Fundamentals of Electrical Engineering

Signals and Systems
1) Definition of a signal
A signal is a function.
electrical signal: electromagnetic waves carrying power and information.
2) Kinds of signals
Analog signal: function of a continuous variable
Digital signal: function of the integers
Images: S(x,y)
Video: S(x,y,t) = {Red(x,y,t), Green(x,y,t), Blue(x,y,t)}
3) Signals and information
Information does not exist without a signal representing it.
Information encoded in a signal by modifying the signal's structure.
example: amplitude modulation ---> AM radio
frequency modulation ---> FM radio
4) Systems
Systems operate on signals to produce a modified signal and to extract information
x(t)--->system--->y(t)
5) Fundamental model of communication
Source---m(t)--->Transmitter---x(t)--->Channel---r(t)--->Receiver---m'(t)--->Sink