- Amplitude and phase-shift keying
Amplitude and Phase-shift keying or Asymmetric Phase-shift keying, (APSK), is a
digital modulationscheme that conveys data by changing, or modulating, both the amplitudeand the phase of a reference signal (the carrier wave). In other words, it combines both Amplitude-shift keying(ASK) and Phase-shift keying(PSK) to increase the symbol-set. It can be considered as a subclass of Quadrature amplitude modulation(QAM). The advantage over conventional QAM, for example 16-QAM, is lower number of possible amplitude levels, resulting in less problems with non-linear amplifiers.
DVB-S2specification permits the use of 16APSKand 32APSKmodes, 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 methods in the uplink station in order to minimize the effect of transponder non-linearity.
Figure - Bit mapping into constellations - (see Ref.2)
* [http://www.ebu.ch/en/technical/trev/trev_300-morello.pdf DVB-S2 — ready for lift off] , article in the EBU technical review
* [http://public.ccsds.org/publications/archive/131x2o1.pdf Flexible Serially Concatenated Convolutional Turbo Codes with Near-Shannon bound performance for telemtery applications ] ,
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