Decoding method
View Patent ↗A method for decoding forward error correction (FEC) encoded data. A stream of units of FEC encoded bits are received, where the units are derived from a transmitted signal, where each unit represents a one-bit data value, and where each unit includes correctness bits. Preferably, the stream of units of FEC encoded bits are decoded by using the quality level of bits to perform soft-decision convolution decoding on the stream of units of FEC bits, where the soft-decision convolution decoding produces, for block decoding, a stream of symbols made up of bits. Subsequences of units that are prone to erroneous soft-decision convolution decoding are detected by determining, for the sub-sequences whether the distribution of quality bits indicate the units are below a threshold level of correctness, and by comparing characteristics of that distribution to a given set of characteristics predetermined to be prone to result in incorrect decoding.
1. A method of ranking bits in a data stream comprising:
at a bit quality evaluator,
defining a binary one bit as a first voltage −V relative to reference voltage and a binary zero bit as a second voltage +V relative to the reference voltage;
defining a first low quality region between a first threshold voltage −T 1 and a second threshold voltage +T 1 , wherein the absolute value of −T 1 is less than the absolute value of −V by a first predetermine amount and the second threshold is less than +V by the first predetermined amount;
defining a second low quality region relative to a third threshold voltage −T 2 , wherein the absolute value of −T 2 is greater than the absolute value of −V by a second predetermine amount;
defining a third low quality region relative to a fourth threshold voltage +T 2 , wherein +T 2 is greater than +V by the second predetermine amount;
defining a first high quality region as between and including −T 1 and −T 2 and a second high quality region as between and including +T 1 and +T 2 ;
identifying a bit as a poor quality bit if its voltage is within a quality region selected from the group consisting of the first low quality region, the second low quality region, and the third low quality region;
tagging the poor quality bits with tagging data, and
sending the data stream and the tagging data to an error detector and a first decoder; at the first decoder,
receiving the data stream and tagging data,
decoding the data stream, and
sending the decoded data stream to a second decoder; at the error detector,
determining whether a concentration of poor quality bits within a sliding window of bits in the data stream exceeds a concentration threshold based on the tagging data,
predicting that the first decoder will fail to correct errors when the concentration of poor quality bits within the sliding window exceeds the concentration threshold, and
instructing the second decoder to perform erasure on symbols likely to contain errors based on the tagging data; and
at the second decoder, outputting decoded corrected data.
2. The method of claim 1 , wherein the reference voltage is zero, the first voltage −V is −1.0 volts, and the second voltage +V is +1.0 volts.
3. The method of claim 1 , wherein the second decoder is a Reed Solomon decoder.
4. The method of claim 1 , wherein the quality of the bits in the data stream is based on a quality of a received transmission signal from which the bits are derived.
5. The method of claim 1 , wherein the first decoder comprises a Viterbi decoder.
6. The method of claim 5 , wherein the sliding window precedes decoding by the Viterbi decoder.
7. The method according to claim 1 , wherein the concentration is expressed as M out of N, where N is a number of bits comprising a sequence of bits in the data stream, and M is a count of bits, in the sequence, that have a quality below the quality threshold.
8. The method of claim 7 , wherein N is a fixed number and corresponds to bit width of the sliding window.
9. The method of claim 7 , wherein N is dynamically set based on conditions within the first decoder.
10. A method of ranking bits in a data stream comprising:
at a bit quality evaluator,
defining a binary one bit as a first voltage −V relative to reference voltage and a binary zero bit as a second voltage +V relative to the reference voltage;
defining a first low quality region between a first threshold voltage −T 1 and a second threshold voltage +T 1 , wherein the absolute value of −T 1 is less than the absolute value of −V by a first predetermine amount and the second threshold is less than +V by the first predetermined amount;
defining a second low quality region relative to a third threshold voltage −T 2 , wherein the absolute value of −T 2 is greater than the absolute value of −V by a second predetermine amount;
defining a third low quality region relative to a fourth threshold voltage +T 2 , wherein +T 2 is greater than +V by the second predetermine amount;
defining a first high quality region as between and including −T 1 and −T 2 and a second high quality region as between and including +T 1 and +T 2 ;
identifying a bit as a poor quality bit if its voltage is within a quality region selected from the group consisting of the first low quality region, the second low quality region, and the third low quality region;
tagging the poor quality bits with tagging data, and
sending the data stream and the tagging data to an error detector and a Viterbi decoder;
at the Viterbi decoder,
receiving the data stream and tagging data,
decoding the data stream, and
sending the decoded data stream to a Reed-Solomon decoder;
at the error detector,
determining whether a concentration of poor quality bits within a sliding window of bits in the data stream exceeds a concentration threshold based on the tagging data,
predicting that the Viterbi decoder will fail to correct errors when the concentration of poor quality bits within the sliding window exceeds the concentration threshold, and
instructing the Reed-Solomon decoder to perform erasure on symbols likely to contain errors based on the tagging data; and
at the Reed-Solomon decoder, outputting decoded corrected data.
11. The method of claim 10 , wherein the reference voltage is zero, the first voltage −V is −1.0 volts, and the second voltage +V is +1.0 volts.
12. The method according to claim 10 , wherein the concentration is expressed as M out of N, where N is a number of bits comprising a sequence of bits in the data stream, and M is a count of bits, in the sequence, that have a quality below the quality threshold.
13. The method of predicting of claim 12 , wherein N is a fixed number and corresponds to bit width of the sliding window.
14. The method of predicting of claim 12 , wherein N is dynamically set based on conditions within the Viterbi decoder.
15. The method of claim 12 , wherein the quality of the bits in the data stream is based on a quality of a received transmission signal from which the bits are derived.