comm.PAMModulator

(Not recommended) Modulate using M-ary pulse amplitude modulation

comm.PAMModulator is not recommended. Use pammod instead. For more information, see Version History.

Description

The comm.PAMModulator System object™ modulates a signal by using M-ary pulse amplitude modulation (PAM) method. The output is a baseband representation of the modulated signal.

To modulate a signal using M-ary pulse amplitude modulation:

1. Create the comm.PAMModulator object and set its properties.

2. 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

pammodulator = comm.PAMModulator

pammodulator = comm.PAMModulator(Name=Value)

pammodulator = comm.PAMModulator(M,Name=Value)

Description

pammodulator = comm.PAMModulator creates a modulator System object that modulates the input signal using M-PAM method.

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

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

Input Arguments

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

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 BitInput property to false, ModulationOrder must be positive even integer.

• When you set the BitInput property to true, ModulationOrder must be an integer power of two.

The comm.PAMModulatorSystem object scales the signal constellation based on how you set the NormalizationMethod property. For more information, see Constellation Size and Scaling.

BitInput — Bit input

0 (false) (default) | 1 (true)

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

• 1(true) — Use this option to specify the object input, x, as a column vector of bit values that represent integers. These 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.

• 0 (false) — Use this option to specify the object input, x, as a column vector of 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 one of these options."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". For more information, see Constellation Size and Scaling.

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

"double" (default) | "single" | "Custom"

Data type of output, specified as "double", "single", or "Custom".

Fixed-Point Properties

CustomOutputDataType — Fixed-point data type of output

numerictype([],16) (default) | numerictype function

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

Dependencies

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

Usage

Syntax

Y = pammodulator(X)

Description

Y = pammodulator(X) modulates the input signal using M-PAM method. The output is the baseband modulated signal.

Input Arguments

X — Input signal

scalar | column vector

Input signal, specified as a scalar or column vector.

Depending on the value of the BitInput property, input X can be an integer or bit-valued column vector with numeric, logical, or fixed-point data types.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | logical | fi

Output Arguments

Y — Modulated baseband signal

scalar | column vector

Modulated baseband signal, returned as a scalar or column vector. Use the OutputDataType property to specify the output data type.

Data Types: single | double | fi
Complex Number Support: Yes

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)

Specific to comm.PAMModulator

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

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

Constellation Size and Scaling

The System object outputs the real-valued constellation symbols as a complex signal with the imaginary part equal to zero. Constellation symbols map an integer m in the range [0, (M – 1)] to the complex value 2m – M + 1.

The comm.PAMModulator scales the default signal constellation based on how you set the NormalizationMethod property. This table lists the possible scaling conditions.

Value of Normalization Method Property	Scaling Condition
"Min. distance between symbols"	The nearest pair of points in the constellation is separated by the value of the "Min. distance between symbols" property.
"Average Power"	The average power of the symbols in the constellation is the"Average Power" property.
"Peak Power"	The maximum power of the symbols in the constellation is the "Peak Power" property.

The SymbolMapping property specifies whether the System object assigns signal constellation points using binary-coded or Gray-coded mapping. For details about Gray coding and symbol mapping, see Digital Baseband Modulation.

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

R2018b: Not recommended

comm.PAMModulator is not recommended. Use pammod 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)