FA-72279 / Error-correcting codes / Member archive

Chase combining saturates after every addition · case 04

Retransmissions that disagree strongly are combined with the wrong sign or magnitude.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Hybrid-ARQ chase combining. txs are equal-length LLR vectors from successive transmissions (None where a position was not received). Combined LLR = sum of received values, saturated once at the end to [-clip, clip]. Hard decision: positive -> 0, negative -> 1, zero -> None (undecided). Return [combined, hard]; empty or ragged input returns None.

Why this case matters

LTE/5G receivers soft-combine retransmissions before decoding; saturating too early discards information.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression [[[-1, 0, 0], [-9, 8, 0], [11, -9, -6]], 7]	`[[4, -2, -6], [0, 1, 1]]`	`[[1, -1, -6], [0, 1, 1]]`	Failed

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