outer_decode_u.asv

来自「短波信道抗多音干扰的性能分析及其仿真」· ASV 代码 · 共 124 行

%function outer_out_u=outer_decode_u(outer_input,trellis,formerstate)
% this function does the MAP decode process of the
% outer convolutional code to recover the information


source=[1,0	1	0	0	0	1	0	0	0];
outer_input=[-80	-30.985	80	-0.28763	-80	71.033	-12.165	13.807	-80	80;
             -80	-18.759	-25.702	5.7169	-80	10.152	-9.7001	-4.3942	-80	-34.39;
            -80	17.744	-27.097	80	-80	-8.6871	-9.3323	80	-80	25.345];
outer_input=outer_input/10;        
trellis=poly2trellis(3,[7,5]);
formerstate(:,:,1)=[0,1;2,3;4,4;4,4];
formerstate(:,:,2)=[4,4;4,4;0,1;2,3];
outer_input=outer_input/2;

number_of_states=trellis.numStates;
nextstate=trellis.nextStates;
fanout=trellis.numInputSymbols;
output=trellis.outputs;
number_of_out=trellis.numOutputSymbols;
depth_of_trellis=length(outer_input);

alpha=zeros(number_of_states,depth_of_trellis);
alpha(:,1)=[0;-1e10*ones(number_of_states-1,1)];
alpha1=zeros(1,fanout);
gamma=zeros(2*fanout,depth_of_trellis);
max=-1e10*ones(1,depth_of_trellis-1);
beta=zeros(number_of_states,depth_of_trellis);
beta(:,depth_of_trellis)=[0;-1e10*ones(number_of_states-1,1)];
beta1=zeros(1,fanout);

%trace forward to compute alpha
for i=1:depth_of_trellis-1
    for j=1:number_of_states
        for k=1:fanout
            if(formerstate(j,1,k)~=number_of_states)
                for h=1:fanout
                    t=output(formerstate(j,h,k)+1,k)+1;
                    if(t~=number_of_out)
                        gamma(h,i)=outer_input(t,i);
                    else
                        gamma(h,i)=0;
                    end
                    alpha1(h)=alpha(formerstate(j,h,k)+1,i)+gamma(h,i);
                    if(alpha1(h)<=-80)
                        alpha1(h)=0;
                    else
                        alpha1(h)=exp(alpha1(h));
                    end
                end
                if(sum(alpha1)>1e-30)
                     alpha(j,i+1)=log(sum(alpha1));
                else
                     alpha(j,i+1)=-1e10;
                end
                if(max(i)<alpha(j,i+1))
                     max(i)=alpha(j,i+1);
                end
            end
        end
    end
    alpha(:,i+1)=alpha(:,i+1)-max(i);
end
for j=1:number_of_states
    for k=1:fanout
        if(formerstate(j,1,k)~=number_of_states)
            for h=1:fanout
                t=output(formerstate(j,h,k)+1,k)+1;
                if(t~=number_of_out)
                    gamma(h,depth_of_trellis)=outer_input(t,depth_of_trellis);
                else
                    gamma(h,depth_of_trellis)=0;
                end
            end
        end
    end
end

for i=depth_of_trellis:-1:2
    temp=zeros(1,fanout);
    for j=1:number_of_states
        for k=1:fanout
            t=output(j,k)+1;
            if(t~=number_of_out)
                gamma(k+fanout,i)=outer_input(t,i);
            else
                gamma(k+fanout,i)=0;
            end
            beta1(k)=beta(nextstate(j,k)+1,i)+gamma(k+fanout,i);
            if(beta1(k)<=-80)
                beta1(k)=0;
            else
                beta1(k)=exp(beta1(k));
            end
            temp(k)=temp(k)+exp(alpha(j,i)+gamma(k+fanout,i)+beta(nextstate(j,k)+1,i));
        end   
        if(sum(beta1)>1e-30)
            beta(j,i-1)=log(sum(beta1))-max(i-1);
        else
            beta(j,i-1)=-1e10;
        end
     end
     [C,I]=max(temp);
     outer_out_u(i)=I-1;
 end
temp=zeros(1,fanout);
for j=1:number_of_states
    for k=1:fanout
        t=output(j,k)+1;
        if(t~=number_of_out)
            gamma(k+fanout,1)=outer_input(t,1);
        else
            gamma(k+fanout,1)=0;
        end
        temp(k)=temp(k)+exp(alpha(j,1)+gamma(k+fanout,1)+beta(nextstate(j,k)+1,1));
    end
end
[C,I]=max(temp);
outer_out_u(1)=I-1;