test covering chapters 6 and 7 next thursday

line codes n such
what can we do to reduce intersymbol interference?
this happens when a bit lasts longer than the allowed bit time
duobinary signaling introduces ISI in a controlled manner so it is easier to deal with

zero-forcing equalizer
used to compensate for distortion caused by the transmission medium
should have a freq characteristic that is the inverse of that of the transmission medium
will restore crit freq components and elim pulse distortion, but will enhance channel noise at these freqs
for a digi comms system, complete equalization is not needed, only need to elim 

use a set of delays and gains to remove noise
res = C(-1)pr(t+Tb) + C(0)pr(t)+C(1)pr(t-Tb)
with vals at +Tb, 0, and -Tb: -1, 3, -1
po(To) = -C(-1) + 3C(0) - C(1)


eye diagrams
useful tool to visually examine the severity of ISI, the accuracy of timing extraction, and noise immunity
eye diagram is generated by applying received sig to the vertical input of an oscilloscope
time base of the scope is triggered at the same rate 1/Tb as that of the incoming pulses
can extract several measurements of sig quality
	max opening point indicates the amount of noise that can be tolerated
	eye width shows sensitivity to timing jitter
	width of eye corners gives info about zero-crossing
	
error free sampling region occurs where ever you can always tell the difference between a 0 and a 1
optimum sample time occurs at largest amount of white space
height of openeing also allows measurement of noise margin, baseline to max, not peak to peak
displays of eye diagrams

raised cosine has a fuzzy eye because of ISI

looking at 4-ary eyes, harder to discern the correct value