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WO2008126047A1 - Trellis coded modulation with unequal error protection - Google Patents

Trellis coded modulation with unequal error protection Download PDF

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Publication number
WO2008126047A1
WO2008126047A1 PCT/IB2008/051398 IB2008051398W WO2008126047A1 WO 2008126047 A1 WO2008126047 A1 WO 2008126047A1 IB 2008051398 W IB2008051398 W IB 2008051398W WO 2008126047 A1 WO2008126047 A1 WO 2008126047A1
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WIPO (PCT)
Prior art keywords
bit
bits
constellation
bit set
symbol constellation
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Ceased
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PCT/IB2008/051398
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French (fr)
Inventor
Seyed-Alireza Seyedi-Esfahani
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Koninklijke Philips NV
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Koninklijke Philips Electronics NV
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Publication of WO2008126047A1 publication Critical patent/WO2008126047A1/en
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/25—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM]
    • H03M13/256—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM] with trellis coding, e.g. with convolutional codes and TCM
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/25—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM]
    • H03M13/258—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM] with turbo codes, e.g. Turbo Trellis Coded Modulation [TTCM]
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/35—Unequal or adaptive error protection, e.g. by providing a different level of protection according to significance of source information or by adapting the coding according to the change of transmission channel characteristics
    • H03M13/356—Unequal error protection [UEP]
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/63—Joint error correction and other techniques
    • H03M13/635—Error control coding in combination with rate matching
    • H03M13/6362—Error control coding in combination with rate matching by puncturing
    • 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
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/007—Unequal error protection

Definitions

  • This invention pertains to the field of data communication, and more particularly to a system and method of encoding and modulating data for transmission.
  • BER bit error rate
  • N 0 spectral noise density
  • EtZN 0 spectral noise density
  • different portions of the data are more critical to successful operation of the application than other portions.
  • N e.g., 24
  • M M-bit words
  • the MSBs of each of these three words are more critical than the LSBs to achieving an accurate representation of the video signal.
  • errors in the MSBs are more detrimental than errors in the LSBs to successful operation of the video application. Accordingly, it would be desirable to provide a method of communicating data which provides greater error protection for more critical data than it provides to less critical data.
  • a method of transmitting data comprises: separating data bits into a first bit set and a second bit set; and mapping the first and second bit sets to a symbol constellation, where an Euclidian distance in the symbol constellation between valu s in the first bit set is less than an Euclidian distance in the symbol constellation between values for the bits in the second bit set; wherein within each of the first and second bit sets, the bits are mapped to the symbol constellation using trellis-coded modulation.
  • a system for transmitting data bits separated into a first bit set and a second bit set comprises a constellation mapper adapted to map the first and second bit sets into a symbol constellation.
  • a Euclidean distance in the symbol constellation between values for the bits in the first bit set is greater than a Euclidean distance in the symbol constellation between values for the bits in the second bit set.
  • the constellation mapper maps bits to the symbol constellation using trellis-coded modulation.
  • FIG. 1 is a functional block diagram of a transmission system employing trellis coded modulation (TCM).
  • TCM trellis coded modulation
  • FIG. 2 is a symbol constellation produced by the transmission system of FIG. 1.
  • FIG. 3 is a functional block diagram of a transmission system employing unequal data protection (UEP).
  • UEP unequal data protection
  • FIG. 4 is a symbol constellation produced by the transmission system of FIG. 3.
  • FIG. 5 is a functional block diagram of one embodiment of a transmission system employing TCM and UEP.
  • FIG. 6 is a symbol constellation produced by the transmission system of FIG. 5.
  • FIG. 7 compares bit error rate (BER) versus Eb/No performance for a transmission scheme employing UEP, against a transmission scheme employing both TCM and UEP.
  • FIG. 1 is a functional block diagram of one exemplary transmission system 100 employing trellis coded modulation (TCM).
  • System 100 includes trellis (e.g., convolutional) coder 110 and 16-QAM TCM constellation mapper 120.
  • trellis e.g., convolutional
  • system 100 receives a group of data bits ai-a3 and generates one transmission symbol S xy from the three data bits.
  • 16-QAM TCM constellation mapper 120 maps four bits bib 2 b3b 4 to each transmission symbol S xy .
