decodeout.m

卷积码译码值最终输出算法

%decode_out is last out.卷积码译码值最终输出算法，输入为软迭代编码输入，输出为软译码输出 即SISO算法。Tested 2005.4.23
function out=decodeout(x1,y1) %x1=L_encodedata1,y1=L_encoderdata2
% data=[1,0,1,1,0,1];
len=length(x1);
%x=zeros(1,len);
%y=zeros(1,len);
x=zeros(1,len+1);
y=zeros(1,len+1);
%z=zeros(1,len+1);
x(2:len+1)=x1(1:len);
y(2:len+1)=y1(1:len);
%z(2:len+1)=z1(1:len);

%out_up=zeros(1,len);
%out_down=zeros(1,len);
out=zeros(1,len);                %输出值
a=zeros(len,8);                  %前向递归值
b=zeros(len+1,8);               %后向递归值
temp=zeros(1,8);                %摸板对数似然比
factor=0;
gama_with_info=0;               %r的值
gama_yk0=0;
gama_yk1=0;
%initialize a0,a1,b             %书上有对应

a(1,1)=1;
b(len+1,1)=1.0/len;
for i=2:8
    a(1,i)=0;                   %1.0/len;
    b(len+1,i)=1.0/len;
end

%compute the gama
judge=zeros(8,8);
c=zeros(8,8);
d=zeros(8,8,2);
%matrix judge[i][j] judge the probability of the state i turn into the state j
	judge(1,1)=1;
    judge(1,2)=1;  
	judge(2,3)=1;
    judge(2,4)=1;
	judge(3,5)=1;
    judge(3,6)=1;
	judge(4,7)=1;
    judge(4,8)=1;
	judge(5,1)=1;
    judge(5,2)=1;
	judge(6,3)=1;
    judge(6,4)=1;
	judge(7,5)=1;
    judge(7,6)=1;
	judge(8,7)=1;
    judge(8,8)=1;
	
%the value of c(i)(j) is the input data of encoder that tansform state i into state j
	c(1,1)=0;
    c(1,2)=1;   
	c(2,3)=0;
    c(2,4)=1;
	c(3,5)=0;
    c(3,6)=1;
	c(4,7)=0;
    c(4,8)=1;
	c(5,1)=0;
    c(5,2)=1;
	c(6,3)=0;
    c(6,4)=1;
	c(7,5)=0;
    c(7,6)=1;
	c(8,7)=0;
    c(8,8)=1;
	
  
 %//  the output data when state i turn into state j

    d(1,1,1)=0;d(1,1,2)=0;%d(state,nextstate,'1'up/'2'down)=output
    d(1,2,1)=1; d(1,2,2)=1;   
	d(2,3,1)=1;d(2,3,2)=1;
    d(2,4,1)=0;d(2,4,2)=0;
	d(3,5,1)=0;d(3,5,2)=1;
    d(3,6,1)=1;d(3,6,2)=0;
	d(4,7,1)=1;d(4,7,2)=0;
    d(4,8,1)=0;d(4,8,2)=1;
	d(5,1,1)=1;d(5,1,2)=1;
    d(5,2,1)=0; d(5,2,2)=0;
	d(6,3,1)=0;d(6,3,2)=0;
    d(6,4,1)=1;d(6,4,2)=1;
	d(7,5,1)=1;d(7,5,2)=0;
    d(7,6,1)=0; d(7,6,2)=1;
	d(8,7,1)=0;d(8,7,2)=1;
    d(8,8,1)=1;d(8,8,2)=0;
	

%var1=computevariance(x1);
%var2=computevariance(y1);

% var1=var(x1);
Lc1=1; Lc2=1;
%Lc1=2/var1;
%Lc2=2/var2;

