% 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 ***************************
