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constellation

Calculate or plot ideal signal constellation

Description

example

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

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

Examples

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Create a QPSK modulator.

mod = comm.QPSKModulator;

Determine the reference constellation points.

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: QPSK,Gray Mapping,PhaseOffset=0.7854rad contains 7 objects of type line, text.

Reconfigure the object for bit input and plot the constellation to show the binary values of the Gray-encoded mapping.

release(mod)
mod.BitInput = true; 
constellation(mod)

Figure contains an axes object. The axes object with title Constellation: QPSK,Gray Mapping,PhaseOffset=0.7854rad contains 7 objects of type line, text.

Create a QPSK demodulator having phase offset set to 0.

demod = comm.QPSKDemodulator(0);

Plot the reference constellation. The constellation method works for both modulator and demodulator objects.

constellation(demod)

Figure contains an axes object. The axes object with title Constellation: QPSK,Gray Mapping,PhaseOffset=0rad contains 7 objects of type line, text.

Create a PSK modulator.

mod = comm.PSKModulator;

Determine the reference constellation points.

refC = constellation(mod)
refC = 8×1 complex

   0.9239 + 0.3827i
   0.3827 + 0.9239i
  -0.3827 + 0.9239i
  -0.9239 + 0.3827i
  -0.9239 - 0.3827i
  -0.3827 - 0.9239i
   0.3827 - 0.9239i
   0.9239 - 0.3827i

Plot the constellation.

constellation(mod)

Figure contains an axes object. The axes object with title Constellation: 8-PSK,Gray Mapping,PhaseOffset=0.3927rad contains 11 objects of type line, text.

Create a PSK demodulator having modulation order 16.

demod = comm.PSKDemodulator(16);

Plot its reference constellation. The constellation method works for both modulator and demodulator objects.

constellation(demod)

Figure contains an axes object. The axes object with title Constellation: 16-PSK,Gray Mapping,PhaseOffset=0.3927rad contains 19 objects of type line, text.

Create a BPSK modulator.

mod = comm.BPSKModulator;

Determine the reference constellation points.

refC = constellation(mod)
refC = 2×1 complex

   1.0000 + 0.0000i
  -1.0000 + 0.0000i

Plot the constellation.

constellation(mod)

Figure contains an axes object. The axes object with title Constellation: BPSK,PhaseOffset=0rad contains 5 objects of type line, text.

Create a BPSK demodulator having phase offset set to π2.

demod = comm.BPSKDemodulator(pi/2);

Determine the reference constellation points.

refC = constellation(demod)
refC = 2×1 complex

   0.0000 + 1.0000i
  -0.0000 - 1.0000i

Plot the reference constellation. The constellation method works for both modulator and demodulator objects.

constellation(demod)

Figure contains an axes object. The axes object with title Constellation: BPSK,PhaseOffset=1.5708rad contains 5 objects of type line, text.

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