JPH0286232A - Variable length coding system - Google Patents

Abstract

PURPOSE:To decrease the deterioration in the quality against an error of a communication line by inserting a fixed length code between variable length codes at a prescribed period. CONSTITUTION:An input signal 1 is distributed into information subject to fixed length coding by a multiplexer 2 and information subject to variable length coding and they are respectively subject to fixed length coding by a fixed length coder 4 and subject to variable length coding by a variable length coder 7 and retarded by an FIFO 9. Signals 5, 10 subject to fixed length coding and variable length coding are outputted by a selector 11 while being switched for each prescribed period. That is, the signal 10 of variable length coding is adjusted by the FIFO 9 so that the code of fixed length coding is inserted at a prescribed period. The variable length code formed by the variable length coder 7 is separated into the fixed length coding part and the variable length coding part periodically at the decoder side. Thus, even if any error takes place in the communication line, most of the fixed length coding part is decoded correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to variable length coding used for information compression in transmission and storage.

2. Description of the Related Art In conventional variable length encoding systems, fixed length encoding sections and variable length encoding sections are encoded in sequence and transmitted as they are. FIG. 5 shows the format of this conventional variable length encoding. The n-th coding unit is composed of a block consisting of a continuous n-th fixed-length coding section and an n-th variable-length coding section, and the same applies to the (n+1)-th coding unit and the (n+2)-th coding unit.

In conventional variable length coding configured as above,
Each block has a different code length.

Problems to be Solved by the Invention However, the conventional variable length codes as described above have the problem that when an error occurs in the communication path, blocks become out of synchronization, making decoding continuously impossible. are doing.

In view of this, an object of the present invention is to provide a variable length encoding method that can decode a large amount of information even when there are errors in the communication path.

Means for Solving the Problems The present invention encodes an input signal using fixed-length coding and variable-length coding, and inserts fixed-length codes between variable-length codes at a constant period. It is characterized by a long coding method and fixed-length coding at the boundaries of variable-length codes, which are inserted between variable-length codes at regular intervals.
In addition, variable-length coding is constructed by performing variable-length coding for each coding unit, fixed-length coding the boundaries of each variable-length code, and inserting fixed-length codes between variable-length codes at a constant cycle. It is a fixed length encoder that encodes an input signal in a fixed length, a variable length encoder that encodes the input signal in variable length, and a FIFO that delays the output of the variable length encoder. A variable length encoding device characterized by comprising a selector that switches between the output of the fixed length encoder and the output of the FIFO at a period of , and an error position detector for detecting errors in communication of input signals; a multiplexer that divides the error position detector output into a fixed length encoder and a variable length encoder; and an FI that adjusts the timing of each of the fixed length code and variable length code output from the multiplexer.
an FO, an error corrector for correcting channel errors in the output of the FIFO, a fixed length decoder and a variable length decoder for decoding the output of the error corrector, and a selector for switching the output of each of the decoders. This is a variable length decoding device characterized by comprising:

Effects of the present invention With the above-described configuration, when an error occurs in the communication path, the variable-length encoding unit will not correctly decode blocks other than the block where the error occurred, but the fixed-length encoding unit will decode the block other than the block where the error occurred. is decoded correctly, so by fixed-length encoding important information and variable-length encoding less important information, it is possible to construct a code that is resistant to errors and has a large information compression effect. In addition, by fixed-length coding the coding position of each variable-length block, even if an error occurs on the communication path, the error will not affect the variable-length coding section outside of a specific range. Not only the long encoder but also the variable length encoder can decode areas other than the location where the error occurs.

Embodiment FIG. 1 shows the format of the variable length encoding system in the first embodiment of the present invention. In Figure 1,
The input signal is divided into coding units, and each coding unit is fixed-length coded and variable-length coded. If we call the encoded n-th coding unit the n-th fixed-length coding unit and the n-th variable-length coding unit, the n-th variable-length coding unit, the n+1-th variable-length coding unit, the n+2-th variable-length coding unit, Variable length coding battle...
An n-th fixed-length coding section, an (n+1)-th fixed-length coding section, and an (n+2)-th fixed-length coding section are inserted at regular intervals between consecutive variable-length coding sections.

The operation of the variable length encoding system of this embodiment configured as described above will be explained below. The input signal is first divided into coded units, and each coded unit is fixed length coded and variable length coded. The variable-length encoder of each encoding unit is sequentially stored in a FIFO (first-in, first-out memory) or the like, and is transmitted while periodically inserting information from the fixed-length encoder. When a transmission error occurs in the variable-length encoder in the communication path, the error propagates to several encoding units before and after, but when a transmission error occurs in the fixed-length encoder, An error occurs only within the coding unit of the fixed length encoder in which the error occurs. Therefore, by encoding important information such as the DC component of the orthogonal transform and the dynamic range in the fixed length encoder, it is possible to make the code more resistant to errors than the conventional variable length code. Also, each encoded block has a fixed length,
Suitable for packet communication and random access.

