Transmission requires encoding electrical signals and decoding the signals at the destination.
0 is Low and 1 is High. Simple, but too many consecutive of the same values may introduce baseline wander.
The average value is used to determine if an electrical signal is a high or low value. Too many of one value or the other will adjust a bias into the average. This bias is Baseline wander.
At a 1 Transition flip current bit and hold it. Do nothing at zero.
XOR (Exclusive OR) of the system clock and the NRZ data
Lecture 3 Slide 10
Lecture 3 Slide 11