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function [y,t]=modulate(x,fc,fs,method,opt)
//Modulates signal according to the modulation method
//Calling Sequence
//y=modulate(x,fc,fs,method,opt)
//[y,t]=modulate(x,fc,fs,method,opt)
//Parameters
//x
//A vector or a matrix
//fc
//Carrier frequency
//fs
//Sampling frequency
//method
//Modulation Method
//opt
//An optional parameter required by certain modulation methods
//Description
//[y,t]=modulate(x,fc,fs,method,opt)
//Returns the modulated vector y and the time vector 't'
//Modulation is performed according to the following table
// METHOD MODULATION SCHEME
// 'am', Amplitude modulation, double side-band, suppressed carrier
// 'amdsb-sc' opt not used. This is the default method.
// 'amdsb-tc' Amplitude modulation, double side-band, transmitted carrier
// opt is a scalar subtracted from x before multiplying x
// with the carrier wave. It defaults to min(min(x)) so that
// the input signal after offset is always non-negative
// 'amssb' Amplitude modulation, single side-band
// OPT not used.
// 'fm' Frequency modulation
// opt is the constant of frequency modulation.
// opt = (fc/fs)*2*pi/max(max(abs(x))) by default
// 'pm' Phase modulation
// OPT is the constant of phase modulation.
// opt = pi/max(max(abs(x))) by default
// Phase lies between -pi and +pi
// 'pwm' Pulse width modulation
// opt='left' corresponds to left justified pulses.
// opt='centered' correspondes to centered pulses.
// The default value of opt is 'left'.
// 'ppm' Pulse position modulation
// opt is a scalar between 0 and 1 which specifies the pulse
// width in fractions of the carrier period with default value 0.1.
// 'qam' Quadrature amplitude modulation
// opt is a matrix of the same size as X which is modulated in
// quadrature with x.
//
// If x is a matrix, its columns are modulated.
//Example
//y =
//
// 1. 1. 0. 0.
//Author
//Ankur Mallick
funcprot(0);
if (argn(2)<3|argn(2)>5) then
error('Incorrect number of input arguments.');
elseif (isreal(fc)&isreal(fs)&fc>fs/2)
error('The career frequency must be less than half the sampling frequency.')
else
flag1=0;
flag2=0;
if (argn(2)<4)
method='am';
end
[M,N]=size(x);
if(M==1)
flag1=1;
x=x(:);
[M,N]=size(x);
end
t=((0:M-1)/fs)';
t=t*ones(1,N);
if(method=='am'|method=='amdsb-sc')
y=x.*cos(2*%pi*fc*t);
elseif(method=='amdsb-tc')
if(argn(2)<5)
opt=min(min(x));
end
y=(x-opt).*cos(2*%pi*fc*t);
elseif(method=='amssb')
y=x.*cos(2*%pi*fc*t)+imag(hilbert(x)).*sin(2*%pi*fc*t);
elseif(method=='fm')
if(argn(2)<5)
opt=max(abs(x(:))); //if all elements of x are zero
if(opt>0)
opt=(fc/fs)*2*%pi/opt;
end
end
y=cos(2*%pi*fc*t + opt*cumsum(x,1));
elseif(method=='pm')
if(argn(2)<5)
opt=%pi/(max(abs(x(:))));
end
y=cos(2*%pi*fc*t + opt*x);
elseif(method=='qam')
if(argn(2)<5)
error('For qam, a 5th input parameter is required.')
else
if(size(opt,1)==1)
opt=opt(:);
end
S=sum(abs(size(opt)-size(x))); //S=0 only if opt and x have the same size
if(S==0)
y = x.*cos(2*%pi*fc*t) + opt.*sin(2*%pi*fc*t)
else
error('For qam input signals must be the same size')
end
end
elseif(method=='pwm')
if(argn(2)<5)
opt='left'
end
if(max(x(:))>1|min(x(:))<0)
error('x must lie between 0 and 1');
else
t=(0:(M*fs/fc-1))';
t=t*ones(1,N);
T=fs/fc;
y=zeros(t);
if(opt~='left'&opt~='centered')
error('5th input parameter not recognized');
else
if(opt=='left')
compar=(pmodulo(t,T))/T;
pos=floor(t/T)+1;
elseif(opt=='centered')
compar1=2*pmodulo(t,T)/T;
compar=min(compar1,2-compar1);
x(M+1,:)=zeros(1,N);
pos=floor(t/T)+1;
r1=ceil(T/2);
r2=floor(T/2);
pos=[pos(r1+1:length(pos));(M+1)*ones(r2,1)];
end
for i=1:N
//x1=matrix(ones(T,1)*x(:,i)',size(t,1),1);
x1=x(pos,i)
y(compar<x1,i)=1;
end
end
end
elseif(method=='ppm'|method=='ptm')
if(argn(2)<5)
opt=0.1
end
t=(0:(M*fs/fc-1))';
t=t*ones(1,N);
T=fs/fc;
y=zeros(t);
if(max(x(:))>1|min(x(:))<0)
error('x must lie between 0 and 1');
elseif(~isscalar(opt)|opt<0|opt>1)
error('opt must be a scalar between 0 and 1')
else
if (max(x) > 1-opt)
warning('Overlapping pulses')
end
for i=1:N
x1=x(:,i)'
start=1+ceil((x1+(0:M-1))*T); //y(1) corresponds to t=0
L=floor(opt*T);
v=(0:1:L-1)';
p1=matrix(ones(L,1)*start,1,M*L)
p2=matrix(v*ones(1,M),1,M*L);
pos=p1+p2;
y(pos,i)=1;
end
y(length(t)+1:length(y),:)=[]; //Truncating vector
end
else
error('Method not recognised');
flag2=1;
end
if(flag2==0)
t=t(:,1); //only first column required
if(flag1==1)
//x is a row vector
y=conj(y');
t=t';
end
end
end
endfunction
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