JP3593244B2 - Data compression device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a data compression apparatus for compressing continuous data, and more particularly to a data compression apparatus for a system for compressing and expanding character string data in real time for data communication and the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in the field of data communication, a data circuit-terminating equipment (DCE) based on a V series recommendation from the International Telegraph and Telephone Consultative Committee, abbreviated as CCITT, has been used as a modem. FIG. 1 shows a schematic configuration of a data line termination device 1 having a data compression function and an error correction control function based on 42bis. The data line terminal device 1 is provided between a data terminal device 2 such as a workstation or a personal computer and a public telephone network 3. The connection with the data termination device 2, abbreviated as DTE, is made via an interconnection circuit 4. The signal conversion between the public telephone network 3 and the public telephone network 3 is performed by the signal converter 5. Error correction and data compression are performed by an error correction unit 7 and a data compression unit 8 controlled by the control unit 6, respectively.
[0003]
The data compression section 8 has a dictionary 9 and performs compression by encoding a character string and decompression by decoding encoded data.
[0004]
FIG. 6 shows the data structure of the dictionary 9. The dictionary 9 is represented by a tree structure 10. This tree structure 10 has a plurality of nodes, and root nodes 11a, 11b, 11c, 11d,... Corresponding to alphabets A, B, C, D,. Represents a character string. FIG. 6 shows “A”, “B”, “BA”, “BAG”, “BAR”, “BAT”, “BI”, “BIN”, “C”, “D”, “DE”, “DO”. "And" DOG "are shown. The nodes 12ba, 12bi, and 12do are located in the middle of the tree structure 10, and the leaf nodes 12de, 13bag, 13bar, 13bat, 13bin, and 13dog that indicate the last character of the character string are at lower levels than the intermediate nodes 12ba, 12bi, and 12do. In the hierarchy. Each node is assigned a codeword for identifying the node. The contents of the dictionary 9 of the tree structure 10 are matched with the code word assignment in the dictionary 9 of the other party that performs data communication via the public telephone network 3.
[0005]
As shown in FIG. 6B, generally, for a node 14 in the middle of the tree structure 10, one parent 15 and one or more children 16 exist. There is no parent for the root nodes 11a to 11d shown in FIG. The root nodes 11a and 11c have no children and are independent nodes. Therefore, at each node 14 on the tree structure 10 shown in FIG. 6B, the code word corresponding to the self, the character corresponding to the self, the code word of the parent 15, and the information indicating the presence or absence of the child 16 are stored. Must have.
[0006]
FIG. A procedure for performing a character string search and compressing according to 42bis will be described. The procedure starts from step a0. In step a1, information on the root node corresponding to the first character of the character string is obtained. In step a2, it is determined whether a child node exists for the target node. If it is determined that a child is present, the information of the next codeword is obtained from this node in the tree structure 10. At step a4, it is determined whether or not the characters of the acquired information of the next codeword match. If the characters match, the process returns to step a2, and it is further determined whether or not there is a child. If the characters do not match in step a4, it is determined in step a5 whether or not the node around the child node has made one round of the dictionary. When it is determined that one round has not been made, the process returns to step a3 to acquire the information of the code word of the next child. In step a5, when it is determined that there is no child code word that matches the character after making a round of the dictionary, a process of adding a non-matching character to the dictionary is performed in step a6. If it is determined in step a2 that there are no children, characters are added to the dictionary in step a8. When the addition to the dictionary in step a6 or step a7 is completed, a code word in a range where the character strings match is output in step a8, and the procedure ends in step a9.
[0007]
A typical prior art for compressing a signal stream for data communication according to the procedure of FIG. 7 is disclosed in, for example, Japanese Patent Publication No. 5-68893. The concept of performing data compression using a dictionary is described in JP-A-60-241157, JP-A-61-232724, JP-A-1-102613, JP-A-2-144661, JP-A-3-038772, JP-A-4-116690, It is also disclosed in JP-A-4-123719, JP-A-4-217021, JP-A-4-223556, JP-A-4-340156 and JP-A-7-23238.
[0008]
[Problems to be solved by the invention]
In a conventional dictionary having a tree structure 10 as shown in FIG. 6, the tree structure 10 is expressed by a link to a parent node of each node. You need to check from end to end, which is time consuming. Therefore, when real-time processing is performed, a high-speed arithmetic device or the like is required.
