Filter input signal, possibly downsampling, using Gaussian FIR filter
Comm Filters
Note:
The Gaussian Filter block is not recommended.
Use the 
The Gaussian Filter block filters the input signal using a Gaussian FIR filter. The block expects the input signal to be upsampled as its input, so that the Input samples per symbol parameter, N, is at least 2. The block's icon shows the filter's impulse response."
The impulse response of the Gaussian filter is
$$h(t)=\frac{\mathrm{exp}\left(\frac{{t}^{2}}{2{\delta}^{2}}\right)}{\sqrt{2\pi}\cdot \delta}$$
where
$$\delta =\frac{\sqrt{\mathrm{ln}(2)}}{2\pi BT}$$
and B is the filter's 3dB bandwidth. The BT product parameter
is B times the input signal's symbol period. For a given BT product,
the Signal Processing Toolbox™ gaussfir
function
generates a filter that is half the bandwidth of the filter generated
by the Communications System Toolbox™ Gaussian Filter block.
The Group delay parameter is the number of symbol periods between the start of the filter's response and the peak of the filter's response. The group delay and N determine the length of the filter's impulse response, which is 2 * N * Group delay + 1.
The Filter coefficient normalization parameter indicates how the block scales the set of filter coefficients:
Sum of coefficients
means
that the sum of the coefficients equals 1.
Filter energy
means that
the sum of the squares of the coefficients equals 1.
Peak amplitude
means that
the maximum coefficient equals 1.
After the block normalizes the set of filter coefficients as above, it multiplies all coefficients by the Linear amplitude filter gain parameter. As a result, the output is scaled by $$\sqrt{N}$$. If the output of this block feeds the input to the AWGN Channel block, specify the AWGN signal power parameter to be 1/N.
This block accepts scalar, column vector, and MbyN matrix input signals. The block filters an MbyN input matrix as follows:
When you set the Input processing parameter
to Columns as channels (frame based)
, the
block treats each column as a separate channel. In this mode, the
block creates N instances of the same filter, each
with its own independent state buffer. Each of the N filters
process M input samples at every Simulink^{®} time
step.
When you set the Input processing parameter
to Elements as channels (sample based)
,
the block treats each element as a separate channel. In this mode,
the block creates M*N instances
of the same filter, each with its own independent state buffer. Each
filter processes one input sample at every Simulink time step.
The output dimensions always equal those of the input signal. For information about the data types each block port supports, see the table on this page.
To examine or manipulate the coefficients of the filter that this block designs, select Export filter coefficients to workspace. Then set the Coefficient variable name parameter to the name of a variable that you want the block to create in the MATLAB workspace. Running the simulation causes the block to create the variable, overwriting any previous contents in case the variable already exists.
A positive integer representing the number of samples per symbol in the input signal.
The product of the filter's 3dB bandwidth and the input signal's symbol period
A positive integer that represents the number of symbol periods between the start of the filter response and its peak.
The block scales the set of filter coefficients so that this
quantity equals 1. Choices are Sum of coefficients
, Filter
energy
, and Peak amplitude
.
Specify how the block processes the input signal. You can set this parameter to one of the following options:
Columns as channels (frame based)
—
When you select this option, the block treats each column of the input
as a separate channel.
Elements as channels (sample based)
—
When you select this option, the block treats each element of the
input as a separate channel.
Note:
The 
This parameter is available only when you set the Rate
options parameter to Allow multirate processing
.
A positive scalar used to scale the filter coefficients after the block uses the normalization specified in the Filter coefficient normalization parameter.
If you check this box, then the block creates a variable in the MATLAB workspace that contains the filter coefficients.
The name of the variable to create in the MATLAB workspace. This field appears only if Export filter coefficients to workspace is selected.
If you click this button, then MATLAB launches the Filter Visualization
Tool, fvtool
, to analyze the Gaussian filter whenever
you apply any changes to the block's parameters. If you launch fvtool
for
the filter, and subsequently change parameters in the mask, fvtool
will
not update. You will need to launch a new fvtool
in
order to see the new filter characteristics. Also note that if you