  • trellis coder 110 is a 1 A rate convolutional coder that receives data bit a 3 and generates therefrom bits b 3 and b 4 for 16-QAM TCM constellation mapper 120. Meanwhile, data bits ao and ai are applied directly to 16-QAM TCM constellation mapper 120 as bits bi and b 2 .
  • 16-QAM TCM constellation mapper 120 maps the bits bib 2 transmission symbol S xy based on the level of protection that each bit has received in the encoding process.
  • 16-QAM TCM constellation mapper 120 maps the bits bi and b 2 onto constellation points such that the 0 and 1 values for each bit have a relatively greater Euclidian distance from each other, and maps the bits b 3 and b 4 onto constellation points such that the 0 and 1 values for each bit have a relatively smaller Euclidian distance from each other.
  • the overall protection that each bit receives is increased.
  • FIG. 2 is a symbol constellation 200, produced by the transmission system 100 of FIG. 1. Each constellation point is shown together with the corresponding bits bib 2 b 3 b 4 that map to that point. As can be seen in FIG. 2 the Euclidian distances dbi and db 2 between 0 and 1 values for bits bi and b 2 , respectively - which were not subject to protection by convolutional coder 110 - are both greater than the Euclidian distances db 3 and db 4 between 0 and 1 values for bits b 3 and b 4 , respectively - which were subject to protection by convolutional coder 110.
  • FIG. 3 is a functional block diagram of a transmission system 300 employing unequal data protection (UEP).
  • System 300 includes first and second convolutional coders 310, 315 and first and second 16-QAM UEP constellation mappers 320 and 325.
  • system 300 receives a group of six data bits ai-a 6 and generates two transmission symbols S xlyl and S x2y2 from the six data bits.
  • data bits ai-a 6 are separated into a first bit set comprising ai-a 3 , and a second bit set comprising a 4 -a 6 .
  • the first bit set ai-a 3 comprises data requires a lower level of protection than data in the second bit set a 4 -a 6 .
  • each pixel is represented by three 6-bit words ai-a 6 to represent the red, green and blue levels.
  • the three MSBs a 4 -a 6 of each of these three words are more critical than the three LSBs ai-a 3 to achieving an accurate representation of the video signal.
  • bits a r a 3 may be referred to as "Low Protection” data bits requiring a lower level of protection against error
  • bits a 4 -a 6 may be referred to as "High Protection” data bits requiring a higher level of protection against error.
  • Each 16-QAM UEP constellation mapper 320/325 maps four bits bib 2 b 3 b 4 to a corresponding transmission symbol S xy .
  • the first and second convolutional coders 310, 315 mvolutional coders that receive data bits ai-a3 and a 4 -a6, respectively, and generate therefrom bits bib 2 b 3 b 4 for each of the 16-QAM UEP constellation mappers 320 and 325.
  • first convolutional coder 310 receives the Low Protection data bits ai-a 3 and produces therefrom the bits bib 2 for each of the two 16-QAM UEP constellation mappers 320 and 325.
  • second convolutional coder 315 receives the High Protection data bits a 4 -a6 and produces therefrom the bits b 3 b 4 for each of the two 16-QAM UEP constellation mappers 320 and 325.
  • each 16-QAM UEP constellation mapper 320/325 maps the bits bib 2 b 3 b 4 to a corresponding transmission symbol S xy based on the protection level of the bits.
  • each 16-QAM UEP constellation mapper 320/325 maps the bits bi and b 2 generated from the first bit set comprising the Low Protection data bits ai-a 3 , to constellation points such that the 0 and 1 values for each bit have a relatively smaller Euclidian distance from each other, and maps the bits b 3 and b 4 generated from the second bit set comprising the High Protection data bits a 4 -a 6 , to constellation points such that the 0 and 1 values for each bit have a relatively greater Euclidian distance from each other.
  • FIG. 4 is a symbol constellation 400 produced by the transmission system 300 of FIG. 3. Each constellation point is shown together with the corresponding bits bib 2 b 3 b 4 that map to that point. It can be seen that the bits b 3 and b 4 map to the "in-phase" component of the symbol constellation, illustrated by a horizontal axis in FIG. 4. Likewise, it can be seen that the bits bi and b 2 map to the "quadrature" component of the symbol constellation, illustrated by a vertical axis in FIG. 4. In symbol constellation 400, it is assumed that the horizontal distance between adjacent constellation points, 2di, is greater than the vertical distance between adjacent constellation points, 2d 2 .
