Pulse-shaping filter specification object
D = fdesign.pulseshaping
D = fdesign.pulseshaping(sps)
D = fdesign.pulseshaping(sps,shape)
d = fdesign.pulseshaping(sps,shape,spec,value1,value2,...)
d = fdesign.pulseshaping
(...,fs)
d = fdesign.
(...,magunits)pulseshaping
Note:
The use of |
D = fdesign.pulseshaping
constructs a specification
object D
, which can be used to design a minimum-order
raised cosine filter object with a default stop band attenuation of
60dB and a rolloff factor of 0.25.
D = fdesign.pulseshaping(sps)
constructs
a minimum-order raised cosine filter specification object d
with
a positive integer-valued oversampling factor, SamplesPerSymbol
.
D = fdesign.pulseshaping(sps,shape)
constructs d
where shape
specifies
the PulseShape
property. Valid entries for shape
are:
'Raised Cosine'
'Square Root Raised Cosine'
'Gaussian'
d = fdesign.pulseshaping(sps,shape,spec,value1,value2,...)
constructs d
where spec
defines
the Specification
properties. The entries for spec
specify
various properties of the filter, including the order and frequency
response. Valid entries for spec
depend upon the shape
property.
For 'Raised Cosine'
and 'Square Root Raised
Cosine'
filters, the valid entries for spec
are:
'Ast,Beta'
(minimum order; default)
'Nsym,Beta'
'N,Beta'
The filter specifications are defined as follows:
Ast
—stopband attenuation
(in dB). The default stopband attenuation for a raised cosine filter
is 60 dB. The default stopband attenuation for a square root raised
cosine filter is 30 dB. If Ast
is specified, the
minimum-order filter is returned.
Beta
—rolloff factor expressed
as a real-valued scalar ranging from 0 to 1. Smaller rolloff factors
result in steeper transitions between the passband and stopband of
the filter.
Nsym
—filter order in symbols.
The length of the impulse response is given by Nsym*SamplesPerSymbol+1
.
The product Nsym*SamplesPerSymbol
must be even.
N
—filter order (must be
even). The length of the impulse response is N+1
.
If the shape
property is specified as 'Gaussian'
,
the valid entries for spec
are:
'Nsym,BT'
(default)
The filter specifications are defined as follows:
Nsym
—filter order in symbols. Nsym
defaults
to 6. The length of the filter impulse response is Nsym*SamplesPerSymbol+1
.
The product Nsym*SamplesPerSymbol
must be even.
BT
—the 3–dB bandwidth-symbol
time product. BT
is a positive real-valued scalar,
which defaults to 0.3. Larger values of BT
produce
a narrower pulse width in time with poorer concentration of energy
in the frequency domain.
d = fdesign.
specifies
the sampling frequency of the signal to be filtered. pulseshaping
(...,fs)fs
must
be specified as a scalar trailing the other numerical values provided.
For this case, fs
is assumed to be in Hz and is
used for analysis and visualization.
d = fdesign.
specifies
the units for any magnitude specification you provide in the input
arguments. Valid entries for
(...,magunits)pulseshaping
magunits
are:
linear
— specify the magnitude
in linear units
dB
— specify the magnitude
in dB (decibels)
squared
— specify the magnitude
in power units
When you omit the magunits
argument, fdesign
assumes
that all magnitudes are in decibels. Note that fdesign
stores
all magnitude specifications in decibels (converting to decibels when
necessary) regardless of how you specify the magnitudes.
After creating the specification object d
,
you can use the design
function
to create a filter object such as h
in the following
example:
d = fdesign.pulseshaping(8,'Raised Cosine','Nsym,Beta',6,0.25); h = design(d);
Normally, the Specification
property of the
specification object also determines which design methods you can
use when you create the filter object. Currently, regardless of the Specification
property,
the design
function uses the window
design method with all fdesign.pulseshaping
specification
objects. The window
method creates an FIR filter
with a windowed impulse response.
Pulse-shaping can be used to change the waveform of transmitted pulses so the signal bandwidth matches that of the communication channel. This helps to reduce distortion and intersymbol interference (ISI).
This example shows how to design a minimum-order raised cosine filter that provides a stop band attenuation of 60 dB, rolloff factor of 0.50, and 8 samples per symbol.
h = fdesign.pulseshaping(8,'Raised Cosine','Ast,Beta',60,0.50); Hd = design(h); fvtool(Hd)
This code generates the following figure.
This example shows how to design a raised cosine filter that spans 8 symbol durations (i.e., of order 8 symbols), has a rolloff factor of 0.50, and oversampling factor of 10.
h = fdesign.pulseshaping(10,'Raised Cosine','Nsym,Beta',8,0.50); Hd = design(h); fvtool(Hd, 'impulse')
This example shows how to design a square root raised cosine filter of order 42, rolloff factor of 0.25, and 10 samples per symbol.
h = fdesign.pulseshaping(10,'Square Root Raised Cosine','N,Beta',42); Hd = design(h); fvtool(Hd, 'impulse')
The following example demonstrates how to create a Gaussian pulse-shaping filter with an oversampling factor (sps) of 10, a bandwidth-time symbol product of 0.2, and 8 symbol periods. The sampling frequency is specified as 10 kHz.