Methodology and apparatus for soft-information detection and LDPC decoding on an ISI channel
View Patent ↗A system comprising a plurality of channel detectors (CDs) receiving quantized and equalized ISI channel information indicative of an LDPC codeword. The channel information is split for input to the CDs, such that each CD receives channel information indicative of a portion of the LDPC codeword. Each CD outputs at least first soft information for bits of the codeword portion of that CD. The first soft information for the codeword is received by an LDPC decoder, which uses the soft information to produce a user bit sequence and second soft information about the user bit sequence. The system can cause the second soft information to be input to the plurality of CDs, such that iterative processing can occur for the codeword. Other aspects include a system providing clocking of one or more CDs at a frequency selected to balance codeword throughput of the CDs with codeword throughput of an LDPC decoder clocked by a second clock, and methods according to each system.
1. A receiver for an intersymbol interference (ISI) channel, comprising:
a plurality of channel detectors (CDs) operable to receive portions of a codeword signaled on the ISI channel, and to output bit decisions and first soft information; and
a low density parity check (LDPC) decoder operable to receive the bit decisions and the first soft information from the plurality of CDs and to output user bits for the codeword and second soft information that indicates the accuracy of the user bits.
2. The receiver of claim 1 , where the LDPC decoder is operable to provide the second soft information for input to the plurality of channel detectors for iterative processing between the plurality of CDs and the LDPC decoder, where the iterative processing begins in the plurality of CDs without intervening further iterations using the second soft information in the LDPC decoder, where a CD processes information for a portion of the codeword, where the iterative processing continues until the second soft information indicate that the outputted user bits meet a confidence threshold and where a CD in the plurality of CDs receives a portion of the codeword that is less than the whole codeword.
3. The decoder of claim 1 , further comprising a memory shared among the plurality of CDs and the LDPC decoder, where the plurality of CDs are operable to store the bit decisions and the first soft information in the memory, and where the LDPC decoder is further operable to retrieve the bit decisions and the first soft information from the memory, and
where the LDPC decoder is further operable to store at least the second soft information in the memory from which the plurality of CDs receive a portion of the second soft information for processing.
4. The decoder of claim 1 , further comprising a first clock operable at a first frequency for provision to the plurality of CDs and a second clock operable at a lower frequency than the first frequency for provision to the LDPC decoder.
5. The decoder of claim 1 , comprising
a read head for reading the channel information from a recording medium; and
a divider operable to divide the codeword into a plurality of portions for the plurality of CDs.
6. The decoder of claim 1 , where the confidence threshold is specified as a number of iterations.
7. The decoder of claim 1 , where the confidence threshold is specified as a number of iterations or as an error rate below a specified amount, where if the error is below the specified amount, remaining iterations are not completed.
8. The decoder of claim 7 , where the error rate is specified as a frame error rate.
9. The decoder of claim 7 , where the error rate is specified as a bit error rate.
10. The decoder of claim 1 , where the first soft information includes Log Likelihood Ratios (LLRs) indicative of a likelihood that a user bit is either a 0 or a 1, and where the LLR is conveyed within a signed value that also conveys a corresponding bit decision.
11. The decoder of claim 1 , where the plurality of CDs are arranged in parallel to receive different portions of the codeword simultaneously.
12. A decoder for an intersymbol interference channel, comprising:
at least two channel detectors (CDs), where a CD is operable to receive information that indicates a portion of a codeword signaled on the channel, and to output first soft information for the portion of the codeword; and
a low density parity check (LDPC) decoder operable to input the first soft information for the codeword and to output user bits for the codeword and second soft information indicating reliability of the user bits outputted, and
where the at least two CDs are operable to process the codeword in a time approximating a time required by the LDPC decoder to process the first soft information and produce the second soft information and the user bits.
13. The decoder of claim 12 , comprising a memory shared between the at least two CDs and the LDPC decoder, where the at least two CDs are operable to store the first soft information in the memory and the LDPC decoder is operable to retrieve the first soft information from the memory; and
where the LDPC decoder is operable to store at least the second soft information in the memory from which the CDs are operable to access the second soft information for processing, and where the CDs operate in parallel on different portions of the codeword.
14. A method of retrieving digital information from an intersymbol interference (ISI) channel, comprising:
receiving information signaled on the ISI channel, where the information is indicative of a low density parity check (LDPC) codeword that includes a plurality of bits;
dividing the channel information into a plurality of portions and distributing different portions of the plurality of portions in parallel to the plurality of channel detectors (CDs);
generating, in the CDs, first soft information for the plurality of portions;
inputting the first soft information into an LDPC decoder; and
decoding the LDPC codeword in the LDPC decoder, and outputting user bits for the codeword and second soft information for the user bits.
15. The method of claim 14 , comprising, at a channel encoder,
interleaving, into a string, user bits for transmission on the ISI channel with a plurality of zero bits determined by multiplying a number of CDs at the decoder by a number of registers in a state machine model of the ISI channel, where the plurality of zero bits are distributed at intervals through the codeword;
generating parity bits for an output of an interleaver based on an LDPC code generator matrix;
assembling the codeword from the user bits interleaved with the plurality of zero bits and the generated parity bits; and
transmitting the codeword on a channel for reception at the LDPC decoder.
16. The method of claim 14 , where the CDs are clocked at a higher frequency than the LDPC decoder.
17. The method of claim 14 , where the plurality of portions is equal to the number of the CDs.
18. The method of claim 14 , where the plurality of portions is more than the number of the CDs.
19. A system for transmitting information over an intersymbol interference (ISI) channel, comprising:
a processor operable to produce a low density parity check (LDPC) codeword comprising user bits and parity bits generated based on the user bits and an LDPC generator matrix;
a channel encoder operable to input the LDPC codeword into the ISI channel;
a receiver to obtain channel data representative of the LDPC codeword from the ISI channel and output the channel data for reception by a plurality of channel detectors (CDs), where the CDs are operable to produce first soft information for bits represented by portions of the channel data; and
an LDPC decoder operable to receive the first soft information, and to perform LDPC decoding for the generator matrix used during encoding, and output user bits and second soft information indicating reliability of the outputted user bits,
where the CDs are operable to receive the second soft information for iterative processing of the channel data, and update the first soft information based on the further processing, the iterative processing continuing until the reliability indicated by the second soft information satisfies a criterion.
20. The system of claim 19 , comprising a memory accessible by the plurality of channel detectors and the LDPC decoder, the memory for storing at least the first soft information and the second soft information, where the LDPC decoder accesses the first soft information from the memory, and where the plurality of CDs access the second soft information from the memory.
21. The system of claim 19 , comprising an interleaver operable to pad a string comprising the user bits and the parity bits with a number of zero bits determined based on a number of the channel detectors (CDs) present at a receiver and a number of states in a model of the ISI channel, where the interleaver is operable to pad the zero bits between sections comprising portions of user bits and parity bits, the number of sections is determined based on the number of CDs in the receiver, and where the plurality of CDs operate in parallel on different portions of the codeword.