constellation

Calculate or plot ideal signal constellation

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Syntax

symbols = constellation(obj)
constellation(obj)

Description

symbols = constellation(obj) returns the numerical values of the constellation.

example

constellation(obj) generates a constellation plot for the object.

Note

For OQPSK, the constellation that displays does not depict the IQ delay introduced by the OQPSK modulator.

Examples

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Open Live Script

Create a OQPSK modulator.

mod = comm.OQPSKModulator;

Determine the reference constellation points. The constellation that displays does not depict the IQ delay introduced by the OQPSK modulator.

refC = constellation(mod)
refC = 4×1 complex

   0.7071 + 0.7071i
  -0.7071 + 0.7071i
  -0.7071 - 0.7071i
   0.7071 - 0.7071i

Plot the constellation.

constellation(mod)

Figure contains an axes object. The axes object with title Constellation: OQPSK,Gray Mapping,PhaseOffset=0rad, xlabel In-phase Amplitude, ylabel Quadrature Amplitude contains 7 objects of type line, text. One or more of the lines displays its values using only markers

Change the phase offset for the modulated symbols. Plot the constellation to show the rotated constellation points.

release(mod)
mod.PhaseOffset = 45*pi/180; 
constellation(mod)

Figure contains an axes object. The axes object with title Constellation: OQPSK,Gray Mapping,PhaseOffset=0.7854rad, xlabel In-phase Amplitude, ylabel Quadrature Amplitude contains 7 objects of type line, text. One or more of the lines displays its values using only markers

Open Live Script

Create comm.PAMModulator and comm.PAMDemodulator System objects, and then calculate their ideal signal constellations.

Create modulator and demodulator objects.

mod = comm.PAMModulator;
demod = comm.PAMModulator;

Calculate the constellation points.

refMod = constellation(mod)
refMod = 4×1

    -3
    -1
     1
     3


refDemod = constellation(demod)
refDemod = 4×1

    -3
    -1
     1
     3

Verify that both objects produce the same points.

isequal(refMod,refDemod)
ans = logical
   1

Display the ideal signal constellation.

constellation(mod)

Figure contains an axes object. The axes object with title Constellation: 4-PAM,Gray Mapping,Min.Dist=2, xlabel In-phase Amplitude, ylabel Quadrature Amplitude contains 7 objects of type line, text. One or more of the lines displays its values using only markers

Input Arguments

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System object to return constellation for, specified as a modulator System object.

Data Types: object

Output Arguments

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Constellation points, returned as a complex vector.

Data Types: double | single
Complex Number Support: Yes

Version History

Introduced in R2012a

See Also

Objects