ddc matlab仿真

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%info%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%email:yangli0534@gmail.com

%data:2013/12/16

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%IFsignalgeneration%%%%%%%%%%%%%%%%%%%%%%%%%

b=2e6;

taup=50/1e6;

fc=20e6;

n=fix(50*taup*b);

t=linspace(-taup/2,taup/2,n);

s=exp(i*pi*(b/taup).*t.^2+i*2*pi*fc.*t);

figure(1)

subplot(4,1,1)

plot(t,real(s),'k')

ylabel('realpartofIFsignals')

xlabel('timeinseconds')

grid

subplot(4,1,2)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(real(s)))),'k');

ylabel('Spectrumofrealpartofs')

xlabel('FrequencyinHz')

grid

subplot(4,1,3)

plot(t,imag(s),'k')

ylabel('imagpartofIFsignals')

xlabel('timeinseconds')

grid

subplot(4,1,4)

plot(freq,fftshift(abs(fft(imag(s)))),'k');

ylabel('Spectrumofimagpartofs')

xlabel('FrequencyinHz')

grid

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%mixer%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

lo=exp(i*2*pi*fc.*t);

smi=real(s).*real(lo);

figure(2)

subplot(4,1,1)

plot(t,smi,'k')

ylabel('realpartofsignalsmaftermixed')

xlabel('timeinseconds')

grid

subplot(4,1,2)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(smi))),'k');

ylabel('Spectrumofsmi')

xlabel('FrequencyinHz')

grid

smq=real(s).*imag(lo);

subplot(4,1,3)

plot(t,smq,'k')

ylabel('imappartofsignalsmaftermixed')

xlabel('timeinseconds')

grid

subplot(4,1,4)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(smq))),'k');

ylabel('Spectrumofsmq')

xlabel('FrequencyinHz')

grid

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%CICfilter%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

decf=10;%DecimationFactor

diffd=1;%DifferentialDelay

numsecs=5;%NumberofSections

hm=mfilt.cicdecim(decf,diffd,numsecs);

sci=double(filter(hm,smi));

scq=double(filter(hm,smq));

n=length(sci);

t=linspace(-taup/2,taup/2,n);

figure(3)

subplot(4,1,1)

plot(t,sci,'k')

ylabel('realpartofsignalsmiaftercicfilter')

xlabel('timeinseconds')

grid

subplot(4,1,2)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(sci))),'k');

ylabel('Spectrumofsci')

xlabel('FrequencyinHz')

grid

subplot(4,1,3)

plot(t,scq,'k')

ylabel('imappartofsignalsmaftermixed')

xlabel('timeinseconds')

grid

subplot(4,1,4)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(scq))),'k');

ylabel('Spectrumofsmq')

xlabel('FrequencyinHz')

grid

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%lpffilter%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Fs=9.98;%SamplingFrequency

Fpass=1;%PassbandFrequency

Fstop=1.5;%StopbandFrequency

Dpass=0.057501127785;%PassbandRipple

Dstop=0.0001;%StopbandAttenuation

dens=20;%DensityFactor

%CalculatetheorderfromtheparametersusingFIRPMORD.

[N,Fo,Ao,W]=firpmord([Fpass,Fstop]/(Fs/2),[10],[Dpass,Dstop]);

%CalculatethecoefficientsusingtheFIRPMfunction.

b=firpm(N,Fo,Ao,W,{dens});

Hd=dfilt.dffir(b);

spi=double(filter(Hd,sci));

spq=double(filter(Hd,scq));

n=length(spi);

t=linspace(-taup/2,taup/2,n);

figure(4)

subplot(4,1,1)

plot(t,spi,'k')

ylabel('realpartofsignalspiafterlpffilter')

xlabel('timeinseconds')

grid

subplot(4,1,2)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(spi))),'k');

ylabel('Spectrumofspi')

xlabel('FrequencyinHz')

grid

subplot(4,1,3)

plot(t,spq,'k')

ylabel('imappartofsignalsmafterlpffilter')

xlabel('timeinseconds')

grid

subplot(4,1,4)

sampling_interval=1/5/fc;

freqlimit=0.5/sampling_interval;

freq=linspace(-freqlimit,freqlimit,n);

plot(freq,fftshift(abs(fft(spq))),'k');

ylabel('Spectrumofsmq')

xlabel('FrequencyinHz')

grid