FA-71929 / Error-correcting codes / Member archive

Convolutional encoder omits the zero tail · case 04

Decoders cannot terminate in state 0 and the last bits decode unreliably.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Rate-1/2, constraint-length-3 convolutional encoder with generators 7 (111) and 5 (101) octal. The register holds the current bit in bit 2 and the two previous bits below it; for each input bit output the g=7 parity then the g=5 parity, then shift. Two zero tail bits terminate the trellis. Return the output bit list.

Why this case matters

Satellite and wireless links protect data with the classic K=3 (7,5) convolutional code.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression [[1, 1, 0, 1, 1, 0, 0]]	`[1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1]`	`[1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0]`	Failed

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