%例四 網(wǎng)孔均衡

%本程序中時(shí)間單位是微秒
%頻率單位為MHz
%碼速率單位是Mb/s

global dt t f df N
close all

N=2^13; %采樣點(diǎn)數(shù)
L=16;   %每碼元的采樣點(diǎn)數(shù)
M=N/L   %碼元數(shù)
Rb=2;		%碼速率是2Mb/s
Ts=1/Rb;        %碼元間隔
dt=Ts/L;        %時(shí)域采樣間隔
df=1/(N*dt)     %頻域采樣間隔
T=N*dt          %截短時(shí)間
Bs=N*df/2       %系統(tǒng)帶寬
Na=4;           %示波器掃描寬度為4個(gè)碼元

alpha=input('滾降系數(shù)=[0.5]');
if alpha==[],alpha=0.5;end

t=[-T/2+dt/2:dt:T/2]; %時(shí)域橫坐標(biāo)
f=[-Bs+df/2:df:Bs]+eps;   %頻域橫坐標(biāo)

%網(wǎng)孔均衡
WK=(pi*f*Ts)./sin(pi*f*Ts).*LPF(1/Ts); 
  
%升余弦
hr1=sin(pi*t/Ts)./(pi*t/Ts);
hr2=cos(alpha*pi*t/Ts)./(1-(2*alpha*t/Ts).^2);
hr=hr1.*hr2;		 
HR=t2f(hr);

%矩形脈沖
G=t2f(rect(Ts));

tt=[0:dt:Na*L*dt];
for ii=1:2
 figure(ii)
 set(ii,'Position',[10+(ii-1)*400,50,350,200])
                %設(shè)定窗口位置及大小 
 hold on
 grid
 axis([0,Na*Ts,-1,1])
 xlabel('t (us)')
 ylabel('V')
end

figure(3)
 set(3,'Position',[10,500,600,200])
                %設(shè)定窗口位置及大小 
 plot(f,abs(WK))
 grid
 axis([0,1/Ts,0,10])
 xlabel('f (MHz)')
 ylabel('網(wǎng)孔濾波特性')
 
 a=sign(randn(1,M));
 imp=zeros(1,N);    %產(chǎn)生沖激序列
 imp(L/2:L:N)=a/dt;
 IMP=t2f(imp);

 S1=IMP.*G;     %NRZ信號(hào)
 S2=S1.*WK.*HR; %加網(wǎng)孔,升余弦滾降
 S3=S1.*HR;     %不加網(wǎng)孔,直接滾降

 s2=real(f2t(S2));
 s3=real(f2t(S3));

 figure(1) 
 for jj=1:Na*L:N/2
  plot(tt,s2(jj:jj+Na*L),'g');
 end
 figure(2)
 for jj=1:Na*L:N/2
  plot(tt,s3(jj:jj+Na*L),'g');
 end