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Discrete-Time Signal Trajectory Scope

Plot modulated signal's in-phase component versus its quadrature component

Library

Comm Sinks

Description

The Discrete-Time Signal Trajectory Scope displays the trajectory of a modulated signal in its signal space by plotting its in-phase component versus its quadrature component.

The Discrete-Time Signal Trajectory Scope block has one input port. This block accepts a complex scalar-valued or column vector input signal. The block accepts a signal with the following data types: double, single, base integer, and fixed-point for input, but will cast it as double.

Line Style and Color

The Line style and Line color parameters on the Rendering Properties panel control the appearance of the signal trajectory. The Line style parameter specifies the style for lines in the signal trajectory. For details on the options for these parameters, see the reference page for the Discrete-Time Eye Diagram Scope block.

Recommended Settings

The following table summarizes the recommended parameter settings for the Discrete-Time Signal Trajectory Scope.

ParameterRecommended Setting
Samples per symbolSame as the Samples per symbol setting in the modulator block, or the Interpolation factor used in the interpolation block
Symbols displayed10 times the alphabet size of the modulator, M
New symbols per display

Same as Symbols displayed for greater speed

A small positive integer for best animation

Line styleSolid dash (-)
Line colorBlue (b)
Color fading

Check Color fading for animation that resembles an oscilloscope.

Clear for greater speed and animation that resembles a plot.

High quality rendering

Check High quality rendering for higher quality rendering.

Clear for greater speed.

Open at start of simulation

Check Open at start of simulation to view the signal at the start of simulation.

Clear to view the signal after convergence to steady state and for greater initial speed.

Y-axis minimumApproximately 10% less than the expected minimum value of the signal
Y-axis maximumApproximately 10% greater than the expected maximum value of the signal

For Rapid Accelerator or External mode, set the scope up for single rate mode. To guarantee the satisfactory behavior of single rate mode, the subsystem below the block mask for this block must operate as a single-rate entity, which means the following conditions are true:

where:

  • sps = Samples per symbol

  • nspd = New symbols per display

  • Sf = Input frame size, in samples

This equation guarantees that the subsystem below the mask for this block operates as a single-rate entity.

    Warning   If you want to use Rapid Accelerator or External mode, set this block up to run as a single rate entity because the block does not support multi-rate in these modes.

    Note:   Before running a model that contains a Discrete-Time Signal Trajectory Scope block in Accelerator, Rapid Accelerator, or External mode, you must select Open scope at start of simulation. If you do not select this check box before running your model for the first time, the scope will not display your simulation data

Behavior in Enabled Subsystems

You can use the Discrete-Time Signal Trajectory Scope block inside an enabled subsystem. However, you cannot use the scope block inside an enabled subsystem when the model is in a multirate multitasking environment.

When you use the scope in a multirate singletasking environment, it may generate unexpected results inside enabled subsystems. To workaround this issue, configure the scope for single-rate mode. See Recommended Settings for the parameter settings that enable single-rate mode.

Dialog Box

Samples per symbol

Number of samples per symbol.

Symbols displayed

Total number of symbols plotted.

New symbols per display

Number of new symbols that appear in each display.

Line markers

The line markers used in the signal trajectory. Tunable.

Line color

The line color used in the signal trajectory. Tunable.

Color fading

When selected, the points in the signal trajectory fade as the interval of time after they are first plotted increases. Tunable.

High quality rendering

When selected, the block renders a slow, higher-quality picture with overwrite raster operations. When cleared, the block renders a fast, lower-quality picture with XOR raster operations. Tunable.

Show grid

Toggles the scope grid on and off. Tunable.

X-axis minimum

Minimum value the scope displays on the x-axis. Tunable.

X-axis maximum

Maximum value the scope displays on the x-axis. Tunable.

Y-axis minimum

Minimum signal value the scope displays on the y-axis. Tunable.

Y-axis maximum

Maximum signal value the scope display on the y-axis. Tunable.

In-phase X-axis label

Label for x-axis. Tunable.

Quadrature Y-axis label

Label for y-axis. Tunable.

Open at start of simulation

When selected, the scope opens at the start of simulation. When cleared, you must double-click the block after the start of simulation to open the scope. Tunable

    Note:   Before running a model that contains a Discrete-Time Signal Trajectory Scope block in Accelerator, Rapid Accelerator, or External mode, you must select Open scope at start of simulation. If you do not select this check box before running your model for the first time, the scope will not display your simulation data

Symbol number

Displays the number of the current symbol in the input sequence. Tunable.

Scope position

A four-element vector of the form [left bottom width height] specifying the position of the scope window. (0,0) is the lower left corner of the display. Tunable.

Title

Title of signal trajectory plot. Tunable.

Examples

For documentation examples that use this block, see View a Sinusoid and View a Modulated Signal.

Also, the following demos in Communications System Toolbox™ software illustrate how to use the Discrete-Time Signal Trajectory Scope:

  • Filtered Offset QPSK vs. Filtered QPSK

  • GMSK vs. MSK

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