Amplitude and phase-shift keying (APSK) is a

digital Digital usually refers to something using discrete digits, often binary digits. Businesses *Digital bank, a form of financial institution *Digital Equipment Corporation (DEC) or Digital, a computer company *Digital Research (DR or DRI), a software ...

modulation Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message ...

scheme that conveys

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

by modulating both the

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

and the

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematica ...

of a

carrier wave In telecommunications, a carrier wave, carrier signal, or just carrier, is a periodic waveform (usually sinusoidal) that conveys information through a process called ''modulation''. One or more of the wave's properties, such as amplitude or freq ...

. In other words, it combines both

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 rate, symbol, representing one or more bits, is sent by transmitting a fixed-a ...

(ASK) and

phase-shift keying Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. I ...

(PSK). This allows for a lower bit error rate for a given modulation order and

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

, at the cost of increased complexity, compared to ASK or PSK alone.

Quadrature amplitude modulation Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signa ...

(QAM) can be considered a subset of APSK because all QAM schemes modulate both the amplitude and phase of the carrier. Conventionally, QAM constellations are rectangular and APSK constellations are circular, however this is not always the case. The distinction between the two is in their production; QAM is produced from two orthogonal signals. The advantage of APSK over conventional QAM is a lower number of possible amplitude levels and therefore a lower peak-to-average power ratio (PAPR). The resilience of APSK to amplifier and channel non-linearities afforded by its low PAPR have made it especially attractive for satellite communications, including

DVB-S2 Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) 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 Digital Video Broadcasting Proj ...

Constellations

There are many APSK constellations. Circular constellations are the most common. There may be multiple circular constellations of the same order, for example 16-APSK could be implemented using a (1, 5, 10) constellation or a (5, 11) constellation. Increasing the number of rings decreases the bit error rate but increases the PAPR. Other APSK constellations include triangular, rectangular and hexagonal constellations. A careful design of the constellation geometry can approach the Gaussian capacity as the constellation size grows to infinity. For the regular QAM constellations, a gap of 1.56 dB is observed.H. Méric
Approaching The Gaussian Channel Capacity With APSK Constellations
''IEEE Communications Letters''. The previous solution, where the constellation has a Gaussian shape, is called constellation shaping.

Constellations

References

Further reading