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comm.PAMDemodulator System object

Package: comm

Demodulate using M-ary PAM method

Description

The PAMDemodulator object demodulates a signal that was modulated using M-ary pulse amplitude modulation. The input is a baseband representation of the modulated signal.

To demodulate a signal that was modulated using M-ary pulse amplitude modulation:

  1. Define and set up your PAM demodulator object. See Construction.

  2. Call step to demodulate the signal according to the properties of comm.PAMDemodulator. The behavior of step is specific to each object in the toolbox.

Construction

H = comm.PAMDemodulator creates a demodulator System object™, H. This object demodulates the input signal using the M-ary pulse amplitude modulation (M-PAM) method.

H = comm.PAMDemodulator(Name,Value) creates an M-PAM demodulator object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

H = comm.PAMDemodulator(M,Name,Value) creates an M-PAM demodulator object, H. This object has the ModulationOrder property set to M, and the other specified properties set to the specified values.

Properties

ModulationOrder

Number of points in signal constellation

Specify the number of points in the signal constellation as a positive, integer scalar value. The default is 4. When you set the BitOutput property to false, this value must be even. When you set the BitOutput property to true, this value requires an integer power of two.

BitOutput

Output data as bits

Specify whether the output consists of groups of bits or integer symbol values. The default is false.

When you set this property to true the step method outputs a column vector of bit values with length equal to log2(ModulationOrder) times the number of demodulated symbols.

When you set this property to false, the step method outputs a column vector, with length equal to the input data vector. This value contains integer symbol values between 0 and ModulationOrder–1.

SymbolMapping

Constellation encoding

Specify how the object maps an integer or group of log2(ModulationOrder) bits to the corresponding symbol as one of Binary | Gray. The default is Gray.

When you set this property to Gray, the object uses a Gray-encoded signal constellation.

When you set this property to Binary, the integer m, between (ModulationOrder–1) maps to the complex value 2m-ModulationOrder+1.

NormalizationMethod

Constellation normalization method

Specify the method used to normalize the signal constellation as one of Minimum distance between symbols | Average power | Peak power. The default is Minimum distance between symbols.

MinimumDistance

Minimum distance between symbols

Specify the distance between two nearest constellation points as a positive, real, numeric scalar value. The default is 2. This property applies when you set the NormalizationMethod property to Minimum distance between symbols.

AveragePower

Average power of constellation

Specify the average power of the symbols in the constellation as a positive, real, numeric scalar value. The default is 1. This property applies when you set the NormalizationMethod property to Average power.

PeakPower

Peak power of constellation

Specify the maximum power of the symbols in the constellation as a positive, real, numeric scalar value. The default is 1. This property applies when you set the NormalizationMethod property to Peak power.

OutputDataType

Data type of output

Specify the output data type as one of Full precision | Smallest unsigned integer | double | single | int8 | uint8 | int16 | uint16 | int32 | uint32. The default is Full precision.

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 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

Methods

cloneCreate M-PAM demodulator object with same property values
constellationCalculate or plot ideal signal constellation
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs from step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
stepDemodulate using M-ary PAM method

Examples

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 = step(hMod, data);
      noisySignal = step(hAWGN, modSignal);
      receivedData = step(hDemod, noisySignal);
      errorStats = step(hError, data, receivedData);
    end
    fprintf('Error rate = %f\nNumber of errors = %d\n', ...
      errorStats(1), errorStats(2))

Algorithms

This object implements the algorithm, inputs, and outputs described on the M-PAM Demodulator Baseband block reference page. The object properties correspond to the block parameters.

See Also

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