% In the name of god
% ASK Modulation
% Author: K.Baghery [email protected]
% My Weblog www.K-Baghery.blogfa.com
%QPSK Implemenatation
clear;
%This is the first part of the problem where we are first generating a
%random input of size 6 bits, which results in 3 QPSk sysmbols;
Input = round(rand(1,6));
%Conversion of the bits to -1 and +1;
s = 2*Input - 1;
%The frequncy of the signal along with its sampling frequency which should
%be 10 times more than the frequency of the signal as recommended;
F = input('F=Enter the frequency of the signal:');
Fs = input('Fs=Enter the sampling frequncy:');
%Generating the in-phase component of the first symbol
I = s(1)*sqrt(2*F)*cos(2*pi*F/Fs*[0:(Fs/F)]);
%Generating the quadrature phase component of the first symbol
Q = s(2)*sqrt(2*F)*sin(2*pi*F/Fs*[0:(Fs/F)]);
%Generating the second and the third symbol of the signal;
for i =2:3
I1 = s(2*i-1)*sqrt(2*F)*cos(2*pi*F/Fs*[0:Fs/F]);
Q1 = s(2*i)*sqrt(2*F)*sin(2*pi*F/Fs*[0:Fs/F]);
I = [I I1];
Q = [Q Q1];
end
%plot for in-phase component
plot(I,'linewidth',5);
title('In-Phase phase component of QPSK');
xlabel('Sampled Time Axis');
ylabel('Amplitude');
figure;
%Plot for Quadrature phase component
plot(Q,'linewidth',5);
title('Quadrature phase component of QPSK');
xlabel('Sampled Time Axis');
ylabel('Amplitude');
figure;
%Obtaning the QPSk Signal
x = I+Q;
title('QPSK Signal');
xlabel('Samples Time Axis');
ylabel('Amplitude');
plot(x,'linewidth',5);
figure;
a2 = s(1);
for j = 0:F/Fs:.01
a1 = s(1);
a2 = [a2 a1];
end
for i = 2:3
a = s(2*i-1);
for j = 0:F/Fs:.01
a = [a s(2*i-1)];
end
a2 = [a2 a];
end
plot(a2,'linewidth',5);
title('I');
figure;
b2 = s(2);
for j = 0:F/Fs:.01
b1 = s(2);
b2 = [b2 b1];
end
for i = 2:3
b = s(2*i);
for j = 0:F/Fs:.01
b = [b s(2*i)];
end
b2 = [b2 b];
end
plot(b2,'linewidth',5);
title('Q');
%Detection of QPSK signals
N=1000;%Number of Iterations
s1=[1 0];
s2=[0 1];
s3=[-1 0];
s4=[0 -1];
No=.1507;
symbolerror=0;% initializing eror
for i=1:N
%generation of uniformly distributed symbols
a=rand;
if(a<=0.25)
data=s1;
elseif(a<=0.5&a>0.25)
data=s2;
elseif(a>0.5&a<=0.75)
data=s3;
else
data=s4;
end
%generation of noise
%corrupting the data with noise
n(1)=randn*sqrt(No/2); %generating noise with variance No/2
n(2)=randn*sqrt(No/2);
% Uncomment if Rayleigh fading
%r=raylrnd(1)*data+n;
r=data+n;
%detection of corrupted signal
d1=dot(r,s1);
d2=dot(r,s2);
d3=dot(r,s3);
d4=dot(r,s4);
d=max([d1 d2 d3 d4]);
if(d==d1)
decision=s1;
elseif(d==d2)
decision=s2;
elseif(d==d3)
decision=s3;
else(d==d4)
decision=s4;
end
if(data~=decision)
symbolerror=symbolerror+1;
end
X(i,:)=r;
end
perr=symbolerror/N;
figure;
plot(X(:,1),X(:,2),'*');%plot of the received signal points
title('Received signal')
figure;
w=[s1;s2;s3;s4];
plot(w(:,1),w(:,2),'r*','linewidth',5);
axis([-2 2 -2 2]);
title('Transmitted signal')
