Communications Blockset™

Discrete-Time Eye Diagram Scope - Display multiple traces of modulated signal

Library

Comm Sinks

Description

The Discrete-Time Eye Diagram Scope block displays multiple traces of a modulated signal to produce an eye diagram. You can use the block to reveal the modulation characteristics of the signal, such as pulse shaping or channel distortions.

The Discrete-Time Eye Diagram Scope block has one input port. The block accepts signal of type double, single, boolean, base integer, and fixed-point data types for input, but will cast it as double. In sample-based mode, the input signal must be a scalar value. In frame-based mode, the input must be a column vector or a scalar value.

Warning Neither the Rapid Accelerator nor external mode allows for the uploading of data to this block, preventing any display on this scope. Run the model in accelerator or normal mode to take full advantage of this scope block.

Marker and Line Styles

The Marker, Line style, and Line color parameters, on the Rendering Properties panel, control the appearance of the signal trajectory. The Marker parameter specifies the marker style for points in the eye diagram. The following table lists some of the available line markers.

Marker Style	Parameter Symbol	Appearance
Plus	`+`
Circle	`o`
Asterisk	`*`
Point	`.`
Cross	`x`

The Line style parameter specifies the style for lines in the eye diagram. The following lists some of the available line styles.

Line Style	Appearance
Solid
Dashed
Dotted
Dash-dot

The Line color parameter specifies the color of the eye diagram. These settings plot the signal channels in the following colors (8-bit RGB equivalents are shown in the center column).

Color	RGB Equivalent	Appearance
Black	(0,0,0)
Blue	(0,0,255)
Red	(255,0,0)
Green	(0,255,0)
Dark purple	(192,0,192)

See the line function in the MATLAB documentation for more information about the available markers, colors, and line styles.

Recommended Settings

The following table summarizes the recommended parameter settings for the Discrete-Time Eye Diagram Scope.

Parameter	Recommended Setting
Samples per symbol	Same as the Samples per symbol setting in the modulator block, or the Interpolation factor setting in the interpolation block
Offset (samples)	`0` to view the open part of the eye (Samples per symbol)/2 to view the closed part of the eye
Symbols per trace	An integer between `1` and `4`
Traces displayed	10 times the alphabet size of the modulator, M
New traces per display	Same as Traces displayed for greater speed A small positive integer for best animation
Marker	None or a point (`.`) to see where the samples are plotted
Line style	Solid dash (`-`)
Line color	Blue (`b`)
Duplicate points at trace boundary	Check Duplicate points at trace boundary for modulations such as PSK and QAM. Clear to display the phase trees for MSK, CPFSK, GFSK, GMSK, and other continuous phase modulations.
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 better animation. Clear for greater speed.
Eye diagram to display	Select `In-phase and Quadrature` to view real and imaginary components. Select `In-phase Only` to view real component only and for greater speed. When the input is real and you choose `In-phase and Quadrature`, the quadrature component of the eye diagram is zero.
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 minimum	Approximately 10% less than the expected minimum value of the signal
Y-axis maximum	Approximately 10% greater than the expected maximum value of the signal

Scope Options

The scope title (in the window title bar) is the same as the block title. You can set the axis scaling by setting the y-axis minimum and y-axis maximum parameters on the Axes Properties panel.

In addition to the standard MATLAB figure window menus (File, Edit, Window, Help), the Vector Scope window has an Axes and a Channels menu.

The properties listed in the Axes menu apply to all channels. Many of the parameters in this menu are also accessible through the block parameter dialog box. These are Autoscale, Show grid, Frame #, and Save Position. Below are descriptions of the other parameters listed in the Axes menu:

Autoscale resizes the y-axis to best fit the vertical range of the data. The numerical limits selected by the autoscale feature are displayed in the Minimum Y-limit and Maximum Y-limit parameters in the parameter dialog box. You can change them by editing those values.
Show grid - When selected, the scope displays a grid according to tick marks on the x- and y-axes.
Frame # - When selected, the scope displays the current frame number at the bottom of the scope window.
Save Position automatically updates the Scope position parameter in the Figure properties panel to reflect the scope window's current position and size. To make the scope window open at a particular location on the screen when the simulation runs, simply drag the window to the desired location, resize it as needed, and select Save Position.

The properties listed in the Channels menu apply to a particular channel. The parameters listed in this menu are Style, Marker, and Color. They correspond to the parameters Line style, Marker, and Line color, respectively.

You can also access many of these options by right-clicking with the mouse anywhere on the scope display. The menu that pops up contains a combination of the options available in both the Axes and Channels menus.

Dialog Box

Samples per symbol: Number of samples per symbol. Use with Symbols per trace to determine the number of samples per trace.
Offset (samples): Nonnegative integer less than the product of Samples per symbol and Symbols per trace, specifying the number of samples to omit before plotting the first point. Tunable.
Symbols per trace: Positive integer specifying the number of symbols plotted per trace.
Traces displayed: Number of traces plotted.
New traces per display: Positive integer less than Traces displayed, specifying the number of new traces that appear in each display.

Markers: The marker for points in the eye diagram. Tunable.
Line style: The line style in the eye diagram. Tunable.
Line color: The line color in the eye diagram. Tunable.
Duplicate points at trace boundary: Check to enable duplicate points at the trace boundary. Clear to disable.
Color fading: When selected, the points in the eye diagram 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.

Y-axis minimum: Minimum signal value the scope displays. Tunable.
Y-axis maximum: Maximum signal value the scope displays. Tunable.
In-phase Y-axis label: Label for y-axis of the in-phase diagram. Tunable.
Quadrature Y-axis label: Label for y-axis of the quadrature diagram. Tunable.

Open scope 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.
Eye diagram to display: Type of eye diagram to display. Choose In-phase and Quadrature to display real and complex components, or In-phase Only to display only the real component. Tunable.
Trace number: Displays the number of the current trace in the input sequenced. 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 eye diagram figure window. Tunable.

Examples

For documentation examples that use this block, see Example: Viewing a Sinusoid and Example: Viewing a Modulated Signal.

Also, the following Communications Blockset™ demos illustrate how to use the Discrete-Time Eye Diagram Scope block:

CPM Phase Tree Example
Filtered Offset QPSK vs. Filtered QPSK
Rayleigh Fading Channel
QPSK vs. MSK