Inport FIR Decimation
Polyphase thinning with FIR filter. The FIR filter coefficients are set via the input port.
Description
The Inport FIR Decimation block performs efficient polyphase thinning using an integer downsampling factor on the first measurement.
Conceptually, FIR thinning (as shown in the schematic) consists of an anti-aliasing FIR filter followed by downsampling.
The FIR filter filters the data in each channel of the input signal with a direct-form FIR filter. The following downsampling reduces the samples of each channel of filtered data by taking each -th sample and discarding samples that follow it, where is the value of the thinning factor, which is set in the Decimation factor parameter. The resulting discrete-time signal has a sampling frequency that is times smaller than the original one.
The Inport FIR Decimation block differs from the Dialog FIR Decimation block only by the fact that the FIR filter coefficients are set through the input port. For more detailed information about the block operation and implemented algorithms see Details and Algorithms.
Ports
Input
#
In
—
input data
scalar | vector | matrix
Details
Input data for a block specified as a scalar, vector or matrix.
| Data types |
|
| Complex numbers support |
Yes |
#
Num
—
coefficients of the numerator of the filter transfer function
vector
Details
Port for input of FIR filter numerator coefficients as a vector.
The transfer function of the FIR filter is defined as:
For operation as an effective smoothing filter, the coefficients generally correspond to a low-pass filter with a normalised cut-off frequency value of no more than , where is the decimation factor.
| Data types |
|
| Complex numbers support |
Yes |
Output
#
Out
—
output data after thinning
scalar | vector | matrix
Details
Output data after thinning, returned as a scalar, vector or matrix.
Block behaviour depends on the value of Rate options parameter:
-
Enforce single-rate processing- when this value is selected, the block keeps the input sampling rate and thins the signal, reducing the output frame size by times. -
Allow multirate processing- when this value is selected, the block thins the signal so that the output sample rate is times smaller than the input sample rate.
The output frame size is the same as the input frame size.
| Data types |
|
| Complex numbers support |
Yes |
Parameters
Main
# Decimation factor — decimation factor
Details
Specify an integer coefficient . The block reduces the sampling rate of the input sequence by this coefficient.
| Default value |
|
| Program usage name |
|
| Tunable |
No |
| Evaluatable |
Yes |
#
Filter structure —
FIR filter structure
Direct form | Direct form transposed
Details
Specify the structure of the FIR filter: Direct form or Direct form transposed.
| Values |
|
| Default value |
|
| Program usage name |
|
| Tunable |
No |
| Evaluatable |
Yes |
#
Input processing —
input signal processing type
Columns as channels (frame based) | Elements as channels (sample based)
Details
Specify whether the unit performs sample-based or frame-based processing. Options to select:
-
Elements as channels (sample based)- each input signal element is treated as an independent channel (sample based processing). -
Columns as channels (frame based)` - each column of the input signal is treated as an independent channel (frame based processing).
| Values |
|
| Default value |
|
| Program usage name |
|
| Tunable |
No |
| Evaluatable |
Yes |
#
Rate options —
the method by which the block thins the input data
Enforce single-rate processing | Allow multirate processing
Details
Specify the method by which the block should thin the input data. Options to choose from:
-
Enforce single-rate processing- when this method is selected, the block retains the sampling rate of the input signal and thins the signal, reducing the output frame size by a factor of . To select this method, the Input processing parameter must be set toColumns as channels (frame based).
If the Rate options parameter is set to Enforce single-rate processing, you can use the Inport FIR Decimation block within the trigger subsystems.
-
Allow multirate processing- when this method is selected, the block thins the signal so that the output sample rate is times lower than the input sample rate.
Dependencies
To use this option, set the Input processing parameter to Columns as channels (frame based).
| Values |
|
| Default value |
|
| Program usage name |
|
| Tunable |
No |
| Evaluatable |
Yes |
#
Rate options —
the method by which the block thins the input data
Allow multirate processing
Details
The block thins the data using the `Allow multirate processing' method - the output sampling rate is times lower than the input rate.
Dependencies
To use this parameter, set the Input processing parameter to Elements as channels (sample based).
| Values |
|
| Default value |
|
| Program usage name |
|
| Tunable |
No |
| Evaluatable |
Yes |
# Allow arbitrary frame length for fixed-size input signals — allow arbitrary frame size for fixed size input signals
Details
Specify whether fixed-size input signals (whose size does not change during simulation) can have an arbitrary frame size, and the frame size does not have to be a multiple of the decimation factor. The block uses this parameter only for fixed-size input signals and ignores it if the input signal has a variable size.
For fixed size input signals:
-
If the Allow arbitrary frame length for fixed-size input signals checkbox is selected, the frame size of the signal does not have to be a multiple of the decimation factor. If the input signal is not a multiple of the decimation factor, the output is usually a variable-sized signal. Therefore, to support arbitrary input size, the block must also support variable-size operations, which can be enabled by selecting the Allow arbitrary frame length for fixed-size input signals checkbox.
-
If Allow arbitrary frame length for fixed-size input signals is unchecked, the input frame size must be a multiple of the decimation factor.
Dependencies
To use this option, set Input processing to Columns as channels (frame based) and Rate options to Enforce single-rate processing.
| Default value |
|
| Program usage name |
|
| Tunable |
No |
| Evaluatable |
Yes |