CA2315952A1 - A turbo tcm scheme with low complexity - Google Patents
A turbo tcm scheme with low complexity Download PDFInfo
- Publication number
- CA2315952A1 CA2315952A1 CA002315952A CA2315952A CA2315952A1 CA 2315952 A1 CA2315952 A1 CA 2315952A1 CA 002315952 A CA002315952 A CA 002315952A CA 2315952 A CA2315952 A CA 2315952A CA 2315952 A1 CA2315952 A1 CA 2315952A1
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- CA
- Canada
- Prior art keywords
- mapping
- bits
- turbo
- encoders
- src
- 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.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0059—Convolutional codes
- H04L1/006—Trellis-coded modulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0041—Arrangements at the transmitter end
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0064—Concatenated codes
- H04L1/0066—Parallel concatenated codes
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0067—Rate matching
- H04L1/0068—Rate matching by puncturing
- H04L1/0069—Puncturing patterns
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0071—Use of interleaving
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/02—Channels characterised by the type of signal
- H04L5/023—Multiplexing of multicarrier modulation signals
Description
A TURBO TCM SCHEME WITH LOW COMPLEXITY
This invention relates to the field of communication systems and in particular to a system and method for improving transmission rate and loop reach in xDSL systems.
BACKGROUND OF INVENTION
There have been a number of proposals to apply powerful turbo coding/decoding technique [ 1 ] to G.lite and G.dmt to improve transmission rate and loop reach. Among them, there are two typical turbo TCM (Trellis Coded Modulation) schemes. One is the symbol-level turbo TCM, which was proposed by [2] and evaluated by Alcatel [3). The other one is the bit-level turbo TCM, proposed by Mitsubishi and Vocal Technologies [4]-[6). Mitsubishi uses the JPL (Jet Propulsion Lab) design [7], and Vocal Technologies uses conventional R=1/2 coding rate turbo codes but with a lot of puncturing and mapping schemes for different constellation size of QAM modulation.
Referring to Figure 1 there is shown a block diagram of a turbo TCM proposed by Vocal technologies.
Information bits are encoded by two parallel-concatenated systematical recursive convolutional (SRC) encoders with an interleaves between the inputs of the SRC encoders. The two encoders are identical and have a coding rate of R=1/2. The respective sets of parity bits output from the encoders are punctured in a predetermined pattern in order to reduce the parity overhead.
Then the systematical information bits and parity bits are grouped and subsequently mapped into a QAM constellation.
Although the turbo TCM shown in figure has very good error performance, its has some drawbacks.
These are 1 ) All information bits are passed into the convolutional encoder for protection, therefore the number of trellis transitions is very large and the decoder is very complicated; 2) The puncturing and mapping patterns are different for different constellation sizes of QAM, which lead to high implementation complexity; and 3) High coding rate can not be obtained for large constellation size because over-puncturing will damage the code, and therefore high data rate can not be achieved.
SUMMARY OF THE INVENTION
An advantage of the present invention is a universal turbo TCM, which has not only good error performance but also has very low decoder complexity.
In accordance with this invention there is provided a A turbo TCM encoder system comprising:
(a) a pair of systematical recursive convolutional (SRC) encoders for generating parity bits from input bits;
(b) an interleaver for interleaving input bits to the encoders;
(c) a puncture unit for determining a puncture rate of the parity bits in response to to an even and odd number of information bits;
(d) a bit grouping module for receiving the punctured bits and the input bits and grouping the bits for mapping into a symbol.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A better understanding of the invention will be obtained by reference to the detailed description below in conjunction with the following drawings.
1. Turbo TCMEncoder with coding rate R=Il2 for 4.QAM or a grog o two 2QAM
As shown in Figure 2, this turbo TCM encoder is used to transmit lbit in 4QAM
symbol or in two 2QAM symbols. For each information bit, two parity bits are generated by two systematical recursive convolutional (SRC) encoders. 'The parity bits generated by each SRC encoder are punctured ?0 alternatively, i.e., one half of the total parity bits are punctured. The overall coding rate is R=1/2. For each information bit v2 , one parity bit vl is generated. (vl , v2 ) are mapped into one 4QAM symbol using Gray mapping.
This invention relates to the field of communication systems and in particular to a system and method for improving transmission rate and loop reach in xDSL systems.
