On–off keying (OOK) denotes the simplest form of
amplitude-shift keying
Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave.
In an ASK system, a symbol, representing one or more bits, is sent by transmitting a fixed-amplitude car ...
(ASK)
modulation that represents
digital data as the presence or absence of a
carrier wave
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has ...
. In its simplest form, the presence of a carrier for a specific duration represents a
binary
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two digits (0 and 1)
* Binary function, a function that takes two arguments
* Binary operation, a mathematical operation that ta ...
one, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. It is analogous to
unipolar encoding
Unipolar encoding is a line code. A positive voltage represents a binary 1, and zero volts indicates a binary 0. It is the simplest line code, directly encoding the bitstream, and is analogous to on-off keying in modulation.
Its drawbacks are t ...
line code
In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained c ...
.
On–off keying is most commonly used to transmit
Morse code over
radio frequencies
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper ...
(referred to as CW (
continuous wave) operation), although in principle any digital encoding scheme may be used. OOK has been used in the
ISM band
The ISM radio bands are portions of the radio spectrum reserved internationally for industrial, scientific and medical (ISM) purposes, excluding applications in telecommunications.
Examples of applications for the use of radio frequency (RF) ener ...
s to transfer data between
computers, for example.
OOK is more
spectrally efficient than
frequency-shift keying, but more sensitive to noise when using a
regenerative receiver or a poorly implemented
superheterodyne receiver.
For a given data rate, the bandwidth of a
BPSK (Binary Phase Shift keying) signal and the bandwidth of OOK signal are equal.
In addition to RF carrier waves, OOK is also used in
optical communication systems (e.g.
IrDA
The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1994 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and the name "IrDA" also ...
).
In aviation, some possibly unmanned airports have equipment that let pilots key their VHF radio a number of times in order to request an
Automatic Terminal Information Service
Automatic terminal information service, or ATIS, is a continuous broadcast of recorded aeronautical information in busier terminal areas, i.e. airports and their immediate surroundings. ATIS broadcasts contain essential information, such as current ...
broadcast, or
turn on runway lights.
OOK is also used in remote garage and gate keys, often operating at 433.92 MHz, in combination with
rolling code
A rolling code (or sometimes called a hopping code) is used in keyless entry systems to prevent replay attacks, where an eavesdropper records the transmission and replays it at a later time to cause the receiver to 'unlock'. Such systems are typi ...
s.
References
External links
*
{{DEFAULTSORT:On-off keying
Quantized radio modulation modes
Fiber-optic communications
Amateur radio