QPSK調(diào)制解調(diào)完整程序(配有自己的注釋

1、QPSK調(diào)制解調(diào)完整程序（配有注釋）clc;clear all;%假定接收端已經(jīng)實現(xiàn)載波同步，位同步（盲信號解調(diào)重點要解決的問題：載波同步（costas環(huán)（未見到相關(guān)代碼），位同步（Gardner算法（未見相關(guān)代碼），幀同步）% carrier frequencyfor modulation and demodulationfc=5e6;%QPSK transmitterdata=5000; %碼數(shù)率為5MHZ %原碼個數(shù)rand_data=randn(1,5000);fori=1:data if rand_data(i)=0.5 rand_data(i)=1; else rand_data(

2、i)=0; endend%seriel to parallel %同時單極性碼轉(zhuǎn)為雙極性碼fori=1:data if rem(i,2)=1 ifrand_data(i)=1 I(i)=1; I(i+1)=1; else I(i)=-1; I(i+1)=-1; end else if rand_data(i)=1 Q(i-1)=1; Q(i)=1; else Q(i-1)=-1; Q(i)=-1; end endend% zero insertion ，此過程稱為成形。成形的意思就是實現(xiàn)由消息到波形的轉(zhuǎn)換，以便發(fā)射，脈沖成形應該是在基帶調(diào)制之后。zero=5; %samplingrate25M

3、 HZ,明白了，zero為過采樣率。它等于 采樣率fs/碼速率。fori=1:zero*data % 采樣點數(shù)目=過采樣率*原碼數(shù)目 if rem(i,zero)=1 Izero(i)=I(fix(i-1)/zero)+1); Qzero(i)=Q(fix(i-1)/zero)+1); else Izero(i)=0; Qzero(i)=0; endend%pulse shape filter， 接著，將進行低通濾波，因為 隨著傳輸速率的增大，基帶脈沖的頻譜將變寬%如果不濾波（如升余弦濾波）進行低通濾波，后面加載頻的時候可能會出現(xiàn)困難。%平方根升余弦濾波器% psf=rcosfir(rf,n_

4、t,rate,fs,sqrt) rate:過采樣率，rf:滾降因子，n_t:濾波器階數(shù)，fs:采樣率%用在調(diào)制或發(fā)送之前，用在解調(diào)或接受之后，用來降低過采樣符號流帶寬并不引發(fā)ISI（碼間串擾）NT=50;N=2*zero*NT; % =500fs=25e6;rf=0.1;psf=rcosfir(rf,NT,zero,fs,sqrt);% psf大小為500Ipulse=conv(Izero,psf);Qpulse=conv(Qzero,psf);%為什么數(shù)字信號傳輸也要過采樣，成形濾波？%答：過采樣的數(shù)字信號處理起來對低通濾波器的要求相對較低，如果不過采樣，濾波的時候濾波器需要很陡峭，指標會很

5、嚴格%成形濾波的作用是保證采樣點不失真。如果沒有它，那信號在經(jīng)過帶限信道后，眼圖張不開，ISI非常嚴重。成形濾波的位置在基帶調(diào)制之后。%因為經(jīng)成形濾波后，信號的信息已經(jīng)有所損失，這也是為避免ISI付出的代價。換句話說，成形濾波的位置在載波調(diào)制之前，僅挨著載波調(diào)制。%即：（發(fā)送端）插值（采樣）-成形-濾波（LPF)-加載頻(載波調(diào)制)-加噪聲至（接收端）乘本振-低通-定時抽取-判決。%modulationfor i=1:zero*data+N %采樣點數(shù)目改變 （因為卷積的緣故） t(i)=(i-1)/(fs);%這里因為假設(shè)載頻與碼速率大小相等，所以用載頻fc乘以過采樣率=采樣率。 Imod(

