正交幅度調制(QAM)及解調Matlab仿真

1、正交幅度調制(QAM)及解調Matlab仿真實驗目的：1. 掌握QAM及解調原理與特性；2. 了解星座圖的原理及用途。實驗內容：1. 編寫MATLAB程序仿真QAM及相干解調；2. 觀察I、Q兩路基帶信號的特征及與輸入NRZ碼上網關系；3. 觀察I、Q調制過程中信號的變化；4. 觀察星座圖在不同噪聲環(huán)境下的變化；5. 分析仿真中觀察的數據，撰寫實驗報告。仿真代碼：function project(N,p)%N為待仿真序列的長度%p為產生1的概率%=%首先產生隨機二進制序列N=input('輸入二進制序列的長度：N=');p=input('輸入產生1的概率：');

2、source=randsrc(1,N,1,0;p,1-p);figure(1);stem(source);axis(1 N -1 2);%對產生的二進制序列進行QAM調制source1,source2=Qam_modulation(source);%=%畫出星座圖figure(2);plot_astrology(source1,source2);%=%兩路信號進行插值（8倍過采樣）sig_insert1=insert_value(source1,8);sig_insert2=insert_value(source2,8);%=%畫出兩路信號的波形圖figure(3);plot_2way(sig

3、_insert1,sig_insert2,length(sig_insert1),0.5);title('兩路信號波形');%=%通過低通濾波器sig_rcos1,sig_rcos2=rise_cos(sig_insert1,sig_insert2,0.25,2);%=%畫出兩路信號信號波形圖figure(4);plot_2way(sig_rcos2,sig_rcos2,length(sig_rcos1)/4,0.5);title('通過低通濾波器后兩路信號波形圖')hold onstem_2way(sig_insert1,sig_insert2,3,0.25,

4、2,length(sig_rcos1)/4);%=%將基帶信號調制到高頻上t,sig_modulate=modulate_to_high(sig_rcos1,sig_rcos2,0.25,2.5);figure(5);plot(t(1:500),sig_modulate(1:500);title('載波調制信號圖');%=%將濾波后的信號加入高斯噪聲snr=10;x1,x2=generate_noise(sig_rcos1,sig_rcos2,snr);sig_noise1=x1'sig_noise2=x2'figure(6);plot_2way(sig_noi

5、se1,sig_noise2,length(sig_noise1)/4,0.5);title('加入高斯白噪聲后的兩路信號波形');%=%經過匹配濾波器sig_match1,sig_match2=rise_cos(sig_noise1,sig_noise2,0.25,2);figure(7);plot_2way(sig_match1,sig_match2,length(sig_match1)/4,0.5);title('經過匹配濾波器后');%=%采樣x1,x2=pick_sig(sig_match1,sig_match2,8);sig_pick1=x1;sig

6、_pick2=x2;%畫出星座圖figure(8)plot_astrology(sig_pick1,sig_pick2);%=%解調signal=demodulate_sig(sig_pick1,sig_pick2);r=signal; %畫出解調后的信號figure(9);stem(r);axis(1 N -1 2);demodulate_sigfunction y=demodulate_sig(x1,x2)%解調xx1(find(x1>=2)=3;xx1(find(x1<2)&(x1>=0)=1;xx1(find(x1>=-2)&(x1<0)=

7、-1;xx1(find(x1<-2)=-3;xx2(find(x2>=2)=3;xx2(find(x2<2)&(x2>=0)=1;xx2(find(x2>=-2)&(x2<0)=-1;xx2(find(x2<-2)=-3;temp1=zeros(1,length(xx1)*2);temp1(find(xx1=-1)*2)=1;temp1(find(xx1=1)*2-1)=1;temp1(find(xx1=1)*2)=1;temp1(find(xx1=3)*2-1)=1;temp2=zeros(1,length(xx2)*2);temp2

8、(find(xx2=-1)*2)=1;temp2(find(xx2=1)*2-1)=1;temp2(find(xx2=1)*2)=1;temp2(find(xx2=3)*2-1)=1;n=length(temp1);for i=1:2:2*n-1 y(i)=temp1(i+1)/2); y(i+1)=temp2(i+1)/2);endgenerate_noisefunction y1,y2=generate_noise(x1,x2,snr)snr1=snr+10*log10(4);ss=var(x1+i*x2,1);y=awgn(x1+j*x2,snr1+10*log10(ss/10),

9、9;measured');y1=real(y);y2=imag(y);insert_valuefunction y=insert_value(x,ratio)%對兩路信號進行插值y=zeros(1,ratio*length(x);a=1:ratio:length(y);y(a)=x;modulate_to_highfunction t,y=modulate_to_high(x1,x2,f,hf)yo1=zeros(1,length(x1)*hf/f*10);yo2=zeros(1,length(x1)*hf/f*10);n=1:length(yo1);yo1(n)=x1(floor(n

10、-1)/(hf/f*10)+1);yo2(n)=x1(floor(n-1)/(hf/f*10)+1);t=(1:length(yo1)/hf*f/10;y=yo1.*cos(2*pi*hf*t)-yo2.*sin(2*pi*hf*t);pick_sigfunction y1,y2=pick_sig(x1,x2,ratio)%采樣y1=x1(ratio*3*2+1:ratio:(length(x1)-ratio*3*2);y2=x2(ratio*3*2+1:ratio:(length(x2)-ratio*3*2);plot_2wayfunction plot_2way(x1,x2,len,t)%

11、繪制正交信號圖subplot(2,1,2);plot(1:len)*t,x2(1:len);axis(0 len*t -4 4);hold on;plot(1:len)*t,x2(1:len),'.','Color','red');hold off;xlabel('虛部信號');subplot(2,1,1);plot(1:len)*t,x1(1:len);axis(0 len*t -4 4);hold onplot(1:len)*t,x1(1:len),'.','Color','red

12、9;);xlabel('實部信號');hold offplot_astrologyfunction plot_astrology(a,b)%畫出星座圖subplot(1,1,1);plot(a,b,'+');axis(-5 5 -5 5);line(-5,5,0,0,'LineWidth',3,'Color','red');line(0,0,-5,5,'LineWidth',3,'Color','red');title('QAM星座圖');Qam_mo

13、dulationfunction yy1, yy2=Qam_modulation(x)N=length(x);a=1:2:N;y1=x(a);y2=x(a+1);a=1:2:N/2;temp11=y1(a);temp12=y1(a+1);y11=temp11*2+temp12;temp21=y2(a);temp22=y2(a+1);y22=temp21*2+temp22;yy1(find(y11=0)=-3;yy1(find(y11=1)=-1;yy1(find(y11=3)=1;yy1(find(y11=2)=3;yy2(find(y22=0)=-3;yy2(find(y22=1)=-1;yy2(find(y22=3)=1;yy2(find(y22=2)=3;endrise_cosfunction y1,y2=rise_cos(x1,x2,fd,fs)%升余弦濾波yf,tf=rcosine(fd,fs,'fir/sqrt');yo1,to1=rcosflt(x1,fd,fs,'filter/Fs',yf);yo2,to2=rcosflt(x2,fd,fs,'filter/Fs',yf);y1=yo1