Table Of Contents

MT Calculate Scaling Factor (ASK) (G Dataflow)

Last Modified: January 9, 2017

Calculates the maximum possible peak amplitude, after pulse-shape filtering and resampling, of a waveform. This calculation is based on system parameters for the ASK modulation scheme.

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ASK system parameters

Parameter values defining the ASK system. Wire the ASK system parameters cluster of MT Generate ASK System Parameters (M) or MT Generate ASK System Parameters (map) to this cluster. Do not alter the values.

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samples per symbol

An even number of samples dedicated to each symbol. Multiply this value by the symbol rate to determine the sample rate.

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Note  

The demodulation and detector nodes use timing recovery, which is optimized for four or more samples per symbol.

Default: 16

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symbol map

An ordered array that maps each symbol to its desired level. The number of ASK levels in the array is 2 N , where N is the number of bits per symbol. The vector length for the symbols farthest from the origin is 1.

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pulse shaping filter coefficients

An ordered array of filter coefficients corresponding to the desired filter response for the pulse-shaping filter used in modulation. The number of coefficients depends on the pulse-shaping filter characteristics specified in the pulse-shaping filter. Refer to MT Generate Filter Coefficients for more information about pulse-shaping filter coefficients.

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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.

Default: no error

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waveform scaling factor

Inverse of the maximum amplitude of the I/Q waveform based on the specified system parameters.

For the frequency modulation schemes (FSK, MSK, and CPM), there is no known analytical method to calculate the maximum amplitude that accounts for effects such as resampling, filtering, and so on. Empirically, a waveform scaling factor of 0.8 should be sufficient for most of your applications. This value results in a maximum dynamic range loss of about 2 dB on third-party (non-NI) RF signal generator devices.

If you receive errors related to this value, your signal might be aliased. For more information about aliasing, refer to MT Modulate CPM or MT Modulate FSK.

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error out

Error information. The node produces this output according to standard error behavior.

Scaling Factor Calculation

This node computes the worst case scaling factor using an interpolation factor of 128 for the pulse-shaping filter coefficients. If the modulated signal has a large amount of excess bandwidth (for example due to a high value of the pulse shaping filter coefficients parameter), any subsequent FIR filtering may cause significant ringing and subsequently the worst case scaling factor this node computes may no longer remain valid. For example, if the modulated signal undergoes resampling using MT Resample (Complex Cluster) with a resampling factor that has a large number of significant digits after the decimal point, the FIR filter in the fractional resampler may cause significant ringing to cause the maximum amplitude of the waveform to exceed the computed maximum amplitude by more than 3 dB.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported


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