GB2336078A - Data compression using string matching tables - Google Patents
Data compression using string matching tables Download PDFInfo
- Publication number
- GB2336078A GB2336078A GB9828065A GB9828065A GB2336078A GB 2336078 A GB2336078 A GB 2336078A GB 9828065 A GB9828065 A GB 9828065A GB 9828065 A GB9828065 A GB 9828065A GB 2336078 A GB2336078 A GB 2336078A
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- United Kingdom
- Prior art keywords
- codeword
- string
- character
- root
- string matching
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
- H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
- H03M7/3084—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction using adaptive string matching, e.g. the Lempel-Ziv method
- H03M7/3088—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction using adaptive string matching, e.g. the Lempel-Ziv method employing the use of a dictionary, e.g. LZ78
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/06—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols the encryption apparatus using shift registers or memories for block-wise or stream coding, e.g. DES systems or RC4; Hash functions; Pseudorandom sequence generators
- H04L9/065—Encryption by serially and continuously modifying data stream elements, e.g. stream cipher systems, RC4, SEAL or A5/3
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- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Theoretical Computer Science (AREA)
- Compression, Expansion, Code Conversion, And Decoders (AREA)
Abstract
A data compression system matches input strings of characters to corresponding codeword entries in a dictionary 140. The dictionary comprises root codeword tables 202, 206, 210 each having an associated sub-codeword table 204, 208, 212 respectively. Initially the root tables are generated and may cover characters "a" to "z" with each table having a single one character entry. The first character of an input stream is matched to a codeword in a root table and a new entry is placed in the linked sub-codeword table by combining this character with the next character in the stream. For example, "a" may be represented by codeword "0" in a root codeword table and strings "aa", "ab" etc have codewords "0-1", "0-2" in the linked sub-codeword table. Faster string matching is achieved with this type of arrangement. A corresponding decoding system for converting the codewords into character strings is also disclosed.
Description
2336078 METHOD FOR ENCODING AND DECODING DATA FOR COMMUNICATION MODEM The
present invention relates to a method for encoding and decoding data; and, more particularly, to a method for encoding and decoding data for a communication modem.
In general, the available frequency bandwidth of a conventional transmission channel is limited in digitally televised systems. Accordingly, in order to transmit a large amount of digital data therethrough, it is necessary to compress or reduce the volume of data through the use of various data compression techniques.
Although many different data compression techniques are known in the art, one of the most useful is the so-called dictionary-based universal compression techniques. Among these, the most well known technique is a standard coding algorithm, e.g., CCITT (International Telegragh and Telephone Consultative Committee) Recommendation V. 42bis, prescribed by CCITT, wherein the standard coding algorithm has been developed as a practical technique for compressing data based on the Ziv-Lempel coding algorithm.
In the CCITT V.42bis, an encoding and a decoding apparatus are provided, each having a fixed, finite amount of memory. This memory, also referred to as a "dictionary", contains a f inite number of entries of characters. Each entry has a unique codeword associated therewith. For example, an input stream of characters, e.g., I'aabacablI, is fed on a character-by-character basis.
According to a conventional data compression method, a plurality of entries within the dictionary are initialized with a predetermined condition, e.g., basic alphabets via" to liZIF' at the beginning. Thereafter, a string matching procedure is performed to the input stream of characters; and then, a longest matched string of characters that matches with one of the plurality of entries within the dictionary is searched. Specifically, a string, i.e., a sequence of characters, is formed from a first character of the input stream of characters. For the first character.a., of the input stream, a longest matched string is matched to an entry of the dictionary. And then, the first character "a" is encoded to a codeword corresponding to the longest matched string found in the string matching procedure.
Next, a second character "all of the input stream is encoded to the same codeword corresponding to the first character "a" through the string matching procedure described since the second character "all is identical to the character 'tall. After encoding the second character,a", a new string Ilaall is generated based on the previously encoded first character "all and the currently encoded second character ['all.
2 And then, the string matching procedure is performed to the new string llaall with reference to the entries of the dictionary. Since the new string llaall is not initially registered to the entries of the dictionary at the beginning, the entries of the dictionary are updated with the new string llaall. The new string llaall is located in a subsequent entry assigned to a new codeword from the entries of the dictionary initialized at the beginning.
is Thereafter, a third character llbll of the input stream is encoded to its corresponding codeword through the string matching procedure described above; and transmitted to the transmitter. After encoding the third character 11b11, according to the conventional data compression method, a new string lab,, is generated based on the previously encoded second character "all and the currently encoded third character "b". Next, the string matching procedure is performed to the new string 'lab" with reference to the entries of the dictionary including the entry corresponding to the newly updated string llaall. Since the new string 'lab" does not exist in the entries of the dictionary, the entries of the dictionary are updated with the new string 'lab". The new string lab" will be located to a subsequent entry assigned to a new codeword from the entries of the dictionary.
