QUADRATURE PHASE SHIFT KEYING (QPSK)

PROGRAM:
clc;
clf;
clear;
bs = input('Enter the input bit sequence :');
f = input('Enter the modulating signal frequency :');
p = input('Enter the modulating signals phase differences[p2,p3,p4] :');
a = input('Enter the modulating signal amplitude :');
c = 0;
d = 0;
l = length(bs);
if  (mod(l,2) ~= 0)
    bs = [bs,0];
end

% code for generating binary signal
for i = 1:l
    t1 = (c:0.01:c+1);
    x = bs(i) * ones(length(t1),1);
    subplot(2,1,1);
    plot(t1,x);
    axis([0 l -1 2]);
    xlabel('time ->');
    ylabel('amplitude ->');
    title('binary signal');
    hold on
    c=c+1;
end

% code for generating qpsk signal
for i=1:2:l
    t=(d:0.01:d+2);
    if (bs(i)==0 && bs(i+1)==0)
        b = sin(2 * pi * f * t);
    elseif (bs(i)==0 && bs(i+1)==1)
        b = sin(2 * pi * f * t + p(1));
    elseif (bs(i)==1 && bs(i+1)==0)
        b = sin(2 * pi * f * t + p(2));
    elseif (bs(i)==1 && bs(i+1)==1)
        b = sin(2 * pi * f * t + p(3));
    end
    subplot(2,1,2);
    plot(t,b);
    xlabel('time ->');
    ylabel('amplitude ->');
    title('qpsk signal');
    hold on
    d=d+2;
end

SAMPLE OUTPUT:
Enter the input bit sequence :[0 0 0 1 1 0 1 1]
Enter the modulating signal frequency :2
Enter the modulating signals phase differences[p2,p3,p4] :[90 180 270]
Enter the modulating signal amplitude :3

PLOT: