matla

MATLAB

幅度调制：

Kf=5;

fc=10;

T=5;

dt=0.001;

t=0:dt:T;

fm=1;

A=sqrt(2);

mt=A*cos(2*pi*fm*t);

%FM调制

mti=1/2/pi/fm*sin(2*pi*fm*t);

FMt=A*cos(2*pi*fc*t+2*pi*Kf*mti);figure(1)

subplot(311);

plot(t,FMt);

holdon;

pl铁壶 ot(t,m罗定皱纱鱼腐 t,'r--');

xlabel('搬家英语 t');ylabel('调制信号');

subplot(312);

[fsf]=FFT_SHIFT(t,FMt);

plot(f,abs(sf));

axis([-252503]);

xlabel('f');ylabel('调制信号幅度谱');

%FM解调

N=length(FMt);

dFMt=zeros(1,N);

fork=1:N-1

dFMt(k)=(FMt(k+1)-FMt(k))/dt;end

envlp=A*2*pi*Kf*mt+A*2*pi*fc;subplot(313);

plot(t,dFMt);holdon;

plot(t,envlp,'r--');

xlabel('t');ylabel('调频信号微分后包络');

N点离散傅⾥叶变换：

function[Xk]=dft(xn,N)

n=[0:1:N-1];

k=[0:1:N-1];

WN=exp(-j*2*pi/N);

nk=n'*k;

WNnk=WN.^nk;

Xk=xn*WNnk;2FSK信号：

functionfskdigital(s,f1,f2)

%s=[10110010];

%f1=200;

%f2=100;

t=0:2*pi/99:2*pi;

m1=[];

c1=[];

b1=[];

forn=1:length(s)

ifs(n)==0

m=ones(1,100);

c=sin(f2*t);

b=zeros(1,100);

els(n)==1

m=ones(1,100);

c=sin(f1*t);

b=ones(1,100);

end

m1=[m1m];

c1=[c1c];

b1=[b1b];

end

fsk=c1.*m1;

subplot(211);

plot(b1,'r')

title('原始信号');

axis([0100*length(s)-0.11.1]);gridon;

subplot(212);

plot(fsk);

title('2FSK信号');

gridon;

2FSK信号练习：

functionfskdigital(s,f1,f2)厌恶的英文

%s=[10110010];

%f1=200;

%f2=100;

T=5;

t=0:2*pi/99:2*pi;

m1=[];

c1=[];

b1=[];

forn=1:length(s)

ifs(n)==0

m=ones(1,100);

c=sin(f2*t);

b=zeros(1,100);

els(n)==1

m=ones男生熬夜 (1,100);

c=sin(f1*t);

b=ones(1,100);

end

m1=[m1m];

c1=[c1c];

b1=[b1b];

end

fsk=c1.*m1;

[f,Xf]=FFT_SHIFT(t,fsk);

%Xf=fft(t,飞机英文怎么读 fsk);

PSD=(abs(Xf.^2))/T;

subplot(311);

plot(b1,'r')

title('原始信号');

axis([0100*length(s)-0.11.1]);

gridon;

subplot(312);

plot(fsk);

title('2FSK信号');

gridon;

subplot(313);

plot(PSD);

title('2FSK信号的功率谱密度');

信号加减：

function[f,k]=sigadd(f1,k1,f2,k2)

k=min(mim(k1),min(k2)):max(max(k1),max(k2));s1=zeros(1,length(k));

s2=s1;

s1(find((k>=min(k1))&(k<=max(k1))==1))=f1;

s1(find((k>=min(k2))&(k<=max(k2))==1))=f2;

f=s1+s2;%f=s1.*s2;

stem(k,f,'fill');

axis([(min(min(k1),min(k2))-1),(max(max(k1),max(k2))+1),(min(f)-0.5),max(f)+0.5)]);

抽样信号恢复：

dt=0.01;

t=0:dt:10;

xt=sin(2*pi*t)+0.5*cos(4*pi*t);

[f,xf]=FFT_SHIFT(t,xt);

fs=4;

sdt=1/fs;

t1=0:sdt:10;

st=sin(2*pi*t1)+0.5*cos(4*pi*t1);

[f,sf]=FFT_SHIFT(t1,st);

t2=-50:dt:50;

gt=sinc(fs*t2);

stt=INSERT0(st,sdt/dt);

xt_t=conv(stt,gt);

figure(1)

subplot(311);

plot(t,xt);

title('原始信号');

subplot(312);

stem(t1,st);

title('抽样信号');

subplot(313);

t3=-50:dt:60+sdt-dt;

plot(t3,xt_t);

title('抽样信号恢复');

axis([010-21]);

