maincx.m

AWGN多径信道中的QPSK系统进行BER性能仿真

%File: c14_threeray.m
%%%%%%%%%%%%%%%%
%Default parameters

NN = 256;  %number of symbols
tb = 0.5;  %bit time
fs = 16;   %samples/symbol
ebn0db = [1:2:14];  %Eb/N0 vector

%%%%%%%%%%%%%%%%%%%%%%%%
%Establish QPSK signals
%%%%%%%%%%%%%%%%%%%%%%%%%%

x=random_binary(NN,fs)+i*random_binary(NN,fs);   %QPSK signal

%%%%%%%%%%%%%%%%%%%%%%%
%Input power and delays
%%%%%%%%%%%%%%%%%%%%%%%%%
p0 = input('Enter p0>');
p1 = input('Enter p1>');
p2 = input('Enter p2>');
delay = input('Enter tau>');
delay0 = 0;
delay1 = 0;
delay2 = delay;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%Set up the Complex Gaussian (Rayleigh) gains'
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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

%%%%%%%%%%%%%%%%%%%%%%%
% Matched filter
%%%%%%%%%%%%%%%%%%%%%%%
b = -ones(1,fs);
b = b/fs;
a = 1;
y = filter(b,a,y2);

%%%%%%%%%%%%%%%%%%%%%%%%%%
%End of simulation
%%%%%%%%%%%%%%%%%%%%%%%%
%Use the semi analytic BER estimator.The following sets up the semi analytic 
%estimator. Find the maximum 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 128bits.
%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('E_b/N_0(dB)');
ylabel('Probability of Error差错概率');
grid;
axis([0 14 10^(-10) 1]);

%End of script file.