decoder.m

很好的OFDM的基于MATLAB的仿真程序包

function [output,Error] = decoder(input)


Linput = length(input);          % length of the input
Error=zeros(1,4);                % error metric for each state, updated each time instant
newError = zeros(1,4);           % update of the error metric
temp_output1 = []  ;             % temporary possible output computed for state1, updated each time instant   
temp_output2 = []  ;             % temporary possible output computed for state2, updated each time instant   
temp_output3 = []  ;             % temporary possible output computed for state3, updated each time instant   
temp_output4 = []  ;             % temporary possible output computed for state4, updated each time instant   


%The first two step in the trellis are particular, since the first state is
%always 00.

%initialization for the first step
Error(1)=sum(input(1:2) ~= [0 0]);
Error(3)=sum(input(1:2) ~= [1 1]);

%for the second step
newError(1)=Error(1)+sum(input(3:4) ~= [0 0]);
temp_output1 = [0 0];
newError(2)=Error(3)+sum(input(3:4) ~= [1 0]);
temp_output2 = [1 0];
newError(3)=Error(1)+sum(input(3:4) ~= [1 1]);
temp_output3 = [0 1];
newError(4)=Error(3)+sum(input(3:4) ~= [0 1]);
temp_output4 = [1 1];

Error=newError;

for k = 5:2:Linput
        
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%for each step in the trellis we update the counter of errors of each state
%and temporary output (the beginning of the possible final output) of each
%state.

%There are two possibilities to reach the state 00 (1):
%_ state 00 (1), input 0 --> code 00
%_ state 01 (2), input 0 --> code 11

        [newError(1),i1] = min([Error(1)+ sum(input(k:k+1)~= [0 0]),Error(2)+ sum(input(k:k+1)~= [1 1])]);
        if i1 == 1
            newtemp_output1 = [temp_output1 0];
        else
            newtemp_output1 = [temp_output2 0];
        end
 
%There are two possibilities to reach the state 01 (2):
%_ state 10 (3), input 0 --> code 10
%_ state 01 (4), input 0 --> code 01

        [newError(2),i2] = min([Error(3)+ sum(input(k:k+1)~= [1 0]),Error(4)+ sum(input(k:k+1)~= [0 1])]);
        if i2 == 1
            newtemp_output2 = [temp_output3 0];
        else
            newtemp_output2 = [temp_output4 0];
        end
        
%There are two possibilities to reach the state 01 (3):
%_ state 00 (1), input 1 --> code 11
%_ state 01 (2), input 1 --> code 00
        
        [newError(3) i3] = min([Error(1)+ sum(input(k:k+1)~= [1 1]),Error(2)+ sum(input(k:k+1)~= [0 0])]);
        if i3 == 1
            newtemp_output3 = [temp_output1 1];
        else
            newtemp_output3 = [temp_output2 1];
        end
        
%There are two possibilities to reach the state 11 (4):
%_ state 10 (3), input 1 --> code 01
%_ state 11 (4), input 1 --> code 10

        [newError(4) i4] = min([Error(3)+ sum(input(k:k+1)~= [0 1]),Error(4)+ sum(input(k:k+1)~= [1 0])]);
        if i4 == 1
            newtemp_output4 = [temp_output3 1];
        else
            newtemp_output4 = [temp_output4 1]; 
        end
        
 %we update the values for the next step
 
        Error=newError;
        temp_output1=newtemp_output1;
        temp_output2=newtemp_output2;
        temp_output3=newtemp_output3;
        temp_output4=newtemp_output4;

end

%At the end, we compare the error metric for each state. We take the min
%value and take the corresponding output.

[Error_total i] = min([Error(1), Error(2), Error(3), Error(4)]);
switch i
    case{1}
        output=temp_output1;
    case{2}
        output=temp_output2;
    case{3}
        output=temp_output3;
    case(4)
        output=temp_output4;
end