In other words, according to the conventional data compression method, the new string generated by the string matching procedure will be stored sequentially in the order 3 - which matches with is of generation. In order to encode the input stream of characters on a character-by-charact-er basis, in the conventional data compression method, the entries of the dictionary are sequentially searched to find a matched entry a character of the input stream. Therefore, in the conventional data compression method, lots of time will be consumed in searching the matched entry containing a string corresponding to the character of the input stream to be compressed.
It is, therefore, a primary object of the present invention to provide a method for encoding and decoding data for a communication modem.
In accordance with one aspect of the present invention, there is provided a method for encoding a sequence of data characters by using a string matching procedure, comprising the steps of:
(a) setting a plurality of root codeword tables in a dictionary with a predetermined string; (b) performing the string matching procedure in order to find one character in the sequence that matches with one of the plurality of codeword tables; (c) determining a masking section for encoding said one character in the sequence based on the string matching result to thereby encode said one character of the sequence with its 1 is matching codeword based on the masking section; (d) generating a new string based on the presently encoded data and previously encoded data; (e) updating the dictionary with the new string in a sub s codeword table thereof; and (f) repeating the steps (b) to (e) for the rest of the sequence.
In accordance with another aspect of the present invention. there is provided a method for decoding codewords by using a string matching procedure, comprising the steps of:
(a) setting a plurality of root codeword tables in a dictionary with a predetermined string; (b) performing the string matching procedure in order to find one of the codewords that matches with one of the plurality of root codeword tables; (c) determining a masking section for decoding one of the codewords based on the string matching result; (d) decoding the codewords based on the dictionary; (e) generating a new string based on the presently decoded data and previously decoded data; (f) updating the dictionary with the new string in a subcodeword table thereof; and (9) repeating the steps (b) to (f) for the rest of the codewords.
In accordance with still another aspect of the present invention, there is provided an apparatus for compressing a - 5 sequence of data characters by using a string matching procedure, comprising: a dictionary block for storing a plurality of entries of characters, each entry is identified by a unique codeword; a string matching block for performing the string matching procedure to find one character of the sequence that matches with one of the plurality of entries of characters; and an encoder for encoding the one character with its corresponding codeword based on the string matching result.
The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:
Fig. 1 shows a schematic block diagram of a data compression system employing a compression method in accordance with the present invention.
Fig. 2 represents a block diagram of a dictionary structure.
Fig. 3 illustrates a schematic block diagram of a data decompression system employing a decompression method in accordance with the present invention.
6 is A preferred embodiment in accordance with the present invention will be described with reference to Figs. 1 to 3. Referring to Fig. 1, there is shown a schematic block diagram of a data compression system employing a compression method in accordance with the present invention. As shown in Fig. 1, the encoding system comprises a memory 110, a string matching block 120, a first and a second switches 130 and 150, a dictionary block 140 and an encoding block 160.
The memory 110 stores an input stream of data characters. It is assumed that the input stream of data characters is "aabacab". The input data stored in the memory 110 is transmitted via a line L11 to the string matching block 120 and the encoding block 160. Thereafter, the string matching block 120 performs a string matching procedure on a characterbycharacter basis by matching each character of the input stream, i.e., "aabacab", with a plurality of entries in the dictionary block 140, wherein each entry is stored in the dictionary block 140 as an initialized string assigned to its corresponding codeword at the beginning.
when a first character "all of the input stream is fed from the memory 110 via the line L11, the string matching block 120 performs a string matching procedure by matching the first character "all of the input stream with the plurality of entries of the dictionary block 140 through the switch 130 connected thereto via a line L17. In response to a control signal generated in the string matching block 120, the switch 7 connects one of the plurality of entries of the dictionary block 140. In the string matching procedure, the string matching block 120 determines which one of entries contains a string corresponding to the first character "all.
Referring to Fig. 2, there is exemplified a block diagram of a structure of the dictionary block 140. As illustrated in Fig. 2, the dictionary block 140 includes initialized codeword tables 202, 206 and 210 and subcodeword tables 204, 208 and 212. The sub-codeword tables 204, 208 and 212 are annexed to the initialized codeword tables 202, 206 and 210, respectively.
Since a string corresponding to the first character "all assigned to an entry with a codeword 1,011 in the initialized codeword table 202, the string matching block 120 generates a selection signal on a line L14 in order to select the string to transmit same to the second switch 150. In response to the selection signal, the second switch 150 receives the codeword llOll corresponding to the string "a" matched to the first character "all through a line L15 to transmit same to the encoding block 160 via a line L16.
Thereafter, the encoding block 160, responsive to a masking signal on a line L13, encodes the first character ['all of the input data fed from the memory 110 via the line L11 with the codeword 11011 based on the codeword "0" fed thereto from the second switch 150 through the line L16; and transmits same to the transmitter for transmission thereof. The masking 8 signal is generated in the string matching block 120 in order to determine an encoding section to the input stream after the string matching procedure is completed.
For a second character "all of the input data, the string matching block 120 performs the same string matching procedure as performed to the first character "a" of the input data. After completing the string matching procedure, the encoding block 160 encodes the second character "a" in a manner similar to the way employed in encoding the first character "all of the input stream.
Thereafter, the string matching block 120 generates a new string llaall combining the first and the second characters 11all and "all, both encoded to the corresponding codeword. And, the string matching block 120 determines whether or not the new string llaall is matched to one of the strings in the dictionary block 140. Since the dictionary block 140 has the iniLialized strings such as, e.g., the basic alphabets "all to 11z11 at first, in accordance with the invention, the new string llaall is updated as, e.g., a string llaall with a codeword 110-1" in the subcodeword table 204 annexed to the initialized codeword table 202.
When a third character 11b11 of the input data is fed from the memory 110 via the line L11, the string matching block 120 performs the string matching procedure on the third character 11b11 by matching it with the updated codeword tables in the dictionary block 140. In the string matching procedure, the 9 string matching block 120 determines which one of codeword tables has a string corresponding to the third character libil.
Since the string corresponding to the third character 11b11 is assigned to the initialized codeword table 206, the string matching block 120 generates a control signal on the line L14 to transmit same to the second switch 150. In response to the control signal fed from the string matching block 120, the second switch 150 receives a codeword corresponding to the string 11b11 matched to the third character 11b11 through the line L15 to transmit same to the encoding block 160 via the line L16.
Thereafter, the encoding block 160, responsive to the masking signal on the line L13, encodes the third character 11b11 of the input data fed from the memory 110 via the line L11 based on the codeword 11111 fed thereto from the second switch 150 through the line L16; and transmits same to the transmitter for transmission thereof.
After encoding the third character 11b11 of the input data, the string matching block 120 generates a new string "ab" combining the second and the third characters "all and "b", both encoded to the corresponding codeword. And, the string matching block 120 determines whether or not the new string I'abIl is matched to one of the strings in the dictionary block 140. Since the dictionary block 140 has the initialized strings and the updated strings llaall only at present time, according to the present invention, the new string lab,, is - 10 updated as, e.g., a string 'lab" with a codeword 110-211 in the sub- codeword table 204 annexed to the initialized codeword table 202.
As described above, in accordance with the present invention, the updated strings are registered to the codeword tables of the dictionary block 140 in the order of the basic alphabet. In other words, when a new string "ball is updated, it is registered to the sub-codeword table 208 annexed to the initialized codeword table 206 having a string 11b11 corresponding to the basic alphabet I'b11. Therefore, the string matching procedure in accordance with the present invention is much faster than the conventional string matching procedure.
Now, with reference to Fig. 3, a data decompression method in accordance with the present invention will be described.
Referring to Fig. 3, there is illustrated a schematic block diagram of a decoding system employing a decoding method in accordance with the present invention. As shown in Fig. 3, the decoding system comprises a memory 310, a decoding block 320, a dictionary block 330, a switch 340 and the string matching block 350. The structure of the dictionary block 330 is identical to that of the dictionary block 140 shown in Fig. 1. The dictionary blocks 140 and 330 at the encoding and the decoding system may be initialized at the beginning to contain identical codewords.
11 is The memory 310 stores sequentially transmitted codewords fed from a transmitter (not shown) to transmit same to the decoding block 320. It is assumed that the transmitted codewords fed from the memory 310 are 110,0, 1,2,0-2,0-2,011 representing the input data "aabcababall at the encoding system.
The decoding block 320 matches a first codeword 11011 of the transmitted codewords to one of the strings of the dictionary block 330 via a line L31. At the beginning of the decoding procedure, since the dictionary block 330 is initialized in a same way as the encoding procedure, the decoding block 320 decodes the first codeword "0" of the transmitted codewords to a character "a". Thereafter, the character "all is transmitted to the string matching block 350 as a decoded data. The string matching block 350 performs a string matching procedure to the decoded data "all. Because a string "all corresponding to the decoded data "all is set in the initialized codeword table 202 as shown in Fig. 2, the dictionary block 330 is not updated with the string "a".
For a second codeword "0" of the transmitted codewords, the decoding block 320 matches it to one of the strings of the dictionary block 330. Since the second codewcrd I'01' is identical to the first codeword "0", the decoding block 320 performs the same decoding procedure as performed on the first codeword 11011 to thereby generate a character "all corresponding to the second codeword 1101' with reference to the dictionary - 12 block 330.
Thereafter, the string matching block 350 generates a new string Ilaall based on the previous decoded data "all and the present decoded data via". The string matching block 350 performs the string matching procedure on the new string Ilaall to determine whether or not a matched string is registered to the dictionary block 330.
Since the dictionary block 330 has the initialized codeword tables, the new string Ilaall does not exist therein.
the string matching block 350 updates the block 330 with the new string Ilaall in a similar manner as done in the encoding system.
While the present invention has been described with respect to certain preferred embodiments only, other modifications and variations may be made without departing from the scope of the present invention as set forth in the following claims.
Therefore, dictionarv - 13
Claims (17)
1. A method for encoding a sequence of data characters by using a string matching procedure, comprising the steps of:
(a) setting a plurality of root codeword tables in a dictionary with a predetermined string; (b) performing the string matching procedure in order to find one character in the sequence that matches with one of the plurality of codeword tables; (c) determining a masking section for encoding said one character in the sequence based on the string matching result to thereby encode said one character of the sequence with its matching codeword based on the masking section; (d) generating a new string based on the presently encoded data and previously encoded data; (e) updating the dictionary with the new string in a subcodeword table thereof; and (f) repeating the steps (b) to (e) for the rest of the sequence.
2. The method of claim 1, wherein the sub-codeword table is annexed to its corresponding root codeword table.
3. The method of claim 2, wherein the root codeword table is arranged in a predetermined condition.
14
4. The method of claim 3, wherein the sub-codeword table is rearranged in the root codeword table arrangement condition.
is
5. A method for decoding codewords by using a string matching procedure, comprising the steps of:
(a) setting a plurality of root codeword tables in a dictionary with a predetermined string; (b) performing the string matching procedure in order to find one of the codewords that matches with one of the plurality of root codeword tables; (c) determining a masking section for decoding one of the based on the string matching result; decoding the codewords based on the dictionary; (e) generating a new string based on the presently decoded data and previously decoded data; (f) updating the dictionary with the new string in a subcodeword table thereof; and (g) repeating the steps (b) to (f) for the rest of the codewords.
codewords (d)
6. The method of claim 5, wherein the sub-codeword table is annexed to its corresponding root codeword table.
7. The method of claim 6, wherein the root codeword table is arranged in a predetermined condition.
is
8. The method of claim 7, wherein the sub-codeword table is rearranged in the root codeword table arrangement condition.
9. An apparatus for compressing a sequence of data characters by using a string matching procedure, comprising: means for storing a plurality of entries of characters, each entry is identified by a unique codeword; means for performing the string matching procedure to find one character of the sequence that matches with one of the plurality of entries of characters; and means for encoding the one character with its corresponding codeword based on the string matching result.
10. The apparatus of claim 9, wherein the string matching is means includes an updating means for updating a new string generated based on a previously encoded character and a currently encoded character.
11. The apparatus of claim 10, wherein the storing means includes root codeword tables and sub-codeword tables.
12. The apparatus of claim 11, wherein the root codeword table is initialized with a predetermined entry at the beginning.
13. The apparatus of claim 12, wherein the sub-codeword table 16 is annexed to its corresponding root codeword table.
14. The apparatus of claim 13, wherein the root codeword table is arranged in a predetermined condition.
15. The apparatus of claim 14, wherein the sub-codeword table is rearranged in the root codeword table arrangement condition.