BACKGROUND OF INVENTION
There have been a number of proposals to apply powerful turbo coding/decoding technique [ 1 ] to G.lite and G.dmt to improve transmission rate and loop reach. Among them, there are two typical turbo TCM (Trellis Coded Modulation) schemes. One is the symbol-level turbo TCM, which was proposed by [2] and evaluated by Alcatel [3). The other one is the bit-level turbo TCM, proposed by Mitsubishi and Vocal Technologies [4]-[6). Mitsubishi uses the JPL (Jet Propulsion Lab) design [7], and Vocal Technologies uses conventional R=1/2 coding rate turbo codes but with a lot of puncturing and mapping schemes for different constellation size of QAM modulation.
Referring to Figure 1 there is shown a block diagram of a turbo TCM proposed by Vocal technologies.
Information bits are encoded by two parallel-concatenated systematical recursive convolutional (SRC) encoders with an interleaves between the inputs of the SRC encoders. The two encoders are identical and have a coding rate of R=1/2. The respective sets of parity bits output from the encoders are punctured in a predetermined pattern in order to reduce the parity overhead.
Then the systematical information bits and parity bits are grouped and subsequently mapped into a QAM constellation.
Although the turbo TCM shown in figure has very good error performance, its has some drawbacks.
These are 1 ) All information bits are passed into the convolutional encoder for protection, therefore the number of trellis transitions is very large and the decoder is very complicated; 2) The puncturing and mapping patterns are different for different constellation sizes of QAM, which lead to high implementation complexity; and 3) High coding rate can not be obtained for large constellation size because over-puncturing will damage the code, and therefore high data rate can not be achieved.
SUMMARY OF THE INVENTION
An advantage of the present invention is a universal turbo TCM, which has not only good error performance but also has very low decoder complexity.
In accordance with this invention there is provided a A turbo TCM encoder system comprising:
(a) a pair of systematical recursive convolutional (SRC) encoders for generating parity bits from input bits;
(b) an interleaver for interleaving input bits to the encoders;
(c) a puncture unit for determining a puncture rate of the parity bits in response to to an even and odd number of information bits;
(d) a bit grouping module for receiving the punctured bits and the input bits and grouping the bits for mapping into a symbol.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A better understanding of the invention will be obtained by reference to the detailed description below in conjunction with the following drawings.
1. Turbo TCMEncoder with coding rate R=Il2 for 4.QAM or a grog o two 2QAM
As shown in Figure 2, this turbo TCM encoder is used to transmit lbit in 4QAM
symbol or in two 2QAM symbols. For each information bit, two parity bits are generated by two systematical recursive convolutional (SRC) encoders. 'The parity bits generated by each SRC encoder are punctured ?0 alternatively, i.e., one half of the total parity bits are punctured. The overall coding rate is R=1/2. For each information bit v2 , one parity bit vl is generated. (vl , v2 ) are mapped into one 4QAM symbol using Gray mapping.
2. Turbo Encoder with coding rate R j2+2k~4+2k) for MQAM (M>16~
As shown in Figure 3, this turbo TCM encoder is used to transmit even number information bits in one QAM symbol. For every two information bits (v3 , v4 ) passed into SRC
encoders, four parity bits are generated by two SRC encoders. The parity bits generated by each SRC encoder will be punctured alternatively, i.e., one half of the total parity bits are punctured. For every two information bits (v3 , v4 ) , two parity bits (v, , v2 ) are generated. (v1, V2 ,..., V2m ) are mapping into one QAM symbol using set-partition mapping [8] and Gray mapping. This mapping is preferred to be operated in one dimension, i.e., two halves of (vl, v2,..., v2m ) are mapped into two 2m -ASK
signals.
Applications: 1) 2/4 16QAM; 2) 4/6 64QAM; 3) 6/8 256QAM; 4) 8/10 1024QAM; 5) 4096QAM; 6) 12/ 14 163 84QAM.
As shown in Figure 3, this turbo TCM encoder is used to transmit even number information bits in one QAM symbol. For every two information bits (v3 , v4 ) passed into SRC
encoders, four parity bits are generated by two SRC encoders. The parity bits generated by each SRC encoder will be punctured alternatively, i.e., one half of the total parity bits are punctured. For every two information bits (v3 , v4 ) , two parity bits (v, , v2 ) are generated. (v1, V2 ,..., V2m ) are mapping into one QAM symbol using set-partition mapping [8] and Gray mapping. This mapping is preferred to be operated in one dimension, i.e., two halves of (vl, v2,..., v2m ) are mapped into two 2m -ASK
signals.
Applications: 1) 2/4 16QAM; 2) 4/6 64QAM; 3) 6/8 256QAM; 4) 8/10 1024QAM; 5) 4096QAM; 6) 12/ 14 163 84QAM.