%compute the value of a                   %前向递推
for k=2:len
    factor=0;
    for m=1:8
        temp(m)=0;
        for fm=1:8
            if (judge(fm,m)==0)
                gama_with_info=0;
            else
                x_up=(2*d(fm,m,1)-1);%*(0.1746);
	            x_down=(2*d(fm,m,2)-1);%*(0.1746);
                gama_with_info=exp(0.5*(x_up*(Lc1*x(k))+Lc2*y(k)*x_down));  %这个公式在书上
                if (gama_with_info==inf)
                       gama_with_info=300;
                elseif(gama_with_info>300)
                       gama_with_info=300;
                   
                end
            end
            temp(m)=temp(m)+gama_with_info*a(k-1,fm); 
            if (temp(fm)==inf)
              temp(fm)=300;
          end
        end
        factor=factor+temp(m);    
    end
   	for i=1:8
	   a(k,i)=temp(i)/factor;        %归一化
    end
end 
%compute the value of b                      %后向递推            
for k=len:-1:2
    factor=0;
    for fm=1:8
        temp(fm)=0;
        for m=1:8
            if (judge(fm,m)==0)
                gama_with_info=0;
            else
                x_up=(2*d(fm,m,1)-1);%*(0.1746);
	            x_down=(2*d(fm,m,2)-1);%*(0.1746);
                gama_with_info=exp(0.5*(x_up*(Lc1*x(k+1))+Lc2*y(k+1)*x_down)); %这个公式在书上
                     if (gama_with_info==inf)
                       gama_with_info=300;
                   elseif(gama_with_info>300)
                       gama_with_info=300;
                   
                    end
            end
           % factor=factor+gama_with_info*a(k,fm);
			temp(fm)=temp(fm)+gama_with_info*b(k+1,m);
            if (temp(fm)==inf)
              temp(fm)=300;
            end
         
        end
         factor=factor+temp(fm);  
    end    
    for i=1:8
		b(k,i)=temp(i)/factor;   %归一化
    end
end

%compute the output y_up and y_down
for k=2:len+1
    temp0=0;  %out(k-1)=log(temp1/temp0);

    temp1=0;
  

    for m=1:8
        for fm=1:8
            if (judge(fm,m)==0)
                gama_yk0=0;                    %分支度量x=-1
                gama_yk1=0;                    %分支度量x=1
                 
            else
                x_up=(2*d(fm,m,1)-1);%*(0.1746);
                x_down=(2*d(fm,m,2)-1);
                 if (c(fm,m)==1)
                    gama_yk0=0;
                    gama_yk1=exp(0.5*(Lc1*x(k)*x_up+Lc2*y(k)*x_down));%y(x)=0,表示删余。gama_yk=1,对求a(k-1,fm),b(k,m)无影响。
                else
                    gama_yk0=exp(0.5*(Lc1*x(k)*x_up+Lc2*y(k)*x_down));
                    gama_yk1=0;
                end
                
                
                    if (gama_yk0==inf)            %inf代表无穷大
                       gama_yk0=300;
                   elseif(gama_yk0>300)
                       gama_yk0=300;
                   
                    end
                    
                    if (gama_yk1==inf)
                       gama_yk1=300;
                    elseif(gama_yk1>300)
                       gama_yk1=300;
                    end
            
            end
            temp1=temp1+gama_yk1*a(k-1,fm)*b(k,m);         %摸板1
			temp0=temp0+gama_yk0*a(k-1,fm)*b(k,m);         %摸板-1
            
        end
    end
       if((temp0==0)&(temp1==0))
           Temp=0;
       elseif((temp0==0)&(temp1~=0))
      Temp=300;
      elseif((temp1==0)&(temp0~=0))
      Temp=-300;
      else
      Temp=log(temp1/temp0);
      end
        if (Temp==Inf)
        out(k-1)=300;
        elseif(Temp==-Inf)
        out(k-1)=-300;
        else
        out(k-1)=Temp;
        end 
       
     
end
%compute the decoding output
% temp = sign(out);
for i=1:len
    if out(i)>0
        out(i) = 1;
    else out(i) = 0;
    end
end