From 12:00 PM - 4:00 PM CST on Thursday, October 18, ni.com will be undergoing system upgrades that may result in temporary service interruption.

We appreciate your patience as we improve our online experience.

Table Of Contents

MT Generate Filter Coefficients (G Dataflow)

Version:
    Last Modified: February 7, 2018

    Calculates filter coefficients for pulse-shaping and matched filters applied by the digital modulation nodes and demodulation nodes.

    connector_pane_image
    datatype_icon

    pulse shaping filter

    Class of filter to generate.

    You must correspond the selection here with the modulation type parameter setting as shown in the following table.

    Modulation Type Valid Pulse-Shaping Type
    PSK, QAM, ASK, PAM none (0)
    spd-note-note
    Note  

    The node ignores the filter length parameter and generates a filter that is always one symbol long.

    Raised Cosine (1)
    Root Raised Cosine (2)
    MSK none (0)
    spd-note-note
    Note  

    The node ignores the filter length parameter and generates a filter that is always one symbol long.

    Raised Cosine (1)
    Root Raised Cosine (2)
    Gaussian (3)
    FSK, CPM none (0)
    spd-note-note
    Note  

    The node ignores the filter length parameter and generates a filter that is always one symbol long.

    Raised Cosine (1)
    Root Raised Cosine (2)
    Gaussian (3)

    Default: none

    datatype_icon

    pulse shaping samples per symbol

    Number of desired samples per symbol for the pulse-shaping filter.

    If you use the pulse-shaping filter for demodulation, this parameter value must match the samples per symbol element of the system parameters cluster passed to the demodulation node. Specify an even number greater than 2.

    spd-note-note
    Note  

    If the pulse-shaping and matched filter coefficients are used by the same demodulation or modulation node, the pulse shaping samples per symbol and matched samples per symbol values must be identical.

    Default: 16

    datatype_icon

    matched samples per symbol

    Number of desired samples per symbol for the demodulation matched filter.

    You must match this parameter value to the samples per symbol element of the system parameters cluster passed to the digital demodulation node. Specify an even number greater than 2.

    Default: 16

    datatype_icon

    filter parameter

    A value that indicates either alpha (rolloff for raised cosine and square root raised cosine filters), or BT (the product of the -3 dB bandwidth and the symbol period for a Gaussian filter). Ignore this parameter when you set the pulse shaping filter parameter to none.

    Default: 0.5

    datatype_icon

    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

    datatype_icon

    modulation type

    Type of modulation or demodulation for which to generate filter coefficients.

    Name Description
    FSK

    Generates FSK filter coefficients.

    PSK

    Generates PSK filter coefficients.

    QAM

    Generates QAM filter coefficients.

    MSK

    Generates MSK filter coefficients.

    PAM

    Generates PAM filter coefficients.

    ASK

    Generates ASK filter coefficients.

    CPM

    Generates CPM filter coefficients.

    Default: FSK

    datatype_icon

    filter length

    The desired length, in symbols, of the pulse-shaping filter. The length of the matched filter can vary according to filter type and modulation type. Valid values are greater than 1.

    Default: 8

    datatype_icon

    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 parameter.

    Number of Coefficients Size for FSK Size for MSK Size for PSK/QAM/ASK/PAM
    none (samples/symbol) (samples/symbol) (samples/symbol)
    raised cosine (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1
    root raised cosine (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1
    Gaussian (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1 N/A
    datatype_icon

    matched filter coefficients

    An ordered array of filter coefficients corresponding to the desired filter response for the matched filter used in demodulation.

    Number of Coefficients Size for FSK Size for MSK Size for PSK/QAM/ASK/PAM
    none (samples/symbol) (samples/symbol) (samples/symbol)
    raised cosine 1 1 1
    root raised cosine (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1 (samples/symbol) × filter length + 1
    Gaussian 14 × (samples/symbol) + 1 3 × (samples/symbol) - 1 N/A
    datatype_icon

    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.

    Filter Impulse Response Calculations

    Use the calculated filter coefficients during modulation to reduce the bandwidth of the transmitted signal and during demodulation to reduce intersymbol interference. The pulse-shaping filter can be used either in transmission or for demodulation of PSK-, FSK-, MSK-, ASK-, PAM-, QAM-, and CPM-modulated signals. Use matched filter only for demodulation.

    The node calculates the impulse response of the filter using the following formulas.

    Filter Type Formula
    Raised Cosine
    h ( t ) = sin c ( t T ) cos ( π α t T ) 1 4 π 2 α 2 t 2 T 2
    where T is the symbol period and α is the filter rolloff factor.
    Root Raised Cosine
    h ( t ) = { 1 α + 4 α π , t = 0 α 2 [ ( 1 + 2 π ) sin ( π 4 α ) + ( 1 + 2 π ) cos ( π 4 α ) ] , t = ± T 4 α sin ( π t T ( 1 α ) ) + 4 α t T cos ( π t T ( 1 α ) ) π t T ( 1 ( 4 α t T ) 2 ) , o t h e r w i s e
    where T is the symbol period and α is the filter rolloff factor.
    Gaussian
    g ( t ) = B T π e ( B T ) 2 t 2
    where T is the symbol period and B is the -3 dB bandwidth of the filter.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported

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


    Recently Viewed Topics