trellis.m

Max Log MAP decoding

function [out, proba] = trellis(t, mp, m, tau, G)
%trellis du codeur R=1/n0; G est la matrice des coeffs des polynomes generateurs
%valeur de sortie: vecteur de longueur n0
%mp et m prennent des valeurs entre 1 et pow2(M)

K = size(G, 2);%constraint length
n0 = size(G, 1);%code rate rho=1/n0
M = K-1;%memory length

state_start = my_de2bi(mp-1, M, 'left-msb');
state_finish = my_de2bi(m-1, M, 'left-msb');

if ( ((t>=M) & (t<=(tau-M)) & (~any(state_start(1:end-1)-state_finish(2:end)))) | ...%all transitions are possible
        ((t<M) & (~any(state_finish(t+1:end)))) )%begin of trellis
    state = state_start;%initial state
    bit_in = state_finish(1);
    bits_out = [];
    for k=1:n0
        bits_out = [bits_out xorsum([bit_in state].*G(k, :))];
    end
    out = (bits_out - 0.5)*2;
    proba = 0.5;
elseif ( (t>(tau-M)) & (~any(state_finish(1:(t-tau+M)))) & (~any(state_start(1:end-1)-state_finish(2:end))) )%end of trellis
    state = state_start;%initial state
    bit_in = state_finish(1);
    bits_out = [];
    for k=1:n0
        bits_out = [bits_out xorsum([bit_in state].*G(k, :))];
    end
    out = (bits_out - 0.5)*2;
    proba = 1;
else
    out = [];
    proba = 0;
end