[0009]
The purpose of the present invention is to provide CCITT recommendation An object of the present invention is to provide a data compression device having a dictionary structure that does not require a high-speed arithmetic device or the like for compression / expansion processing of 42 bis or the like and can suppress an increase in storage capacity due to a change in the dictionary structure as much as possible.
[0010]
[Means for Solving the Problems]
The present invention has a tree structure according to a preset standard for compressing and decompressing an input data sequence, in which heading data is represented according to a path from a node at the highest level to each node, and A dictionary having link information for the upper-level node and information on the presence / absence of the lower-level node, encoding a subsequence of the input data that matches the heading data, and converting the input data that does not match the heading data into the dictionary. In a data compression device that repeats addition,
Each node in the dictionary has the first node at the next level after your level and the link information to the next node at the same level as yourself.
Dictionary search means for searching the dictionary using the added link information;
A data compression apparatus comprising: link addition means for adding link information to nodes at a plurality of levels within a predetermined range when input data is added to a dictionary.
[0011]
According to the present invention, heading data is represented according to a path from the highest level node of the tree-structured dictionary to each node, and an input data sequence is encoded in a range matching the heading data, and data compression is performed. Is performed. For each node in the dictionary, the link information to the first node at the level next to your level and the link to the next node at the same level as you are added, and the dictionary search means also uses the added link information Then, the dictionary is searched, so that it is possible to reduce the search time when determining whether or not the data string matches the index data stored in the dictionary. The link adding means adds the link information to the nodes at a plurality of levels within a predetermined range when adding the input data to the dictionary. Therefore, even when searching for the index data including the added data, the link information is added. Can be used to perform a quick search. Since the retrieval speed of the dictionary is increased, the compression / decompression processing can be accelerated without requiring a high-speed operation device or the like. Since the link information added to the tree-structured dictionary can be reduced, an increase in the storage capacity of the dictionary can be suppressed.
[0012]
In the present invention, the data string is a character string for data communication,
According to the present invention, the apparatus further comprises processing means for encoding a character string using the dictionary according to the preset standard, transmitting the encoded character string to a communication path, and decoding a signal received from the communication path using the dictionary.
[0013]
According to the present invention, at the time of data communication, a dictionary search for compressing / expanding a character string is performed at high speed, and the compression / expansion processing using the dictionary can be sufficiently supported even at a high communication speed. .
[0014]
Further, the link information added in the present invention is:
Link information from the parent high-level node in the tree structure to the first-lower-level child eldest node added first,
It is characterized in that the order of addition is continuous between nodes of the same level sharing the same node as a parent, and is link information from the node of the preceding brother to the node of the subsequent brother.
[0015]
According to the present invention, the link information from the parent to the eldest son and the link information from the brother to the younger brother are added between the siblings. Search can be performed, and the time required for compression or decompression can be reduced.
[0016]
In the present invention, the previously set standard is defined in Recommendation V.4 of the International Telegraph and Telephone Consultative Committee. 42 bis.
[0017]
According to the present invention, the recommendation V.1 of the International Telegraph and Telephone Consultative Committee. Data compression based on 42bis can be speeded up by shortening the dictionary search time.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a schematic electrical configuration of a data line termination device 21 according to an embodiment of the present invention. The data line terminating device 21 is provided as a DCE between the data terminating device 22 which is a DTE and the public telephone network 23. The data terminating device 22 is a personal computer or various types of information terminals called PED. The public telephone network 23 is a public telephone line, a wireless public telephone network such as ISDN or PHS.
[0019]
The data line terminating device 21 includes an interconnecting circuit 24 with the data terminating device 22, a signal converting unit 25 with the public telephone network 23, a control unit 26 for internal control, and an error correcting unit for error correction. 27, and a data compression unit 28 for compressing and expanding data. The data compression unit 28 includes a tree-structured dictionary 29, a dictionary search unit 30, and a link addition unit 31.
[0020]
FIG. 2 shows a basic tree structure 40 of the dictionary 29 of FIG. FIG. 2A shows an expression example of the tree structure 40, and FIG. 2B shows the contents of codeword information stored corresponding to each node. Assuming that a node in the middle of the tree structure 40 is the self 41, there is a node serving as a parent 42 at an upper level of the tree structure 40. From the user 41 to the parent 42, a link 43 to the parent can be traced. A plurality of children including the self 41 and the younger brother 44 can branch from the same parent 42. The plurality of children with respect to the parent 42 have sibling relationships according to the order in which they are added to the dictionary. When the user 41 is not a leaf node, there is one or more child nodes. The first node added is the eldest son 46, and there may be children 48 following the second son. When there is a child 48 after the second son, the eldest son 46 is provided with a link to the younger brother. 46 and children 48 can be shown in sequence.
