Decoding based on randomized hard decisions
View Patent ↗An apparatus having a memory and a controller is disclosed. The memory is configured to store a codeword. The controller is configured to (i) determine one or more least-reliable bit positions in a soft-decision version of the codeword in response to failing to decode a hard-decision version of the codeword, (ii) generate a trial codeword by selecting at random a respective value in one or more trial positions among the least-reliable bit positions in the hard-decision codeword and (iii) perform a hard-decision decoding of the trial codeword.
1. An apparatus comprising:
a memory configured to store data; and
a controller configured to receive a codeword from the memory, determine a plurality of log-likelihood ratios of the codeword in response to a failure to decode the codeword using a hard-decision decoding, determine one or more least-reliable bit positions in the codeword based on the log-likelihood ratios, generate a trial codeword by selecting at random a respective value in one or more trial positions among the least-reliable bit positions in the codeword, and perform the hard-decision decoding on the trial codeword.
2. The apparatus according to claim 1 , wherein the log-likelihood ratios are obtained via a plurality of reads of the codeword from the memory at a plurality of reference voltages.
3. The apparatus according to claim 1 , wherein the controller is further configured to generate the log-likelihood ratios.
4. The apparatus according to claim 1 , wherein the selection of the respective value of a particular one of the trial positions is weighted based on a corresponding one of the log-likelihood ratios.
5. The apparatus according to claim 1 , wherein the controller is further configured to iterate a selection of the trial positions, the generation of the trial codeword, and the hard-decision decoding of the trial codeword until an end condition is reached.
6. The apparatus according to claim 5 , wherein the end condition comprises a successful decoding of a current iteration of the trial codeword.
7. The apparatus according to claim 1 , wherein the hard-decision decoding comprises one of a low density parity check decoding, a Bose-Chaudhuri-Hocquenghem decoding, and a Reed-Solomon decoding.
8. The apparatus according to claim 1 , wherein the least-reliable bit positions are determined by comparing the log-likelihood ratios of the codeword to a threshold.
9. The apparatus according to claim 1 , wherein the memory and the controller form part of a solid-state drive.
10. A method of decoding based on randomized hard decisions, comprising the steps of:
receiving a codeword at a controller from a memory;
determining a plurality of log-likelihood ratios of the codeword in response to a failure to decode the codeword using a hard-decision decoding;
determining one or more least-reliable bit positions in the codeword based on the log-likelihood ratios;
generating a trial codeword by selecting at random a respective value in one or more trial positions among the least-reliable bit positions in the codeword; and
performing the hard-decision decoding on the trial codeword.
11. The method according to claim 10 , further comprising the step of:
generating the log-likelihood ratios in the controller.
12. The method according to claim 10 , wherein the selection of the respective value of a particular one of the trial positions is weighted based on a corresponding one of the log-likelihood ratios.
13. The method according to claim 10 , further comprising the step of:
iterating a selection of the trial positions, the generation of the trial codeword, and the hard-decision decoding of the trial codeword until an end condition is reached.
14. The method according to claim 13 , wherein the end condition comprises a successful decoding of a current iteration of the trial codeword.
15. The method according to claim 10 , wherein the hard-decision decoding comprises one of a low density parity check decoding, (ii) a Bose-Chaudhuri-Hocquenghem decoding, and (iii) a Reed-Solomon decoding.
16. The method according to claim 10 , further comprising the step of:
selecting the trial positions in an ascending order of reliability from a predetermined number of the least-reliable bit positions.
17. The method according to claim 10 , further comprising the step of:
selecting the trial positions at random from a predetermined number of the least-reliable bit positions.
18. An apparatus comprising:
an interface configured to process a plurality of read/write operations to/from a memory; and
a control circuit configured to receive a codeword from the memory via the interface, determine a plurality of log-likelihood ratios of the codeword in response to a failure to decode the codeword using a hard-decision decoding, determine one or more least-reliable bit positions in the codeword based on the log-likelihood ratios, generate a trial codeword by selecting at random a respective value in one or more trial positions among the least-reliable bit positions in the codeword, and perform the hard-decision decoding on the trial codeword.
19. The apparatus according to claim 18 , wherein the interface and the control circuit are part of a solid-state drive.
20. The method according to claim 10 , wherein the steps are performed in a solid-state drive.