Demodulate CPFSKmodulated data
CPM, in Digital Baseband sublibrary of Modulation
The CPFSK Demodulator Baseband block demodulates a signal that was modulated using the continuous phase frequency shift keying method. The input to this block is a baseband representation of the modulated signal. The Mary number parameter, M, is the size of the input alphabet. M must have the form 2^{K} for some positive integer K.
This block supports multih Modulation index. See CPM Modulator Baseband for details.
When you set the Output type parameter
to Integer
, then the block produces odd
integers between (M1) and M1.
When you set the Output type parameter
to Bit
, then the block produces groupings
of K bits. Each grouping is called a binary word.
In binary output mode, the block first maps each input symbol
to an intermediate value as in the integer output mode. The block
then maps the odd integer k to the nonnegative integer (k+M1)/2.
Finally, the block maps each nonnegative integer to a binary word,
using a mapping that depends on whether the Symbol set ordering parameter
is set to Binary
or Gray
.
This block accepts a scalarvalued or column vector input signal
with a data type of single
or double
.
In singlerate processing mode, the input and output signals have the same port sample time. The block implicitly implements the rate change by making a size change at the output when compared to the input. The input width must be an integer multiple of the Samples per symbol parameter value, and the input can be a column vector.
When you set Output type to Bit
,
the output width is K times the number of input
symbols.
When you set Output type to Integer
,
the output width is the number of input symbols.
In multirate processing mode, the input and output signals have different port sample times. The input must be a scalar. The output symbol time is the product of the input sample time and the Samples per symbol parameter value.
When you set Output type to Bit
,
the output width equals the number of bits per symbol.
When you set Output type to Integer
,
the output is a scalar.
Internally, this block creates a trellis description of the modulation scheme and uses the Viterbi algorithm. The Traceback depth parameter, D, in this block is the number of trellis branches that the algorithm uses to construct each traceback path. D influences the output delay, which is the number of zero symbols that precede the first meaningful demodulated value in the output.
When you set the Rate options parameter
to Allow multirate processing
, and the
model uses a variablestep solver or a fixedstep solver with the Tasking
Mode parameter set to SingleTasking,
then
the delay consists of D+1 zero symbols.
When you set the Rate options parameter
to Enforce singlerate processing
, then
the delay consists of D zero symbols.
The optimal Traceback depth parameter value is dependent on minimum squared Euclidean distance calculations. Alternatively, a typical value, dependent on the number of states, can be chosen using the "fivetimestheconstraintlength" rule, which corresponds to 5·log2(numStates).
For the definition of the number of states, see CPM Demodulator Baseband Help page.
The size of the alphabet.
Determines whether the output consists of integers or groups of bits.
Determines how the block maps each integer to a group of output
bits. This field is active only when Output type is
set to Bit
.
Specify the modulation index {h_{i}}. The
default is 0.5
. The value of this property must
be a real, nonnegative scalar or column vector.
This block supports multih Modulation index. See CPM Modulator Baseband for details.
The initial phase of the modulated waveform.
The number of input samples that represent each modulated symbol, which must be a positive integer. For more information, see Upsample Signals and Rate Changes in Communications System Toolbox™ User's Guide.
Select the rate processing method for the block.
Enforce singlerate processing
—
When you select this option, the input and output signals have the
same port sample time. The block implements the rate change by making
a size change at the output when compared to the input. The output
width is the number of symbols (which is given by dividing the input
length by the Samples per symbol parameter value
when the Output type parameter is set to Integer
).
Allow multirate processing
—
When you select this option, the input and output signals have different
port sample times. The output period is the same as the symbol period
and equals the product of the input period and the Samples
per symbol parameter value.
Note:
The option 
For more information, see SingleRate Processing and Multirate Processing in the Description section of this page.
The number of trellis branches that the CPFSK Demodulator Baseband block uses to construct each traceback path.
The output data type can be boolean
, int8
, int16
, int32
,
or double
.
Port  Supported Data Types 

Input 

Output 

[1] Anderson, John B., Tor Aulin, and CarlErik Sundberg. Digital Phase Modulation. New York: Plenum Press, 1986.