psk_8.m

4PSK误码仿真率

%=============   2008.4.21   ======%

%==========  “根” 升余弦 脉冲
clear;
clc;

fs=12000;           % sample rate
ts=1/fs;
tb=ts*5;
fc=1800;            % carrier frequency
df=1;             

alpha=0.25;

t=(-4*tb):ts:(4*tb);       % time sample
N=100;

s=randint(1,N,8); % stream of bits

%=============脉冲波形
xrc=sin(pi*t/tb)./(pi*t/tb).*(2*cos(pi*t/tb)+tb^2./(4*t.^2*alpha^2-1).*cos(pi*t*alpha/tb));
for k=1:4*2*5
    if mod(k,5)==1
        xrc(k)=0;
    end;
end;
xrc(21)=2-tb^2;

%=============脉冲叠加形成待调制波形
total=41+5*(N-1);
    wi=zeros(1,total);
    wq=zeros(1,total);
    map=[1;0.707+i*0.707;i;-70707+i*0.707;
        -1;-0.707-i*0.707;-i;0.707-i*0.707];
    
for k=1:N
    switch s(k)
        case 0
            si=1,sq=0;
        case 1
            si=0.707,sq=0.707;
        case 2
            si=0,sq=1;
        case 3
            si=-0.707,sq=0.707;
        case 4
            si=-1,sq=0;
        case 5
            si=-0.707,sq=-0.707;
        case 6
            si=0,sq=-1;
        otherwise
            si=0.707,sq=-0.707;
    end;

        tempi=[zeros(1,(k-1)*5),xrc*si,zeros(1,total-length(xrc)-(k-1)*5)];
        tempq=[zeros(1,(k-1)*5),xrc*sq,zeros(1,total-length(xrc)-(k-1)*5)];
        wi=wi+tempi;
        wq=wq+tempq;
end;
subplot(5,2,1),plot(wi);
subplot(5,2,2),plot(wq);


%=============调制到1800Hz载频
t=0:ts:((N-1)*5+40)*ts;
ci=cos(2*pi*fc*t);     
cq=-sin(2*pi*fc*t);

xi=wi.*ci; 
xq=wq.*cq;
subplot(5,2,3),plot(xi);
subplot(5,2,4),plot(xq);

x=xi+xq;
subplot(5,2,5),plot(x);

%=============接收后再乘以载波
yi=x.*ci; 
yq=x.*cq; 
subplot(5,2,7),plot(yi);
subplot(5,2,8),plot(yq);

%=============匹配滤波
f_out_i=conv(yi,xrc);
f_out_q=conv(yq,xrc);
subplot(5,2,9),plot(f_out_i);
subplot(5,2,10),plot(f_out_q);

%=============采样判决
for k=1:N
    d_i(k)=f_out_i((k-1)*5+41);
    d_q(k)=f_out_q((k-1)*5+41);
       
    for l=1:8
        tt=d_i(k)+i*d_q(k);
        distance(l)=abs(map(l)-tt);
        md=min(distance);
        switch md
            case distance(1)
                out(k)=0;
            case distance(2)
                out(k)=1;
            case distance(3)
                out(k)=2;
            case distance(4)
                out(k)=3;
            case distance(5)
                out(k)=4;
            case distance(6)
                out(k)=5;
            case distance(7)
                out(k)=6;
            case distance(8)
                out(k)=7;
                
        end;
    end;
end;

err=0;
for k=1:N
    if out(k)~=s(k)
        err=err+1;
    else;
    end;
end;
        
    
 


% %==============观察解调后的波形
% for i=1:N      % 形成方波
%     u((i-1)*5+1:(i-1)*5+5)=g*d(i);
% end;
% subplot(6,1,6),plot(u);axis([1,600,-2,2]);
% %==============观察解调后的波形