qpsk.m

用MATLAB语言实现QPSK调制的误码率性能分析

%********************相关参数设置***************************************
ml=2;%调制电平(BPSK:ml=1, QPSK:ml=2, 16QAM:ml=4)
nd =10;   % 传输的符号数 
fc=5; %载波频率
qifs=199;%每个正弦波形对应的采样数为qifs+1/2
fs=qifs+1

%*******************信源与调制************************************
data1=rand(1,nd*ml)>0.5
[ich,qch]=qpskmod(data1,nd,ml)
imo = mycos(fc,qifs);
qmo = mysin(fc,qifs);
k=1;
 for jj=1:nd%符号数等于nd
    for jjj=1:qifs+1  
        iout(1,k)=ich(1,jj)*sqrt(0.5)*imo(1,jjj);
        qout(1,k)=qch(1,jj)*sqrt(0.5)*qmo(1,jjj);
        out(1,k)=iout(1,k)+qout(1,k);
        if (jjj<=(qifs+1)/2&&jjj>=1)
             indata(1,k)=ich(1,jj);
         elseif (jjj>(qifs+1)/2&&jjj<=qifs+1)
             indata(1,k)=qch(1,jj); 
         end
        k=k+1;
    end
end
%********************通过瑞利衰落信道************************************
 %[iray,qray]=ray(1,nd*(qifs+1));%产生幅值和相位都变化的瑞利衰落信道
 %iout1=iray.*iout-qray.*qout;
 %qout1=qray.*iout+iray.*qout;
[mag]=ray(1,nd*(qifs+1));%产生幅值变化的瑞利衰落信道
iout1=iout.*mag;
qout1=qout.*mag;

%********************加高斯白噪声****************************************
y=wgn(1,nd*(qifs+1),0);
iout2=iout1+y;
qout2=qout1+y;
out3=iout2+qout2;
%********************接收端进行解调***************************************
k=1
for jj=1:nd%符号数等于nd
    for jjj=1:qifs+1  
        iout3(1,k)=iout2(1,k)*imo(1,jjj);
        qout3(1,k)=qout2(1,k)*qmo(1,jjj);
        k=k+1;
    end
end
%********************解调后的信号通过低通滤波器***************************************
%
[b,s]=butter(4,2/((qifs+1)/2)); % lowpass Butt.
iout4=filter(b,s,iout3); 
qout4=filter(b,s,qout3);

%
%********************通过判决器进行判决***************************************
%  
%*****************************抽样判决****************************************
k=0;
for jj=1:nd
    ioutx(1,jj)= iout4(1,k+1*(qifs+1)/2);
    qoutx(1,jj)=qout4(1,k+1*(qifs+1)/2);
    if iout4(1,k+1*(qifs+1)/2)>0
        iout5(1,jj)=1;
    else 
        iout5(1,jj)=-1;
    end
    if qout4(1,k+1*(qifs+1)/2)>0
        qout5(1,jj)=1;
    else 
        qout5(1,jj)=-1;
    end
    k=k+qifs+1;
end

%*********************并/串转换及信号恢复**************************************
count1=0;
for jj=1:nd %nd为符号数
    out1(1,1+count1)=iout5(1,jj);
    out1(1,2+count1)=qout5(1,jj);	 
	count1=count1+2;
end
k=0;
for jj=1:2*nd
     if out1(1,jj)==1
        out2(1,k+1:k+(qifs+1)/2)=ones(1,(qifs+1)/2);
    else 
        out2(1,k+1:k+(qifs+1)/2)=-ones(1,(qifs+1)/2);
    end
    k=k+(qifs+1)/2;
end
%********************绘制相关图形***************************************
x=1:nd*(qifs+1);
x2=1:2*nd*(qifs+1)
yy=0;
%figure(1)
%psd(indata,[],fs,[]);
%title('input baseband power spectrum')
%figure(2)
%psd(out,[],fs,[]);
%title('QPSK modulated signal power spectrum')
%figure(3)
%psd(out3,[],fs,[]);
%title('AWGN channel output power spectrum')

%figure(4)
%plot(x,indata,'r');
%title('input baseband waveform');
%xlabel('t');
%figure(5)
%plot(x,out,'r',x,yy,'r');
%title('QPSK module waveform ');
%xlabel('t');
%figure(6)
%plot(x,out3,'r',x,yy,'r');
%title('AWGN output waveform ');
%xlabel('t');

figure(7)
subplot(3,1,1)
plot(x,indata,'r');
ylabel('input baseband waveform');
xlabel('t');
subplot(3,1,2);
plot(x,out,'r',x,yy,'r');
ylabel('QPSK module waveform ');
xlabel('t');
subplot(3,1,3);
plot(x,out3,'r',x,yy,'r');
ylabel('AWGN output waveform ');
xlabel('t');


figure(8);
plot(ich,qch,'*r');
axis([-1.5,1.5,-1.5,1.5]);
title('input baseband constellations ');
figure(9);
plot(iout4,qout4,'*r');
title('Ray channel constellations');


%axis([-4,4,-4,4]);