# Phase-Shift Keying

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Phase-shift keying (PSK) in digital transmission refers to a type of angle modulation in which the carrier phase is discretely varied to represent data being transmitted, either in relation to a reference phase or to the phase of the immediately preceding signal element.

Modulation PSK Format M-ary Differential
BPSK Normal 2
DBPSK Enable
QPSK 4
DQPSK Enable
8-PSK 8
D8-PSK Enable
16-PSK 16
D16-PSK Enable
Offset QPSK OQPSK -
π/4-QPSK π/4-QPSK -
π/4-DQPSK Enable
π/8-8PSK π/8-8PSK -
π/8-D8PSK Enable

## Normal PSK

Demodulated bits correspond to the ideal symbol in the symbol map that is closest to the demodulated symbol.

The following images show the default symbol map used by each of the PSK modulation types.

## Differential PSK

When differential mapping is enabled, the demodulated bits represent the phase transition between two consecutive symbols.

The default differential mapping used by each of the PSK modulation types is shown in the following images. The differential map is obtained using the Normal PSK map rotated by π/M radians, where M is the number of states in the map.

## Offset QPSK (OQPSK)

During transmission using the OQPSK modulation scheme, the quadrature (Q) channel is offset by half the symbol period with respect to the in-phase (I) channel of the QPSK symbol.

To obtain demodulated bits during demodulation, the Q channel of the demodulated signal is unoffset by half the symbol duration to align with the I channel to get a QPSK constellation. These symbols are then mapped to bits using a process similar to that used in QPSK.

The measurement waveform samples are not compensated for the Q channel offset.

## π/4-QPSK

During transmission using the π/4-QPSK modulation scheme, the QPSK symbols are shifted by π/4 radians for every symbol, in a counter-clockwise direction.

During demodulation, the symbol phase is unshifted by π/4 for every symbol, in a clockwise direction, to get a QPSK constellation. These symbols are then mapped to bits using a process similar to that used in QPSK.

When differential mapping is enabled, the symbols are mapped to bits, thus representing the phase transition between two consecutive QPSK symbols. The measurement waveform samples are not compensated for the π/4 phase shift introduced by the modulation. Hence, the constellation looks like that of 8-PSK as shown in the following image.

## π/8-8PSK

During transmission using the π/8-8PSK modulation scheme, the 8-PSK symbols are shifted by π/8 radians for every symbol, in an anticlockwise direction.

During demodulation, the symbol phase is unshifted by π/8 for every symbol, in a clockwise direction, to get an 8-PSK constellation. These symbols are then mapped to bits using a process similar to that used in 8-PSK.

When differential mapping is enabled, the symbols are mapped to bits, thus representing the phase transition between two consecutive 8-PSK symbols. The measurement waveform samples are not compensated for the π/8 phase shift introduced by the modulation. Hence, the constellation looks like that of 16-PSK, as shown in the following image.