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

Class of filter to generate.

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

**Default: ****none**

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.

**Default: **16

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

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

Error conditions that occur before this node runs. The node responds to this input according to standard error behavior.

**Default: **no error

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

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

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**

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 |

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 |

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

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 |
$h\left(t\right)=\mathrm{sin}c\left(\frac{t}{T}\right)\frac{\mathrm{cos}\left(\frac{\pi \alpha t}{T}\right)}{1-\frac{4{\pi}^{2}{\alpha}^{2}{t}^{2}}{{\text{}}^{{T}^{2}}}}$
where T is the symbol period and α is the filter rolloff factor. |

Root Raised Cosine |
$h\left(t\right)=\{\begin{array}{c}1-\alpha +\frac{4\alpha}{\pi},\text{\hspace{0.17em}}t=0\\ \frac{\alpha}{\sqrt{2}}\left[(1+\frac{2}{\pi})\mathrm{sin}\left(\frac{\pi}{4\alpha}\right)+(1+\frac{2}{\pi})\mathrm{cos}\left(\frac{\pi}{4\alpha}\right)\right],\text{\hspace{0.17em}}t=\pm \frac{T}{4\alpha}\\ \frac{\mathrm{sin}\left(\pi \frac{t}{T}(1-\alpha )\right)+4\alpha \frac{t}{T}\mathrm{cos}\left(\pi \frac{t}{T}(1-\alpha )\right)}{\pi \frac{t}{T}(1-{\left(\frac{4\alpha t}{T}\right)}^{2})},\text{\hspace{0.17em}}otherwise\end{array}$
where T is the symbol period and α is the filter rolloff factor. |

Gaussian |
$g\left(t\right)=\sqrt{\frac{BT}{\pi}{e}^{-{\left(BT\right)}^{2}{t}^{2}}}$
where T is the symbol period and B is the -3 dB bandwidth of the filter. |

**Installed By: **LabVIEW Communications System Design Suite (introduced in 1.0)

**Where This Node Can Run: **

Desktop OS: Windows

FPGA: Not supported