Keying (telecommunications)
Encyclopedia
Keying is a family of modulation
forms where the modulating signal takes one of two (or more) values at all times. The goal of keying is to transmit a digital signal over an analogue channel. The name derives from the Morse code
key used for telegraph
signaling.
Modulation is the general technique of shaping a signal to convey information. When a digital message has to be represented as an analogue waveform, the technique and term keying (or digital modulation) is used. Keying is characterized by the fact that the modulating signal will have a limited number of states (or values) at all times, to represent the corresponding digital states (commonly zero and one, although this might depend on the number of symbols used). This is in contrast to analogue modulation, where an analogue signal is transmitted over an analogue channel, and where the modulated analogue signal will have an infinite number of meaningful states.
Furthermore, note that keying or digital modulation applies to transmitting a digital signal over an analogue passband channel. When a digital signal is to be transmitted over an analogue baseband channel, the modulation technique is termed line coding.
Several keying techniques exist, including phase-shift keying
, frequency-shift keying
and amplitude-shift keying
. Bluetooth
, for example, uses phase-shift keying to exchange information between devices.
An overview of keying techniques is given on the modulation
page.
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
forms where the modulating signal takes one of two (or more) values at all times. The goal of keying is to transmit a digital signal over an analogue channel. The name derives from the Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
key used for telegraph
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...
signaling.
Modulation is the general technique of shaping a signal to convey information. When a digital message has to be represented as an analogue waveform, the technique and term keying (or digital modulation) is used. Keying is characterized by the fact that the modulating signal will have a limited number of states (or values) at all times, to represent the corresponding digital states (commonly zero and one, although this might depend on the number of symbols used). This is in contrast to analogue modulation, where an analogue signal is transmitted over an analogue channel, and where the modulated analogue signal will have an infinite number of meaningful states.
Furthermore, note that keying or digital modulation applies to transmitting a digital signal over an analogue passband channel. When a digital signal is to be transmitted over an analogue baseband channel, the modulation technique is termed line coding.
Several keying techniques exist, including phase-shift keying
Phase-shift keying
Phase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
, frequency-shift keying
Frequency-shift keying
Frequency-shift keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK . BFSK uses a pair of discrete frequencies to transmit binary information. With this scheme, the "1" is called...
and amplitude-shift keying
Amplitude-shift keying
Amplitude-shift keying is a form of modulation that represents digital data as variations in the amplitude of a carrier wave.Any digital modulation scheme uses a finite number of distinct signals to represent digital data. ASK uses a finite number of amplitudes, each assigned a unique pattern of...
. Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
, for example, uses phase-shift keying to exchange information between devices.
An overview of keying techniques is given on the modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
page.