CDMA Reference Blockset

Using the Demos

This section describes how to open and run the demos, and view the results. More advanced users can also change parameters and customize the demo.

Opening a Demo

To open a demo, follow these steps:

1. Open the main CDMA Reference Blockset library by typing cdmalibv1p1 at the MATLAB prompt.
2. Double-click on the Demos icon. This opens the MATLAB Demos window and selects the CDMA Reference Blockset in the left pane.
3. In the lower right pane of the MATLAB Demos window, double-click on the name of the demo that you want to open.

Alternatively, you can open a demo by typing the demo filename at the MATLAB prompt. For a list of filenames, see the List of Demos.

Exploring and Running a Demo

You can examine the demo before running it. Here are some suggestions to get you started:

• Study the block diagram, noticing which blocks are in the model and how they are connected.
• Double-click on any icon to open it (if it is a subsystem that has no mask) or to see its parameter dialog box. A parameter dialog box briefly describes the block, shows its parameter values, allows you to change any of the parameter values, and also includes a Help button. If the block is linked to a library instead of being a custom block for the demo, then the Help button links to online help for the block.
• Select any CDMA Reference Blockset block, and then select Go to library link from the model window's Edit menu, to open the blockset library in which the block resides. This shows you where to find the block if you later want to use it in your own model.

To run the demo after opening it, select Start from the model window's Simulation menu. To stop or pause the simulation while it is running, select Stop or Pause from the Simulation menu.

Viewing or Collecting Results from a Demo

Some of the demos use Display and Scope blocks, both from the Simulink Sinks library, to show performance results such as the bit error rate (BER). These blocks display data continuously during the simulation using curves or a numeric display of the values.

To help retrieve and further process the resulting data, you can also connect any number of To Workspace blocks, from the Simulink Sinks library, to parts of the model that interest you. The To Workspace block transfers the data from the simulation to the MATLAB workspace. Then you can plot and analyze the data in the MATLAB workspace.

To save data directly in MATLAB format, you can connect the To File block (from the Simulink Sinks library) to parts of the model that interest you. The writing of data on the disk may slow down the simulation. However, when logging a large data series, it is better to write to a file than to fill the system memory as the To Workspace block would do.

Changing a Demo's Parameters

To understand the function of a demo, you should first run it with the parameters provided. If you later want to modify the configuration to be tested or the conditions under which a demo is run, you can change the parameters in the blocks of the demo.

Note    Before attempting to change a demo's parameters, you should have a good understanding of how the demo works.

To view a block's parameters, double-click on the block's icon. To change a parameter, enter a new value in the parameter dialog box and click the OK or Apply button.

Note    Some blocks or systems impose consistency constraints on various block parameters. For instance, to change the channel types from the default, you might need to change parameters in several blocks. Furthermore, you might need to change parameters such as sizes of data vectors from the model's sources appropriately.

Some typical properties of the demos that you can modify by changing parameters include:

• Simulation duration
• Data rate for the user channel
• Type of logical channel
• Signal-to-noise (SNR) ratio
• Multipath channel fade rate or Doppler frequency

Customizing a Demo

You can customize any demo by adding, removing, and modifying blocks from the CDMA Reference Blockset, Communications Toolbox, or DSP Blockset. By customizing the demos, you can vary the aspects of the CDMA system that the demos simulate. Possible changes include:

• Different control channels
• Different traffic channel configurations
• Further simulation of system algorithms such as timing acquisition, gain control and frequency control

Note    Before attempting to customize a demo, you should have a good understanding of how it works.

Demo Models

IS-95A Forward Traffic Channel Detection Demo