Error correction using PAM4 modulation
Disclosed is an electronic device, which includes an ECC decoder that performs ECC decoding on a flit including a plurality of PAM-4 symbols for each of a plurality of ECC groups, a CRC decoder that performs CRC decoding on the ECC decoded flit to obtain data, and an erasure decoding unit that calculates an LLR for each of the PAM-4 symbols when the CRC decoding fails, extracts an error symbol candidate from among the plurality of PAM-4 symbols for each of the plurality of ECC groups based on the LLR, and performs the ECC decoding again after erasing the error symbol candidate.
1. An electronic device comprising:
an Error Correction Code (ECC) decoder configured to perform ECC decoding on a flit including a plurality of Pulse Amplitude Modulation-4 (PAM-4) symbols arranged into a plurality of groups to generate an ECC decoded flit for each of the groups;
a cyclic redundancy check (CRC) decoder configured to perform CRC decoding on each ECC decoded flit to obtain data; and
an erasure decoding unit,
wherein when the CRC decoding fails,
for each of the groups, the erasure decoding unit is configured to:
calculate a log likelihood ratio (LLR) for each of the PAM-4 symbols of the corresponding group, to extract an error symbol candidate from among the PAM-4 symbols of the corresponding group based on the LLR; and
erase the error symbol candidate from the corresponding group to update the flit, and
the electronic device is configured to perform the ECC decoding on the updated flit.
2. The electronic device of claim 1 , wherein the erasure decoding unit comprises:
an LLR calculation unit configured to calculate the LLR for each of 2-bits included in each of the PAM-4 symbols;
a least reliable symbol (LRS) search unit configured to compare the LLR with a preset threshold value in units of bits, to extract the error symbol candidate, and to generate an LRS array corresponding to position information of the error symbol candidate; and
an erasure decoder configured to carry out the perform of the ECC decoding on the updated flit based on the LRS array.
3. The electronic device of claim 2 , wherein the LRS search unit comprises:
a threshold comparing unit configured to generate a least reliable bit (LRB) array by binarizing a bit having the LLR less than the preset threshold value and a bit having the LLR greater than or equal to the preset threshold value in the flit; and
a logic circuit configured to convert the LRB array into ECC symbol units using a logical OR operation to generate the LRS array.
4. The electronic device of claim 3 , wherein the LRS search unit comprises:
an LRS counter configured to count the number of error symbol candidates from the LRS array;
a comparing unit configured to compare the number of error symbol candidates with a preset number of candidates, and configured to output the LRS array to the erasure decoder when the number of error symbol candidates is the same as the preset number of candidates; and
a threshold control unit configured to adjust the preset threshold value when the number of error symbol candidates is different from the preset number of candidates.
5. The electronic device of claim 4 , wherein the threshold control unit increases the preset threshold value when the number of error symbol candidates is less than the preset number of candidates, and decreases the preset threshold value when the number of error symbol candidates exceeds the preset number of candidates.
6. The electronic device of claim 4 , wherein the comparing unit iterates an operation of comparing the number of error symbol candidates with the preset number of candidates by a preset number of loops, and when the preset number of loops is reached, outputs an LRS array corresponding to the number of error symbol candidates when the number of error symbol candidates does not match the preset number of candidates.
7. The electronic device of claim 2 , wherein the erasure decoder randomly extracts at least two error symbol candidates from among the error symbol candidates, and carries out the perform of the ECC decoding on the updated flit after erasing the at least two error symbol candidates.
8. The electronic device of claim 1 , wherein the extract of the error symbol candidate extracts two or more error symbol candidates for at least one group among the plurality of groups.
9. The electronic device of claim 1 , wherein the flit is interleaved with respect to the plurality of ECC groups.
10. The electronic device of claim 1 , wherein the CRC decoder performs the CRC decoding on the updated flit and requests retransmission of the flit when the CRC decoding of the updated flit fails.
