M-PAM Modulator Baseband
Modulate using M-ary pulse amplitude modulation
Library
AM, in Digital Baseband sublibrary of Modulation
Description
The M-PAM Modulator Baseband block modulates using M-ary pulse amplitude modulation. The output is a baseband representation of the modulated signal. The M-ary number parameter, M, is the number of points in the signal constellation. It must be an even integer.
Note
All values of power assume a nominal impedance of 1 ohm.
Constellation Size and Scaling
Baseband M-ary pulse amplitude modulation using the block's default signal constellation maps an integer m between 0 and M-1 to the complex value
2m - M + 1
Note
This value is actually a real number. The block's output signal is a complex data-type signal whose imaginary part is zero.
The block scales the default signal constellation based on how you set the Normalization method parameter. The following table lists the possible scaling conditions.
| Value of Normalization Method Parameter | Scaling Condition |
|---|---|
Min. distance between symbols
| The nearest pair of points in the constellation is separated by the value of the Minimum distance parameter |
Average Power
| The average power of the symbols in the constellation is the Average power parameter |
Peak Power
| The maximum power of the symbols in the constellation is the Peak power parameter |
Integer-Valued Signals and Binary-Valued Signals
This block accepts a scalar or column vector input signal.
When you set the Input type parameter to Integer,
the block accepts integer values between 0 and M-1. M represents
the M-ary number block parameter.
When you set the Input type parameter to Bit,
the block accepts binary-valued inputs that represent integers. The
block collects binary-valued signals into groups of K =
log2(M) bits
where
K represents the number of bits per symbol.
The input vector length must be an integer multiple of K. In this configuration, the block accepts a group of K bits and maps that group onto a symbol at the block output. The block outputs one modulated symbol for each group of K bits.
The Constellation ordering parameter indicates how the block assigns binary words to points of the signal constellation.
If Constellation ordering is set to
Binary, then the block uses a natural binary-coded constellation.If Constellation ordering is set to
Gray, then the block uses a Gray-coded constellation.For details about the Gray coding, see the reference page for the M-PSK Modulator Baseband block.
Constellation Visualization
The M-PAM Modulator Baseband block provides the capability to visualize a signal constellation from the block mask. This Constellation Visualization feature allows you to visualize a signal constellation for specific block parameters. For more information, see the Constellation Visualization section of the Communications Toolbox™ User's Guide.
Parameters
- M-ary number
The number of points in the signal constellation. It must be an even integer.
- Input type
Indicates whether the input consists of integers or groups of bits. If this parameter is set to
Bit, then the M-ary number parameter must be 2K for some positive integer K.- Constellation ordering
Determines how the block maps each group of input bits to a corresponding integer.
- Normalization method
Determines how the block scales the signal constellation. Choices are
Min. distance between symbols,Average Power, andPeak Power.- Minimum distance
The distance between two nearest constellation points. This field appears only when Normalization method is set to
Min. distance between symbols.- Average power, referenced to 1 ohm (watts)
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.- Peak power, referenced to 1 ohm (watts)
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.- Output data type
The output data type can be set to
double,single,Fixed-point,User-defined, orInherit via back propagation.Setting this parameter to
Fixed-pointorUser-definedenables fields in which you can further specify details. Setting this parameter toInherit via back propagation, sets the output data type and scaling to match the following block.- Output word length
Specify the word length, in bits, of the fixed-point output data type. This parameter is only visible when you select
Fixed-pointfor the Output data type parameter.- User-defined data type
Specify any signed built-in or signed fixed-point data type. You can specify fixed-point data types using the
sfix(Simulink),sint(Simulink),sfrac(Simulink), andfixdt(Simulink) functions from Fixed-Point Designer™ software. This parameter is only visible when you selectUser-definedfor the Output data type parameter.- Set output fraction length to
Specify the scaling of the fixed-point output by either of the following methods:
Choose
Best precisionto have the output scaling automatically set such that the output signal has the best possible precision.Choose
User-definedto specify the output scaling in the Output fraction length parameter.
This parameter is only visible when you select
Fixed-pointfor the Output data type parameter or when you selectUser-definedand the specified output data type is a fixed-point data type.- Output fraction length
For fixed-point output data types, specify the number of fractional bits, or bits to the right of the binary point. This parameter is only visible when you select
Fixed-pointorUser-definedfor the Output data type parameter andUser-definedfor the Set output fraction length to parameter.
Supported Data Types
| Port | Supported Data Types |
|---|---|
Input |
|
Output |
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