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// Example no. 7.2
// To calculate exact and approximate Q-factor if the signal is (a)OOK, (b) PSK
// Page no. 311
clc;
clear;
// Given data
lambda=1.55*10^(-6); // Wavelength of given signal
meanPin=1; // Mean fiber launch power in dBm
alpha=0.2; // fiber loss in dB/km
l=240; // fiber length in km
neta=0.7; // quantum efficiency
T = 290; // Tempearture in K
RL=100; // Length resistance in Ω
PLOdBm = 10; // Power at local oscillator in dBm
Be = 7.5*10^9; // Efficient bandwidth of filter in Hz
c=3*10^8; // Speed of ligth in air in m/s
loss=alpha*l; // Total fiber loss
q=1.602*10^(-19); // Charge of electron
h=6.626*10^(-34); // Planck constant
kB=1.38*10^(-23); // Bolzman constant
f=c/lambda; // mean frequency
R=(neta*q)/(h*f); // Responsivity
//For OOK
Pin=10*log10(2)+meanPin; // peak power in dBm
P1rdBm=Pin-loss; // received peak power in dBm
P1r=(10^(P1rdBm/10))*10^(-3); // received peak power in W
PLO=(10^(PLOdBm/10))*10^(-3); // Power at local oscillator in W
I1=2*R*sqrt(P1r*PLO); // mean of bit 1
sigma1=2*q*Be*R*(P1r+PLO)+(4*kB*T*Be)/RL; // Square of variance of bit 1
I0=0; // mean of bit 0
sigma0=sigma1; // Square of variance of bit 0
Q1=(I1-I0)/(2*sqrt(sigma1)); // Exact Q-factor
Q2=sqrt((neta*P1r)/(2*h*f*Be)); // Approximate Q-factor
// Displaying the result in command window
printf('\n Exact Q-factor if the signal is OOK = %0.1f',Q1);
printf('\n Approximate Q-factor if the signal is OOK = %0.1f',Q2);
// For PSK
P1rdBm=meanPin-loss; // received peak power in dBm
P1r=(10^(P1rdBm/10))*10^(-3); // received peak power in W
I1=2*R*sqrt(P1r*PLO); // mean of bit 1
sigma1=2*q*Be*R*(P1r+PLO)+(4*kB*T*Be)/RL; // Square of variance of bit 1
I0=-I1; // mean of bit 0
sigma0=sigma1; // Square of variance of bit 0
Q1=I1/sqrt(sigma1); // Exact Q-factor
Q2=sqrt((2*neta*P1r)/(h*f*Be)); // Approximate Q-factor
// Displaying the result in command window
printf('\n Exact Q-factor if the signal is PSK = %0.2f',Q1);
printf('\n Approximate Q-factor if the signal is PSK = %0.2f',Q2);
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