User`s guide

FIR Interpolation
5-200
5FIR Interpolation
Purpose Upsample and filter an input signal.
Library Filtering / Multirate Filters
Description The FIR Interpolation block resamples the discrete-time input at a rate
L times faster than the input sample rate, where the integer L is specified by
the
Interpolation factor parameter. This process consists of two steps:
•The block upsamples the input to a higher rate by inserting L-1 zeros
between samples.
•The block filters the upsampled data with a direct-form II transpose FIR
filter.
The FIR Interpolation block implements the above upsampling and FIR
filtering steps together using a polyphase filter structure, which is more
efficient than straightforward upsample-then-filter algorithms.
The
FIR filter coefficients parameter specifies the numerator coefficients of
the FIR filter transfer function H(z).
The coefficient vector,
[b(1) b(2) ... b(m)], can be generated by one of the
filter design functions in the Signal Processing Toolbox (such as
fir1), and
should have a length greater than the interpolation factor (m>L). The filter
should be lowpass with normalized cutoff frequency no greater than 1/L. All
filter states are internally initialized to zero.
Sample-Based Operation
An M-by-N sample-based matrix input is treated as M∗N independent
channels, and the block interpolates each channel over time. The output
sample period is L times shorter than the input sample period (T
so
=T
si
/L), and
the input and output sizes are identical.
Frame-Based Operation
An M
i
-by-N frame-based matrix input is treated as N independent channels,
and the block decimates each channel over time. The
Framing parameter
determines how the block adjusts the rate at the output to accommodate the
added samples. There are two available options:
Hz() Bz() b
1
b
2
z
1–
… b
m
z
m 1–()–
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