AM,FM,PM modulation in matlab

%Parameters for signal creation
Fs = 8000; %sampling frequency
t = (0:1000-1)/Fs; %Time vector
s = 4*cos(2*pi*500*t); %modulating signal

sdft = fft(s);
N=length(s);
sdft = sdft(1:N/2+1);
psdy1 = (1/(Fs*N)) * abs(sdft).^2;
psdy1(2:end-1) = 2*psdy1(2:end-1);
freq = 0:Fs/length(s):Fs/2;
figure;plot(freq,10*log10(psdy1)); %FD spectrum of unmodulated signal

y = modulate(s,3e3,Fs,'am',0.1); %modulated signal
ydft = fft(y);
N=length(y);
ydft = ydft(1:N/2+1);
psdy = (1/(Fs*N)) * abs(ydft).^2;
psdy(2:end-1) = 2*psdy(2:end-1);
freq = 0:Fs/length(y):Fs/2;
figure;plot(freq,10*log10(psdy)); %FD spectrum of modulated signal