M-PAM Demodulator Baseband

Demodulate M-PAM-modulated data

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Libraries:
Communications Toolbox / Modulation / Digital Baseband Modulation / AM

Description

The M-PAM Demodulator Baseband block demodulates a signal that was modulated using M-ary pulse amplitude modulation.

Note

All values of power assume a nominal impedance of 1 ohm.

Examples

ATSC Digital Television

The vestigial sideband modulation with 8 discrete amplitude levels (8-VSB) transmission subsystem of the Advanced Television Systems Committee (ATSC) digital television standard [ 1 ]. The standard describes the characteristics of the U.S. advanced television system that is designed to transmit high-quality video, audio, and ancillary data within a single 6 MHz terrestrial television broadcast channel.

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Ports

Input

In — M-PAM-modulated signal

scalar | column vector

M-PAM-modulated signal, specified as a scalar or column vector. This port is unnamed on the block.

Data Types: double | single | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point
Complex Number Support: Yes

Output

Out — Demodulated signal

scalar | vector

Demodulated signal, returned as a scalar or vector. The dimensions of the demodulated signal depend on the value you specify for the Output data type parameter. This port is unnamed on the block.

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Main

M-ary number — Modulation order

4 (default) | positive, even integer

Modulation order, specified as a positive, even integer. The modulation order, M, specifies the number of points in the signal constellation. The block scales the signal constellation based on how you set the Normalization method parameter.

Output type — Output type

Integer (default) | Bit

Output type, specified as Integer or Bit. When you set this parameter to Bit, the M-ary number parameter must be 2^K for some positive integer K.

Constellation ordering — Mapping order of symbols

Binary (default) | Gray

Mapping order of the symbols, specified as Gray or Binary. This parameter determines how the block maps each symbol to a group of output bits or an integer.

The Constellation ordering parameter indicates how the block assigns binary words to points of the signal constellation. For more information, see Integer-Valued Signals and Binary-Valued Signals.

Normalization method — Scaling method for the constellation

Min. distance between symbols (default) | Average Power | Peak Power

Scaling method for the constellation, specified as Min. distance between symbols, Average Power, or Peak Power. For more information, see Integer-Valued Signals and Binary-Valued Signals.

Minimum distance — Distance between two nearest constellation points

2 (default) | positive scalar

Distance between the two nearest constellation points, specified as a positive scalar.

Dependencies

This parameter appears when you set Normalization method to Min. distance between symbols.

Average power, referenced to 1 ohm (watts) — Average power

1 (default) | positive scalar

Average power of the symbols in the constellation in watts, specified as a positive scalar. Power values assume a nominal impedance of 1 ohm.

Dependencies

This parameter appears when you set Normalization method to Average Power.

Peak power, referenced to 1 ohm (watts) — Maximum power

1 (default) | positive scalar

Maximum power of the symbols in the constellation in watts, specified as a positive scalar. Power values assume a nominal impedance of 1 ohm.

Dependencies

This parameter appears when you set Normalization method to Peak Power.

Data Types

Output data type — Output data type

Inherit via internal rule (default) | Smallest unsigned integer | double | single | int8 | uint8 | int16 | uint16 | int32 | uint32 | boolean

Output data type, specified as Inherit via internal rule, Smallest unsigned integer, double, single, int8, uint8, int16, uint16, int32, uint32, or boolean.

• When you select Inherit via internal rule, the block inherits the data type based on an internal rule. For more information on this rule, see Inherit via Internal Rule. The output data type is the same as the input data type if the input is of type single or double. Otherwise, the output data type is the same as for 'Smallest unsigned integer'.

• When you select 'Smallest unsigned integer', the block sets the output data type based on the settings in the Hardware Implementation pane of the Configuration Parameters dialog box. If ASIC/FPGA is selected in the Hardware Implementation pane, the output data type is the ideal minimum size, that is, 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 (for example, uint8).

• For integer outputs, you can set this parameter 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.

For information about specifying data types, see Data Type Assistant.

Denormalization factor — Denormalization factor data type

Inherit: Same word length as input (default) | fixdt(1,16) | <data type expression>

Specify the denormalization factor data type as Inherit: Same word length as input, fixdt(1,16), or <data type expression>. This scaling factor is derived from Normalization method and other parameter of the block. The block always uses a best-precision fraction length.

For information about specifying data types, see Data Type Assistant.

Dependencies

This parameter applies only when the input signal is fixed-point and the derived denormalization factor is a nonunity value (not equal to 1).