3. Turbo Encoder with coding rate R ~3+2k~(4+2 ~ for MQAM (M>16,~
As shown in Figure 4, this turbo TCM encoder is used to transmit odd number information bits in one QAM symbol. For every 3 information bits passed into the two SRC encoders, 6 parity bits are generated by the two SRC encoders. The parity bits generated by each SRC
encoder will be punctured with the puncturing rate 5/6, i.e., 5 from 6 parity bits are punctured. For every three information bits (v2 , v3 , v4 ) , one parity bit vl are generated. (vl , V2 ,..., v2m ) are mapped into one QAM symbol using set-partition mapping and Gray mapping. This mapping is preferred to be operated in one dimension, i.e., two halves of (vl , v2 ,..., v2m ) are mapped into two 2 "' -ASK
signals.
Applications: 1) 3/4 16QAM; 2) 5/6 64QAM; 3) 7/8 256QAM; 4) 9/10 1024QAM; 5) 4096QAM; 6) 13/14 16384QAM.
As shown in Figure 4, this turbo TCM encoder is used to transmit odd number information bits in one QAM symbol. For every 3 information bits passed into the two SRC encoders, 6 parity bits are generated by the two SRC encoders. The parity bits generated by each SRC
encoder will be punctured with the puncturing rate 5/6, i.e., 5 from 6 parity bits are punctured. For every three information bits (v2 , v3 , v4 ) , one parity bit vl are generated. (vl , V2 ,..., v2m ) are mapped into one QAM symbol using set-partition mapping and Gray mapping. This mapping is preferred to be operated in one dimension, i.e., two halves of (vl , v2 ,..., v2m ) are mapped into two 2 "' -ASK
signals.
Applications: 1) 3/4 16QAM; 2) 5/6 64QAM; 3) 7/8 256QAM; 4) 9/10 1024QAM; 5) 4096QAM; 6) 13/14 16384QAM.
4.1. Uniaue Mappin>? Schemes~(1) mixed Gray m~nin are set~artition mapping In order to achieve better error performance and low decoder complexity, an unique mapping scheme is used. The mapping of (vl , v2,..., v2m ) into 22"' -QAM is operated by mapping each half of (vl , v2 ,..., v2,~ ) into one 2 m -ASK signal. For example, (vl , v3 ,..., v2m-I ) is mapped into one 2 m -ASK
signal and (v2, V,I,..., V2m ) is mapped into another 2m -ASK signal. Figure 5 shows this unique mapping (set-partition plus Gray mapping) for 4-ASK and 8-ASK. For 4-ASK, it is Gray mapping. For 8-ASK, the first most significant bit is set partition mapping and the two least significant bits are Gray mapping. For general 2m -ASK, the first (m-2) most significant bits are set partition mapping and the two least significant bits are Gray mapping. Suppose that BI , B2 ,..., B2,"
are a mapping for 2 m -ASK
(m> 1 ), where Bk (1 < k <_ 2'~ ) is a m-bit string, then the mapping for 2'"+I -ASK can be generated by 1BI ,1B2 ,...,lB2m ,OBI ,OB2 ,...,OB2," , i.e., append 1 bit to all BI , B2 ,..., B2m to get first half and append Obit to all BI , B2 ,..., B2m to get the second half.
4.2. Unigue Mapping Schemes: (2) Concatenated Gray moping Both the coded bits such as (vl , v3 ) or (v2 , v4 ) and uncoded bits such as (vs , v~ ,..., v2m-I ) or (v6 , vg ,..., v2m ) are Gray mapping, and then they are concatenated. For example, m = 4 , both (v~ , v3 ) and (vs, v~ ) are Gray mappings as shown in Figure 5(a). The concatenated Gray code is as shown in Figure 5(c). The two least significant bits are the Gray mapping of coded bits (v, , v3 ) , which will repeat every four mappings. The two most significant bits are the Gray mapping of the uncoded bits (v5 , v~ ) , which are same for each group of 4 mappings.
S. An Universal Implementation of Turbo TCMEncoderfor MOAM
Figure 6 shows a universal implementation scheme for the above turbo TCM
encoders. The (a, b) data paths in Figures 3 to 4 are combined if the interleaver provides that the bits at even number positions are interleaved to even number positions and the bits at odd number positions are interleaved to odd number positions. The puncture rate for each SRC encoder is either P=1/2 or P=5/6, which is controlled by the even/odd number of information bits. Finally, the bits passed into SRC encoders and their parity bits are grouped into 4-bit by 4-bit for MQAM(M>4), or are grouped into 2-bit by 2-bit for 4QAM.
