Data Communication

Data vs. Signal

Data – information formatted in human/machine readable form examples: voice, music, image, file

Signal – electric or electromagnetic representation of data transmission media work by conducting energy along a physical path; thus, to be transmitted, data must be turned into energy in the form of electro-magnetic signals.

Transmission – communication of data through propagation and processing of signals


Signal Representation – typically in 2D space, as a function of time, space or frequency when horizontal axis is time, graph displays the value of a signal at one particular point in space as a function of time when horizontal axis is space, graph displays the value of a signal at one particular point in time as a function of space.


The time- and space- representation of a signal often resemble each other, though the signal envelope in the space-representation is different (signal attenuates over distance).

Analog vs. Digital Data         

Analog data – representation variable takes on continuous values in some interval, e.g. voice, temperature, etc.

Digital data – representation variable takes on discrete (a finite & countable number of) values in a given interval, e.g. text, digitized images, etc.

Analog vs. Digital Signal              

Analog signal – signal that is continuousin time and can assume an infinite number of values in a given range (continuous in time and value)

Discrete (digital) signal – signal that is continuous in time and assumes only a limited number of values (maintains a constant level and then changes to another constant level)


Both analog and digital data can be transmitted using either analog or digital signals.


 example: analog signaling of analog and digital data

Classification of Analog Signals

Simple Analog Signal – cannot be decomposed into simpler signals

  1. Sinewave – most fundamental form of periodic analog signal – mathematically described with 3 parameters s(t)  A  sin(2πft   )
  2. Peak amplitude (A) – absolute value of signal’s highest intensity – unit: volts [V]
  3. Frequency (f) – number of periods in one second – unit: hertz [Hz] = [1/s] – inverse of period (T)!
  4. Phase (φ) – absolute position of the waveform relative to an arbitrary origin – unit: degrees [º] or radians [rad]

Composite Analog Signal

composed of multiple sinewaves

seconds (s)1 shertz (Hz)1 Hz
milliseconds (ms)10–3 skilohertz (KHz)103 Hz
microseconds (s)10–6 smegahertz (MHz)106 Hz
nanoseconds (ns)10–9 sgigahertz (GHz)109 Hz
picoseconds (ps)10–12 sterahertz (THz)1012 Hz