liu5.m

认知无线电系统中多载波信号带外干扰的抑制

%实验五  升余弦滚降滤波系统的误码率
global dt t f df N T %全局变量
close all
clear Eb_N0 Pe
N=2^15; 					%采样点数
L=4; 						%每码元的采样点数  
M=N/L						%码元数   
Rb=2;						%码速率是2Mb/s		
Ts=1/Rb; 				%码元间隔      
dt=Ts/L;					%时域采样间隔					        
df=1/(N*dt)				%频域采样间隔     
T=N*dt 					%截短时间        
Bs=N*df/2 				%系统带宽     
alpha=0.5				%滚降系数=0.5	

t=linspace(-T/2,T/2,N); %时域横坐标
f=linspace(-Bs,Bs,N)+eps; %频域横坐标  

figure(1)
 set(1,'Position',[10,30,500,200])
                 %设定窗口位置及大小
hr1=sin(pi*t/Ts)./(pi*t/Ts);
hr2=cos(alpha*pi*t/Ts)./(1-(2*alpha*t/Ts).^2);
hr=hr1.*hr2;
HR=abs(t2f(hr));
GT=sqrt(HR);
GR=GT;

for loop1=1:10
 Eb_N0(loop1)=(loop1-1)  %分贝值变为真值
 eb_n0(loop1)=10^(Eb_N0(loop1)/10);
 Eb=1;	
 n0=Eb/eb_n0(loop1);   	%信道噪声谱密度 
 sita=n0*Bs; 				%噪声功率

 n_err=0;     				%误码计数

 for loop2=1:3  
  a=sign(randn(1,M));	%发送码元
  imp=zeros(1,N);    
  imp(L/2:L:N)=a/dt;
  IMP=t2f(imp);
  
  n_ch=sqrt(sita)*randn(size(t)); %信道噪声
  nr=real(f2t(t2f(n_ch).*GR));    

  sr=real(f2t(IMP.*HR))+nr;       
  y=sr(L/2:L:N);						%以L/2为起点，步长L,取样点N  
  aa=sign(y);                    %接收码元    
  n_err=n_err+length(find(aa~=a)) ; 
 end
 Pe(loop1)=n_err/(M*loop2);		%误码率Pe'=n_err/(M*loop2)
 figure(1) 
  semilogy(Eb_N0,Pe,'g');
  eb_n0=10.^(Eb_N0/10);				%还原为真值 
  hold on
  semilogy(Eb_N0,0.5*erfc(sqrt(eb_n0)));
  axis([0,9,1e-4,1])
  xlabel('Eb/N0')
  ylabel('Pe')
 end

end