Getting Started

Building the FSK Model

You can build the FSK model by adding blocks to the model shown in the figure Channel Noise Model. To open the channel noise model, type channeldoc at the MATLAB prompt. Then save the model as my_fsk in the directory where you keep your work files. See Saving a Model.

You need to add the following blocks to the model.

M-FSK Modulator and Demodulator Passband

The M-FSK Modulator Passband block, from FM in the Digital Passband sublibrary of the Modulation library, modulates the binary signal onto a sinusoidal carrier of 10000 Hz. The block modulates a 0 by shifting the frequency of the carrier up to 10500 Hz, and a 1 by shifting the frequency down to 9500 Hz.

The M-FSK Demodulator Passband block, from FM in the Digital Passband sublibrary of the Modulation library, demodulates the signal.

Relational Operator

The Relational Operator block, from the Simulink Math Operations library, compares the transmitted signal, from the Bernoulli Binary Generator block, with the received signal, from the M-FSK Demodulator Passband block. The block outputs a 0 when the two signals agree, and a 1 when they differ.

Spectrum Scope

The Spectrum Scope block, from the DSP Sinks library, calculates the fast Fourier transform (FFT) of the signal and displays its spectrum. When you run the model, a scope appears, as in the figure FSK Spectrum.

Scope

The Scope block, from the Simulink Sinks library, displays the transmitted signal, the received signal, and the output of the Relational Operator block. To create three input ports for the block, follow these steps:

1. Double-click the block to open the scope.
2. Click the Parameters button on the toolbar.
3. Set Number of axes to 3.
4. Set Time range to 1.
5. Click OK.

To set the limits on the vertical axes:

1. Right-click the vertical axis at the left side of the upper scope.
2. In the context menu, select Axes properties.
3. In the Y-min field type -1.
4. In the Y-max field type 2.
5. Click OK.

Repeat these steps for the middle and lower vertical axes.

Integer Delay

The Integer Delay Block, from the DSP Blockset Signal Operations library, delays the transmitted signal so that it can be accurately compared with the received signal. Its purpose is explained further in Delays in the Model.

Drag these blocks into the model window and connect them as shown in the figure FSK Model. The next section explains how to set the parameters for these blocks.

Building a Frequency-Shift Keying Model

Setting Parameters in the FSK Model