comm.PAMDemodulator

(Not recommended) Demodulate using M-ary pulse amplitude demodulation

comm.PAMDemodulator is not recommended. Use pamdemod instead. For more information, see Version History.

Description

The comm.PAMDemodulator System object™ demodulates a signal that was modulated using M-ary pulse amplitude modulation (M-PAM) method. The input is a baseband representation of the modulated signal.

To demodulate a signal that was modulated using M-PAM method:

Create the comm.PAMDemodulator object and set its properties.
Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

pamdemodulator = comm.PAMDemodulator

pamdemodulator = comm.PAMDemodulator(Name=Value)

pamdemodulator = comm.PAMDemodulator(M,Name=Value)

Description

pamdemodulator = comm.PAMDemodulator creates a demodulator System object that demodulates the input signal using the M-PAM method.

pamdemodulator = comm.PAMDemodulator(Name=Value) sets Properties using one or more name-value arguments. For example, ModulationOrder=2 sets the number of points in the signal constellation to 2.

pamdemodulator = comm.PAMDemodulator(M,Name=Value) sets the ModulationOrder property by using M input argument.

Input Arguments

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`M` — Modulation order
positive even integer

Modulation order, specified as an positive even integer. M represents the number of points in signal constellation.

Data Types: double

Properties

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Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

General Properties

`ModulationOrder` — Number of points in signal constellation
`4` (default) | positive even integer

Number of points in the signal constellation, specified as one of these options.

When you set the BitOutput property to false, ModulationOrder must be positive even integer.
When you set the BitOutput property to true, ModulationOrder must be an integer power of two.

The comm.PAMDemodulatorSystem object scales the signal constellation based on how you set the NormalizationMethod property.

`BitOutput` — Bit output
`0` (`false`) (default) | `1` (`true`)

Bit output, specified as a numeric or logical 0 (false) or 1 (true).

1(true) — Use this option to set the object output, Y, to a column vector of bit values that represents integers. The binary-valued signals are grouped in K = log₂(M) bits, where K is the number of bits per symbol and M is the modulation order. The output vector length must be an integer multiple of K.
0 (false) — Use this option to set the object output, Y, to a column vector with length equal to the input vector, X. This value contains integer symbol values in the range [0, M - 1]. M is the modulation order.

Data Types: logical

`SymbolMapping` — Constellation encoding
`"Gray"` (default) | `"Binary"`

Constellation encoding, specified as "Gray" or "Binary".

Symbol mapping specifies how the object maps an integer or group of log₂(ModulationOrder) input bits to the corresponding symbol.

When you set this property to "Gray", the object uses a Gray-encoded signal constellation.
When you set this property to "Binary", the input integer m maps to the complex value 2m – M + 1. M is the property ModulationOrder value and m lies in the range [0, (M – 1)].

`NormalizationMethod` — Constellation normalization method
`"Minimum distance between symbols"` (default) | `"Average power"` | `"Peak power"`

Constellation normalization method used to normalize the signal constellation, specified as "Minimum distance between symbols", "Average power", or "Peak power".

`MinimumDistance` — Minimum distance between two symbols
`2` (default) | positive scalar

Minimum distance between two symbols, specified as a positive scalar.

Dependencies

To enable this property, set the NormalizationMethod property is set to "Minimum distance between symbols".

Data Types: double

`AveragePower` — Average power of symbols in constellation
`1` (default) | positive scalar

Average power of the symbols in the constellation, specified as a positive scalar.

Dependencies

To enable this property, set the NormalizationMethod property is set to "Average power".

Data Types: double

`PeakPower` — Peak power of symbols in constellation
`1` (default) | positive scalar

Peak power of the symbols in the constellation, specified as a positive scalar.

Dependencies

To enable this property, set the NormalizationMethod property is set to "Peak power".

Data Types: double

`OutputDataType` — Data type of output
`"Full precision"` (default) | `"Smallest unsigned integer"` | `"double"` | `"single"` | `"int8"` | `"uint8"` | `"int16"` | `"uint16"` | `"int32"` | `"uint32"` | `"logical"`

Data type of output, specified as either "Full precision", "Smallest unsigned integer", "double", "single", "int8", "uint8", "int16", "uint16", "int32", "uint32", or "logical".

