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MT Generate Fading Profile (MT Rician Fading Profile (Gans)) (G Dataflow)

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    Last Modified: February 7, 2018

    Generates a Rician flat-fading profile for the multipath channel. The envelope for the first path statistically obeys the Rician distribution, while the envelope for the remaining path obeys the Rayleigh distribution implemented using the Gans model.

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    profile length

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

    Default: 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: 1

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    doppler spread

    The desired input Doppler spread f m 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 f c is transmitted, the received signal spectrum, called the Doppler spectrum, has components in the range (f c - f m ) to (f c + f m ). The Doppler spread is related to the mobile velocity v, carrier frequency f c , and the speed of light c by the relation f m = v f c /c.

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    Note  

    The inverse of the Doppler spread T c = 1 / 16 π f m (known as the coherence time) is the time duration over which the channel impulse response is essentially invariant.

    Default: 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: -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

    Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

    error in does not contain an error error in contains an error
    If no error occurred before the node runs, the node begins execution normally.

    If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

    If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

    Default: No error

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    rician parameter k

    The desired ratio, in dB, of the dominant line-of-sight (LOS) path to the scattering component. A large positive value of k represents a strongly additive white Gaussian noise channel, while a large negative value of k represents a Rayleigh fading (predominantly scattering) channel.

    Mathematical definition of Rician parameter k

    Mathematically, the Rician parameter k is defined as:

    K ( d B ) = 10 × log ( P o w e r [ L O S c o m p o n e n t ] P o w e r [ s c a t t e r i n g c o m p o n e n t ] )

    The Rician fading profile is generated by adding a DC specular component to a Rayleigh distributed scattering component. var denotes the requested fading variance, which is the variance of the underlying Rayleigh fading profile. The amplitude (A) of the specular DC component is given by the following formula:

    A = var × K

    By varying K, you can parameterize the extent of the scattering component relative to the LOS component of fading. For a strongly Gaussian channel, K approaches infinity, while K < 0 indicates a strongly scattering (Rayleigh fading) channel.

    Default: 0

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    fading variance

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

    Default: 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: 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

    Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

    error in does not contain an error error in contains an error
    If no error occurred before the node runs, the node begins execution normally.

    If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

    If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

    Rician Distribution Equation

    The Rician fading profile describes a time-varying channel with an envelope that follows a Rician distribution. The channel can be characterized by a single-tap impulse response comprising a dominant line-of-sight (LOS) path superimposed on a random multipath. The limiting case of a Rician fading channel (when the LOS path is much weaker than the random multipath) is the Rayleigh fading channel. The Rician distribution is given by:

    p ( r ) = r σ 2 exp ( r 2 + A 2 2 σ 2 ) I 0 ( A r σ 2 ) u ( r )

    where A denotes the peak amplitude of the dominant signal, I0() denotes the modified Bessel function of the first kind and zero-order, and 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.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported

    Web Server: Not supported in VIs that run in a web application


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