Trellis modulation protocols for a VDSL system
View Patent ↗A new protocol is proposed for transmission of data through lines such as telephone lines. The tones of a signal are grouped, and Trellis encoding is performed only of the members of a group. The computational cost of coding and decoding the data is reduced (compared to treating all the tones of a given direction equivalently), and the invention makes it possible to significantly reduce the computational and memory requirements of the encoder and decoder. Furthermore, Trellis decoding errors are not propagated between the groups.
1. A communication apparatus to implement a process of two-directional communication of data over a transmission line, the communication employing a bandwidth partitioned into a number of bands and including at least one band associated with each of the two directions, the apparatus including:
a signal generation section for generating a signal by encoding the data carried in each direction by modulation of a plurality of tones defined within the at least one band associated with that direction, the tones being grouped into a plurality of groups of tones, each group of tones including a plurality of the tones, the signal generation section including:
an input section for receiving data;
an encoder for Trellis encoding together a portion of the data to be encoded by modulation of that group of tones; and
a modulator for modulating the tones of the group using the respective portion of Trellis encoded data;
a signal transmission section for transmitting the generated signal, wherein each of the plurality of groups include tones from multiple bands;
a quality determination unit for deriving a measure of a quality of transmission of each of the tones; and
a processor for determining for each group of tones, in dependence on said measure of the quality of the transmission for each of the tones of the group, a scheme for modulating the tones of the group to encode a respective portion of data associated with the group of tones, and for controlling the modulator in accordance with the determined modulation scheme.
2. The apparatus according to claim 1 wherein the quality determination unit is arranged at intervals to perform a re-determination of the measure of the quality of transmission of each of the tones of the group, and the modulator is arranged in accordance with the results of the re-determination to modify the way in which the tones of the group are modulated to encode subsequent data.
3. The apparatus according to claim 1 wherein said signal generation section includes at least two processing paths, the determination of how the tones of the group are modulated to encode the data including a determination of which processing path is used to encode data on each tone.
4. The apparatus according to claim 1 wherein said processor is arranged to determine for each tone of the group the respective proportion of the data to be carried by that tone.
5. The apparatus according to claim 1 wherein:
the quality determination unit is arranged to perform at intervals a re-determination of the measure of the quality of transmission of each of the tones of the group; and
the processor is arranged, according to said re-determination of the transmission quality of the tones to modify the proportions of the data encoded using the respective tones.
6. The apparatus according to claim 1 wherein said processor is arranged to determine a respective gain for each of the tones.
7. The apparatus according to claim 1 , wherein the signal transmission section comprises a line driver.
8. A method of two-directional communication of data over a transmission line, the communication employing a bandwidth partitioned into a number of bands and including at least one band associated with each of the two directions, the method including encoding the data carried in each direction by modulation of a plurality of tones defined within the at least one band associated with that direction, the tones being grouped into a plurality of groups of tones, each group of tones including a plurality of tones, the method including:
obtaining data, each portion of the data being associated with a group of tones;
separately Trellis encoding together each portion of data; and
modulating the tones of the group using the respective portion of Trellis encoded data, wherein one or more of the groups include tones within at least two different respective bands.
9. The method according to claim 8 wherein each of the groups includes tones from multiple bands.
10. The method according to claim 8 further comprising performing a pre-processing step, in which the groups of tones are defined.
11. The method according to claim 8 further comprising deriving a measure of the quality of transmission of each of the tones wherein a relative quality of transmission of the tones of the group determines how the tones of that group are modulated to encode the data.
12. The method according to claim 11 further comprising re-determining the measure of the quality of transmission of each of the tones of the group and, in accordance with the results of the re-determination, modifying the way in which the tones of the group are modulated to encode subsequent data.
13. The method according to claim 11 wherein said determination of how the tones of the group are modulated to encode the data includes a determination of which of at least two processing paths is used to encode data on each tone.
14. The method according to claim 11 wherein said determination of how the tones of the group are modulated to encode the data includes determining for each tone of the group the respective proportion of the data to be carried by that tone.
15. The method according to claim 14 and further comprising:
re-determining the measure of the quality of transmission of each of the tones of the group; and
according to said re-determination of the quality of transmission, modifying the proportions of the data encoded using the respective tones.
16. The method according to claim 11 wherein said determination of how the tones of the group are modulated to encode the data includes a determination of a respective gain for each of the tones.
17. The method according to claim 8 further comprising switching between a high data transmission rate mode and a low data transmission rate mode, the switching operation including ceasing to transmit data using one or more of said groups of tones.
18. A communication apparatus for use to implement a process of two-directional communication of data over a transmission line, the communication employing a bandwidth partitioned into a number of bands and including at least one band associated with each of the two directions, the apparatus including:
a signal generation section for generating a signal by encoding the data carried in each direction by modulation of a plurality of tones defined within the at least one band associated with that direction, the tones being grouped into a plurality of groups of tones, each group of tones including a plurality of the tones, the signal generation section including:
an input section for receiving data;
an encoder for Trellis encoding together a portion of the data to be encoded by modulation of that group of tones; and
a modulator for modulating the tones of the group using the respective portion of Trellis encoded data; and
a signal transmission section for transmitting the generated signal, wherein one or more of the groups include tones within at least two different respective bands.
19. The apparatus according to claim 18 wherein said signal generation section includes at least two processing paths, the determination of how the tones of the group are modulated to encode the data including a determination of which processing path is used to encode data on each tone.
20. The apparatus according to claim 18 , wherein the signal transmission section comprises a line driver.
21. A method of two-directional communication of data over a transmission line, the communication employing a bandwidth partitioned into a number of bands and including at least one band associated with each of the two directions, the method including:
obtaining data, each portion of the data being associated with a group of tones, the group of tones include tones within at least two different respective bands;
separately Trellis encoding together each portion of data; and
modulating the tones of the group using the respective portion of Trellis encoded.
22. The method according to claim 21 further comprising performing a pre-processing step in which the group of tone is defined.
23. The method according to claim 21 further comprising deriving a measure of a quality of transmission of each of the tones wherein the relative quality of transmission of the tones of the group determines how the tones of the group are modulated to encode the data.
24. The method according to claim 21 further comprising switching between a high data transmission rate mode and a low data transmission rate mode, the switching operation including ceasing to transmit data using the group of tones.