When you set this property to "Full precision", and the input data type is single or double precision, the output data has the same data type as that of the input.
When the input signal is an integer data type, you must have a Fixed-Point Designer™ user license to use this property in "Smallest unsigned integer" or "Full precision" mode.
When the input data is of a fixed-point type, the output data type behaves as if you had set the OutputDataType property to "Smallest unsigned integer".
When you set the BitOutput property to true, then "logical" data type becomes a valid option.

Fixed-Point Properties

`FullPrecisionOverride` — Full precision override for fixed-point arithmetic
`1` (`true`) (default) | `0`(`false`)

Full precision override for fixed-point arithmetic, specified as a numeric or logical 0 (false) or 1 (true).

When you set this property to true, the object computes all internal arithmetic and output data types using full precision rules. These rules provide the most accurate fixed-point numerics. It also turns off the display of other fixed-point properties because they do not apply individually. These rules guarantee that no quantization occurs within the object. Bits are added, as needed, to ensure that no roundoff or overflow occurs.
When you set this property to false, fixed-point data types are controlled through individual fixed-point property settings.

For more information, see Full Precision for Fixed-Point System Objects.

Data Types: logical

`DenormalizationFactorDataType` — Data type of denormalization factor
`"Same word length as input"` (default) | `"Custom"`

Data type of denormalization factor, specified as "Same word length as input" or "Custom".

`CustomDenormalizationFactorDataType` — Fixed-point data type of denormalization factor
`numerictype([],16)` (default) | `numerictype` function

Fixed-point data type of denormalization factor, specified as an unscaled numerictype (Fixed-Point Designer) function with the Signedness name-value argument set to "Auto".

Dependencies

To enable this property, set the DenormalizationFactorDataType property to "Custom".

`ProductDataType` — Product data type
`"Full precision"` (default) | `"Custom"`

Product data type, specified as "Full precision" or "Custom". When you set this property to "Full precision" the comm.PAMDemodulator calculates the full-precision product word and fraction lengths.

Dependencies

To enable this property, set the FullPrecisionOverride property to false.

`CustomProductDataType` — Fixed-point data type of product
`numerictype([],32)` (default) | `numerictype` function

Fixed-point data type of the product, specified as an unscaled numerictype (Fixed-Point Designer) function with the Signedness name-value argument set to "Auto".

Dependencies

To enable this property, set the FullPrecisionOverride property to false and the ProductDataType property to "Custom".

`ProductRoundingMethod` — Rounding of fixed-point numeric value of product
`"Floor"` (default) | `"Ceiling"` | `"Convergent"` | `"Nearest"` | `"Round"` | `"Simplest"` | `"Zero"`

Rounding of fixed-point numeric value of the product, specified as either "Ceiling", "Convergent", "Floor", "Nearest", "Round", "Simplest", or "Zero".

This property applies when the object is not in a full precision configuration

`ProductOverflowAction` — Product overflow action
`"Wrap"` (default) | `"Saturate"`

Product overflow action when fixed-point numeric value of product overflows, specified as "Wrap" or "Saturate".

This property applies when the object is not in a full precision configuration.

`SumDataType` — Data type of sum
`"Full precision"` (default) | `"Same as product"` | `"Custom"`

Data type of sum, specified as one either "Full precision", "Same as product", or "Custom". When you set this property to "Full precision", the object calculates the full-precision sum word and fraction lengths.

Dependencies

To enable this property, set the FullPrecisionOverride property to false.

`CustomSumDataType` — Fixed-point data type of sum
`numerictype([],32)` (default) | `numerictype` function

Fixed-point data type of sum, specified as an unscaled numerictype (Fixed-Point Designer) function with the Signedness name-value argument set to "Auto".

Dependencies

To enable this property, set the FullPrecisionOverride property to false and SumDataType property to "Custom".

Usage

Syntax

Y = comm.PAMDemodulator(X)

Description

Y = comm.PAMDemodulator(X) demodulates the input data using the M-PAM demodulator System object. The output is the demodulated data.

example

Input Arguments

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`X` — M-PAM modulated baseband signal
scalar | column vector

M-PAM modulated baseband signal, specified as a scalar or column vector.

