MT Rayleigh Fading Profile (Gans)

Generates a Rayleigh flat-fading profile with an envelope that statistically obeys the Rayleigh distribution, using the Gans fading model.

1378

Inputs/Outputs

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profile length

The number of complex-valued fading profile samples (having Rayleigh-distributed envelopes) to generate.

Default value: 1000

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sampling frequency

The system sample rate, in hertz (Hz). This rate is the product of the symbol rate × samples per symbol.

Default value: 1

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doppler spread

The desired input Doppler spread fm of the channel, in hertz (Hz).

This parameter denotes the measure of the spectral broadening caused by the time rate of change of the channel. Doppler spread is defined as the range of frequencies over which the received Doppler spectrum is essentially nonzero. When a pure sine tone at frequency fc is transmitted, the received signal spectrum, called the Doppler spectrum, has components in the range (fc - fm) to (fc + fm). The Doppler spread is related to the mobile velocity v, carrier frequency fc, and the speed of light c by the relation fm = vfc/c.

Note The inverse of the Doppler spread Tc = 1 / 16fm (known as the coherence time) is the time duration over which the channel impulse response is essentially invariant.

Default value: 0.01

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seed in

The initial state for generating the fading profile. If seed in is set to -1, the generated fading profile is randomly chosen during every call when reset? is set to TRUE. Otherwise, the generated fading profile returns the same set of fading coefficients when reset? is set to TRUE.

Default value: -1

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Default value: No error

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fading variance

The desired variance of the complex-valued Rayleigh distributed fading profile.

Default value: 1

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reset?

A Boolean that determines whether the fading profile generation is reset on subsequent calls to this node.

TRUE Resets the fading profile generation on every call to this node.
FALSE Continues generating the fading profile from the previous iteration on subsequent calls.

Default value: TRUE

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fading profile

Complex-valued coefficients of the generated fading profile size that equals profile length. Wire this parameter to MT Apply Fading Profile to apply this fading profile to a baseband I/Q signal.

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seed out

The internal state of the node at the end of generation of the fading profile for the current iteration. When reset? is set to FALSE, this state is used to continue the fading profile generation at the beginning of the next iteration.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Rayleigh Distribution Equation

The Rayleigh distribution describes a flat-fading channel characterized by a single-tap impulse response with a time-varying envelope that is Rayleigh-distributed. This model describes the statistical time-varying nature of the received envelope of a flat fading channel or the envelope of an individual multipath component. The Rayleigh distribution has a probability density function (PDF) given by the following equation:

p ( r ) = r σ 2 exp ⁡ ( − r 2 2 σ 2 ) u ( r ) p ( r ) = r σ 2 exp ⁡ ( − r 2 2 σ 2 ) u ( r )

where r is the specified fading variance.

Gans Model Equation

The Gans model generates the Rayleigh fading profile by passing quadrature Gaussian I/Q components through a Doppler filter with a U-shaped power spectral density profile. For the selective fading model, the implementation ensures that the generated fading profile for all paths is uncorrelated.