6、i)=Ipulse(i)*sqrt(2)*cos(2*pi*fc*t(i); Qmod(i)=Qpulse(i)*(-sqrt(2)*sin(2*pi*fc*t(i);endsum=Imod+Qmod;%QPSKreceiver%demodulation for i=1:zero*data+N Idem(i)=sum(i)*sqrt(2)*cos(2*pi*fc*t(i); Qdem(i)=sum(i)*(-sqrt(2)*sin(2*pi*fc*t(i); end %matchedfilter mtf=rcosfir(rf,NT,zero,fs,sqrt); Imat=conv(Idem,m

7、tf); Qmat=conv(Qdem,mtf); %data selection fori=1:zero*data Isel(i)=Imat(i+N); Qsel(i)=Qmat(i+N); end %sampler %提取碼元 for i=1:data Isam(i)=Isel(i-1)*zero+1); Qsam(i)=Qsel(i-1)*zero+1); end %decisionthreshold threshold=0.2; fori=1:data if Isam(i)=threshold Ifinal(i)=1; else Ifinal(i)=-1; end if Qsam(i)

8、=threshold Qfinal(i)=1; else Qfinal(i)=-1; end end %parallel to serial for i=1:data if rem (i,2)=1 if Ifinal(i)=1 final(i)=1; else final(i)=0; end else ifQfinal(i)=1 final(i)=1; else final(i)=0; end end end % 繪圖 figure(1) plot(20*log(abs(fft(rand_data); axis(0data-40100); grid on; title(spectrumof i

9、nput binary data); figure(2) subplot(221); plot(20*log(abs(fft(I); axis(0 data -40 140); gridon; title(spectrum of I-channel data); subplot(222); plot(20*log(abs(fft(Q); axis(0data -40140); gridon; title(spectrum of Q-channel data); subplot(223); plot(20*log(abs(fft(Izero); axis(0 zero*data-20140);

10、gridon; title(spectrum of I-channel after zero insertion); subplot(224); plot(20*log(abs(fft(Qzero); axis(0zero*data -20 140); gridon; title(spectrum of Q-channel after zero insertion); figure(3); subplot(221); plot(psf); axis(200 300 -0.2 0.6); title(time domain response of pulse shaping filter); g

11、ridon; subplot(222); plot(20*log(abs(fft(psf); axis(0N -350 50); grid on; title(transferfunctionof pulseshaping filter); subplot(223); plot(20*log(abs(fft(Ipulse); axis(0zero*data+N-250 150); grid on; title(spectrum of I-channel afterimpulse shaping filter); subplot(224); plot(20*log(abs(fft(Qpulse)

12、; axis(0zero*data+N -250150); gridon; title(spectrum of Q-channelafter pluse shapingfilter); figure(4) subplot(211); plot(20*log(abs(fft(Imod); axis(0zero*data+N-250 150); gridon ; title(spectrum of I-channelafter modulation); subplot(212); plot(20*log(abs(fft(Qmod); axis(0zero*data+N-250 150); grid

13、on; title(spectrumofQ-channel after modulation); figure(5) subplot(221); plot(20*log(abs(fft(Idem); axis(0 zero*data-200150); grid on; title(spectrumof I-channel afterdemodulation); subplot(222); plot(20*log(abs(fft(Qdem); axis(0zero*data+N-200150 ); gridon; title(spectrum of Q-channel after demodul

14、ation); subplot(223); plot(20*log(abs(fft(Imat); axis(0zero*data-400200); gridon; title(spectrumof I-channelaftermatched filter); subplot(224); plot(20*log(abs(fft(Qmat); axis(0zero*data-400200); gridon; title(spectrum ofQ-channel after matched filter); figure(6) subplot(221); plot(20*log(abs(fft(Is

15、am); axis(0 data-40150); gridon; title(spectrum of I-channel after sampler); subplot(222); plot(20*log(abs(fft(Qsam); axis(0data -40150 ); gridon; title(spectrum of Q-channel aftersampler); subplot(223); plot(20*log(abs(fft(Ifinal); axis(0 data-40150); grid on; title(spectrum ofI-channel afterdecision threshold); subplot(224); plot(20*log(abs(fft(Qfinal); axis(0 data-40150); grid on; title(spectrum ofQ-channel afterdecision threshold); figure(7) plot(Isel,Qsel); axis(-1.6 1.6-1.61.6); gr