Demodulate PAMmodulated data
AM, in Digital Baseband sublibrary of Modulation
The MPAM Demodulator Baseband block demodulates a signal that was modulated using Mary pulse amplitude modulation. The input is a baseband representation of the modulated signal.
The signal constellation has M points, where M is the Mary number parameter. M must be an even integer. The block scales the signal constellation based on how you set the Normalization method parameter. For details on the constellation and its scaling, see the reference page for the MPAM Modulator Baseband block.
This block accepts a scalar or column vector input signal. For information about the data types each block port supports, see Supported Data Types.
Note: All values of power assume a nominal impedance of 1 ohm. 
When you set the Output type parameter
to Integer
, the block outputs integer values
between 0
and M1
. M represents
the Mary number block parameter.
When you set the Output type parameter
to Bit
, the block outputs binaryvalued
signals that represent integers. The block represents each integer
using a group of K = log_{2}(M)
bits, where K represents the number of bits per
symbol. The output vector length must be an integer multiple of K.
The Constellation ordering parameter indicates how the block assigns binary words to points of the signal constellation. More details are on the reference page for the MPAM Modulator Baseband block.
The demodulator algorithm maps received input signal constellation values to Mary integer symbol indices between 0 and M1 and then maps these demodulated symbol indices to formatted output values.
The integer symbol index computation is performed by first scaling the real part of the input signal constellation (possibly with noise) by a denormalization factor derived from the Normalization method and related parameters. This denormalized value is added to M1 to translate it into an approximate range between 0 and 2 x (M1) plus noise. The resulting value is then rescaled via a dividebytwo (or, equivalently, a rightshift by one bit for fixedpoint operation) to obtain a range approximately between 0 and M1 (plus noise). The noisy index value is rounded to the nearest integer and clipped, via saturation, to the exact range of [0 M1]. Finally, based on other block parameters, the integer index is mapped to a symbol value that is formatted and cast to the selected Output data type.
The following figures contains signal flow diagrams for floatingpoint
and fixedpoint algorithm operation. The floatingpoint diagrams apply
when the input signal data type is double
or single
.
The fixedpoint diagrams apply when the input signal is a signed fixedpoint
data type. Note that the diagram is simplified when using normalized
constellations (i.e., denormalization factor is 1).
SignalFlow Diagrams with Denormalization Factor Equal to 1
SignalFlow Diagrams with Nonunity Denormalization Factor
The number of points in the signal constellation. It must be an even integer.
Determines whether the output consists of integers or groups
of bits. If this parameter is set to Bit
,
then the Mary number parameter must be 2^{K} for
some positive integer K.
Determines how the block maps each integer to a group of output bits.
Determines how the block scales the signal constellation. Choices
are Min. distance between symbols
, Average
Power
, and Peak Power
.
The distance between two nearest constellation points. This
field appears only when Normalization method is
set to Min. distance between symbols
.
The average power of the symbols in the constellation, referenced
to 1 ohm. This field appears only when Normalization method is
set to Average Power
.
The maximum power of the symbols in the constellation, referenced
to 1 ohm. This field appears only when Normalization method is
set to Peak Power
.
When the parameter is set to 'Inherit via internal
rule'
(default setting), the block will inherit the output
data type from the input port. The output data type will be the same
as the input data type if the input is of type single
or double
.
Otherwise, the output data type will be as if this parameter is set
to 'Smallest unsigned integer'
.
When the parameter is set to 'Smallest unsigned integer'
,
the output data type is selected based on the settings used in the Hardware
Implementation pane of the Configuration Parameters dialog
box of the model. If ASIC/FPGA
is selected in the Hardware
Implementation pane, the output data type is the ideal
minimum size, i.e., ufix(1)
for bit outputs, and ufix(ceil(log2(M)))
for
integer outputs. For all other selections, it is an unsigned integer
with the smallest available word length large enough to fit the ideal
minimum size, usually corresponding to the size of a char (e.g., uint8
).
For integer outputs, this parameter can be set to Smallest
unsigned integer
, int8
, uint8
, int16
, uint16
, int32
, uint32
, single
,
and double
. For bit outputs, the options are Smallest
unsigned integer
, int8
, uint8
, int16
, uint16
, int32
, uint32
, boolean
, single
,
or double
.
This parameter applies when a fixedpoint input is not normalized.
It can be set to Same word length as input
or Specify
word length
, in which case a field is enabled for user input.
A bestprecision fraction length is always used.
This parameter only applies when the input is a fixedpoint
signal and there is a nonunity (not equal to 1) denormalized factor.
It can be set to Inherit via internal rule
or Specify
word length
, which enables a field for user input.
Setting to Inherit via internal rule
computes
the fullprecision product word length and fraction length. Internal
Rule for Product Data Types (DSP System Toolbox) in DSP System Toolbox™ User's
Guide describes the fullprecision Product output internal
rule.
Setting to Specify word length
allows you
to define the word length. The block computes a bestprecision fraction
length based on the word length specified and the precomputed worstcase
(min/max) real world value Product output result.
The worstcase Product output result is precomputed
by multiplying the denormalized factor with the worstcase (min/max)
input signal range, purely based on the input signal data type.
The block uses the Rounding method when the result of a fixedpoint calculation does not map exactly to a number representable by the data type and scaling storing the result. For more information, see Rounding Modes (DSP System Toolbox) in the DSP System Toolbox documentation or Rounding Mode: Simplest (FixedPoint Designer) in the FixedPoint Designer™ documentation.
This parameter only applies when the input is a fixedpoint
signal. It can be set to Inherit via internal rule
, Same
as product output
, or Specify word length
,
in which case a field is enabled for user input
Setting Inherit via internal rule
computes
the fullprecision sum word length and fraction length, based on the
two inputs to the Sum in the fixedpoint Hard Decision Algorithm signal
flow diagram. The rule is the same as the fixedpoint inherit rule
of the internal Accumulator data type parameter
in the Simulink^{®} Sum (Simulink) block.
Setting Specify word length
allows you to
define the word length. A best precision fraction length is computed
based on the word length specified in the precomputed maximum range
necessary for the demodulated algorithm to produce accurate results.
The signed fixedpoint data type that has the best precision fully
contains the values in the range 2 * (M1) for the specified word
length.
Setting to Same as product output
allows
the Sum data type to be the same as the Product output data
type (when Product output is used). If the Product
output is not used, then this setting will be ignored and
the Inherit via internal rule
Sum setting will
be used.
Port  Supported Data Types 

Input 

Output 