Furthermore, since variable length encoding is performed, more compression can be performed than when everything is fixed length encoded.

As described above, according to this embodiment, by periodically inserting a fixed length encoder into a variable length encoder, variable length encoding that is resistant to channel errors can be performed.

FIG. 2 shows a format of a variable length encoding system showing a second embodiment of the present invention. This figure is almost the same as FIG. 1, but the boundary information of each variable-length encoder is further encoded into fixed-length encoders and inserted into the fixed-length encoder of each block in FIG. 1.

The operation of the variable length encoding system of the second embodiment configured as described above will be described below.

The input signal is first divided into coded units, and each coded unit is fixed length coded and variable length coded. The variable length encoder of each encoding unit is sequentially stored in a FIFO or the like, and the code length of the variable length encoder is also stored as separate information. Next, the boundary information of the variable-length coding section calculated from the code length of the long code is fixed-length coded, and the two pieces of information of the fixed-length coding section of the original coding unit are stored in the FIFO.
It is transmitted while being inserted into the variable length encoder output at regular intervals. If a transmission error occurs in a variable length encoder on a communication channel, an error will occur in the variable length encoder within the encoding unit that includes the variable length encoder where the error occurred, but in other cases can be correctly decoded. In addition, if an error occurs in the fixed-length coding section, an error will occur in all coding units included in the coding block only if the boundary information of the variable-length coding section is damaged, but otherwise In this case, an error occurs only in the coding unit in which the error occurred.

As described above, according to this embodiment, the boundary information of the variable length encoder is fixed-length encoded and inserted into the variable-length encoder at regular intervals together with the fixed-length encoder of the original encoding unit. Therefore, it is possible to significantly reduce decoding errors when errors occur on the communication path.

FIG. 3 is a block diagram of a variable length encoding device showing a third embodiment of the present invention. In the figure, 1 is an input signal, 2 is a multiplexer that switches the input signal,
3 is the output of the multiplexer 2, 4 is a fixed length encoder for fixed length encoding the multiplexer output 3, 5 is the fixed length encoded output of the fixed length encoder 4, and 6 is the fixed length encoder output of the fixed length encoder 4. 7 is a variable length encoder for variable length encoding the multiplexer output 6; 8 is a variable length encoded output of the variable length encoder 7; 9 is a variable length encoder for variable length encoding the multiplexer output 6; F to delay long encoded output
IFO, 10 is a variable length encoded output which is the output of the FIFO, 11 is a selector for switching between the fixed length encoded output 5 and the variable length encoded output 10,
12 is the selector output.

The operation of the variable length encoder of the third embodiment configured as described above will be explained below. An input signal 1 is distributed by a multiplexer 2 into fixed length coded information and variable length coded information. The information to be fixed length encoded is fixed length encoded by the fixed length encoder 4. Information to be variable length encoded is variable length encoded by a variable length encoder 7 and delayed by a FIFO 9. The fixed-length coded and variable-length coded signals are switched and outputted at regular intervals by the selector 11.

That is, the variable length encoded signal is adjusted by the FIFO 9 so that the fixed length encoded signal can be inserted at a constant cycle. The variable-length code constructed by this variable-length encoder can be periodically separated from the fixed-length encoding section and the variable-length encoding section on the decoding side, so even if an error occurs in the communication path, the fixed-length encoding can still be performed. Most of the parts can be decoded correctly.

As described above, according to this embodiment, by periodically inserting a fixed length encoder into a variable length encoder, variable length encoding that is resistant to channel errors can be performed.

FIG. 4 shows a variable length decoding device showing a fourth embodiment of the present invention. In the same figure, 13 is an input signal, 14 is an error position detector that detects the position of an error occurring in the communication path, 15 is the output of the error position detector, and 16 is the output of the error position detector 15. 17 is the output of the multiplexer 16,
18 is a FIF that delays the multiplexer output 17;
0, 19 is the output of the FIFOL8, and 20
is an error corrector that corrects the channel error included in the FIFO output 19; 21 is the output of the error corrector 20; and 22 is a fixed length decoder that decodes the error correction type output 21. , 23 is the output of the fixed length decoder 22, 24 is the output of the multiplexer 16, and 25 is an FI that delays the multiplexer output 24.
FO, 26 is the output of the FIr'025,
27 is an error corrector for correcting channel errors included in the FIFO output 26; 28 is an output of the error corrector 27; and 29 is a variable length decoder for decoding the error correction type output 28. , 30 is the output of the variable length decoder, 31 is a selector for switching between the fixed length decoding two outputs 23 and the variable length decoder output 30, and 32 is the selector output.

