www.pudn.com > Simulation.zip > SoftVitDec.m

function [xx, BestMetric] = SoftVitDec(G, y, ZeroTail); 
 
% 
% SoftVitDec			This function performs Viterbi Decoding for Soft Decision Inputs 
% 
% 						Inputs: G = [g1; g2; ...; gN] - matrix of generation polynomials 
%                                    y - encoded sequence 
%                                    ZeroTail - 1/0 - defines if contains zero tail 
% 
% 						Outputs: xx - recovered encoded bits 
%                                       BestMetric - final best metric 
% 
%           Rule =  MAXIMAL METRIC WINS (Likelihood function) 
%            
 
L = size(G, 1);     % --- num of output chips 
K= size(G, 2);      % --- length of generation polinom 
N = 2^(K-1);         % --- number of states 
T = length(y)/L;                % --- maximum trellis depth 
 
%------- Output Generation Matrix Definition (contains all possible state transactions)------------- 
OutMtrx = zeros(N, 2*L); 
for s = 1:N 
    in0 = ones(L, 1)*[0, (dec2bin((s-1), (K-1))-'0')]; 
    in1 = ones(L, 1)*[1, (dec2bin((s-1), (K-1))-'0')]; 
     
    out0 = mod(sum((G.*in0)'), 2); 
    out1 = mod(sum((G.*in1)'), 2); 
     
    OutMtrx(s, :) = [out0, out1]; 
end 
OutMtrx = sign(OutMtrx-1/2); 
 
%--------------------------------------------------------------------------------------------- 
%------------------------------------ Trellis SECTION ---------------------------------- 
%--------------------------------------------------------------------------------------------- 
%------- Path Mertrix Initialization ------------- 
PathMet = [100; zeros((N-1), 1)];       % Initial State = 100 (better initial conditions) 
PathMetTemp = PathMet(:,1); 
 
Trellis = zeros(N, T); 
Trellis(:,1) = [0 : (N-1)]'; 
 
%------------------------ MAIN Trellis Calculation Loop --------------------------- 
y = reshape(y, L, length(y)/L); 
for t = 1:T 
     
    yy = y(:, t); 
    for s = 0:N/2-1 
        [B0 ind0] = max(  PathMet(1+[2*s, 2*s+1]) + [OutMtrx(1+2*s, 0+[1:L]) * yy; OutMtrx(1+(2*s+1), 0+[1:L])*yy] ); 
        [B1 ind1] = max(  PathMet(1+[2*s, 2*s+1]) + [OutMtrx(1+2*s, L+[1:L]) * yy; OutMtrx(1+(2*s+1), L+[1:L]) * yy] ); 
         
        PathMetTemp(1+[s, s+N/2]) =  [B0; B1]; 
        Trellis(1+[s, s+N/2], t+1) = [2*s+(ind0-1); 2*s + (ind1-1)];         
    end 
   PathMet = PathMetTemp; 
     
end 
 
%--------------------------------------------------------------------------------------------- 
%---------------------------------- Trace Back Section ----------------------------- 
%--------------------------------------------------------------------------------------------- 
%------- Find Best Path Mertric ------------- 
xx = zeros(T, 1); 
if (ZeroTail) 
    BestInd = 1; 
else 
    [Mycop, BestInd]  = max(PathMet); 
end 
 
BestMetric = PathMet(BestInd); 
xx(T) = floor((BestInd-1)/(N/2)); 
 
%------------------------ MAIN Trace Back Loop --------------------------- 
NextState = Trellis(BestInd, (T+1)); 
for t=T:-1:2 
    xx(t-1) = floor(NextState/(N/2)); 
    NextState = Trellis( (NextState+1), t); 
end 
 
if (ZeroTail) 
    xx = xx(1:end-K+1); 
end