  • FIG. 5 is a functional block diagram of one embodiment of a transmission system 500 employing trellis coded modulation and unequal error protection.
  • System 500 includes first involutional coders 510, 515 and first and second 16-QAM UEP&TCM constellation mappers 520 and 525.
  • system 500 receives a group of six data bits ai-a 6 and generates two transmission symbols S xlyl and S X2y2 from the six data bits.
  • data bits ai-a 6 are separated into a first bit set comprising ai-a3, and a second bit set comprising a 4 -a 6 .
  • the first bit set ai-a 3 comprises data that requires a lower level of protection than data in the second bit set a 4 -a6. For example, consider a case of video data where each pixel is represented by three 6-bit words ai-a 6 to represent the red, green and blue levels.
  • the three MSBs a 4 -a6 of each of these three words are more critical than the three LSBs ai-a3 to achieving an accurate representation of the video signal.
  • errors in the MSBs a 4 -a 6 are more detrimental than errors in the LSBs ai-a 3 to successful operation of the video application.
  • data bits ai-a 3 may be referred to as "Low Protection” data bits requiring a lower level of protection against error
  • data bits a 4 -a 6 may be referred to as "High Protection" data bits requiring a higher level of protection against error.
  • Each 16-QAM UEP&TCM constellation mapper 520/525 maps four bits bib 2 b 3 b 4 to a corresponding transmission symbol S xy .
  • the first and second convolutional coders 510 and 515 are 1 A rate convolutional coders that receive data bits a3 and a 6 , respectively, and generate therefrom bits b 2 and b 4 , respectively, for both of the two 16-QAM UEP&TCM constellation mappers 520 and 525.
  • first convolutional coder 510 receives the Low Protection data bit a 3 and produces therefrom the bit b 2 for both of the two 16-QAM UEP&TCM constellation mappers 520 and 525.
  • second convolutional coder 515 receives the High Protection data bit a 6 and produces therefrom the bit b 4 for both of the two 16-QAM UEP&TCM constellation mappers 520 and 525.
  • each 16-QAM UEP&TCM constellation mapper 520/525 maps the bits bib 2 b 3 b4 to a corresponding transmission symbol S xy based on the protection level of the bits.
  • each 16-QAM UEP&TCM constellation mapper 520/525 maps the bits bi and b 2 generated from the first bit set comprising the Low Protection bits ai-a 3 , to constellation points such that the 0 and 1 values for each bit have a relatively smaller Euclidian distance from each other, and maps the bits b 3 and b 4 generated from the second bit set comprising the High Protection bits a 4 -a 6 , to constellation points such that the 0 and 1 values for each bit have a relatively greater Euclidian distance from each other. Furthermore, in the system 100, the encoding and mapping of the data bits are not performed independently.
  • 16-QAM UEP&TCM constellation mappers 520/525 map the bits within each bit set to each transmission symbol S xy based on the level of protection that each bit has received in the encoding process. Accordingly, within the first bit set, since bit b 2 is subject to "protection" by convolutional encoder 110 while bit bi is not, 16-QAM UEP&TCM constellation mappers 520/525 map the bits bi and b 2 to constellation points such that the 0 and 1 values for bit bi have a relatively greater Euclidian distance from each other, than the 0 and 1 values for bit b 2 . As a result, the overall protection that each bit receives is increased.
  • FIG. 6 is a symbol constellation 600 produced by the transmission system 500 of FIG. 5. Each constellation point is shown together with the corresponding bits bib 2 b 3 b 4 that map to that point. It can be seen that the bits b 3 and b 4 map to the "in-phase" component of the symbol constellation, illustrated by a horizontal axis in FIG. 6. Likewise, it can be seen that the bits bi and b 2 map to the "quadrature" component of the symbol constellation, illustrated by a vertical axis in FIG. 6. In symbol constellation 600, it is assumed that the horizontal distance between adjacent constellation points, 2di, is greater than the vertical distance between adjacent constellation points, 2d 2 .