Data Types: single | double | int8 | int16 | int32 | int64 | signed fi
Complex Number Support: Yes

Output Arguments

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`Y` — Demodulated data
scalar | column vector

Demodulated data, returned as a scalar or column vector.

Depending on the BitOutput property value, Y can be integer or bit-valued. The dimensions of the demodulated signal depend on the value that you specify for the OutputDataType property.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

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Specific to `comm.PAMDemodulator`

constellation Calculate or plot ideal signal constellation

Common to All System Objects

`step`	Run System object algorithm
`release`	Release resources and allow changes to System object property values and input characteristics
`clone`	Create duplicate System object
`isLocked`	Determine if System object is in use

Examples

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Apply 16-PAM

Modulate and demodulate a signal using 16-PAM modulation.

hMod = comm.PAMModulator(16);
hAWGN = comm.AWGNChannel("NoiseMethod", ...
    "Signal to noise ratio (SNR)", ...
    SNR=20, SignalPower=85);
hDemod = comm.PAMDemodulator(16);
% Create an error rate calculator
hError = comm.ErrorRate;
for counter = 1:100
    % Transmit a 50-symbol frame
    data = randi([0 hMod.ModulationOrder-1],50,1);
    modSignal = hMod(data);
    noisySignal = hAWGN(modSignal);
    receivedData = hDemod(noisySignal);
    errorStats = hError(data,receivedData);
end
fprintf('Error rate = %f\nNumber of errors = %d\n', ...
    errorStats(1), errorStats(2))

Error rate = 0.112600
Number of errors = 563

Algorithms

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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.

To translate the received signal into the approximate range of [0, 2(M – 1)] plus noise, add the denormalized value to (M – 1).
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).
Round the noisy index value to the nearest integer and clip, via saturation, to the exact range of [0 M – 1].
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.

These 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 are shown for 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 unity denormalization factor.

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

Full Precision for Fixed-Point System Objects

FullPrecisionOverride is a convenience property that, when you set it to true, automatically sets the appropriate properties for an object to use full-precision to process fixed-point input.

For System objects, full precision, fixed-point operation refers to growing just enough additional bits to compute the ideal full-precision result. This operation has no minimum or maximum range overflow nor any precision loss due to rounding or underflow. It is also independent of any hardware-specific settings. The data types chosen are based only on known data type ranges and not on actual numeric values. Full-precision for System objects does not optimize coefficient values. When you set the FullPrecisionOverride property to true, the other fixed-point properties it controls no longer apply and any of their nondefault values are ignored. These properties are also hidden. To specify individual fixed-point properties, first set FullPrecisionOverride to false.

Extended Capabilities

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

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2012a

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R2018b: Not recommended

comm.PAMDEmodulator is not recommended. Use pamdemod instead.

n = 10000;              % Number of symbols to process
M = 8;                  % Modulation order
x = randi([0 M-1],n,1); % Create message signal

%% Using PAM modulation and demodulation system objects
pammodObj = comm.PAMModulator(M);
pamdemodObj = comm.PAMDemodulator(M);
yOld = pammodObj(x);    % Modulate
% ... channel filtering ...
zOld = pamdemodObj(complex(yOld)); % Demodulate

%% Using PAM modulation and demodulation functions
yNew = pammod(x,M);     % Modulate
% ... channel filtering ...
zNew = pamdemod(y,M);   % Demodulate
isequal(zOld,zNew)

comm.PAMDemodulator

Description

Creation

Syntax

Description

Input Arguments

M — Modulation order positive even integer

Properties

General Properties

ModulationOrder — Number of points in signal constellation 4 (default) | positive even integer

BitOutput — Bit output 0 (false) (default) | 1 (true)

SymbolMapping — Constellation encoding "Gray" (default) | "Binary"

NormalizationMethod — Constellation normalization method "Minimum distance between symbols" (default) | "Average power" | "Peak power"

MinimumDistance — Minimum distance between two symbols 2 (default) | positive scalar

Dependencies

AveragePower — Average power of symbols in constellation 1 (default) | positive scalar

