constellation

Calculate or plot ideal signal constellation

Syntax

symbols = constellation(obj)

constellation(obj)

Description

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

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

Plot QPSK Reference Constellation

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)

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)

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)

Plot PSK Reference Constellation

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)

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)

Plot BPSK Reference Constellation

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)

Create a BPSK demodulator having phase offset set to $\frac{\pi }{2}$.

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)

Plot OQPSK Reference Constellation

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)

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)

Calculate Ideal PAM Signal Constellation

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)

Input Arguments

obj — System object™ to return constellation for

System object

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

Data Types: object

Output Arguments

symbols — Constellation points

complex vector (default)

Constellation points, returned as a complex vector.

Data Types: double | single
Complex Number Support: Yes

Version History

Introduced in R2012a