  • transmission system 500 protects the High Protection data bits a 4 -a6 to a greater extent compared to the Low Protection data bits ai-a 3 . hin each of the in-phase and quadrature components of the constellation map, the bits are mapped according to a TCM scheme.
  • FIG. 7 compares bit error rate (BER) versus Eb/No performance for a transmission scheme employing UEP, against a transmission scheme employing both TCM and UEP.
  • the transmission scheme employing TCM and UEP produces superior BER performance for both cases.
  • the transmission scheme employing TCM and UEP produces superior BER performance for both High Protected and Low Protection data.

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  • Physics & Mathematics (AREA)
  • Probability & Statistics with Applications (AREA)
  • Theoretical Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
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Abstract

A method and system (500) of transmitting data separates data bits into a first bit set and a second bit set; and maps the first and second bit sets to a symbol constellation, where an Euclidian distance in the symbol constellation between values for the bits in the first bit set is less than an Euclidian distance in the symbol constellation between values for the bits in the second bit set, and wherein within each of the first and second bit sets, the bits are mapped to the symbol constellation using trellis-coded modulation (520, 525).

Description

TRELLIS CODED MODULATION WITH UNEQUAL ERROR PROTECTION CROSS-REFERENCES TO RELATED APPLICATIONS
This patent application claims the priority benefit under 35 U. S. C. § 119(e) of
U.S. Provisional Patent Application 60/911,521, filed on 13 April 2007, the entirety of which is hereby incorporated by reference as if fully set forth herein.
This invention pertains to the field of data communication, and more particularly to a system and method of encoding and modulating data for transmission. As new communication systems are developed, there continues to be a desire for more flexible, and efficient data communication techniques. For example, in general it is desirable to transmit data such that a desired bit error rate (BER) can be achieved with a lower ratio of energy-per-bit (Eb) to the spectral noise density (N0) (i.e., EtZN0) - or conversely, to achieve a lower BER for a given EtZN0. Depending upon the application, this can allow greater transmission distances, higher data transmission rates, lower transmit power levels, or some combination of these benefits. Toward this end, new error correction and data modulation techniques continue to be developed.
In some applications, different portions of the data are more critical to successful operation of the application than other portions. For example, consider a case of video data where each pixel is represented by N (e.g., 24) data bits comprising three M-bit words (e.g., M= 8) to represent the red, green and blue levels. In that case, the MSBs of each of these three words are more critical than the LSBs to achieving an accurate representation of the video signal. In other words, errors in the MSBs are more detrimental than errors in the LSBs to successful operation of the video application. Accordingly, it would be desirable to provide a method of communicating data which provides greater error protection for more critical data than it provides to less critical data. It would also be desirable to provide such a method that can provide a low BER for a given EtZN0. It would be desirable to provide a system of communicating data which provides greater error protection for more critical data than it provides to less critical data. It would also be desirable to provide such a system that can provide a low BER for a given Eb/N0.
In one aspect of the invention, a method of transmitting data comprises: separating data bits into a first bit set and a second bit set; and mapping the first and second bit sets to a symbol constellation, where an Euclidian distance in the symbol constellation between valu s in the first bit set is less than an Euclidian distance in the symbol constellation between values for the bits in the second bit set; wherein within each of the first and second bit sets, the bits are mapped to the symbol constellation using trellis-coded modulation. In another aspect of the invention, a system for transmitting data bits separated into a first bit set and a second bit set comprises a constellation mapper adapted to map the first and second bit sets into a symbol constellation. A Euclidean distance in the symbol constellation between values for the bits in the first bit set is greater than a Euclidean distance in the symbol constellation between values for the bits in the second bit set. Within each bit set, the constellation mapper maps bits to the symbol constellation using trellis-coded modulation.
FIG. 1 is a functional block diagram of a transmission system employing trellis coded modulation (TCM).
FIG. 2 is a symbol constellation produced by the transmission system of FIG. 1. FIG. 3 is a functional block diagram of a transmission system employing unequal data protection (UEP).
FIG. 4 is a symbol constellation produced by the transmission system of FIG. 3. FIG. 5 is a functional block diagram of one embodiment of a transmission system employing TCM and UEP. FIG. 6 is a symbol constellation produced by the transmission system of FIG. 5.
