MT Apply Pulse Shaping Filter (FSK)

Applies a pulse-shaping filter to an input stream comprised of FSK-modulated symbols. The node performs filtering using the specified pulse shaping filter coefficients followed by accumulation on the phase of the information symbols to generate the oversampled FSK-modulated complex baseband waveform. This process is the digital equivalent of continuous-time analog frequency modulation.

Note If you set the symbol phase continuity to discontinuous, the node ignores the pulse shaping filter coefficients parameter. Instead, the node generates the baseband waveform after sampling the output of M separate complex exponential oscillators.

This node first upsamples (zero-insertion) the symbols array by a factor equal to the samples per symbol value, then filters the symbols stream with the pulse-shaping filter that you specify.

1378

Inputs/Outputs

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symbols

Array of symbols (comprised of frequency deviations) corresponding to information bits. Wire the symbols parameter of MT Map Bits to Symbols to this parameter.

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pulse shaping filter coefficients

An ordered array containing sample-spaced coefficients for the desired pulse-shaping filter. Wire the pulse shaping filter coefficients parameter of MT Generate Filter Coefficients to this parameter. Ensure that the value of the samples per symbol parameter passed to this node matches the pulse shaping samples per symbol value used to generate the filter coefficients.

Note When reset? is set to TRUE, there is a transient response of ½ the filter length at the start of the modulated signal, and the returned data is shortened by approximately ½ the filter length. When reset? is set to FALSE, the node uses data from the previous iteration to eliminate the transient.
You can also specify custom pulse-shaping filter coefficients.
Note This node does not verify absence of intersymbol interference in custom filter coefficients before applying the pulse-shaping filter.
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samples per symbol

Number of samples per information symbol in the output complex waveform. Multiply this value by the symbol rate to determine the system sample rate.

Default value: 16

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symbol rate

The symbol rate in symbols per second.

Default value: 1.0

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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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symbol phase continuity

Continuity of phase transitions between symbols.

continuous

Continuous phase transitions between symbols.

discontinuous

Discontinuous phase transitions between symbols, that is, discontinuous phase FSK (DPFSK).

With discontinuous phase-FSK (DPFSK), modulation consists of selecting the appropriate sinusoid based on the input data. Thus, when switching between symbols, there is a discontinuity in the FSK signal phase. To emulate a hardware-based DPFSK source, this node maintains the phase of each independent sinusoid versus time. Thus, the DPFSK modulator acts like a hardware-based (multiple switched tone generator) FSK modulator.

Default value: continuous

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reset?

A Boolean that determines whether the node continues pulse-shape filtering using the previous iteration states.

TRUE Resets the pulse-shape filtering.
FALSE Continues pulse shaping at the previous iteration state on subsequent calls.

Default value: TRUE

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output phase waveform

The output pulse-shaped continuous-time phase waveform.

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t0

Trigger (start) time of the Y array.

Default value: 0

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dt

Time interval between data points in the Y array. The reciprocal of this value is equal to the system sample rate.

Default value: 1.0

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Y

The complex-valued signal-only baseband phase waveform.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior