% Program 3-19
% gmsk_fading.m
%
% Simulation program to realize GMSK transmission system
% (under one path fading)
%
% Programmed by R.Sawai and H.Harada
%
%******************** Preparation part *************************************
sr=256000.0; % Symbol rate
ml=1; % ml:Number of modulation levels
br=sr.*ml; % Bit rate
nd = 100; % Number of symbols that simulates in each loop
ebn0=15; % Eb/N0
IPOINT=8; % Number of oversamples
%************************* Filter initialization ***************************
irfn=21; % Number of taps
B=0.25*sr;
B2=0.6*sr;
[xh] = gaussf(B,irfn,IPOINT,sr,1); %Transmitter filter coefficients
[xh2] =gaussf(B2,irfn,IPOINT,sr,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=320;
% 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=1000; % 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
%*************************** GMSK Modulation ********************************
data11=2*data1-1;
data2=oversamp(data11,length(data11),IPOINT);
data3=conv(data2,xh); % NEW for GMSK
th=zeros(1,length(data3)+1);
ich2=zeros(1,length(data3)+1);
qch2=zeros(1,length(data3)+1);
for ii=2:length(data3)+1
th(1,ii)=th(1,ii-1)+pi/2*data3(1,ii-1)./IPOINT;
end
ich2=cos(th);
qch2=sin(th);
%************************** 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]=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-IPOINT/2+1;
ich5=ich4(syncpoint:IPOINT:length(ich4));
qch5=qch4(syncpoint:IPOINT:length(qch4));
%**************************** GMSK Demodulation *****************************
demoddata2(1,1)=-1;
for k=3:2:nd*ml+1
demoddata2(1,k)=ich5(1,k)*qch5(1,k-1)*cos(pi*(k))>0;
end
for n=2:2:nd*ml+1
demoddata2(1,n)=ich5(1,n-1)*qch5(1,n)*cos(pi*(n))>0;
end
[demodata]=demoddata2(1,2:nd*ml+1);
%************************** 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 = noe/nod;
fprintf('%d\t%d\t%d\t%e\n',ebn0,noe,nod,noe/nod); % fprintf: built in function
fid = fopen('BERgmskfad.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 of file ***************************
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