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% Author	: Krishna
% Email		: krishna@dsplog.com
% Version	: 1.0
% Date		: 18 January 2008
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% script for generting transmit waveforms in a minimum shift 
% keying, a form of continuous phase frequency shift keying

clear all
close all

rand('seed',777); % initializing the random state
N = 7; % number of bits
ipBin = rand(1,N) > 0.5; % binary 0's and 1's

fs = 100;
fc = 1;
T = 1;

ts = [0:1/fs:T]; % generting the sampling instants
ts = ts(1:end-1);
tsR = kron(ones(1,N),ts);

ip =  2*ipBin-1; % converting 0's to -1, 1's to 1

% generating two frequencies corresponding to 0 and 1
% 0 --> fc - 1/4T
% 1 --> fc + 1/4T
fm = ip/(4*T); 
fmR = kron(fm,ones(1,fs)); % repeating

% genertaing the phase
theta = pi/2*filter([0 1],[1 -1],ip);
thetaR = kron(theta,ones(1,fs)); % repeating

xt = cos(2*pi*(fc+fmR).*tsR + thetaR );

% plotting
subplot(3,1,1),plot(kron(ip,ones(1,fs)));
axis([0 N*fs -1.25 1.25]);grid on
subplot(3,1,2), plot(xt);
axis([0 N*fs -1 1]);grid on
subplot(3,1,3),plot(kron(mod(theta*180/pi,360),ones(1,fs)))
axis([0 N*fs -360 360]);grid on