Inport FIR Decimation
Polyphase thinning with FIR filter. The FIR filter coefficients are set via the input port.
blockType: SubSystem
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Path in the library: |
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 |
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| 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 |
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| 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 |
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| Complex numbers support |
Yes |
Parameters
Main
# Decimation factor — decimation coefficient
Details
Specify the integer coefficient . The block reduces the sampling rate of the input sequence by this factor.
| Default value |
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| Program usage name |
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| 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 |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
#
Input processing —
input signal processing type
Columns as channels (frame based) | Elements as channels (sample based)
Details
Specify whether the block performs processing based on a reference or frame. Options to choose from:
-
Elements as channels (sample based)— each element of the input signal is considered as an independent channel (sample-based processing). -
Columns as channels (frame based)— each column of the input signal is considered as an independent channel (frame-based processing).
For more information, see Signal processing by frames and counts.
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
#
Rate options —
the method by which the block decimates the input data
Enforce single-rate processing | Allow multirate processing
Details
Specify the method by which the block should thin out the input data. Options to choose from:
-
'Enforce single-rate processing` — when this method is selected, the unit saves the sampling rate of the input signal and decimates the signal, reducing the size of the output frame in once. To select this method, the Input processing parameter must have the value
Columns as channels (frame based).
If the Rate options parameter is set to `Enforce single-rate processing', then the Inport FIR Decimation block can be used inside trigger subsystems.
-
`Allow multirate processing' — when this method is selected, the unit decimates the signal in such a way that the output sampling rate in times less than the entrance one.
Dependencies
To use this parameter, set the Input processing parameter to Columns as channels (frame based).
| Values |
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| Default value |
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| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |
#
Rate options —
the method by which the block decimates the input data
Allow multirate processing
Details
The block decimates the data using the 'Allow multirate processing' method — the output sampling rate in times less than the entrance one.
Dependencies
To use this parameter, set the Input processing parameter to Elements as channels (sample based).
| Values |
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| Default value |
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| Program usage name |
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| 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, then the size of the signal frame does not have to be a multiple of the decimation factor. If the input signal is not a multiple of the decimation factor, then the output is usually a variable-size signal. Therefore, in order to support an arbitrary input size, the block must also support variable-size operations, which can be enabled by checking the Allow arbitrary frame length for fixed-size input signals checkbox.
-
If the Allow arbitrary frame length for fixed-size input signals checkbox is unchecked, the input frame size must be a multiple of the decimation factor.
Dependencies
To use this parameter, set the Input processing parameter to Columns as channels (frame based), and the Rate options parameter to Enforce single-rate processing.
| Default value |
|
| Program usage name |
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| Tunable |
No |
| Evaluatable |
Yes |