Methods and apparatus to improve SNR for signaling across multi-channel cables

1. An Ethernet transceiver integrated circuit (IC) chip, comprising:

multiple physical sub-channels, each sub-channel to transfer data symbols along a wired link, each data symbol representing a group of multiple data bits;

PAM modulation circuitry to determine a signal quality parameter value for each of the sub-channels, and to assign modulations to the sub-channels;

wherein, for each sub-channel,

in a first mode where a given sub-channel exhibits a first signal quality parameter value above a first predetermined threshold, the PAM modulation circuitry assigns a modulation of a first type associated with a first constellation,

in a second mode where a given sub-channel exhibits a second signal quality parameter value below the first predetermined threshold, the PAM modulation circuitry assigns a modulation of a second type associated with a second constellation that is sparser than the first constellation;

wherein a second sub-channel exhibits a third signal quality parameter value above a third predetermined threshold that is higher than the first threshold, and wherein the PAM modulation circuitry assigns a modulation of a third type associated with a third constellation that is denser than the first constellation; and

wherein an aggregate data rate along the given sub-channel and the second sub-channel is constant whether operating in the first mode or the second mode.

2. The Ethernet transceiver IC chip of claim 1 , further comprising distribution logic to distribute data among the multiple sub-channels based on detected quality parameters for each sub-channel.

3. The Ethernet transceiver IC chip of claim 1 , wherein the first constellation comprises a DSQ128 constellation, the second constellation comprises an SQ64 constellation, and the third constellation comprises an SQ256 constellation.

4. The Ethernet transceiver IC chip of claim 2 , wherein the distribution logic comprises a multiplexer disposed between a low-density parity-check (LDPC) encoder output and a Tomlinson-Harashima precoding (THP) precoder input.

5. The Ethernet transceiver IC chip of claim 2 , wherein the distribution logic distributes the data based on bit assignments determined during a training mode of operation.

6. The Ethernet transceiver IC chip of claim 5 , wherein the bit assignments are communicated to a second Ethernet transceiver IC chip during the training mode of operation via an Infofield exchange protocol.

7. The Ethernet transceiver IC chip of claim 1 , wherein the PAM modulation circuitry assigns the modulations during a training mode of operation.

8. A method of operation in an Ethernet transceiver integrated circuit (IC) chip, the IC chip having multiple physical sub-channels, each sub-channel to transfer data symbols along a wired link, each data symbol representing a group of multiple data bits, the method comprising:

determining a signal quality parameter value for each of the sub-channels using PAM modulation circuitry;

assigning modulations to the sub-channels using the PAM modulation circuitry;

wherein, for each sub-channel,

in a first mode where a given sub-channel exhibits a first signal quality parameter value above a first predetermined threshold, assigning a modulation of a first type associated with a first constellation,

in a second mode where a given sub-channel exhibits a second signal quality parameter value below the first predetermined threshold, assigning a modulation of a second type associated with a second constellation that is sparser than the first constellation;

wherein a second sub-channel exhibits a third signal quality parameter value above a third predetermined threshold that is higher than the first threshold, and assigning a modulation of a third type associated with a third constellation that is denser than the first constellation; and

wherein an aggregate data rate along the given sub-channel and the second sub-channel is constant whether operating in the first mode or the second mode.

9. The method of claim 8 , further comprising distributing data among the multiple sub-channels based on detected quality parameters for each sub-channel.

10. The method of claim 9 , wherein the distributing data is based on bit assignments determined during a training mode of operation.

11. The method of claim 10 , wherein the bit assignments are communicated to a second Ethernet transceiver IC chip during the training mode of operation via an Infofield exchange protocol.

12. The method of claim 8 , wherein the assigning modulations occurs during a training mode of operation.

13. A method of operation in an Ethernet transceiver integrated circuit (IC) chip, the IC chip having multiple physical sub-channels, each sub-channel to transfer data symbols along a wired link, each data symbol representing a group of multiple data bits, the method comprising:

during a training process having a predetermined number of steps, for each sub-channel,

in a first mode where a given sub-channel exhibits a first signal quality parameter value above a first predetermined threshold, assigning a modulation of a first type associated with a first constellation,

in a second mode where a given sub-channel exhibits a second signal quality parameter value below the first predetermined threshold, assigning a modulation of a second type associated with a second constellation that is sparser than the first constellation;

wherein a second sub-channel exhibits a third signal quality parameter value above a third predetermined threshold that is higher than the first threshold, and assigning a modulation of a third type associated with a third constellation that is denser than the first constellation; and

wherein an aggregate data rate along the given sub-channel and the second sub-channel is constant whether operating in the first mode or the second mode.

14. The method of claim 13 , wherein:

during a data transmission mode,

detecting a change in a noise environment associated with each sub-channel; and

readjusting the density of the constellation associated with each sub-channel.

15. The method of claim 14 , further comprising:

communicating the readjustments to a link partner via an Infofield Exchange protocol.

16. The method of claim 15 , further comprising:

performing a re-training process following the readjusting, the re-training process having fewer steps than the predetermined number of steps.