16. A method for encoding and decoding a sequence of data characters substantially as herein described with respect to or as shown in Figures 1 to 3 of accompanying drawings.
17. An apparatus for encoding a sequence of data characters constructed and arranged substantially as herein described with respect to or as shown in Figures 1 and 2 of accompanying drawings.
17
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1019980011178A KR19990076303A (en) | 1998-03-31 | 1998-03-31 | Data encoding and decoding method for modem |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9828065D0 GB9828065D0 (en) | 1999-02-17 |
| GB2336078A true GB2336078A (en) | 1999-10-06 |
Family
ID=19535616
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9828065A Withdrawn GB2336078A (en) | 1998-03-31 | 1998-12-18 | Data compression using string matching tables |
Country Status (2)
| Country | Link |
|---|---|
| KR (1) | KR19990076303A (en) |
| GB (1) | GB2336078A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7706348B2 (en) | 1999-07-06 | 2010-04-27 | Samsung Electronics Co., Ltd. | Apparatus and method for encoding/decoding transport format combination indicator in CDMA mobile communication system |
| WO2011085666A1 (en) * | 2010-01-13 | 2011-07-21 | Huawei Technologies Co., Ltd. | System and method for securing wireless transmissions |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5151697A (en) * | 1990-10-15 | 1992-09-29 | Board Of Regents Of The University Of Washington | Data structure management tagging system |
| WO1993017378A2 (en) * | 1992-02-21 | 1993-09-02 | Salient Software, Inc. | Method and apparatus for locating longest prior target string matching current string in buffer |
| US5262776A (en) * | 1989-06-30 | 1993-11-16 | Siemens Aktiengesellschaft | Process for use with lempel/gin encoding |
| WO1994009567A1 (en) * | 1992-10-08 | 1994-04-28 | Salient Software, Inc. | String search using the longest and closest match in a history buffer |
| EP0688104A2 (en) * | 1990-08-13 | 1995-12-20 | Fujitsu Limited | Data compression method and apparatus |
| EP0687995A2 (en) * | 1994-06-16 | 1995-12-20 | Seiko Epson Corporation | Data compressing method |
| US5534861A (en) * | 1993-04-16 | 1996-07-09 | International Business Machines Corporation | Method and system for adaptively building a static Ziv-Lempel dictionary for database compression |
-
1998
- 1998-03-31 KR KR1019980011178A patent/KR19990076303A/en not_active Application Discontinuation
- 1998-12-18 GB GB9828065A patent/GB2336078A/en not_active Withdrawn
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5262776A (en) * | 1989-06-30 | 1993-11-16 | Siemens Aktiengesellschaft | Process for use with lempel/gin encoding |
| EP0688104A2 (en) * | 1990-08-13 | 1995-12-20 | Fujitsu Limited | Data compression method and apparatus |
| US5151697A (en) * | 1990-10-15 | 1992-09-29 | Board Of Regents Of The University Of Washington | Data structure management tagging system |
| WO1993017378A2 (en) * | 1992-02-21 | 1993-09-02 | Salient Software, Inc. | Method and apparatus for locating longest prior target string matching current string in buffer |
| WO1994009567A1 (en) * | 1992-10-08 | 1994-04-28 | Salient Software, Inc. | String search using the longest and closest match in a history buffer |
| US5534861A (en) * | 1993-04-16 | 1996-07-09 | International Business Machines Corporation | Method and system for adaptively building a static Ziv-Lempel dictionary for database compression |
| EP0687995A2 (en) * | 1994-06-16 | 1995-12-20 | Seiko Epson Corporation | Data compressing method |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7706348B2 (en) | 1999-07-06 | 2010-04-27 | Samsung Electronics Co., Ltd. | Apparatus and method for encoding/decoding transport format combination indicator in CDMA mobile communication system |
| WO2011085666A1 (en) * | 2010-01-13 | 2011-07-21 | Huawei Technologies Co., Ltd. | System and method for securing wireless transmissions |
| US8468343B2 (en) | 2010-01-13 | 2013-06-18 | Futurewei Technologies, Inc. | System and method for securing wireless transmissions |
| RU2542578C2 (en) * | 2010-01-13 | 2015-02-20 | Хуавэй Текнолоджиз Ко., Лтд. | Wireless transmission security system and method |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9828065D0 (en) | 1999-02-17 |
| KR19990076303A (en) | 1999-10-15 |
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