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Constellation Diagram

Display and analyze input signals in IQ-plane

  • Library:
  • Communications Toolbox / Comm Sinks

    Communications Toolbox HDL Support / Comm Sinks

  • Constellation Diagram block

Description

The Constellation Diagram block displays real- and complex-valued floating- and fixed-point signals in the IQ plane. Use this block to perform qualitative and quantitative analysis on modulated single-carrier signals. Specifically, the IQ-plane displays the in-phase and quadrature components of modulated signals on the real and imaginary axis of an xy-plot.

Constellation diagram displaying QSPK,16-QAM, and 8-DPSK signals, and signal quality measurements.

In the Constellation Diagram window, you can:

  • Input and plot multiple signals on a single constellation diagram. To define a reference constellation for each input signal, use the Reference Constellation parameter.

  • Select signals in the legend to toggle visibility of individual channels. To display the legend, use the Legend parameter on the Plot tab. For a multichannel signal, specify the input as a matrix with individual signals defined in the columns of the matrix.

  • Display calculated error vector magnitude (EVM) and modulation error ratio (MER) measurements for individual signals. To view and configure the measurements, select EVM/MER on the Measurements tab. When multiple signals are input, you can select which signal to use for measurements in the Channel section.

Ports

Input

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Signals, specified as separate arguments of Nsym-by-1 column vectors or Nsym-by-Nchannel matrices. Nsym is the number of symbols, and Nchannel is the number of input signal channels. Signals can have different data types and dimensions.

You must specify N input ports, where N is the Number of input ports parameter value. You can visualize up to 20 individual or collective signal channels in the constellation diagram. For example, if you create a two-channel signal for every input, then you can define up to 10 input ports.

Example: [-1 + 1i; -1 - 1i; 1 + 1i; 1 - 1i] specifies a four-symbol input signal.

Data Types: double
Complex Number Support: Yes

Parameters

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Plot

In the Plot tab, you can adjust settings of the constellation diagram configuration, simulate the model, take a snapshot of the plot, copy the display, and print the figure. Parameters unique to the constellation diagram scope are described.

On the Plot tab, click Settings to open the Configuration Plot Settings window. This window includes parameter subsections to configure the data and axes, labels, and color and styling. Parameters unique to the constellation diagram are described on this page.

Specify the number of input ports on the scope block as an integer in the range [1, 20].

The total number of input signal channels cannot exceed 20. When you specify multichannel input signals, the total number of input signal channels limits the maximum number of input ports.

Specify the number of samples used to represent each symbol as a positive integer. The signal is downsampled by the value of this parameter before it is plotted.

Specify the number of samples to skip before plotting points as a nonnegative integer less than the Samples per symbol parameter value. This value specifies the number of samples to skip when Samples per symbol is greater than 1.

Specify the maximum number of symbols to display by selecting Input frame length or specifying a positive integer. To specify a positive integer, select and then replace <user-defined> with your desired value. Use this parameter to limit the maximum number of symbols that the constellation diagram displays when you input long signals. The block plots the most recently received symbols.

On the Plot tab or Measurements tab, click Reference Constellation, to open the Reference Constellation window. This window includes parameters to configure the reference constellation for each input port.

Select this parameter to show reference constellations on the plot.

Configure the reference constellation parameters for the specified input port.

Each input port has its own reference constellation. For a multichannel input signal, the block applies a single reference constellation for all signals in that input port.

Specify the reference constellation by selecting Custom, BPSK, QPSK, 8-PSK, 16-QAM, 64-QAM, or 256-QAM. To specify a custom value, first select Custom. Then in the Custom value parameter, replace the entry with your custom vector of symbol values.

Each input port had its own reference constellation. For a multichannel input signal, the block applies a single reference constellation for all signals in that input port.

The EVM/MER measurements use the specified reference constellation to calculate the signal quality of the modulated input signal. For more information about the signal quality measurements, see EVM and MER Measurements.

Specify the reference constellation for an input as a vector that defines symbol values for the custom modulation scheme.

Dependencies

To enable this parameter, set the Reference constellation parameter to Custom Reference Constellation.

Data Types: char | double
Complex Number Support: Yes

Specify the normalization method that the block uses for the constellation diagram by selecting Average power, Minimum distance, or Peak power.

Dependencies

To enable this parameter, set the Reference constellation parameter to 16-QAM, 64-QAM, or 256-QAM.

Specify the average power of the reference constellation as a positive scalar. The average power is referenced to a one-ohm load. Units are in watts.

Dependencies

To enable this parameter, set the Reference constellation parameter to BPSK, QPSK, 8-PSK, 16-QAM, 64-QAM, or 256-QAM.

Specify the phase offset of the reference constellation as a scalar. Units are in radians.

Dependencies

To enable this parameter, set the Reference constellation parameter to BPSK, QPSK, 8-PSK, 16-QAM, 64-QAM, or 256-QAM.

  • The default value is 0 for BPSK, 16-QAM, 64-QAM, and 256-QAM.

  • The default value is pi/4 for 8-PSK.

  • The default value is pi/8 for QPSK.

On the Plot tab, click Legend to toggle the display of the legend. The names listed in the legend are the names for signals connected to input ports as specified in the model. The legend does not display until the model runs with an input signal.

In the scope legend, click a signal name to toggle the signal visibility in the scope.

On the Plot tab, click Trajectory to toggle the display of the trajectory. Select this parameter to display the trajectory between constellation points for the plotted signals.

Measurements

In the Measurements tab, you can select the active channel, configure the signal quality measurements, and toggle the Measurements pane.

For more information about the signal quality measurements, see EVM and MER Measurements.

Channel

Select the active input channel for measurements from the list of input channels. Click EVM/MER to display the signal quality measurements for the active channel.

The total number of input signal channels cannot exceed 20. When you specify multichannel input signals, the total number of input signal channels limits the maximum permitted value for the Number of input ports parameter.

Measurements

Specify the duration of the EVM and MER measurement in symbols by selecting Current Display, or All displays or by specifying a positive integer. To specify a positive integer, select and then replace <user-defined> with your desired value. The value must be a positive value in the range [1, Symbols to display). The block computes measurements after the number of input data samples exceeds the measurement interval.

Specify the normalization method that the block uses for the EVM normalization by selecting Average constellation power or Peak constellation power.

On the Plot tab or Measurements tab, click Reference Constellation, to open the Reference Constellation window. This window includes parameters to configure the reference constellation for each input port. For parameter descriptions, see the Reference Constellation parameter in the Plot section.

On the Measurements tab, click EVM/MER to toggle display the signal quality measurements pane. For more information, see EVM and MER Measurements.

Block Characteristics

Data Types

Boolean | double | enumerated | fixed point | integer | single

Direct Feedthrough

no

Multidimensional Signals

no

Variable-Size Signals

yes

Zero-Crossing Detection

no

More About

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Extended Capabilities

Version History

Introduced in R2013b