modulation: process by which an information sig is converted to a sinusoidal waveform
3 features of sinusoid: amp, freq, phase
digital modulation is process wher ethe amp, freq, phase or a combination is varied in accordance with the info to be xmitted
when receiver exploits knowledge of the carrier's phase to detect signals, the process is coherent detection
when rx does not use the phase ref info, the process is noncoherent detection
binary amp shift keying (ASK):
	baseband sig is m(t) = sum<>(akp(t-kTb))
	where ak is the data value and p(t) is the pulse shape
	for rect pulse, get a sig or get no sig

alternatively, antipodal signaling maps to 1/-1 instead of 1/0, so you get sharp phase shifts when changing between 1 and 0


binary phase shift keying (PSK) equivalent to ASK when the amps are negatives of each other
	S0(t) = cos(wct+pi)*p(t) = -cos(wct)p(t)
	S0(t) = cos(wct)*p(t)
	gives very nice phase shifts on zero crossing, so causes a reflection

FSK frequency shift keying causes different frequencies to be seen for 1 or 0

psd of ask, psk, fsk
modulated sigs can be written as
PHI(t) = m(t)cos(wct)
PSD: Sphi=lim as T to inf(mag(PSIt(f))^2/T)
PHIt(f) is FT of the truncated sig PHIt(t) = PHI(t)(u(t+T/2) - u(t-T/2)) = mt(t)cos(wct)
rect applied to PSI
PSIt(f) = F{PHIt(t)} = 1/2 * (Mt(f-fc) +Mt(f+fc))
Sphi(f) = 1/4 * lim as t to inf(mag(Mt(f-fc) + Mt(f+fc))^2/T)
= 1/4 * lim as t to inf((Mt(f-fc)Mt*(f+fc) + Mt(f+fc)Mt*(f-fc))/T)
= 1/4 * lim, t to inf(|Mt(f-fc)|^2/T + |Mt(f+fc)|^2/T)
= 1/4 * Sm(f+fc) + 1/4 * Sm(f-fc)

ASK: OOK
PHIask(t) = m(t)cos(wct)
m(t) = sum<>(akp(t-kTb))
p(t) = rect((t-Tb/2)/Tb)
m has the PSD: Sm(f) = |P(f)|^2/4Tb * (1+1/Tb * sum<n=inf>(delta(f-n/Tb)))
P(f) = Tbsinc(fpi*Tb)e^(-jfpi*Tb)
Sm(f) = Tb/4 * sinc^2(fpi*Tb)*(1+1/Tb * sum<n=inf>(delta(f-n/Tb)))
looks like a sinc^2 with a DC component