FIG. 7 compares bit error rate (BER) versus Eb/No performance for a transmission scheme employing UEP, against a transmission scheme employing both TCM and UEP. FIG. 1 is a functional block diagram of one exemplary transmission system 100 employing trellis coded modulation (TCM). System 100 includes trellis (e.g., convolutional) coder 110 and 16-QAM TCM constellation mapper 120.
In operation, system 100 receives a group of data bits ai-a3 and generates one transmission symbol Sxy from the three data bits. 16-QAM TCM constellation mapper 120 maps four bits bib2b3b4 to each transmission symbol Sxy. In the system 100, trellis coder 110 is a 1A rate convolutional coder that receives data bit a3 and generates therefrom bits b3 and b4 for 16-QAM TCM constellation mapper 120. Meanwhile, data bits ao and ai are applied directly to 16-QAM TCM constellation mapper 120 as bits bi and b2.
Beneficially, in the system 100, the encoding and mapping of the data bits are not performed independently. Instead, 16-QAM TCM constellation mapper 120 maps the bits bib2 transmission symbol Sxy based on the level of protection that each bit has received in the encoding process. In particular, since bits b3 and b4 are subject to "protection" by convolutional encoder 110 while bits bi and b2 are not, 16-QAM TCM constellation mapper 120 maps the bits bi and b2 onto constellation points such that the 0 and 1 values for each bit have a relatively greater Euclidian distance from each other, and maps the bits b3 and b4 onto constellation points such that the 0 and 1 values for each bit have a relatively smaller Euclidian distance from each other. As a result, the overall protection that each bit receives is increased.
FIG. 2 is a symbol constellation 200, produced by the transmission system 100 of FIG. 1. Each constellation point is shown together with the corresponding bits bib2b3b4 that map to that point. As can be seen in FIG. 2 the Euclidian distances dbi and db2 between 0 and 1 values for bits bi and b2, respectively - which were not subject to protection by convolutional coder 110 - are both greater than the Euclidian distances db3 and db4 between 0 and 1 values for bits b3 and b4, respectively - which were subject to protection by convolutional coder 110.
FIG. 3 is a functional block diagram of a transmission system 300 employing unequal data protection (UEP). System 300 includes first and second convolutional coders 310, 315 and first and second 16-QAM UEP constellation mappers 320 and 325.
In operation, system 300 receives a group of six data bits ai-a6 and generates two transmission symbols Sxlyl and Sx2y2 from the six data bits.
In the system 300, data bits ai-a6 are separated into a first bit set comprising ai-a3, and a second bit set comprising a4-a6. Beneficially, the first bit set ai-a3 comprises data requires a lower level of protection than data in the second bit set a4-a6. For example, consider a case of video data where each pixel is represented by three 6-bit words ai-a6 to represent the red, green and blue levels. In that case, the three MSBs a4-a6 of each of these three words are more critical than the three LSBs ai-a3 to achieving an accurate representation of the video signal. In other words, errors in the MSBs a4-a6 are more detrimental than errors in the LSBs ai-a3 to successful operation of the video application. So bits ara3 may be referred to as "Low Protection" data bits requiring a lower level of protection against error, and bits a4-a6 may be referred to as "High Protection" data bits requiring a higher level of protection against error.
Each 16-QAM UEP constellation mapper 320/325 maps four bits bib2b3b4 to a corresponding transmission symbol Sxy. The first and second convolutional coders 310, 315 mvolutional coders that receive data bits ai-a3 and a4-a6, respectively, and generate therefrom bits bib2b3b4 for each of the 16-QAM UEP constellation mappers 320 and 325. In particular, first convolutional coder 310 receives the Low Protection data bits ai-a3 and produces therefrom the bits bib2 for each of the two 16-QAM UEP constellation mappers 320 and 325. Also, second convolutional coder 315 receives the High Protection data bits a4-a6 and produces therefrom the bits b3b4 for each of the two 16-QAM UEP constellation mappers 320 and 325.
