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
- Sinewave – most fundamental form of periodic analog signal – mathematically described with 3 parameters s(t) A sin(2πft )
- Peak amplitude (A) – absolute value of signal’s highest intensity – unit: volts [V]
- Frequency (f) – number of periods in one second – unit: hertz [Hz] = [1/s] – inverse of period (T)!
- 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 s||hertz (Hz)||1 Hz|
|milliseconds (ms)||10–3 s||kilohertz (KHz)||103 Hz|
|microseconds (s)||10–6 s||megahertz (MHz)||106 Hz|
|nanoseconds (ns)||10–9 s||gigahertz (GHz)||109 Hz|
|picoseconds (ps)||10–12 s||terahertz (THz)||1012 Hz|