Data Communication System Overview (Lecture Slides)
Class lecture
Signals
A signal is a function of a variable(s) that describe a physical/abstract phenomenon.
Electrical signals - voltage/current as a function of time. They come from an electricity phenomena.
DC Signal
AC Signal
Periodic and non-periodic
Digital and analog (digital must be symmetric when considering magnitude and polarity)
Electronic signals - produced/modified using semiconductor/electronic devices.
Electromagnetic signals
Also known as radio signals
Made up of the electric field wave and the magnetic field wave. Electric field is found on the vertical plane, whereas magnetic field is drawn in the horizontal plane.
Sinusoidal in form
Moves along the z direction
Moves well in space/vacuum, as opposed to water or wire where the magnetic field is reduced. In other words, they do not need a physical material to travel, as opposed to electrical signals which depend on electrons to travel.
a propagating magnetic field generates an electric field and vice versa
They travel perpetually as long as the electric field has enough energy. Nonetheless, as energy travels, their energy diminishes due to attenuation.
Light
Color is determined by frequency of the sinusoidal components of the electromagnetic signal
Red to Violet is the visible spectrum or the range of visible light
Analog signals are continuous while digital signals have a discrete amplitude/levels (ideally also discrete in the time domain).
Communications that carry voltage or current (communication involving wires) generate unwanted electromagnetic signals. Anything that goes out of the receiver is lost energy while anything that goes out of the wire is a security risk. Anything generated outside of the wire causes interference.
FCC certified labels are added to electromagnetic devices to indicate they are able to meet the electromagnetic signal limits set by the FCC (to limit the signals generated by any electromagnetic device/component).
Periodic has perfect repetition while non-periodic does not
Characteristics of Periodic
Amplitude (peak and peak-to-peak)
Period - time between repetitions (spans 360 degrees)
Frequency - 1/Period
Phase angle - angle relative to start
Characteristics of Non-Periodic
Duration
Minimum and maximum amplitude
Signal Plots
Sine wave in time domain (amplitude and time)
Sine wave in frequency domain (amplitude and frequency)
Composite signal the sum/combination of multiple periodic signals.
A non-periodic signal has infinite number of sine wave components, which can be represented as a distribution in the frequency domain.
Two components of a frequency signals can produce an effect when their phase is modified relative to each other.
same phase = add two components
opposite phase = subtract two components
vector addition applies whereby the output signal is the resultant
Any digital signal is comprised of multiple sine waves (they are a composite signal).