turbo-map.m

turbo编码的map算法

clc;clear 
t=cputime; 
disp('islem yapiliyor. Lutfen bekleyiniz...') 
son=4; 
for snr=0:son 
    hata(snr+1)=0; 
    snr 
    carpan=[100 100 1000 1000 10000 100000]; 
    for j=1:carpan(snr+1)         
        n=100; 
        u=randint(1,n-2); 
        u(n)=0; 
        kafes=poly2trellis(3,[5 7]); 
        v=convenc(u,kafes); 
        for i=1:2*n 
            s(i)=2*v(i)-1; 
        end 
        r = awgn(s,snr,'measured'); 
        %Asagidaki x degerleri BPSK mod黮asyona g鰎e bulunmustur. 
        x111=-1;x112=-1;x121=1;x122=1; 
        x231=-1;x232=1;x241=1;x242=-1; 
        x311=1;x312=1;x321=-1;x322=-1; 
        x431=1;x432=-1;x441=-1;x442=1; 
        %gamalarin hesabi 
        k=0; 
       Eb=2;N0=Eb/(10^(snr/10));sigma=N0/2; 
       for i=1:2:2*n 
            k=k+1; 
            gama11(k)=exp((-(r(i)-x111)^2-(r(i+1)-x112)^2)/2/sigma); 
            gama12(k)=exp((-(r(i)-x121)^2-(r(i+1)-x122)^2)/2/sigma); 
            gama23(k)=exp((-(r(i)-x231)^2-(r(i+1)-x232)^2)/2/sigma); 
            gama24(k)=exp((-(r(i)-x241)^2-(r(i+1)-x242)^2)/2/sigma); 
            gama31(k)=exp((-(r(i)-x311)^2-(r(i+1)-x312)^2)/2/sigma); 
            gama32(k)=exp((-(r(i)-x321)^2-(r(i+1)-x322)^2)/2/sigma); 
            gama43(k)=exp((-(r(i)-x431)^2-(r(i+1)-x432)^2)/2/sigma); 
            gama44(k)=exp((-(r(i)-x441)^2-(r(i+1)-x442)^2)/2/sigma); 
        end 
        %alfalarin hesabi: 
        alfa1(1)=gama11(1);alfa2(1)=gama12(1);alfa3(1)=0;alfa4(1)=0; 
        for i=2:n 
            alfa1(i)=alfa1(i-1)*gama11(i)+alfa3(i-1)*gama31(i); 
            alfa2(i)=alfa1(i-1)*gama12(i)+alfa3(i-1)*gama32(i); 
            alfa3(i)=alfa2(i-1)*gama23(i)+alfa4(i-1)*gama43(i); 
            alfa4(i)=alfa2(i-1)*gama24(i)+alfa4(i-1)*gama44(i); 
        end 
        %Betalarin hesabi 
        beta1(n-1)=gama11(n);beta3(n-1)=gama31(n);beta2(n-1)=0;beta4(n-1)=0; 
        for i=n-2:-1:1 
            beta1(i)=beta1(i+1)*gama11(i+1)+beta2(i+1)*gama12(i+1); 
            beta2(i)=beta3(i+1)*gama23(i+1)+beta4(i+1)*gama24(i+1); 
            beta3(i)=beta1(i+1)*gama31(i+1)+beta2(i+1)*gama32(i+1); 
            beta4(i)=beta3(i+1)*gama43(i+1)+beta4(i+1)*gama44(i+1); 
        end 
        %L(ak)larin hesabi 
        payda=gama12(1)*beta2(1); 
                L_a(1)=log((gama11(1)*beta1(1))/(payda)); 
        for i=2:n-2 
            pay=(alfa1(i-1)*gama11(i)*beta1(i)+alfa2(i-1)*gama23(i)*beta3(i)+... 
                 alfa3(i-1)*gama31(i)*beta1(i)+alfa4(i-1)*gama43(i)*beta3(i)); 
            payda=(alfa1(i-1)*gama12(i)*beta2(i)+alfa2(i-1)*gama24(i)*beta4(i)+... 
                   alfa3(i-1)*gama32(i)*beta2(i)+alfa4(i-1)*gama44(i)*beta4(i)); 
            L_a(i)=log(pay/payda); 
        end  
        for i=1:n-2 
            if L_a(i)>0 
                a(i)=0; 
            else 
                a(i)=1; 
            end 
        end 
        a(n)=0; 
        hata(snr+1)=hata(snr+1)+sum(abs(u-a)); 
    end     
    hata(snr+1); 
    bit_hata_orani(snr+1)=hata(snr+1)/100/carpan(snr+1) 
end 
snr=0:son; 
semilogy(snr,bit_hata_orani),grid 
title('MAP');xlabel('Eb/N0(dB)');ylabel('Bit Error Rate'); 
zaman=cputime-t 
 
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