QPSK调制解调完整程序(配有自己的注释

1、QPSK调制解调完整程序（配有注释）clc;clear all;%假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 frequencyfor modulation and demodulationfc=5e6;%QPSK transmitterdata=5000; %码数率为5MHZ %原码个数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 %同时单极性码转为双极性码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; %samplingrate25M

3、 HZ,明白了，zero为过采样率。它等于 采样率fs/码速率。fori=1:zero*data % 采样点数目=过采样率*原码数目 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， 接着，将进行低通滤波，因为 随着传输速率的增大，基带脉冲的频谱将变宽%如果不滤波（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。%平方根升余弦滤波器% psf=rcosfir(rf,n_

4、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（码间串扰）NT=50;N=2*zero*NT; % =500fs=25e6;rf=0.1;psf=rcosfir(rf,NT,zero,fs,sqrt);% psf大小为500Ipulse=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，如果不过采样，滤波的时候滤波器需要很陡峭，指标会很

5、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。%因为经成形滤波后，信号的信息已经有所损失，这也是为避免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。%即：（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 %采样点数目改变 （因为卷积的缘故） t(i)=(i-1)/(fs);%这里因为假设载频与码速率大小相等，所以用载频fc乘以过采样率=采样率。 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 %提取码元 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 % 绘图 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