Beneficially, in the system 300, each 16-QAM UEP constellation mapper 320/325 maps the bits bib2b3b4 to a corresponding transmission symbol Sxy based on the protection level of the bits. In particular, each 16-QAM UEP constellation mapper 320/325 maps the bits bi and b2 generated from the first bit set comprising the Low Protection data bits ai-a3, to constellation points such that the 0 and 1 values for each bit have a relatively smaller Euclidian distance from each other, and maps the bits b3 and b4 generated from the second bit set comprising the High Protection data bits a4-a6, to constellation points such that the 0 and 1 values for each bit have a relatively greater Euclidian distance from each other.
FIG. 4 is a symbol constellation 400 produced by the transmission system 300 of FIG. 3. Each constellation point is shown together with the corresponding bits bib2b3b4 that map to that point. It can be seen that the bits b3 and b4 map to the "in-phase" component of the symbol constellation, illustrated by a horizontal axis in FIG. 4. Likewise, it can be seen that the bits bi and b2 map to the "quadrature" component of the symbol constellation, illustrated by a vertical axis in FIG. 4. In symbol constellation 400, it is assumed that the horizontal distance between adjacent constellation points, 2di, is greater than the vertical distance between adjacent constellation points, 2d2. In that case, it is readily seen that the Euclidian distances between 0 and 1 values for bits bi and b2, respectively - which were generated from the Low Protection data bits ai-a3 - are less than the Euclidian distances between 0 and 1 values for bits b3 and b4, respectively - which were generated from the High Protection data bits a4-a6. Consequently, transmission system 300 protects the High Protection data bits a4-a6 to a greater extent compared to the Low Protection data bits ai-a3. However, system 400 provides sub-optimal transmission in terms of bit error rate
(BER) versus Eb/No. A system providing improved performance is desired.
FIG. 5 is a functional block diagram of one embodiment of a transmission system 500 employing trellis coded modulation and unequal error protection. System 500 includes first involutional coders 510, 515 and first and second 16-QAM UEP&TCM constellation mappers 520 and 525.
In operation, system 500 receives a group of six data bits ai-a6 and generates two transmission symbols Sxlyl and SX2y2 from the six data bits. In the system 500, data bits ai-a6 are separated into a first bit set comprising ai-a3, and a second bit set comprising a4-a6. Beneficially, the first bit set ai-a3 comprises data that requires a lower level of protection than data in the second bit set a4-a6. For example, consider a case of video data where each pixel is represented by three 6-bit words ai-a6 to represent the red, green and blue levels. In that case, the three MSBs a4-a6 of each of these three words are more critical than the three LSBs ai-a3 to achieving an accurate representation of the video signal. In other words, errors in the MSBs a4-a6 are more detrimental than errors in the LSBs ai-a3 to successful operation of the video application. So data bits ai-a3 may be referred to as "Low Protection" data bits requiring a lower level of protection against error, and data bits a4-a6 may be referred to as "High Protection" data bits requiring a higher level of protection against error.
Each 16-QAM UEP&TCM constellation mapper 520/525 maps four bits bib2b3b4 to a corresponding transmission symbol Sxy.
The first and second convolutional coders 510 and 515 are 1A rate convolutional coders that receive data bits a3 and a6, respectively, and generate therefrom bits b2 and b4, respectively, for both of the two 16-QAM UEP&TCM constellation mappers 520 and 525. In particular, first convolutional coder 510 receives the Low Protection data bit a3 and produces therefrom the bit b2 for both of the two 16-QAM UEP&TCM constellation mappers 520 and 525. Also, second convolutional coder 515 receives the High Protection data bit a6 and produces therefrom the bit b4 for both of the two 16-QAM UEP&TCM constellation mappers 520 and 525.
