qpsk_fading.m

QPSK算法

% Program 3-6
% qpsk_fading.m
%
% Simulation program to realize QPSK transmission system
% (under one path fading)
%
% 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=10;     % 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 

%******************* Fading initialization ********************
% If you use fading function "sefade", you can initialize all of parameters.
% Otherwise you can comment out the following initialization.
% The detailed explanation of all of valiables are mentioned in Program 2-8.

% Time resolution

tstp=1/sr/IPOINT; 

% Arrival time for each multipath normalized by tstp
% If you would like to simulate under one path fading model, you have only to set 
% direct wave.

itau = [0];

% Mean power for each multipath normalized by direct wave.
% If you would like to simulate under one path fading model, you have only to set 
% direct wave.
dlvl = [0];

% Number of waves to generate fading for each multipath.
% In normal case, more than six waves are needed to generate Rayleigh fading
n0=[6];

% Initial Phase of delayed wave
% In this simulation four-path Rayleigh fading are considered.
th1=[0.0];

% Number of fading counter to skip 
itnd0=nd*IPOINT*100;

% Initial value of fading counter
% In this simulation one-path Rayleigh fading are considered.
% Therefore one fading counter are needed.
  
itnd1=[1000];

% Number of directwave + Number of delayed wave
% In this simulation one-path Rayleigh fading are considered
now1=1;        

% Maximum Doppler frequency [Hz]
% You can insert your favorite value
fd=160;       

% You can decide two mode to simulate fading by changing the variable flat
% flat     : flat fading or not 
% (1->flat (only amplitude is fluctuated),0->nomal(phase and amplitude are fluctutated)
flat =1;

%******************** START CALCULATION *************************************

ebn0=0:40
nloop=100;  % Number of simulation loops
for i=1:length(ebn0)
noe = 0;    % Number of error data
nod = 0;    % Number of transmitted data
noep=0;
nodp=0;

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(ifade,qfade,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));
  
%********************* Add White Gaussian Noise (AWGN) without fading*********
	
    [ichp3,qchp3]= comb(ich2,qch2,attn);% add white gaussian noise
	[ichp4,qchp4]= compconv(ichp3,qchp3,xh2);

    syncpoint=irfn*IPOINT+1;
    ichp5=ichp4(syncpoint:IPOINT:length(ichp4));
    qchp5=qchp4(syncpoint:IPOINT:length(qchp4));
        
%**************************** QPSK Demodulation *****************************

    [demodata]=qpskdemod(ich5,qch5,1,nd,ml);
    [demodatap]=qpskdemod(ichp5,qchp5,1,nd,ml);

%************************** Bit Error Rate (BER) ****************************

    noe2=sum(abs(data1-demodata));  % sum: built in function
	noep2=sum(abs(data1-demodatap));
    nod2=length(data1);  % length: built in function
    nodp2=nod2;
	noe=noe+noe2;
	noep=noep+noep2;
    nod=nod+nod2;
    nodp=nodp+nodp2

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

end % for iii=1:nloop    

%********************** Output result ***************************
berp(i)=noep/nodp;
ber(i) = noe/nod;
Qx=(1/2).*erfc(sqrt(10.^(ebn0./10)));
Fx=(1/2).*(1-1./sqrt(1+10.^(-ebn0./10)));
fprintf('%d\t%e\n',i,ber(i));
%fprintf('%d\t%d\t%d\t%e\n',ebn0,noe,nod,noe/nod);  % fprintf: built in function
%fid = fopen('BERqpskfad.dat','a');
%fprintf(fid,'%d\t%e\t%f\t%f\t\n',ebn0,noe/nod,noe,nod);  % fprintf: built in function
%fclose(fid);
end

figure;
semilogy(ebn0,Qx,'r-',ebn0,berp,'-',ebn0,Fx,'-',ebn0, ber, 'b-');
xlabel('Eb/No (dB)'); ylabel('BER');
title('Performance of QPSK');
axis([0 40 1E-4 1]);
legend('QPSK AWGN (Theory)','QPSK AWGN(Simulation)','QPSK Rayleigh (theory)','QPSK Rayleigh(Simulation)');
grid on;
%******************** end of file ***************************