Rayleigh Noise Generator (Communications Blockset)

Generate Rayleigh distributed noise

Library

Noise Generators sublibrary of Comm Sources

Description

The Rayleigh Noise Generator block generates Rayleigh distributed noise. The Rayleigh probability density function is given by

where is known as the fading envelope of the Rayleigh distribution.

The block requires you to specify the Initial seed for the random number generator. If it is a constant, then the resulting noise is repeatable. The sigma parameter can be either a vector of the same length as the Initial seed, or a scalar. When sigma is a scalar, every element of the output signal shares that same value.

Initial Seed

The Initial seed parameter initializes the random number generator that the Rayleigh Noise Generator block uses to add noise to the input signal. For best results, the Initial seed should be a prime number greater than 30. Also, if there are other blocks in a model that have an Initial seed parameter, you should choose different initial seeds for all such blocks.

You can choose seeds for the Rayleigh Noise Generator block using the Communications Blockset's randseed function. At the MATLAB prompt, type the command

```
randseed
```

This returns a random prime number greater than 30. Typing randseed again produces a different prime number. If you add an integer argument, randseed always returns the same prime for that integer. For example, randseed(5) always returns the same answer.

Attributes of Output Signal

The output signal can be a frame-based matrix, a sample-based row or column vector, or a sample-based one-dimensional array. These attributes are controlled by the Frame-based outputs, Samples per frame, and Interpret vector parameters as 1-D parameters. See Signal Attribute Parameters for Random Sources in Using the Communications Blockset for more details.

The number of elements in the Initial seed parameter becomes the number of columns in a frame-based output or the number of elements in a sample-based vector output. Also, the shape (row or column) of the Initial seed parameter becomes the shape of a sample-based two-dimensional output signal.

Dialog Box

Sigma: Specify as defined in the Rayleigh probability density function.
Initial seed: The initial seed value for the random number generator.
Sample time: The period of each sample-based vector or each row of a frame-based matrix.
Frame-based outputs: Determines whether the output is frame-based or sample-based. This box is active only if Interpret vector parameters as 1-D is unchecked.
Samples per frame: The number of samples in each column of a frame-based output signal. This field is active only if Frame-based outputs is checked.
Interpret vector parameters as 1-D: If this box is checked, then the output is a one-dimensional signal. Otherwise, the output is a two-dimensional signal. This box is active only if Frame-based outputs is unchecked.

See Also

Multipath Rayleigh Fading Channel; raylrnd (Statistics Toolbox)

References

[1] Proakis, John G. Digital Communications, Third edition. New York: McGraw Hill, 1995.

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