qpsk.m

QPSK算法

% Program 3-5
% qpsk.m
%
% Simulation program to realize QPSK transmission system
%
% Programmed by H.Harada and T.Yamamura
%

%******************** Preparation part *************************************
clear all;
sr=256000.0; % Symbol rate
ml=2;        % ml:Number of modulation levels (BPSK:ml=1, QPSK:ml=2, 16QAM:ml=4)
br=sr .* ml; % Bit rate
nd = 100;   % Number of symbols that simulates in each loop
%ebn0=3;      % Eb/N0
IPOINT=8;    % Number of oversamples

%************************* Filter initialization ***************************

irfn=21;                  % Number of taps
alfs=0.5;                 % Rolloff factor
[xh] = hrollfcoef(irfn,IPOINT,sr,alfs,1);   %Transmitter filter coefficients 
[xh2] = hrollfcoef(irfn,IPOINT,sr,alfs,0);  %Receiver filter coefficients 

%******************** START CALCULATION *************************************
ebn0=0:10;
nloop=100; % Number of simulation loops

for i = 1:length(ebn0)
noe = 0;    % Number of error data
nod = 0;    % Number of transmitted data
Eb=ebn0;    % Since N0=1

for iii=1:nloop
    
%*************************** Data generation ********************************  
	
    data1=rand(1,nd*ml)>0.5;  % rand: built in function
    
%*************************** QPSK Modulation ********************************  

    [ich,qch]=qpskmod(data1,1,nd,ml);
	[ich1,qch1]= compoversamp(ich,qch,length(ich),IPOINT); 
	[ich2,qch2]= compconv(ich1,qch1,xh); 
     
%**************************** Attenuation Calculation ***********************
	
    spow=sum(ich2.*ich2+qch2.*qch2)/nd;  % sum: built in function
	attn=0.5*spow*sr/br*10.^(-ebn0(i)/10);
	attn=sqrt(attn);  % sqrt: built in function
     
%********************** Fading channel **********************

  % Generated data are fed into a fading simulator
  % [ifade,qfade]=sefade(ich2,qch2,itau,dlvl,th1,n0,itnd1,now1,length(ich2),tstp,fd,flat);
  
  % Updata fading counter
  %itnd1 = itnd1+ itnd0;

%********************* Add White Gaussian Noise (AWGN) **********************
	
    [ich3,qch3]= comb(ich2,qch2,attn);% add white gaussian noise
	[ich4,qch4]= compconv(ich3,qch3,xh2);

    syncpoint=irfn*IPOINT+1;
    ich5=ich4(syncpoint:IPOINT:length(ich4));
    qch5=qch4(syncpoint:IPOINT:length(qch4));
        
%**************************** QPSK Demodulation *****************************

    [demodata]=qpskdemod(ich5,qch5,1,nd,ml);

%************************** Bit Error Rate (BER) ****************************
    noe2=sum(abs(data1-demodata));  % sum: built in function
	nod2=length(data1);  % length: built in function
	noe=noe+noe2;
	nod=nod+nod2;

%	fprintf('%d\t%e\n',iii,noe2/nod2);  % fprintf: built in function

end % for iii=1:nloop    

%********************** Output result ***************************

ber(i) = noe/nod;

Qx=(1/2)*erfc((10.^(Eb/10))/sqrt(2));   %Q function

end
% figure
figure
semilogy(ebn0,ber,'bo-',ebn0, Qx,'rx-');
Title('Performence of QPSK');
axis([0 10 1E-4 1]);
xlabel('Eb/N0(dB)');
ylabel('BER');
legend ('QPSK AWGN (Simulation)','QPSK AWGN (Theory)');
grid on;
%******************** end of file ***************************