Amplitude and Phase-shift keying or Asymmetric Phase-shift keying, (APSK), is a digital

Digital

A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 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...

 scheme that conveys data by changing, or modulating, both the amplitude

Amplitude

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

 and the phase

Phase (waves)

Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

 of a reference signal (the carrier wave

Carrier wave

In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...

). In other words, it combines both 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...

 (ASK) and 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 ....

 (PSK) to increase the symbol-set. It can be considered as a superclass of Quadrature amplitude modulation

Quadrature amplitude modulation

Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...

 (QAM). The advantage over conventional QAM, for example 16-QAM, is lower number of possible amplitude levels, resulting in fewer problems with non-linear amplifiers.

Applications

The DVB-S2

DVB-S2

Digital Video Broadcasting - Satellite - Second Generation is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the , an international industry consortium, and ratified by ETSI in March 2005...

 specification permits the use of 16APSK and 32APSK modes, allowing 16 and 32 different symbols respectively and are intended for mainly professional, semi-linear applications. They can be also used for broadcasting but they require a higher level of available C/N and an adoption of advanced pre-distortion

Predistortion

Predistortion is a technique used to improve the linearity of radio transmitter amplifiers.Radio transmitter amplifiers in most telecommunications systems are required to be "linear", in that they must accurately reproduce the signal present at their input...

methods in the uplink station in order to minimize the effect of transponder non-linearity.
Figure - Bit mapping into constellations - (see Ref.2)