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MT Calculate Scaling Factor (PSK) (G Dataflow)

Last Modified: January 9, 2017

Calculates the maximum possible peak amplitude, after pulse-shape filtering and resampling, of a waveform for the PSK modulation scheme.

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PSK system parameters

Parameter values defining the PSK system. Wire this parameter to the corresponding system parameters cluster of MT Modulate PSK, MT Demodulate PSK, or MT Detect PSK.

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samples per symbol

Number of samples per symbol in the modulated output complex waveform. For error-free operation, the samples per symbol value must be an even number.

Default: 16

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symbol map

An ordered array that maps each Boolean symbol to its desired coordinates in the complex plane. The number of PSK states in the array must be 2 N , where N is the number of bits per symbol.

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differential PSK

Status of the differential PSK.

Name Description
disable

Disables bit sequence encoding.

enable

Enables bit sequence encoding.

Default: enable

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PSK type

Type of PSK modulation.

Name Description
normal

Sets the modulation type to regular PSK.

shifted

Rotates the constellation by π /M each symbol.

offset

Sets the modulation type to offset quadrature phase-shift keying (OQPSK). This modulation scheme is a form of phase-shift keying in which four different phase angles are used. This scheme is sometimes referred to as staggered quadrature phase-shift keying (SQPSK). For offset PSK, the ideal symbol timing for Q is offset by 1/2 of a symbol period from the ideal symbol timing for I. offset is currently only supported for M= 4.

Default: normal

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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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