Attaining Forney's bound for erasure decision by likelihood-ratio test plus threshold decision

We propose a new erasure decision scheme for decoding with erasures and show that the scheme also attains the bounds on the erasure probability and undetected error probability which are first derived for Forney's (1968) optimal scheme. The new scheme gives, when applied to convolutional codes, bounds which are related to those for block codes by Forney's inverse concatenation construction without substantial increase in decoder complexity.