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求大神讲解每句意思

%绘制调制波形00101010????

clear all;

Ts=1/16000;%基带信号周期为1/16000s,即为16KHz

Tb=1/32000;%输入信号周期为Ts/2=1/32000s,即32KHz

BbTb=0.5;%取BbTb为0.5

Bb=BbTb/Tb;%3dB带宽

Fc=32000;%载波频率为32KHz

F_sample=64;%每载波采样64个点

B_num=8;%基带信号为8个码元

B_sample=F_sample*Fc*Tb;%每基带码元采样点数

Dt=1/Fc/F_sample;%采样间隔

B_sample=Tb/Dt

t=0:Dt:B_num*Tb-Dt;%仿真时间

T=Dt*length(t);%仿真时间值

Ak=[0 0 1 0 1 0 1 0];%产生8个基带信号

Ak=2*Ak-1;

gt=ones(1,B_sample);%每码元对应的载波信号

Akk=sigexpand(Ak,B_sample);%码元扩展

temp=conv(Akk,gt);%进行卷积运算，达到滤波效果

Akk=temp(1:length(Akk));

tt=-2.5*Tb:Dt:2.5*Tb-Dt;

gausst=erfc(2*pi*Bb*(tt-Tb/2)/sqrt(log(2))/sqrt(2))/2-erfc(2*pi*Bb*(tt+Tb/2)/sqrt(log(2))/sqrt(2))/2;

J_g=zeros(1,length(gausst));

for i=1:length(gausst)

if i==1

J_g(i)=gausst(i)*Dt;

else

J_g(i)=J_g(i-1)+gausst(i)*Dt;

end;

end;

J_g=J_g/2/Tb;

Alpha=zeros(1,length(Akk));

k=1;

L=0;

for j=1:B_sample

J_Alpha=Ak(k+2)*J_g(j);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+L*pi/2;

end;

k=2;

L=0;

for j=1:B_sample

J_Alpha=Ak(k+2)*J_g(j)+Ak(k+1)*J_g(j+B_sample);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+L*pi/2;

end;

k=3;

L=0;

for j=1:B_sample

J_Alpha=Ak(k+2)*J_g(j)+Ak(k+1)*J_g(j+B_sample)+Ak(k)*J_g(j+2*B_sample);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+L*pi/2;

end;

k=4;

L=0;

for j=1:B_sample

J_Alpha=Ak(k+2)*J_g(j)+Ak(k+1)*J_g(j+B_sample)+Ak(k)*J_g(j+2*B_sample)+Ak(k-1)*J_g(j+3*B_sample);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+L*pi/2;

end;

L=0;

for k=5:B_num-2

if k==5

L=0;

else

L=L+Ak(k-3);

end;

for j=1:B_sample

J_Alpha=Ak(k+2)*J_g(j)+Ak(k+1)*J_g(j+B_sample)+Ak(k)*J_g(j+2*B_sample)+Ak(k-1)*J_g(j+3*B_sample)+Ak(k-2)*J_g(j+4*B_sample);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+mod(L,4)*pi/2;

end;

end;

%B_num-1;

k=B_num-1;

L=L+Ak(k-3);

for j=1:B_sample

J_Alpha=Ak(k+1)*J_g(j+B_sample)+Ak(k)*J_g(j+2*B_sample)+Ak(k-1)*J_g(j+3*B_sample)+Ak(k-2)*J_g(j+4*B_sample);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+mod(L,4)*pi/2;

end;

%B_num;

k=B_num;

L=L+Ak(k-3);

for j=1:B_sample

J_Alpha=Ak(k)*J_g(j+2*B_sample)+Ak(k-1)*J_g(j+3*B_sample)+Ak(k-2)*J_g(j+4*B_sample);

Alpha((k-1)*B_sample+j)=pi*J_Alpha+mod(L,4)*pi/2;

end;

S_Gmsk=cos(2*pi*Fc*t+Alpha);

subplot(311)

plot(t/Tb,Akk);

axis([0 8 -1.5 1.5]);

title('基带波形');

subplot(312)

plot(t/Tb,Alpha*2/pi);

axis([0 8 min(Alpha*2/pi)-1 max(Alpha*2/pi)+1]);

title('相位波形');

subplot(313)

plot(t/Tb,S_Gmsk);

axis([0 8 -1.5 1.5]);

title('GMSK波形');

%解调?

for n=1:512;

if n<=B_sample

Alpha1(n)=0;

else Alpha1(n)=Alpha(n-B_sample);

end

end

a=[0 1 1 1 1 1 1 1]

ak=sigexpand(a,B_sample);

temp=conv(ak,gt);

ak=temp(1:length(ak));

S_Gmsk1=cos(2*pi*Fc*(t-Tb)+Alpha1+pi/2).*ak;

figure

subplot(311)

plot(t/Tb,S_Gmsk1);

axis([0 8 -1.5 1.5]);

title('延迟1bt,移相pi/2GMSK波形');

xt=S_Gmsk1.*S_Gmsk;

x=0;

subplot(312)

plot(t/Tb,xt,t/Tb,x,'r:');

axis([0 8 -1.5 1.5]);

title('相乘后波形')

Fs=10000;

rp=3;

rs=50;

wp=2*pi*50;

ws=2*pi*800;

[n,wn]=buttord(wp,ws,rp,rs,'s')

[z,p,k]=buttap(n);

[bp,ap]=zp2tf(z,p,k);

[bs,as]=lp2lp(bp,ap,wn);

[b,a]=bilinear(bs,as,Fs)

y=filter(b,a,xt);

subplot(313)

plot(t/Tb,y,t/Tb,x,'r:');

axis([0 8 -1.5 1.5]);

title('经过低通滤波器后波形');

for i=1:8

if y(i*B_sample)>0

bt(i)=1

else

bt(i)=0

end

end

bt=2*bt-1;

btt=sigexpand(bt,B_sample);

temp1=conv(btt,gt);

btt=temp1(1:length(btt));

figure

subplot(311)

plot(bt)

title('抽样值');

axis([0 8 -1.5 1.5]);

subplot(312)

plot(t/Tb,Akk);

axis([0 8 -1.5 1.5]);

title('原基带波形');

subplot(313)

plot(t/Tb,btt);

axis([0 8 -1.5 1.5]);

title('解调后波形');