Meanwhile, "Low Protection" data bits ao and ai are applied to 16-QAM UEP&TCM constellation mappers 520 and 525, respectively, as bit bi. Similarly, "High Protection" data bits a4 and as are applied to 16-QAM UEP&TCM constellation mappers 520 and 525, respectively, as bit b3. So, the data bits ai-a6 are first mapped to a group of four bits bib2b3b4 for each symbol, wherein the first (Low Protection) data bit set ai-a3 is mapped to a first bit set comprising bits bib2, and the second (High Protection) data bit set a4-a6 is mapped to a second bit set comprising bits b3b4. illy, in the system 500, each 16-QAM UEP&TCM constellation mapper 520/525 maps the bits bib2b3b4 to a corresponding transmission symbol Sxy based on the protection level of the bits. Accordingly, each 16-QAM UEP&TCM constellation mapper 520/525 maps the bits bi and b2 generated from the first bit set comprising the Low Protection bits ai-a3, to constellation points such that the 0 and 1 values for each bit have a relatively smaller Euclidian distance from each other, and maps the bits b3 and b4 generated from the second bit set comprising the High Protection bits a4-a6, to constellation points such that the 0 and 1 values for each bit have a relatively greater Euclidian distance from each other. Furthermore, in the system 100, the encoding and mapping of the data bits are not performed independently. Instead, 16-QAM UEP&TCM constellation mappers 520/525 map the bits within each bit set to each transmission symbol Sxy based on the level of protection that each bit has received in the encoding process. Accordingly, within the first bit set, since bit b2 is subject to "protection" by convolutional encoder 110 while bit bi is not, 16-QAM UEP&TCM constellation mappers 520/525 map the bits bi and b2 to constellation points such that the 0 and 1 values for bit bi have a relatively greater Euclidian distance from each other, than the 0 and 1 values for bit b2. As a result, the overall protection that each bit receives is increased.
FIG. 6 is a symbol constellation 600 produced by the transmission system 500 of FIG. 5. Each constellation point is shown together with the corresponding bits bib2b3b4 that map to that point. It can be seen that the bits b3 and b4 map to the "in-phase" component of the symbol constellation, illustrated by a horizontal axis in FIG. 6. Likewise, it can be seen that the bits bi and b2 map to the "quadrature" component of the symbol constellation, illustrated by a vertical axis in FIG. 6. In symbol constellation 600, it is assumed that the horizontal distance between adjacent constellation points, 2di, is greater than the vertical distance between adjacent constellation points, 2d2. In that case, it is readily seen that the Euclidian distances between 0 and 1 values for bits bi and b2, respectively - which were generated from the Low Protection bits ai-a3 - are less than the Euclidian distances between 0 and 1 values for bits b3 and b4, respectively - which were generated from the High Protection bits a4-a6. Consequently, transmission system 500 protects the High Protection data bits a4-a6 to a greater extent compared to the Low Protection data bits ai-a3. hin each of the in-phase and quadrature components of the constellation map, the bits are mapped according to a TCM scheme. Accordingly, bits bi and b3 are mapped to have larger Euclidian distances between their 0 and 1 values, than bits b2 and b4, respectively. FIG. 7 compares bit error rate (BER) versus Eb/No performance for a transmission scheme employing UEP, against a transmission scheme employing both TCM and UEP. FIG. 7 includes plots in a first case, where the horizontal distance between adjacent constellation points, 2di, is equal to the vertical distance between adjacent constellation points, 2d2, and a second case where the horizontal distance between adjacent constellation points, 2di = 4d2. As can be seen in FIG. 7, the transmission scheme employing TCM and UEP produces superior BER performance for both cases. Furthermore, in the second case, the transmission scheme employing TCM and UEP produces superior BER performance for both High Protected and Low Protection data.
While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. For example, other constellations (e.g., 64-QAM), mappings, and/or code rates are possible. Also, convolutional codes that are employed may be punctured or non-punctured. Furthermore, the bits and/or symbols may or may not be interleaved. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.

Claims

1. A method of transmitting data, comprising: separating data bits into a first bit set and a second bit set; and mapping the first and second bit sets to a symbol constellation (600), where an
Euclidian distance in the symbol constellation (600) between values for the bits in the first bit set is less than an Euclidian distance in the symbol constellation (600) between values for the bits in the second bit set, wherein within each of the first and second bit sets, the bits are mapped to the symbol constellation (600) using trellis-coded modulation (520, 525).
2. The method of claim 1, wherein the symbol constellation (600) is a 16-QAM constellation.
3. The method of claim 1, wherein mapping the first and second bit sets to a symbol constellation (600) includes performing a convolutional encoding (510, 515) on at least one data bit in each of the first and second bit sets.