11. An electronic device comprising:
a first circuit configured to generate a converted signal by performing an analog-to-digital conversion (ADC) and equalizing a Pulse Amplitude Modulation-4 (PAM-4) signal received through a link;
a second circuit configured to convert the converted signal into a flit including a plurality of PAM-4 symbols arranged into a plurality of groups, and to perform Error Correction Code (ECC) decoding and cyclic redundancy check (CRC) decoding on the flit to generate an ECC decoded flit for each of the plurality of groups; and
an erasure decoding unit,
wherein when the CRC decoding fails,
for each of the groups, the erasure decoding unit is configured to:
calculate a log likelihood ratio (LLR) for each of the PAM-4 symbols of the corresponding group, to extract an error symbol candidate from among the PAM- 4 symbols of the corresponding group based on the LLR, and
erase the error symbol candidate from the corresponding group to update the flit, and
the electronic device is configured to perform the ECC decoding on the updated flit.
12. The electronic device of claim 11 , wherein the first circuit is configured to generate the converted signal for each of a plurality of lanes included in the link.
13. The electronic device of claim 11 , wherein the second circuit comprises:
an ECC decoder configured to perform the ECC decoding on the flit; and
a CRC decoder configured to perform the CRC decoding on the ECC decoded flit to obtain data.
14. The electronic device of claim 11 , wherein the erasure decoding unit comprises:
an LLR calculation unit configured to calculate the LLR for each of 2-bits included in each of the PAM-4 symbols from the converted signal;
a least reliable symbol (LRS) search unit configured to compare the LLR with a preset threshold value in units of bits, to extract the error symbol candidate, and to generate an LRS array corresponding to position information of the error symbol candidate; and
an erasure decoder configured to carry out the perform of the ECC decoding on the updated flit based on the LRS array.
15. The electronic device of claim 14 , wherein the LRS search unit further comprises:
a threshold comparing unit configured to generate a least reliable bit (LRB) array by binarizing a bit having the LLR less than the preset threshold value and a bit having the LLR greater than or equal to the preset threshold value in the flit;
a logic circuit configured to convert the LRB array into ECC symbol units using a logical OR operation to generate the LRS array;
an LRS counter configured to count the number of error symbol candidates from the LRS array;
a comparing unit configured to compare the number of error symbol candidates with a preset number of candidates, and configured to output the LRS array to the erasure decoder when the number of error symbol candidates is the same as the preset number of candidates; and
a threshold control unit configured to adjust the preset threshold value when the number of error symbol candidates is different from the preset number of candidates.
16. The electronic device of claim 14 , wherein the LRS array specifies a position of the error symbol candidate.
17. A method of operating an electronic device, the method comprising:
performing Error Correction Code (ECC) decoding on a flit including a plurality of Pulse Amplitude Modulation-4 (PAM-4) symbols arranged into a plurality of groups to generate an ECC decoded flit for each of the plurality groups;
performing cyclic redundancy check (CRC) decoding on the ECC decoded flit;
when the CRC decoding fails,
for each of the groups,
calculating a log likelihood ratio (LLR) for each of the PAM-4 symbols of the corresponding group;
extracting an error symbol candidate from among the PAM-4 symbols of the corresponding group based on the LLR; and
performing erasure decoding on the corresponding group based on the error symbol candidate to update the flit.
18. The method of claim 17 , wherein the erasure decoding erases the error symbol candidate from the corresponding group to update the flit and performs the ECC decoding on the updated flit.
19. The method of claim 17 , further comprising:
generating a least reliable bit (LRB) array by binarizing a bit having the LLR less than a preset threshold value and a bit having the LLR greater than or equal to the preset threshold value in the flit; and
converting the LRB array into ECC symbol units to generate a least reliable symbol (LRS) array.
20. The method of claim 19 , further comprising:
increasing the preset threshold value when the number of error symbol candidates is less than the preset number of candidates, and decreasing the preset threshold value when the number of error symbol candidates exceeds the preset number of candidates.