The operation of the variable length decoder of the fourth embodiment configured as described above will be explained below. The input signal 13 is
The error position detector 14 detects the position of an error that has occurred on the communication path, and records the position as information. The error position detector output signal 15 is separated by a multiplexer 16 into a fixed-length encoding section and a variable-length encoding section, each of which is FIFO-coded.
18 and FIFO 25, blank portions caused by multiplexing fixed length encoding and variable length encoding are deleted. The output 19 of the FIFO 18 is corrected for errors by an error corrector 20 based on the error position information recorded by the error position detector 14, and is decoded by a fixed length decoder 22. Further, the output 26 of the FIFO 25 is corrected for errors by an error corrector 27 based on the error position information recorded by the error position detector 14, and is decoded by a variable length decoder 29. The fixed length decoder output 23 and the variable length decoder output 30 are switched and outputted by a selector 31. Here, since the error position detector 14 multiplexes fixed-length codes and variable-length codes, when an error occurs on the communication path, the position of the error becomes important. For example, if a high-order frequency component of the orthogonally transformed signal is incorrect, it is desirable to correct it by setting the decoded value to zero, and in the case of a DC component, it is desirable to correct the decoded value by interpolation. With the above configuration, it is possible to decode the fixed length encoder and the variable length encoder.

As described above, according to this embodiment, by periodically inserting a fixed length encoder into a variable length encoder, variable length encoding that is resistant to channel errors can be performed.

In the first and second embodiments, the fixed length encoding section is placed at the beginning of the block, but it may be placed after or in the middle of the variable length encoding section. Further, in the second embodiment, the variable length section position information is set at the last position of the fixed length encoding section, but it may be set at any position of the fixed length encoding section. Furthermore, in all embodiments, it is not necessary that all the fixed length encoders have the same length (it is sufficient that the positions of the fixed length encoders have a certain period. For example, the fixed length encoder The length is (10, 20, 10, 20, 10° cloudy...)
It may be repeated.

Effects of the Invention As described above, according to the present invention, it is possible to perform variable length encoding with little deterioration in quality due to errors in the communication path, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a format diagram of a variable length encoding system according to an embodiment of the present invention, FIG. 2 is a format diagram of a variable length encoding system according to another embodiment of the invention, and FIG. Block configuration diagram of a specific device for long encoding method, No. 4
This figure is a block diagram of a specific device for the variable length decoding method shown in FIG. 2, and FIG. 5 is a format diagram of a conventional variable length encoding method. 4. Fixed length encoder, 7. Variable length encoder, 14
・Error position detector, 20.27...Error corrector, 22.
・Fixed length decoder, 29...Variable length decoder, 9, 1
8.25...FIF○.

Claims (6)

[Claims] (1) A variable-length encoding method characterized by encoding an input signal using fixed-length encoding and variable-length encoding, and inserting fixed-length codes between variable-length codes at regular intervals. (2) Each coding unit is coded with a fixed length and a variable length, and a signal obtained by fixed-length coding the length of the variable-length coded signal adjacent to each fixed-length code is included in the fixed-length code. , a variable-length encoding system constructed by inserting fixed-length codes between variable-length codes at a constant cycle. (3) The variable-length encoding system according to claim 1 or 2, wherein the DC component of the orthogonally transformed data is fixed-length encoded, and the other components are variable-length encoded. (4) The variable length encoding method according to claim 1 or 2, wherein fixed length encoding is performed when each encoding unit can be independently decoded, and variable length encoding is performed in other cases. (5) a fixed length encoder for fixed length encoding an input signal;
A variable length encoder that variable length encodes the input signal, a FIFO that delays the output of the variable length encoder, and a selector that switches between the output of the fixed length encoder and the output of the FIFO at a constant cycle. A variable length encoding device characterized by: (6) an error position detector that detects errors in communication of input signals; a multiplexer that divides the output of the error position detector into a fixed-length encoder and a variable-length encoder; and a fixed-length code and a variable-length encoder output from the multiplexer. a FIFO that adjusts the timing of each long code; an error corrector that corrects channel errors in the output of the FIFO; a fixed length decoder and a variable length decoder that decode the output of the error corrector; A variable length decoding device comprising a selector for switching outputs of each of the decoders.