Dependencies

PeakPower — Peak power of symbols in constellation 1 (default) | positive scalar

Dependencies

OutputDataType — Data type of output "Full precision" (default) | "Smallest unsigned integer" | "double" | "single" | "int8" | "uint8" | "int16" | "uint16" | "int32" | "uint32" | "logical"

Fixed-Point Properties

FullPrecisionOverride — Full precision override for fixed-point arithmetic 1 (true) (default) | 0(false)

DenormalizationFactorDataType — Data type of denormalization factor "Same word length as input" (default) | "Custom"

CustomDenormalizationFactorDataType — Fixed-point data type of denormalization factor numerictype([],16) (default) | numerictype function

Dependencies

ProductDataType — Product data type "Full precision" (default) | "Custom"

Dependencies

CustomProductDataType — Fixed-point data type of product numerictype([],32) (default) | numerictype function

Dependencies

ProductRoundingMethod — Rounding of fixed-point numeric value of product "Floor" (default) | "Ceiling" | "Convergent" | "Nearest" | "Round" | "Simplest" | "Zero"

ProductOverflowAction — Product overflow action "Wrap" (default) | "Saturate"

SumDataType — Data type of sum "Full precision" (default) | "Same as product" | "Custom"

Dependencies

CustomSumDataType — Fixed-point data type of sum numerictype([],32) (default) | numerictype function

Dependencies

Usage

Syntax

Description

Input Arguments

X — M-PAM modulated baseband signal scalar | column vector

Output Arguments

Y — Demodulated data scalar | column vector

Object Functions

Specific to comm.PAMDemodulator

Common to All System Objects

Examples

Apply 16-PAM

Algorithms

Hard Decision M-PAM Demodulation

Full Precision for Fixed-Point System Objects

Extended Capabilities

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

Version History

R2018b: Not recommended

See Also

`M` — Modulation order
positive even integer

`ModulationOrder` — Number of points in signal constellation
`4` (default) | positive even integer

`BitOutput` — Bit output
`0` (`false`) (default) | `1` (`true`)

`SymbolMapping` — Constellation encoding
`"Gray"` (default) | `"Binary"`

`NormalizationMethod` — Constellation normalization method
`"Minimum distance between symbols"` (default) | `"Average power"` | `"Peak power"`

`MinimumDistance` — Minimum distance between two symbols
`2` (default) | positive scalar

`AveragePower` — Average power of symbols in constellation
`1` (default) | positive scalar

`PeakPower` — Peak power of symbols in constellation
`1` (default) | positive scalar

`OutputDataType` — Data type of output
`"Full precision"` (default) | `"Smallest unsigned integer"` | `"double"` | `"single"` | `"int8"` | `"uint8"` | `"int16"` | `"uint16"` | `"int32"` | `"uint32"` | `"logical"`

`FullPrecisionOverride` — Full precision override for fixed-point arithmetic
`1` (`true`) (default) | `0`(`false`)

`DenormalizationFactorDataType` — Data type of denormalization factor
`"Same word length as input"` (default) | `"Custom"`

`CustomDenormalizationFactorDataType` — Fixed-point data type of denormalization factor
`numerictype([],16)` (default) | `numerictype` function

`ProductDataType` — Product data type
`"Full precision"` (default) | `"Custom"`

`CustomProductDataType` — Fixed-point data type of product
`numerictype([],32)` (default) | `numerictype` function

`ProductRoundingMethod` — Rounding of fixed-point numeric value of product
`"Floor"` (default) | `"Ceiling"` | `"Convergent"` | `"Nearest"` | `"Round"` | `"Simplest"` | `"Zero"`

`ProductOverflowAction` — Product overflow action
`"Wrap"` (default) | `"Saturate"`

`SumDataType` — Data type of sum
`"Full precision"` (default) | `"Same as product"` | `"Custom"`

`CustomSumDataType` — Fixed-point data type of sum
`numerictype([],32)` (default) | `numerictype` function

`X` — M-PAM modulated baseband signal
scalar | column vector

`Y` — Demodulated data
scalar | column vector

Specific to `comm.PAMDemodulator`

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