Implements four LDPC code analyses for photon-starved optical channels:
- Rate sweep: compare FER across 1/2, 1/3, 1/4, 1/6, 1/8 IRA staircase codes
- Matrix comparison: original staircase vs improved staircase vs PEG ring
- Quantization sweep: 4-16 bit and float precision impact on FER
- Shannon gap: binary-input Poisson channel capacity limits via binary search
Core infrastructure includes generic IRA staircase builder, GF(2) Gaussian
elimination encoder for non-triangular matrices, parameterized layered
min-sum decoder with variable check degree, and BFS girth computation.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
- Fixed cyclic shift convention (QC-LDPC P_s is left shift, not right)
- Fixed encoder to solve rows sequentially (row 0 first for p1, then 1-6)
- Fixed decoder to only gather connected columns per CN (staircase has dc=2-3)
- Fixed LLR sign convention: positive = bit 0 more likely
- Decoder validates at lam_s >= 4 photons/slot (~90% frame success)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