Product output — Product output data type

Inherit: Inherit via internal rule (default) | fixdt(1,16) | <data type expression>

Specify the product data type as Inherit: Inherit via internal rule, fixdt(1,16), or <data type expression>.

When you select Inherit: Inherit via internal rule, the block computes the full-precision product word length and fraction length. For information about the full-precision Product output internal rule, see Internal Rule for Product Data Types.

The block uses rounding mode when the result of a fixed-point calculation does not map exactly to a number representable by the data type and scaling storing the result. For more information, see Rounding Modes or Rounding Mode: Simplest (Fixed-Point Designer).

For information about specifying data types, see Data Type Assistant.

Dependencies

This parameter applies only when the input is a fixed-point signal and the derived denormalization factor is a nonunity value (not equal to 1).

Rounding mode — Rounding mode for fixed-point operations

Wrap (default) | Saturate

Specify the rounding mode for Product output fixed-point operations as Wrap or Saturate. The block uses rounding mode when the result of a fixed-point calculation does not map exactly to a number representable by the data type. For more information, see Rounding Modes or Rounding Mode: Simplest (Fixed-Point Designer).

Dependencies

This parameter applies for Product output only.

Saturate on integer overflow — Option to saturate on integer overflow

off (default) | on

Select this check box to saturate on integer overflow.

Dependencies

This parameter applies for Product output only.

Sum — Sum data type

Inherit: Inherit via internal rule (default) | Inherit: Same as product output | fixdt(1,16) | <data type expression>

Specify the sum data type as Inherit: Inherit via internal rule, Inherit: Same as product output, fixdt(1,16), or <data type expression>.

• When you select Inherit: Inherit via internal rule, the block computes the full-precision sum word length and fraction length, based on the two inputs to the sum in the flow diagram of the fixed-point Hard Decision Algorithm signal. The rule is the same as the fixed-point inherit rule of the internal Accumulator data type parameter in the Sum (Simulink) block.

• When you select Inherit: Same as product output and Product output applies, the block configures the data type of the Sum parameter to be the same as the Product output data type.

• When you select Inherit: Same as product output and Product output does not apply, then the block ignores this setting and uses the Inherit: Inherit via internal rule and computed sum.

For information about specifying data types, see Data Type Assistant.

Dependencies

This parameter applies only when the input is a fixed-point signal.

Block Characteristics

Data Types	Boolean | double | fixed pointa, b | integer | single
Multidimensional Signals	no
Variable-Size Signals	yes
a Fixed-point inputs must be signed. b When ASIC/FPGA is selected in the Hardware Implementation Pane, output is ufix(1) for bit outputs, and ufix(ceil(log2(M))) for integer outputs.

More About

Data Type Assistant

The Data Type Assistant helps you set data attributes. To use the Data Type Assistant, click . For more information, see Specify Data Types Using Data Type Assistant (Simulink).

Algorithms

Hard Decision M-PAM Demodulation

The demodulator algorithm maps received input signal constellation values to M-ary integer symbol indices in the range [0, M – 1] and then maps these demodulated symbol indices to formatted output values.

The demodulator computes the integer symbol index by first scaling the real part of the received input signal by a denormalization factor derived from the normalization method and related parameters.

1. To translate the received signal into the approximate range of [0, 2(M – 1)] plus noise, add the denormalized value to (M – 1).

2. To obtain a range approximately between [0, M – 1] plus noise, rescale the resulting value via a divide-by-two (or, equivalently, a right-shift by one bit for fixed-point operation).

3. Round the noisy index value to the nearest integer and clip, via saturation, to the exact range of [0 M – 1].

4. Finally, based on other block parameters, map the integer index to a symbol value that is formatted and cast to the selected output data type.

The following figures contain side-by-side signal flow diagrams for floating-point and fixed-point algorithm operation.

• The floating-point diagrams apply when the input signal data type is double or single.

• The fixed-point diagrams apply when the input signal is a signed fixed-point data type.

Separate signal flows show the denormalization factor set to unity or nonunity. Setting the denormalization factor to 1 normalizes the constellation and simplifies the signal flow.

This figure shows the floating-point and fixed-point demodulation signal-flow diagram with a unity denormalization factor.

This figure shows the floating-point and fixed-point demodulation signal-flow diagram with a nonunity denormalization factor.

Integer-Valued Signals and Binary-Valued Signals

When you set the Output type parameter to Integer, the block outputs integer values in the range [0, (M – 1)]. M represents the M-ary number block parameter.

When you set the Output type parameter to Bit, the block outputs binary-valued signals that represent integers. The block represents each integer using a group of K = log₂(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. For more information about the constellation, see the M-PAM Modulator Baseband block.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a