插⼊函数：

functionout=INSE消防基本常识 RT0(d,M)

N=length(d);

out=zeros(1,M*N);

fori=0:N-1

out(i*M+1)=d(i+1);

end;

2ASK编码：

functionaskdigital(s,f)

t=0:2*pi/99:2*pi;

%s=[10110010];

%f=2;

m1=[];

c1=[];

forn=1:length(s)

ifs(n)==0

m=zeros(1,100);

els(n)==1

m=ones(1,100);

end

c=sin(f*t);

m1=[m1m];

c1=[c1c]

end

ask=c1.*m1;

subplot(211);

plot(m1)

title('原始信号');

axis([0100*length(s)-0.11.1]);subplot(212);

plot(ask)

title('ASK信号');

AM调幅：

dt=0.001;

fmax=1;

fc=10;

T=5;

N=T/dt;

t=[0:N-1]*dt;

mt=sqrt(2)*cos(2*pi*fmax*t);A=2;

s_am=(A+mt).*cos(2*pi*fc*t);[f,Xf]=FFT_SHIFT(t,s_am);PSD=(abs(Xf).^2)/T;

figure(1)

subplot(211);

plot(t,s_am);holdon;

plot(t,A+mt,'r--');

title('AM调制信号及检波');xlabel('t');

subplot(212);

plot(f,PSD);

axis([-2*fc2*fc01.5*max(PSD)]);title('AM信号功率谱');

xlabel('f');

FFT_SHIFT定义：

function[f,sf]=FFT_SHIFT(t,st)

dt=t(2)-t(1);

T=t(end);

dt=1/T;

N=length(t);

f=[-N/2:N/2-1]*df;

sf=fft(st);

sf=T/N*fftshift(sf);

2ASK编码练习题：

functionaskdigital(s,f)

t=[0:99]/100;

s=[10011100];

f=2;

T=5

m1=[];

c1=[];

forn=1:length(s)

ifs(n)==0

m=zeros(1,100);

els(n)==1

m=ones(1,100);

end

c=sin(2*pi*f*t);

m1=[m1m];

c1=[c1c]

end

ask=c1.*m1;

[fa,Xf]=FFT_SHIFT(t,ask);

PSD=(abs(Xf).^2)/T

subplot(311);

plot(m1)

title('原始信号');

axis([0100*length(s)-0.11.1]);subplot(312);

plot(ask)

title('ASK信号');

subplot(313);

plot(PSD);

信号翻褶：

t=0:0.02:1;

x=3*t;

f=fliplr(x);

t1=-1:0.02:0;

gridon;

plot(t,x,t1,f,'r');

title('信号的翻褶');

gtext('翻褶信号x=-3t');

gtext('原始信号x=3t');

legend('x=3t','x=-3t',3);

信号DSB调幅：

dt=0.001;

fmax=1;

fc=10;

T=5;

t=0:dt:T;

mt=sqrt(2)*cos(2*pi*fc*t);

s_dsb=mt.*cos(2*pi*fc*t);

[f,sf]=FFT_SHIFT(t,s_dsb);

PSD=(abs(sf).^2)/T;

figure(1)

subplot(211);

plot(t,s_dsb);holdon;

plot(t,mt,'r--');

title('DSB调制信号及其包络');

xlabel('t');

subplot(212);

plot(t,PSD);

axis([-2*fc2*fc0max(PSD)]);

title('DSB信号功率谱');

xlabel('f');

信号的均匀量化：

function[sqnr,xq_tz,code]=UniPcm(x,n)%t=[0:0.1:2*pi];

%x=sin(t);

%n=16;xmax=max(abs(x));

x_qtz=x/xmax;

b_qtz=x_qtz;

delta=2/n;

q=delta*[0:n-1]-(n-1)/2*delta;

For

i=1:n

index=find((q(i)-delta/2<=x_qtz)&(x_qtz<=q(i)+delta/2));

x_qtz(index)=q(i)*ones(1,length(index));

b_qtz(find(x_qtz==q(i)))=(i-1)*ones(1,length(find(x_qtz==q(i))));

end

x_qtz=x_qtz*xmax;

nu=ceil(log2(n));

code=zeros(length(胃绞痛吃什么药 x),nu);

fori=1:length(x)

forj=nu:-1:0

if(fix(b_qtz(i)/(2^j))==1);

code(i,nu-j)=1;

b_qtz(i)=b_qtz(i)-2^j;

end

end

end

sqnr=20*log(norm(x)./norm(x-x_qtz));

plot(xq_tz)