[0021]
FIG. 2B shows an example of the content of the codeword information stored at each node. In the case of the code word information about the user 41 shown in FIG. 2A, the first 12 bits are the code word 41a corresponding to the user 41, the next 8 bits are the character 41b corresponding to the user 41, and the next 12 bits. The bit is the code word 42a of the parent 42, and the next one bit becomes a flag 41c indicating whether or not there is a child such as the eldest son 46 or the child 48. The code word 41a, the character 41b, the parent code word 42a, and the flag 41c indicating whether or not there is a child are conventionally used in the V.264. It is stored in the dictionary for 42bis. In the dictionary corresponding to the tree structure 40 of the present embodiment, the next 12-bit eldest son code word 46a indicated by shading, a flag 41d indicating whether or not there is a 1-bit younger brother, and a 12-bit younger brother code Add the word 44a. As a result, the code word information, which was 33 bits in the past, is added to 25 bits, and is increased to 58 bits. However, the increase in the storage capacity in the dictionary 29 has not yet doubled.
[0022]
FIG. 3 shows a tree structure 50 of the dictionary 29 corresponding to a character string similar to FIG. FIG. 3A shows an example of expression using the tree structure 50, and FIG. 3B shows an example of the content of codeword information stored at each node. In FIG. 3B, the portion of the additional information according to the present invention is shown with shading.
[0023]
In the tree structure 50 shown in FIG. 3A, root nodes 51a, 51b, 51c, and 51d correspond to alphabetical letters A, B, C, and D, and intermediate nodes 52ba, 52bi, 52do to leaf nodes 52de, 53bag, and 52do. For 53 bar, 53 bat, 53 bin, and 53 dog, a link 45 to the younger brother and a link 47 to the eldest son are added in addition to the conventional link 43 to the parent.
[0024]
FIG. 4 shows a procedure for performing data compression by performing a character string search in a dictionary having a tree structure 50 as shown in FIG. The procedure is started from step b0, and information on the root nodes 51a to 51d corresponding to the first character of the character string is obtained in step b1. In step b2, the presence or absence of a child is determined according to the flag 41c in FIG. When it is determined that there is a child, the information of the eldest son is acquired using the codeword 46a of the eldest son as the link 47 to the eldest son. In step b4, it is determined whether or not the character 41b of the eldest node matches the character to be searched in the input character string. When it is determined that they do not match, in step b5, the flag 41d is referred to as to whether or not there is a node to be a younger brother with respect to the eldest node. If there is a younger brother, information of the next younger brother is obtained in step b6. If it is determined in step b5 that there is no younger brother, a process of adding a character that does not match to the dictionary is performed in step b7. When it is determined in step b5 that there are no children, the last character is added to the dictionary in step b8. At the time of this addition, the link adding means 31 assigns a character to the new node, and adds a flag 41d indicating whether or not there is a younger brother to the codeword information of the node corresponding to the older brother node immediately before the new node. Is changed to the code word 48a.
[0025]
In the dictionary addition in step b8, a node which is the eldest son is newly added, the code word 46a of the eldest son is set, and the flag 41c as to whether or not there is a child is changed. When step b7 or step b8 ends, a code word is output in step b9 corresponding to a character string in a range that matches the dictionary, and the procedure ends in step b10.
