lxl.m

这是个关于瑞利信道仿真的程序

% 主程序scriptfile：
% 两径瑞利衰落信道仿真
% 设定默认参数
NN=256;          % 传输符号个数
tb=0.5;          % 一比特时间
fs=10;           % 每符号采样数
ebn0db=[1:2:15]; % 设定Eb/N0
% 建立QPSK信号
x=random_binary(NN,fs)+i*random_binary(NN,fs);  % x为QPSK信号
% 输入功率和延迟
p0=0;           % 视距LOS分量
p1=20;           % 第一路径分量
p2=1;         % 第二路径分量
delay=1;        % 按照每符号采样数决定的延迟
delay0=0;delay1=0;delay2=delay;
% 设定复高斯（瑞利）衰减
gain1=sqrt(p1)*abs(randn(1,NN)+i*randn(1,NN));
gain2=sqrt(p2)*abs(randn(1,NN)+i*randn(1,NN));
for k=1:NN
    for kk=1:fs
        index=(k-1)*fs+kk;
        ggain1(1,index)=gain1(1,k);
        ggain2(1,index)=gain2(1,k);
    end
end
y1=x;
for k=1:delay2
    y2(1,k)=y1(1,k)*sqrt(p0);
end
for k=(delay2+1):(NN*fs)
    y2(1,k)=y1(1,k)*sqrt(p0)+y1(1,k-delay1)*ggain1(1,k)+y1(1,k-delay2)*ggain2(1,k);
end
% 匹配滤波器
b=-ones(1,fs);b=b/fs;a=1;
y=filter(b,a,y2);
% 仿真结束
% Use the semianalytic BER estimator . The following sets up the semi
% analytic estimator . Find the maximun magnitude of the cross correlation
% and the corresponding lag .
[cor lags]=vxcorr(x,y);
cmax=max(max(abs(cor)));
nmax=find(abs(cor)==cmax);
timelag=lags(nmax);
corrmag=cmax;
theta=angle(cor(nmax));
y=y*exp(-i*theta);     % derotate
% Noise BW calibration
hh=impz(b,a);ts=1/16;nbw=(fs/2)*sum(hh.^2);
% Delay the input ,and do BER estimation on the last 128 bits . Use middle
% sample .Make sure the index does not exceed number of input points .Eb
% should be computed at the receiver input .
index=(10*fs+8:fs:(NN-10)*fs+8);
xx=x(index);
yy=y(index-timelag+1);
[n1 n2]=size(y2);ny2=n1*n2;
eb=tb*sum(sum(abs(y2).^2))/ny2;
eb=eb/2;
[peideal,pesystem]=qpsk_berest(xx,yy,ebn0db,eb,tb,nbw);
figure
semilogy(ebn0db,peideal,'b*-',ebn0db,pesystem,'r+-')
xlabel('Eb/N0 (db)');ylabel('Probability of Error');
grid on 
axis([0 14 10^(-10) 1]);
% End of script file.