Bridging the Gap Between Parallel and Serial Concatenated Codes Naveen Chandran CMG plc Richmond, VA Matthew C. Valenti (presenter) Lane Dept. of Comp. Sci. & Elect. Eng. West Virginia University This work was supported by the Office of Naval Research under grant N00014-00-0655
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Bridging the Gap Between Parallel and Serial Concatenated Codes
Naveen Chandran CMG plc Richmond, VA Matthew C. Valenti (presenter) Lane Dept. of Comp. Sci. & Elect. Eng. West Virginia University This work was supported by the Office of Naval Research under grant N00014-00-0655. Bridging the Gap Between Parallel and Serial Concatenated Codes. - PowerPoint PPT Presentation
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Bridging the Gap Between
Parallel and Serial Concatenated Codes
Naveen ChandranCMG plc
Richmond, VA
Matthew C. Valenti (presenter)Lane Dept. of Comp. Sci. & Elect. Eng.
West Virginia University
This work was supported by the Office of Naval Researchunder grant N00014-00-0655
Overview Review of Concatenated Convolutional
Codes Parallel (PCCC) vs. serial (SCCC) concatenation
PCCC’s are a special case of SCCC’s In other words, SCCC’s are a generalization of
PCCC’s. It is possible to modify a SCCC encoder to
make it produce a PCCC. Illustrative proof Implications
A new class of hybrid concatenated codes Simulation results
RSC: Recursive Systematic Convolutional Codes. For PCCC both encoders are RSC. For SCCC at least the inner encoder is recursive.
Iterative decoding algorithm. MAP/APP based.
“SISO” Soft-Input, Soft-Output Log-MAP: In logarithmic domain.
PCCC’s Features of parallel concatenated
convolutional codes (PCCC’s): Both encoders are RSC. Performance close to capacity limit for BER
down to about 10-5 or 10-6. BER flooring effect at high SNR.
RSCEncoder #1
RSCEncoder #2
NonuniformInterleaver
Input
ParityOutput
Systematic Output
ix
SCCC’s Features of serially concatenated
convolutional codes (SCCC’s): Inner encoder must be recursive.
Could even be just a differential encoder. Outer encoder can be recursive or nonrecursive. Performance not as good as PCCC’s at low SNR. However, performance is better than PCCC’s at
Observations Results for larger frame sizes (1K, 2K,
4K, and 8K) are given in the paper. In general,
A double parity puncturing ratio close to 100% gives performance close to PCCC.
A double parity puncturing ratio close to 50% gives performance close to SCCC.
A double parity puncturing ratio of about 80% gives performance halfway between PCCC & SCCC
Relationship to Divsalar and Pollara’s Hybrid Codes Hybrid codes have been previously
proposed by D. Divsalar and F. Pollara, “Hybrid concatenated codes and iterative
decoding,” JPL TDA Progress Report, April 1997.
Our hybrid codes are different Only 1 interleaver and 2 encoders. Similar performance, but at less complexity.
Conclusion An SCCC encoder can be used to encode a
PCCC. This result was used to develop a new class of
hybrid concatenated codes with performance between that of SCCC and PCCC codes.
The decision to use PCCC or SCCC codes no longer needs to be “black and white”; rather a middle ground (shades of “gray”) exists that can give the system designer more flexibility.
Formal guidelines for designing hybrid codes are needed