have launched fvtool
, then it will remain open
even after the model is closed.
Select the rounding mode for fixedpoint operations. The filter
coefficients do not obey this parameter; they always round to Nearest
.
The block uses the Rounding selection if a number
cannot be represented exactly by the specified data type and scaling,
it is rounded to a representable number. For more information, see Rounding Modes in
the DSP System Toolbox™ documentation or Rounding Mode: Simplest in
the FixedPoint Designer™ documentation.
Select the overflow mode for fixedpoint operations. The filter coefficients do not obey this parameter; they are always saturated.
The block implementation uses a DirectForm FIR filter. The Coefficients parameter controls which data type represents the coefficients when the input data is a fixedpoint signal.
Choose how you specify the word length and the fraction length of the filter coefficients (numerator and/or denominator). See Filter Structure Diagrams in the DSP System Toolbox Reference Guide for illustrations depicting the use of the coefficient data types in this block:
When you select Same word length as input
,
the word length of the filter coefficients match that of the input
to the block. In this mode, the fraction length of the coefficients
is automatically set to the binarypoint only scaling that provides
you with the best precision possible given the value and word length
of the coefficients.
When you select Specify word length
,
you are able to enter the word length of the coefficients, in bits.
In this mode, the fraction length of the coefficients is automatically
set to the binarypoint only scaling that provides you with the best
precision possible given the value and word length of the coefficients.
When you select Binary point scaling
,
you are able to enter the word length and the fraction length of the
coefficients, in bits. If applicable, you are able to enter separate
fraction lengths for the numerator and denominator coefficients.
When you select Slope and bias scaling
,
you are able to enter the word length, in bits, and the slope of the
coefficients. If applicable, you are able to enter separate slopes
for the numerator and denominator coefficients. This block requires
poweroftwo slope and a bias of zero.
The filter coefficients do not obey the Rounding
mode and the Overflow mode parameters;
they are always saturated and rounded to Nearest
.
Use this parameter to specify how you would like to designate the product output word and fraction lengths. See Multiplication Data Types and Multiplication Data Types in the DSP System Toolbox Reference Guide for illustrations depicting the use of the product output data type in this block:
When you select Same as input
,
these characteristics match those of the input to the block.
When you select Binary point scaling
,
you are able to enter the word length and the fraction length of the
product output, in bits.
When you select Slope and bias scaling
,
you are able to enter the word length, in bits, and the slope of the
product output. This block requires poweroftwo slope and a bias
of zero.
Use this parameter to specify how you would like to designate the accumulator word and fraction lengths. See Filter Structure Diagrams and Multiplication Data Types for illustrations depicting the use of the accumulator data type in this block:
When you select Same as input
,
these characteristics match those of the input to the block.
When you select Same as product output
,
these characteristics match those of the product output.
When you select Binary point scaling
,
you are able to enter the word length and the fraction length of the
accumulator, in bits.
When you select Slope and bias scaling
,
you are able to enter the word length, in bits, and the slope of the
accumulator. This block requires poweroftwo slope and a bias of
zero.
Choose how you specify the output word length and fraction length:
When you select Same as input
,
these characteristics match those of the input to the block.
When you select Same as accumulator
,
these characteristics match those of the accumulator.
When you select Binary point scaling
,
you are able to enter the word length and the fraction length of the
output, in bits.
When you select Slope and bias scaling
,
you are able to enter the word length, in bits, and the slope of the
output. This block requires poweroftwo slope and a bias of zero.
Select this parameter to prevent any fixedpoint scaling you specify in this block mask from being overridden by the autoscaling tool in the FixedPoint Tool.
Port  Supported Data Types 

In 

Out 

[1] 3GPP TS 05.04 V8.4.0 — 3rd Generation Partnership Project; Technical Specification Group GSM/EDGE Radio Access Network; Digital cellular telecommunications system (Phase 2+); Modulation (Release 1999)