qpsk.m

本问对软件无线电中常用的梳状滤波器进行仿真

% qpsk
% qpsk.m
% Simulation program to realize QPSK transmission system
% (under one path fading)

%******************** Preparation part *************************************

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
%*********************************Main loop****************************
for ebn0=0:2:6;
%************************* 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 *************************************

nloop=100;  % Number of simulation loops

noe = 0;    % Number of error data
nod = 0;    % Number of transmitted data

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.^(-ebn0/10);
	attn=sqrt(attn);  % sqrt: built in function
     
%********************** Fading channel **********************

  % Generated data are fed into a fading simulator
    [ifade,qfade]=Rayleigh_channel(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
    ich3 = randn(1,length(ifade)).*attn;
    qch3 = randn(1,length(ifade)).*attn;
 
   ich3 = ich3+ifade(1:length(ifade));
   qch3 = qch3+qfade(1:length(qfade));

    
    
    
	[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);
    para=1;
    demodata=zeros(para,ml*nd);
    demodata((1:para),(1:ml:ml*nd-1))=ich5((1:para),(1:nd))>=0;
    demodata((1:para),(2:ml:ml*nd))=qch5((1:para),(1:nd))>=0;


%************************** 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;
    ber(:,iii)=noe2/nod2;              %BER of the system

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

end % for iii=1:nloop    
berave(:,ebn0/2+1)=sum(ber)/100;        %BER for certain ebn0
fprintf('%d\t%e\n',ebn0,berave(:,ebn0/2+1));



%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



%**************Theoretical BER Under AWGN and Rayleigh channel*****************%
ebn0=0:2:6;
ebn1=0:0.1:6;
for i=1:length(ebn1)
    SNR=exp(ebn1(i)*log(10)/10);            % signal to noise ratio
    theo_err_prb(i)=0.5*erfc(sqrt(SNR));
    theo_err_prb2(i)=0.5*(1-1/sqrt(1+1/SNR));
end
% %****************Calculation of Signal Spectrum******************



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

% Output of  simulated BER and theoretical BER
figure(1);
semilogy(ebn0,berave,'*');
title('Performance of QPSK');
xlabel('EB/N0(DB)');
ylabel('BER');
hold
semilogy(ebn1,theo_err_prb,'r');
semilogy(ebn1,theo_err_prb2);
legend('QPSK Rayleigh (simulated)','QPSK AWGN (theroy)','QPSK Rayleigh (theroy)')

figure(2);
%Input baseband waveform
subplot(3,2,1);
plot(data1);
xlabel('Input baseband waveform');
% Power spectrum of Input 
subplot(3,2,2);
data1_s=abs(fft(data1));
plot(fftshift(data1_s));

xlabel('Power spectrum of Input');
%  QPSK modulaed singal 
subplot(3,2,3);
para=1;
moddata=zeros(para,ml*nd);
moddata((1:para),(1:ml:ml*nd-1))=ich2((1:para),(1:nd));
moddata((1:para),(2:ml:ml*nd))=qch2((1:para),(1:nd));
plot(moddata);
xlabel(' QPSK modulaed singal');
% Power spectrum of QPSK modulaed singal 
subplot(3,2,4);
moddata_s=abs(fft(moddata));
plot(fftshift(moddata_s));
xlabel('Power spectrum of QPSK modulaed singal');
% AWGN channel output
subplot(3,2,5);
data_agwn=zeros(para,ml*nd);
data_agwn((1:para),(1:ml:ml*nd-1))=ich3((1:para),(1:nd));
data_agwn((1:para),(2:ml:ml*nd))=qch3((1:para),(1:nd));
plot(data_agwn);
xlabel('AWGN channel output');
% Power spectrum of AWGN channel output
subplot(3,2,6);
plot(abs(fft(data_agwn)));
xlabel('Power spectrum of AWGN channel output');
figure(3);
subplot(2,1,1);
 plot(ich2,qch2);
subplot(2,1,2);
plot(ifade,qfade);
%******************** end of file ***************************