[0026]
Hereinafter, a state in which a character string “BIN” is searched for in the procedure of FIG. 4 will be specifically described. In step b1, information of "B" is obtained from the root node 51b of FIG. Recommendation V. CCITT. Since 42bis indicates that the root node “B” is the code word “045”, the information of the code word “045” is obtained from FIG. 3B. In step b2 of FIG. 4, it is confirmed whether or not a child exists at the root node "045". In FIG. 3B, since the flag indicating whether or not there is a child corresponding to the code word “045” is indicated by a circle, it is confirmed that there is a child. In step b3, it is determined whether or not “codeword 2” as the codeword corresponding to the eldest son matches “I” which is the second character of the search character. In this case, since the character of the eldest son is "A", it is confirmed that the character does not match the second character "I" of the search character. In step b5, a flag indicating whether or not there is a younger brother is checked. In FIG. 3 (b), the circle mark indicates that there is a younger brother. In step b6, the information of "codeword 8" is obtained from the information of the younger brother of "codeword 2". Next, returning to step b4, it is confirmed that "code word 8" matches the second character "I" of the search character. Further, returning to step b2, it is confirmed whether or not "codeword 8" has a child. In FIG. 3B, since it is indicated by a circle, it is confirmed that a child is present. In step b3, information on the eldest son of “codeword 8” is obtained as “codeword 6”. In step b4, it is confirmed that "code word 6" matches the third character "N" of the search character, and the search for the character string "BIN" is completed. Therefore, the code word of the character string “BIN” is “code word 6”.
[0027]
【The invention's effect】
As described above, according to the present invention, it is possible to increase the search speed by adding the link information to the dictionary for compressing and expanding the data string, and it is not necessary to increase the speed of the arithmetic unit or the like, thereby increasing the power consumption. Can be suppressed. Therefore, the burden on the power source of the portable information terminal device or the like can be reduced, and the size and weight can be reduced.
[0028]
Further, according to the present invention, it is possible to easily perform data communication at a high transmission rate with compression and decompression of a character string using a dictionary.
[0029]
According to the present invention, the link information from the parent to the eldest son and the link information from the brother to the younger brother are added to speed up the search of the dictionary, thereby suppressing an increase in the storage capacity of the dictionary. It is possible to prevent an obstacle to miniaturization when incorporated in a portable information terminal device or the like.
[0030]
According to the invention, the International Telegraph and Telephone Advisory Committee recommendation V. It is possible to quickly search a dictionary during data communication according to 42bis.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic electrical configuration of an embodiment of the present invention.
FIG. 2 is a diagram and a chart showing a basic tree structure 10 of the dictionary 29 of FIG. 1;
FIG. 3 is a diagram and a table of a tree structure 50 showing a state in which a specific character string is associated with the tree structure 40 of FIG. 2;
FIG. 4 is a flowchart showing a procedure for performing a data compression process by searching the dictionary 29 of FIG. 1;
FIG. 5 is a block diagram showing a schematic electrical configuration of a conventional data compression device.
6 is a diagram showing a tree structure of the dictionary 9 shown in FIG.
FIG. 7 is a flowchart showing a procedure for searching the dictionary 9 of FIG. 5 and performing data compression.
[Explanation of symbols]
21 data line terminator 22 data terminator 23 public telephone network 26 control unit 28 data compression unit 29 dictionary 30 dictionary search means 31 link addition means 40, 50 tree structure 41 own 42 parent 43 link to parent 44 brother 45 brother Link 46 eldest son 47 link to eldest son 48 children 51a, 51b, 51c, 51d root nodes 52ba, 52bi, 52do nodes 52de, 53bag, 53bar, 53bat, 53bin, 53dog leaf nodes

Claims (4)

For compression and decompression of the input data string, it has a tree structure according to a preset standard, heading data is expressed according to the path from the highest level node to each node, and the upper level A dictionary having link information for nodes and presence / absence information of lower-level nodes is searched, and encoding of a substring of input data that matches heading data and addition of input data that does not match heading data to the dictionary are repeated. In a data compression device,
Each node in the dictionary has the first node at the next level after your level and the link information to the next node at the same level as yourself.
Dictionary search means for searching the dictionary using the added link information;
A data adding device for adding link information to nodes at a plurality of levels within a predetermined range when adding input data to the dictionary. The data string is a character string for data communication,
In accordance with the preset standard, the apparatus further comprises processing means for encoding a character string using the dictionary, transmitting the encoded character string to a communication path, and decoding a signal received from the communication path using the dictionary. Item 2. The data compression device according to Item 1. The added link information is:
Link information from the parent high-level node in the tree structure to the first-lower-level child eldest node added first,
The node added at the same level sharing the same node as a parent, the order of addition is continuous, and it is link information from the node of the preceding brother to the node of the subsequent brother. 2. The data compression device according to 2. The previously set standard is described in Recommendation V.4 of the International Telegraph and Telephone Consultative Committee. 4. The data compression device according to claim 1, wherein the data compression device is 42 bis.

Images