Quadrature phase shift keying

Matlab program for Quadrature phase shift keying.

Matlab code

clc; clear all; close all;

A1=1;   %Amplitude of Carrier Wave

fc=input('Enter the frequency of carrier wave (fc) = ');

n=input('Enter the no of bit (Multiples of 2) = ');

r=input('Enter the Bite Rate (In bits/sec) = ');

tpb=1/r; %Time duration for per bit

x=rand(1,n); x

   fori=1:length(x)

       ifx(i)>=0.5

           B(i)=1;

       else

           B(i)=0;

       end;

   end;

B  

t1=0;         %Temporary variable for time

st1=[];       %Variable for store time of bit stream

st2=[];       %Variable for store time of qpsk wave

Sbs=[];      %Variable for store Bit stream

Sqpsk=[];  %Variable for store qpsk signal

for i=1:length(B)

    ifB(i)==0                        % When bit is 0 --

        t=t1:0.001:t1+tpb;       % for time duration tpb behaviour of--

        Bs=zeros(1,length(t)); % Bit stream and--

     else

        t=t1:0.001:t1+tpb;

        Bs=ones(1,length(t));

    end;

    st1=[st1 t];        % Storing tpb duration of time

    Sbs=[Sbs Bs];   % Storing Bit stream in tpb duration

    t1=t1+tpb;         % Initial value of next tpb duration for iteration

end;

t1=0;

for i=1:2:length(B)

    ifB(i)==0&&B(i+1)==0

        t=t1:0.001:t1+2*tpb;

        qpsk=A1*cos(2*pi*fc*t);

    elseifB(i)==0&&B(i+1)==1

        t=t1:0.001:t1+2*tpb;

        qpsk=A1*cos(2*pi*fc*t+pi/2);

    elseifB(i)==1&&B(i+1)==1

        t=t1:0.001:t1+2*tpb;

        qpsk=A1*cos(2*pi*fc*t+pi);  

    elseifB(i)==1&&B(i+1)==0

        t=t1:0.001:t1+2*tpb;

        qpsk=A1*cos(2*pi*fc*t+3*pi/2);

    end;

    st2=[st2 t];                 % Storing tpb duration of time

    Sqpsk=[Sqpsk qpsk]; % Storing qpsk signal in tpb duration

    t1=t1+2*tpb;              % Initial value of next tpb duration for iteration

end;

Sc=A1*cos(2*pi*fc*st2); %Carrier Wave

subplot(4,1,1);

plot(st1,Sbs);

axis([0 tpb*n -2 2])

xlabel('Time');ylabel('Amplitude');title('Bit stream');

subplot(4,1,2);

plot(st2,Sc);

xlabel('Time');ylabel('Amplitude');title('Carrier wave');

subplot(4,1,3);

plot(st2,Sqpsk);

xlabel('Time');ylabel('Amplitude');title('QPSK Signal');

subplot(4,1,4);

plot(st1,Sbs,'r');

axis([0 tpb*n -2 2])

hold on;

plot(st2,Sqpsk);

xlabel('Time');ylabel('Amplitude');title('Bit stream and QPSK Signal');

h=legend('Bit stream','QPSK Signal');

Command window

Enter the frequency of carrier wave (fc) = 3

Enter the no of bit (Multiples of 2) = 12

Enter the Bite Rate (In bits/sec) = 1

x =

  Columns 1 through 10

    0.9172    0.2858    0.7572    0.7537    0.3804    0.5678    0.0759    0.0540    0.5308    0.7792

  Columns 11 through 12

    0.9340    0.1299

B =

     1     0     1     1     0     1     0     0     1     1     1     0

Figure window