Contents

dpskmod

Differential phase shift keying modulation

Syntax

y = dpskmod(x,M)
y = dpskmod(x,M,phaserot)
y = dpskmod(x,M,phaserot,symbol_order)

Description

y = dpskmod(x,M) outputs the complex envelope y of the modulation of the message signal x using differential phase shift keying modulation. M is the alphabet size and must be an integer. The message signal must consist of integers between 0 and M-1. If x is a matrix with multiple rows and columns, the function processes the columns independently.

y = dpskmod(x,M,phaserot) specifies the phase rotation of the modulation in radians. In this case, the total phase shift per symbol is the sum of phaserot and the phase generated by the differential modulation.

y = dpskmod(x,M,phaserot,symbol_order) specifies how the function assigns binary words to corresponding integers. If symbol_order is set to 'bin' (default), the function uses a natural binary-coded ordering. If symbol_order is set to 'gray', it uses a Gray-coded ordering.

    Note:   An initial phase rotation of 0 is used in determining the first element of the output y (or the first row of y if it is a matrix with multiple rows), because two successive elements are required for a differential algorithm.

Examples

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Modulate a DPSK Signal and View its Signal Trajectory

This example shows how to plot the output of the dspkmod function. The image shows the possible transitions from each symbol in the DPSK signal constellation to the next symbol.

Set the modulation order to 4 to model DQPSK modulation.

M = 4;

Generate a sequence of 4-ary random symbols.

x = randi([0 M-1],500,1);

Apply DQPSK modulation to the input symbols.

y = dpskmod(x,M,pi/8);

Create a constellation diagram object and set its properties to display a signal trajectory diagram and to disable the display of the reference constellation. Use the step function to display the trajectory.

h = comm.ConstellationDiagram('ShowTrajectory',true,'ShowReferenceConstellation',false);
step(h,y)

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