Method end device for source decoding a variable-length soft-input codewords sequence

A method for source decoding a variable-length soft-input codewords sequence (y [1:T]) into a soft-output bit sequence (Λv [1:T]), the variable-length soft-input input codewords sequence (y [1:T]) encoded in accordance with a VLC codewords table,

• the method comprising the acts of:
• A. a first stage of implementing a stack decoding algorithm for a sequential estimation of a hard-output bit sequence of said variable length soft-input codewords sequence, including storage of intermediate data contained in the stack and generated by the stack decoding algorithm ;
• and
• B. a second subsequent stage of post-processing the stored intermediate data for generating the soft-output bit sequence (Λv [1:T]), a soft-output (Λ(x [t])) being provided for each bit, wherein the second subsequent stage of post-processing the stored intermediate data comprises the step of approximating each soft-output Λ(x [t]) for each bit by:
• Λ(x[t])=log (Σe−μPi/Σe−μPi)
• 1≦i≦r 1≦i≦r
• TPi>=t TPi>=t
• {circumflex over (x)}Pi[t]=1 {circumflex over (x)}Pi[t]=0
• where Pi (i ∈ [1, . . . r]) are the r examined paths stored in the stack and μPi is the cumulative metric of path Pi, TPi is the length of path Pi and {circumflex over (x)}pi (t) is the tth hard bit of an hard bit sequence corresponding to path Pi.

A decoder apparatus for source decoding a variable-length soft-input codewords sequence (y [1:T]) into a soft-output bit sequence (Λv [1:T]),

• the variable-length soft-input input codewords sequence (y [1:T]) encoded in accordance with a VLC codewords table,
• the decoder comprising:
• means for implementing a stack decoding algorithm for a sequential estimation of an hard-output bit sequence of said variable length soft-input input codewords sequence, wherein at each step of the sequential estimation, a stack of paths is reordered placing a current path having a smallest cumulative metric among paths listed in the stack at a top of the stack, including storage means for storing intermediate data contained in the stack and generated by the stack decoding algorithm;
• and
• means for post-processing the stored intermediate data for generating the soft-output bit sequence (Λv [1:T]), a soft-output (Λ(x [t])) being provided for each bit.