4. The method of claim 1 , wherein the first bit set is mapped to one of an in-phase component (I) and a quadrature component (Q) of the symbol constellation (600), and wherein the second bit set is mapped to an other of the in-phase component (I) and the quadrature component (Q) of the symbol constellation (600).
5. The method of claim 4, wherein at least one bit in the first bit set is mapped such that its values have a Euclidian distance from each other in the symbol constellation (600) that is greater than a Euclidian distance between values of a second bit in the first bit set, and wherein at least one bit in the second bit set is mapped such that its values have a Euclidian distance from each other in the symbol constellation (600) that is greater than a Euclidian distance between values of a second bit in the second bit set.
6. The method of claim 1, wherein the data bits are first mapped to a group of four bits bib2b3b4 for each symbol, wherein the first bit set is mapped to bits bib2, and the second bit set is mapped to bits bsb4, wherein b3 and b4 are then mapped to one of an in- phas t (I) and a quadrature component (Q) of the symbol constellation (600) and bi and b2 are mapped to an other of the in-phase component (I) and the quadrature component (Q) of the symbol constellation (600), wherein values of b3 and values of b4 have a larger Euclidian distance between them in symbol constellation (600), respectively, compared to an Euclidian distance in the symbol constellation (600) of values of bits bi and b2, respectively.
7. The method of claim 6, wherein values for bi have a larger Euclidian distance between them in the symbol constellation (600) compared to values for b2, and values for b3 have a larger Euclidian distance between them in the symbol constellation (600) compared to values for b4.
8. The method of claim 7, wherein b2 and b4 are convolutional encoded (510, 515).
9. A system for transmitting data bits separated into a first bit set and a second bit set, the system comprising a constellation mapper (500) adapted to map the first and second bit sets into a symbol constellation (600), where an Euclidean distance in the symbol constellation (600) between values for the bits in the first bit set is greater than an Euclidean distance in the symbol constellation between values for the bits in the second bit set, and wherein within each bit set, the constellation mapper (500) maps bits to the symbol constellation (600) using trellis-coded modulation (520, 525).
10. The system of claim 9, wherein the symbol constellation (600) is a 16-QAM constellation.
11. The system of claim 9, wherein the constellation mapper (500) includes: a first convolutional encoder (510) for encoding at least one data bit in the first bit set; and a second convolutional encoder (515) for encoding at least one data bit in the second bit set.
12. The system of claim 9, wherein the constellation mapper (500) is adapted to map the first bit set to one of an in-phase component (I) and a quadrature component (Q) of the i ellation (600), and further adapted to map the second bit set to an other of the in-phase component (I) and the quadrature component (Q) of the symbol constellation.
13. The system of claim 12, wherein the constellation mapper (500) is adapted to map at least one bit in the first bit set to have a Euclidian distance in the symbol constellation (600) that is greater than a Euclidian distance of a second bit in the first bit set, and further adapted to map at least one bit in the second bit set to have a Euclidian distance n the symbol constellation (600) that is greater than a Euclidian distance of a second bit in the second bit set.
14. The system of claim 9, wherein the constellation mapper (500) is adapted to map the data bits first to a group of four bits bib2b3b4 for each symbol, wherein the first bit set is mapped to bits bib2, and the second bit set is mapped to bits b3b4, wherein b3 and b4 are then mapped to one of an in-phase component (I) and a quadrature component (Q) of the symbol constellation and bi and b2 are mapped to an other of the in-phase component (I) and the quadrature component (Q) of the symbol constellation (600), wherein b3 and b4 have a larger Euclidian distance in the symbol constellation (600) compared to bi and b2.
15. The system of claim 14, wherein the constellation mapper (500) is adapted to map bi to have a larger Euclidian distance in the symbol constellation (600) compared to b2, and further adapted to map b3 to have a larger Euclidian distance in the symbol constellation (600) compared to b4.
16. The system of claim 15, wherein the constellation mapper (500) includes: a first convolutional encoder (510) adapted to encode at least one data bit in the first bit set; and a second convolutional encoder (515) adapted to encode at least one data bit in the second bit set, and wherein b2 and b4 are output from the convolutional encoders (510, 515).
PCT/IB2008/051398 2007-04-13 2008-04-11 Trellis coded modulation with unequal error protection Ceased WO2008126047A1 (en)

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