Y
signal and (v2, V,I,..., V2m ) is mapped into another 2m -ASK signal. Figure 5 shows this unique mapping (set-partition plus Gray mapping) for 4-ASK and 8-ASK. For 4-ASK, it is Gray mapping. For 8-ASK, the first most significant bit is set partition mapping and the two least significant bits are Gray mapping. For general 2m -ASK, the first (m-2) most significant bits are set partition mapping and the two least significant bits are Gray mapping. Suppose that BI , B2 ,..., B2,"
are a mapping for 2 m -ASK
(m> 1 ), where Bk (1 < k <_ 2'~ ) is a m-bit string, then the mapping for 2'"+I -ASK can be generated by 1BI ,1B2 ,...,lB2m ,OBI ,OB2 ,...,OB2," , i.e., append 1 bit to all BI , B2 ,..., B2m to get first half and append Obit to all BI , B2 ,..., B2m to get the second half.
4.2. Unigue Mapping Schemes: (2) Concatenated Gray moping Both the coded bits such as (vl , v3 ) or (v2 , v4 ) and uncoded bits such as (vs , v~ ,..., v2m-I ) or (v6 , vg ,..., v2m ) are Gray mapping, and then they are concatenated. For example, m = 4 , both (v~ , v3 ) and (vs, v~ ) are Gray mappings as shown in Figure 5(a). The concatenated Gray code is as shown in Figure 5(c). The two least significant bits are the Gray mapping of coded bits (v, , v3 ) , which will repeat every four mappings. The two most significant bits are the Gray mapping of the uncoded bits (v5 , v~ ) , which are same for each group of 4 mappings.
S. An Universal Implementation of Turbo TCMEncoderfor MOAM
Figure 6 shows a universal implementation scheme for the above turbo TCM
encoders. The (a, b) data paths in Figures 3 to 4 are combined if the interleaver provides that the bits at even number positions are interleaved to even number positions and the bits at odd number positions are interleaved to odd number positions. The puncture rate for each SRC encoder is either P=1/2 or P=5/6, which is controlled by the even/odd number of information bits. Finally, the bits passed into SRC encoders and their parity bits are grouped into 4-bit by 4-bit for MQAM(M>4), or are grouped into 2-bit by 2-bit for 4QAM.
Y
Claims (7)
1. A turbo TCM encoder system comprising:
(a) a pair of systematical recursive convolutional (SRC) encoders for generating parity bits from input bits;
(b) an interleaver for interleaving input bits to the encoders;
(c) a puncture unit for determining a puncture rate of the parity bits in response to to an even and odd number of information bits;
(d) a bit grouping module for receiving the punctured bits and the input bits and grouping the bits for mapping into a symbol.
(a) a pair of systematical recursive convolutional (SRC) encoders for generating parity bits from input bits;
(b) an interleaver for interleaving input bits to the encoders;
(c) a puncture unit for determining a puncture rate of the parity bits in response to to an even and odd number of information bits;
(d) a bit grouping module for receiving the punctured bits and the input bits and grouping the bits for mapping into a symbol.
2. A system as defined in claim 1, said interleaver including a pair of interleavers.
3. A system as defined in claim 1, said mapping comprising mapping one two-dimensional QAM into two one-dimensional ASK.
4. A system as defined in claim 1, said mapping including a mixed Gray mapping and set partition mapping.
5. A system as defined in claim 1, said mapping including concatenated Gray mapping.
6. A method for turbo TCM encoding according to the present invention.
7. A system as defined in claim 2, said pair of interleavers being implemented by an interleaver with even-odd patterns.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002315952A CA2315952A1 (en) | 2000-08-11 | 2000-08-11 | A turbo tcm scheme with low complexity |
| US09/912,068 US7173978B2 (en) | 2000-07-21 | 2001-07-23 | Method and system for turbo encoding in ADSL |
| CA002353426A CA2353426A1 (en) | 2000-07-21 | 2001-07-23 | A method and system for turbo encoding in adsl |
| AU2001277130A AU2001277130A1 (en) | 2000-07-21 | 2001-07-23 | Method and system for turbo encoding in adsl |
| PCT/US2001/023256 WO2002009300A2 (en) | 2000-07-21 | 2001-07-23 | Method and system for turbo encoding in adsl |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002315952A CA2315952A1 (en) | 2000-08-11 | 2000-08-11 | A turbo tcm scheme with low complexity |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2315952A1 true CA2315952A1 (en) | 2002-02-11 |
Family
ID=4166891
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002315952A Abandoned CA2315952A1 (en) | 2000-07-21 | 2000-08-11 | A turbo tcm scheme with low complexity |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2315952A1 (en) |
-
2000
- 2000-08-11 CA CA002315952A patent/CA2315952A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |