QPSK调制解调完整程序配有自己的注释知识分享

1、QPSK调制解调完整程序配有自己的注释QPS咽制解调完整程序(配有注释)clc;clear all;%贸定接收端已经实现载波同步,位同步(盲信号解调重点要解决的问题：载波同步(costas环(未见到相关代码),位同步(Gardner算法(未见相关代码),帧同步)% carrier frequency for modulation and demodulation fc=5e6;%QPSK transmitterdata=5000;涮数率为5MHZ %M码个数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%同时单极性码转为双极性码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,此过程称为成形.成形的意思就是实现由消息到波形的转换,以便发射,脉冲成形应该是在基带调制之后.zero=5;%sampling ra

3、te 25M HZ ,明白了,zero 为过采样率.它等于 采样率fs/码速率.for i=1:zero*data%采样点数目=过采样率*原码数目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 ,接着,将进行低通滤波,由于随着传输速率的增大,基带脉冲的频谱将变宽呦口果不滤波(如升余弦滤波)进行低通滤波,后面加载频的时候可能会出现困难.%¥方根升余弦滤波器% psf=rcosfir(rf

4、,n_t,rate,fs,'sqrt')rate:过采样率,rf:滚降因子,n_t:滤波器阶数,fs:采样率%用在调制或发送之前,用在解调或接受之后,用来降低过采样符号流带宽并不引发ISI (码问串扰)NT=50;N=2*zero*NT; % =500fs=25e6;大小为500rf=0.1;psf=rcosfir(rf,NT,zero,fs,'sqrt');% psf Ipulse=conv(Izero,psf);Qpulse=conv(Qzero,psf);%为什么数字信号传输也要过采样,成形滤波？%答：过采样的数字信号处理起来对低通滤波器的要求相对较低,如

5、果不过采样,滤波的时候滤波器需要很陡峭,指标会很严格%成形滤波的作用是保证采样点不失真.如果没有它,那信号在经过带限信道后,眼图张不开,ISI非常严重.成形滤波的位置在基带调制之后.%由于经成形滤波后,信号的信息已经有所损失,这也是为防止ISI付出的代价.换句话说,成形滤波的位置在载波调制之前,仅挨着载波调制.%W:(发送端)插值(采样)-成形-滤波(LPF)-加载频(载波调制)-加噪声至(接收端)乘本振-低通-定时抽取-判决.%modulationfor i=1:zero*data+N%:样点数目改变(由于卷积的缘故)t(i)=(i-1)/(fs);溢里由于假设载频与码速率大小相等,所以用载

6、频fc乘以过采样率=采样率.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%提取码元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%绘图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(