This algorithm is reserved to the implementation of the Bahl, Cocke, Jelinek and Raviv (BCJR)
% algorithm. This function takes as input the channel output (corrupted
% data) and the a priori prob (we will set it to 1/2) and returns as output
% the APP Log Likelihood Ratio (LLR) for every data input. It is usually called a
% Soft Input Soft Output (SISO) decoder. It can be applied to any code
% having a finite state machine, in our case we will use it for rate-1/n convolutional codes.