On-off keying (OOK) is a type of modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. In telecommunications, modulation is the process of varying a periodic waveform, i. ... A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ... For other uses, see Data (disambiguation). ... This article or section does not adequately cite its references or sources. ... The binary numeral system, or base-2 number system, is a numeral system that represents numeric values using two symbols, usually 0 and 1. ...

On-off keying is most commonly used to transmit Morse code over radio frequencies (referred to as continuous wave operation), although in principle any digital encoding scheme may be used. OOK has been used in the ISM bands to transfer data between computers, for example. 1922 Chart of the Morse Code Letters and Numerals Morse code is a method for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a message. ... It has been suggested that this article or section be merged with Radio waves. ... A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ... The industrial, scientific and medical (ISM) radio bands were originally reserved internationally for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purposes. ... A BlueGene supercomputer cabinet. ...

OOK is not very spectrally efficient due to the abrupt changes in amplitude of the carrier wave. At low to medium signalling speeds, this can be mitigated by adjusting the rise and fall rates of the carrier's amplitude. At high speeds, more efficient modulation modes (such as frequency-shift keying) are normally used instead. Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ... In telecommunication, data signaling rate (DSR) is the aggregate rate at which data pass a point in the transmission path of a data transmission system. ... It has been suggested that this article or section be merged with audio frequency-shift keying. ...

In addition to RF carrier waves, OOK is also used in optical communication systems (e.g. IrDA). Optical communication is any form of telecommunication that uses light as the transmission medium. ... The initials IRDA can refer to various things: In Information Technology and Communications, IrDA refers to Infrared Data Association, a standard for communication between devices (such as computers, PDAs and mobile phones) over short distances using infrared signals. ...