map_decoder_1.m

turbo 码matlab编译码程序

function [decision_c,extrin_information,ln_c]=map_decoder_1(x,x1,CONS,prior_information)
% map algorithm,zero force RSC,in the first interation ,extrinc is zero sequence from decoder 1 to
% decoder 2

K=length(x);
for t=1:K
    for l=1:8                       % l is the trellis numbers
        p_exp(t)=exp(prior_information(t));
        p_1(t)=p_exp(t)/(1+p_exp(t));
        p_0(t)=1/(1+p_exp(t));
        
        [next_state_1,x_p]=nxt_stat1513(l-1,1);
        R_r_1(t,next_state_1+1)=p_1(t)*exp(CONS*((x(t)-1)^2+(x1(t)-(2*x_p-1))^2));
        [next_state_0,x_p]=nxt_stat1513(l-1,0);
        R_r_0(t,next_state_0+1)=p_0(t)*exp(CONS*((x(t)+1)^2+(x1(t)-(2*x_p-1))^2));
        
    end   
end
A_a_initial(1)=1;
A_a_initial(2:8)=0;    
for t=1:K
    for ll=1:8
        A_a(t,ll)=0;
    end
    A_a_totall(t)=0;
    for ll=1:8
        
        [next_state_0,x_p]=nxt_stat1513(ll-1,0); 
        [next_state_1,x_p]=nxt_stat1513(ll-1,1);
        
        if t==1
            A_a(t,next_state_0+1)=A_a(t,next_state_0+1)+A_a_initial(ll)*R_r_0(t,next_state_0+1);
            A_a(t,next_state_1+1)=A_a(t,next_state_1+1)+A_a_initial(ll)*R_r_1(t,next_state_1+1);
        else
            A_a(t,next_state_0+1)=A_a(t,next_state_0+1)+A_a(t-1,ll)*R_r_0(t,next_state_0+1);
            A_a(t,next_state_1+1)=A_a(t,next_state_1+1)+A_a(t-1,ll)*R_r_1(t,next_state_1+1);
            
        end
        
    end 
    for ll=1:8
        A_a_totall(t)= A_a_totall(t)+A_a(t,ll);
    end
    for ll=1:8
        A_a(t,ll)=A_a(t,ll)/A_a_totall(t);
    end
end

B_b_K(1)=1;
B_b_K(2:8)=0;

for t=K-1:-1:1
    for ll=1:8
        B_b(t,ll)=0;
    end
    B_b_totall(t)=0;
    for ll=1:8
        
        [next_state_0,x_p]=nxt_stat1513(ll-1,0); 
        [next_state_1,x_p]=nxt_stat1513(ll-1,1);
        
        if t==K-1
            B_b(t,ll)=B_b_K(next_state_0+1)*R_r_0(t+1,next_state_0+1)+B_b_K(next_state_1+1)*R_r_1(t+1,next_state_1+1);
        else
            B_b(t,ll)=B_b(t+1,next_state_0+1)*R_r_0(t+1,next_state_0+1)+B_b(t+1,next_state_1+1)*R_r_1(t+1,next_state_1+1);
        end
        
    end 
    
    B_b_totall(t)=A_a_totall(t+1);
    
    for ll=1:8
        B_b(t,ll)=B_b(t,ll)/B_b_totall(t);
    end
end

for t=1:K
    ln_1(t)=0;
    ln_0(t)=0;
    for ll=1:8
        if t==1            
            [next_state_1,x_p]=nxt_stat1513(ll-1,1);
            ln_1(t)=ln_1(t)+A_a_initial(ll)*R_r_1(t,next_state_1+1)*B_b(t,next_state_1+1);
            [next_state_0,x_p]=nxt_stat1513(ll-1,0);
            ln_0(t)=ln_0(t)+A_a_initial(ll)*R_r_0(t,next_state_0+1)*B_b(t,next_state_0+1);            
        else if t>1&t<K                
                [next_state_1,x_p]=nxt_stat1513(ll-1,1);
                ln_1(t)=ln_1(t)+A_a(t-1,ll)*R_r_1(t,next_state_1+1)*B_b(t,next_state_1+1);
                [next_state_0,x_p]=nxt_stat1513(ll-1,0);
                ln_0(t)=ln_0(t)+A_a(t-1,ll)*R_r_0(t,next_state_0+1)*B_b(t,next_state_0+1);
            else
                [next_state_1,x_p]=nxt_stat1513(ll-1,1);
                ln_1(t)=ln_1(t)+A_a(t-1,ll)*R_r_1(t,next_state_1+1)*B_b_K(next_state_1+1);
                [next_state_0,x_p]=nxt_stat1513(ll-1,0);
                ln_0(t)=ln_0(t)+A_a(t-1,ll)*R_r_0(t,next_state_0+1)*B_b_K(next_state_0+1);                
            end
        end        
        ln_c(t)=log(ln_1(t)/ln_0(t));
        if ln_c(t)>0
            decision_c(t)=1;
        else
            decision_c(t)=0;
        end        
    end
end 

extrin_information=ln_c+4*CONS*x-prior_information;
% bit_error=0;
% for t=1:K
%     if decision_c(t)~=C_information(t)
%         bit_error=bit_error+1;
%     end
% end