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% EVALUATION OF ERROR PROBABILITY UNDER ISI AND AWGN
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% The overall impulse response of the channel is modeled by chebyshev pulse
% Binary modulation is considered
% 1000 interference terms are assumed to be nonzero, others have negligible
% ampliture
A1 = 0.4032; %paramters of the chebyshev pulse
A2 = 0.7163;
w1 = 2.839;
w2 = 1.176;
phi1 = 0.7553;
phi2 = 0.1602;
bet1 = 0.4587;
bet2 = 1.107;
t = -10:0.01:10;
h=(A1*cos((w1*abs(t)/0.5)-phi1).*exp(-bet1*abs(t)/0.5))+...
(A2*cos((w2*abs(t)/0.5)-phi2).*exp(-bet2*abs(t)/0.5));
std = 0.2:0.05:1.25; %standard deviation of the AWGN
lev = 2;
en_d = 1/3*(lev^2-1);
en = 0;
lam = 0.5;
zo = 0.1;
p = 1;
Pe_wid_isi = [];
Pe_widout_isi_psk = [];
Pe_widout_isi_fsk = [];
va = std.^2; %variance of the noise
center = (length(t)-1)/2;
snr = h(center)^2./fliplr(va); %vector of SNR
snr_db = 10*log(snr);
for s = 1.25:-0.05:0.2 %start of algorithm
for k = 1:(length(t)-1)/2
f(k) = h(k)/s;
end
for k = 1:500
en = en+f(k)^2*en_d;
p = p*(sinh(2*lam*f(k))/(2*sinh(lam*f(k))));
end
Pet = qfunc(f(center)-zo)*exp(0.5*en*lam^2-lam*zo)*p;
Pe_wid_isi = [Pe_wid_isi,2*Pet];
end
Pe_widout_isi_psk = qfunc(sqrt(2*snr));
Pe_widout_isi_fsk = qfunc(sqrt(snr));
% main code ends here
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% PLOTTING
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figure(1)
plot(t,h);
title('impulse response of the channel');
xlabel('Time');
ylabel('Impulse response');
grid;
figure(2)
plot(snr_db,Pe_wid_isi,'r');
hold on;
plot(snr_db,Pe_widout_isi_psk,'g');
hold on;
plot(snr_db,Pe_widout_isi_fsk);
title('error probability curves');
xlabel('SNR(dB)');
ylabel('bit error probability');
grid;
