QPSK調(diào)制解調(diào)完整程序配有自己的注釋知識(shí)分享

1、QPSK調(diào)制解調(diào)完整程序配有自己的注釋QPS咽制解調(diào)完整程序(配有注釋)clc;clear all;%貿(mào)定接收端已經(jīng)實(shí)現(xiàn)載波同步,位同步(盲信號(hào)解調(diào)重點(diǎn)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 frequency for modulation and demodulation fc=5e6;%QPSK transmitterdata=5000;涮數(shù)率為5MHZ %M碼個(gè)數(shù)rand_data=randn(1,5000);for i=1:dataif rand_data(i)>=0.5rand_data(

2、i)=1;elserand_data(i)=0; endend%seriel to parallel%同時(shí)單極性碼轉(zhuǎn)為雙極性碼for i=1:dataif rem(i,2)=1if rand_data(i)=1I(i)=1;I(i+1)=1; elseI(i)=-1;I(i+1)=-1; end elseif rand_data(i)=1Q(i-1)=1;Q(i)=1;elseQ(i-1)=-1;Q(i)=-1;endendend% zero insertion,此過程稱為成形.成形的意思就是實(shí)現(xiàn)由消息到波形的轉(zhuǎn)換,以便發(fā)射,脈沖成形應(yīng)該是在基帶調(diào)制之后.zero=5;%sampling ra

3、te 25M HZ ,明白了,zero 為過采樣率.它等于 采樣率fs/碼速率.for i=1:zero*data%采樣點(diǎn)數(shù)目=過采樣率*原碼數(shù)目if rem(i,zero)=1Izero(i)=Ifix(i-1)/zero)+1);Qzero(i)=Q(fix(i-1)/zero)+1);elseIzero(i)=0;Qzero(i)=0;endend%pulse shape filter ,接著,將進(jìn)行低通濾波,由于隨著傳輸速率的增大,基帶脈沖的頻譜將變寬呦口果不濾波(如升余弦濾波)進(jìn)行低通濾波,后面加載頻的時(shí)候可能會(huì)出現(xiàn)困難.%¥方根升余弦濾波器% psf=rcosfir(rf

4、,n_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(hào)流帶寬并不引發(fā)ISI (碼問串?dāng)_)NT=50;N=2*zero*NT; % =500fs=25e6;大小為500rf=0.1;psf=rcosfir(rf,NT,zero,fs,'sqrt');% psf Ipulse=conv(Izero,psf);Qpulse=conv(Qzero,psf);%為什么數(shù)字信號(hào)傳輸也要過采樣,成形濾波？%答：過采樣的數(shù)字信號(hào)處理起來對(duì)低通濾波器的要求相對(duì)較低,如

5、果不過采樣,濾波的時(shí)候?yàn)V波器需要很陡峭,指標(biāo)會(huì)很嚴(yán)格%成形濾波的作用是保證采樣點(diǎn)不失真.如果沒有它,那信號(hào)在經(jīng)過帶限信道后,眼圖張不開,ISI非常嚴(yán)重.成形濾波的位置在基帶調(diào)制之后.%由于經(jīng)成形濾波后,信號(hào)的信息已經(jīng)有所損失,這也是為防止ISI付出的代價(jià).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.%W:(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(shí)抽取-判決.%modulationfor i=1:zero*data+N%:樣點(diǎn)數(shù)目改變(由于卷積的緣故)t(i)=(i-1)/(fs);溢里由于假設(shè)載頻與碼速率大小相等,所以用載

6、頻fc乘以過采樣率=采樣率.Imod(i)=Ipulse(i)*sqrt(2)*cos(2*pi*fc*t(i);Qmod(i)=Qpulse(i)*(-sqrt(2)*sin(2*pi*fc*t(i); end sum=Imod+Qmod; %QPSK receiver %demodulation for i=1:zero*data+NIdem(i)=sum(i)*sqrt(2)*cos(2*pi*fc*t(i);Qdem(i)=sum(i)*(-sqrt(2)*sin(2*pi*fc*t(i); end %matched filter mtf=rcosfir(rf,NT,zero,fs,&

7、#39;sqrt');Imat=conv(Idem,mtf);Qmat=conv(Qdem,mtf); %data selection for i=1:zero*dataIsel(i)=Imat(i+N);Qsel(i)=Qmat(i+N);end%sampler%提取碼元for i=1:dataIsam(i)=Isel(i-1)*zero+1);Qsam(i)=Qsel(i-1)*zero+1); end %decision threshold threshold=0.2; for i=1:data if Isam(i)>=threshold Ifinal(i)=1; else

8、Ifinal(i)=-1;end if Qsam(i)>=thresholdQfinal(i)=1; elseQfinal(i)=-1; end end %parallel to serial for i=1:data if rem (i,2)=1if Ifinal(i)=1 final(i)=1;else final(i)=0;end elseif Qfinal(i)=1 final(i)=1;else final(i)=0;end endend%繪圖figure(1)plot(20*log(abs(fft(rand_data); axis(0 data -40100);grid on

9、;title('spectrum of input binary data');figure(2)subplot(221);plot(20*log(abs(fft(I);axis(0 data -40 140);grid on;title('spectrum of I-channel data');subplot(222);plot(20*log(abs(fft(Q);axis(0 data -40140);grid on;title('spectrum of Q-channel data');subplot(223);plot(20*log(a

10、bs(fft(Izero);axis(0 zero*data -20140);grid on;title('spectrum of I-channel after zero insertion');subplot(224);plot(20*log(abs(fft(Qzero);axis(0 zero*data -20 140);grid on;title('spectrum of Q-channel after zero insertion');figure(3);subplot(221);plot(psf);axis(200300-0.20.6);title(

11、'time domain response of pulse shaping filter');grid on;subplot(222);plot(20*log(abs(fft(psf);axis(0 N -350 50);grid on;title('transferfunction of pulse shaping filter');subplot(223);plot(20*log(abs(fft(Ipulse);axis(0 zero*data+N -250 150);grid on;title('spectrum of I-channel aft

12、er subplot(224);plot(20*log(abs(fft(Qpulse);axis(0 zero*data+N -250 grid on;title('spectrum of Q-channelimpulse shaping filter');150);after pluse shapingfilter');figure(4)subplot(211);plot(20*log(abs(fft(Imod);axis(0 zero*data+N grid on ;title('spectrum of I-channel subplot(212);plot

13、(20*log(abs(fft(Qmod);axis(0 zero*data+N grid on;-250 150);after modulation');-250 150);title('spectrumofQ-channel after modulation');figure(5)subplot(221);plot(20*log(abs(fft(Idem);axis(0 zero*data grid on;title('spectrum subplot(222);-200150);of I-channel afterdemodulation');pl

14、ot(20*log(abs(fft(Qdem);axis(0 zero*data+N -200150 );grid on;title('spectrum of Q-channel after demodulation');subplot(223);plot(20*log(abs(fft(Imat);200);axis(0 zero*data -400 grid on;title('spectrum subplot(224);of I-channelaftermatched filter');plot(20*log(abs(fft(Qmat);title('

15、;spectrum of200);axis(0 zero*data -400 grid on;Q-channel after matched filter');figure(6)subplot(221);plot(20*log(abs(fft(Isam);axis(0 data-40150);grid on;title('spectrum of I-channel after sampler');subplot(222);plot(20*log(abs(fft(Qsam);axis(0 data -40150 );grid on;title('spectrum

16、of Q-channel aftersampler');subplot(223);plot(20*log(abs(fft(Ifinal);axis(0 data -40150);grid on;title('spectrum ofI-channel after decision threshold');subplot(224);plot(20*log(abs(fft(Qfinal);axis(0 data -40150);grid on;title('spectrum ofQ-channel afterdecision threshold');title('constellationofmatchedfigure(8)plot(Isam,Qsam,'X');axis(