such as when the error concealment strength value variable p is (p = 0 to 4), the error concealment process is as follows. Slice replacement within a two-dimensional frame is performed.

Then, the error concealment strength value variable p is (p =
5 to 10), the error concealment processing is switched to data replacement in the I picture. At this time, a moving vector is referred to.

Further, the error concealment strength value variable p is (p = 1
0 to p14), the S / N ratio is poor, making it difficult to reproduce moving images. At this time, the image is frozen with the most recently decoded I picture, and the still image is reproduced.

Further, the error concealment strength value variable p is (p = 1
5 to p19), it becomes difficult to reproduce the image, and the image is muted.

Further, the error concealment strength value variable p is (p = 2
When the value is larger than 0), the mute of the image is released.
The reason why the muting of the image is released is to notify the user that there is no signal. S / N
When the ratio is very bad, it is difficult to reproduce the image, and it is conceivable to mute the image. However,
If the image is muted, the user may erroneously recognize that the failure has occurred. In this example, when the S / N ratio is very bad, the user dares to show an image to prevent the user from being mistaken for a failure.

As shown in FIG. 5, in the audio error concealment process, the error concealment strength value variable p is set to (p = 0 to 1).
In the case of 5), linear interpolation or previous value hold is performed.

When the error concealment strength value variable p is (p = 15 to p
In the case of 19), it is difficult to reproduce the audio, so that the audio is muted.

Further, the error concealment strength value variable p is (p = 2
If it becomes larger than 0), the audio mute is released. The reason why the audio mute is released is to notify the user that there is no signal, as in the case of the image.

The switching of the error concealment processing with respect to the S / N ratio is not limited to the above-described example, and various methods can be considered. Simply, when the S / N ratio is large,
Two-stage switching may be performed when the S2N ratio is small. Further, in the above-described example, the error concealment processing for the S / N ratio is switched for video and audio, but such processing may be performed for only one of them. For example, the error concealment processing for the S / N ratio may be switched for video, but not performed for audio.

In the above-described example, the reception state of the received digital data is detected by the error detection / correction unit for detecting the S / N ratio. May be detected.

[0059]

According to the present invention, the method of the error concealment processing is switched according to the reception state of the input signal, that is, the S / N ratio.

When the error concealment processing setting is fixed,
If the error concealment strength is increased in order to conceal a rare and extremely deteriorated stream error, strong error concealment processing will be performed even for minor stringer errors, or the extremely deteriorated stream error For a long time, the reproduced image / sound may not be output at all for a long time, which may result in the user accumulating stress.

On the other hand, in the present invention, the error concealment processing system is switched according to a value reflecting an error state of the input signal such as the S / N ratio. For this reason, the error concealment strength can be kept at an appropriate level one by one, and the error can be concealed while suppressing the viewing stress on the user.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example of a satellite broadcast receiving apparatus to which the present invention is applied.

FIG. 2 is a schematic diagram used for explaining an error concealment process;

FIG. 3 is a flowchart used for describing one embodiment of the present invention.

FIG. 4 is a schematic diagram used for describing an embodiment of the present invention.

FIG. 5 is a schematic diagram used for describing an embodiment of the present invention.

[Explanation of symbols]

11: Tuner unit, 13: Error detection / correction unit, 17: Demultiplexer unit, 18: Image decoding unit, 19: Voice decoding unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C059 KK01 MA00 MA23 PP01 PP05 PP06 PP07 RF09 SS02 SS30 TA01 TA09 TA76 TC01 TC12 TC21 TD12 TD13 UA05 5J064 AA00 AA05 BA13 BB03 BB04 BB07 BB08 BC01 BC02 BC07 BC25 BD02

Claims (7)

[Claims] 1. A receiving apparatus for receiving transmitted digital data, comprising: detecting means for detecting a receiving state of the digital data; and selecting a predetermined decoding error concealment processing method based on the receiving state of the digital data. A decoding unit for performing a decoding process of the digital data by the decoding error concealment processing method. 2. The receiving apparatus according to claim 1, wherein said detecting means detects said receiving state based on an S / N ratio of a received signal. 3. The receiving apparatus according to claim 1, wherein the concealment processing method includes a method of performing interpolation using an image of a spatially adjacent picture in the same picture. 4. The receiving apparatus according to claim 1, wherein the concealment processing method includes a method of performing interpolation using an image of an adjacent picture. 5. The receiving apparatus according to claim 4, wherein the concealment processing method refers to a motion vector. 6. A digital data decoding method, comprising: a step of receiving transmitted digital data; a step of detecting a reception state of the digital data; and a predetermined decoding error concealment based on the reception state of the digital data. Selecting a processing method and performing decoding processing of the digital data by the decoding error detection method. 7. The digital data decoding method according to claim 6, wherein said detecting means detects said receiving state based on an S / N ratio of a received signal.