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comm.DQPSKDemodulator System object

Package: comm

Demodulate using DQPSK method

Description

The DQPSKDemodulator object demodulates a signal that was modulated using the differential quaternary phase shift keying method. The input is a baseband representation of the modulated signal.

To demodulate a signal that was modulated using differential quaternary phase shift keying:

  1. Define and set up your DQPSK modulator object. See Construction.

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

Construction

H = comm.DQPSKDemodulator creates a demodulator System object™, H. This object demodulates the input signal using the differential quadrature phase shift keying (DQPSK) method.

H = comm.DQPSKDemodulator(Name,Value) creates a DQPSK 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.DQPSKDemodulator(PHASE,Name,Value) creates a DQPSK demodulator object, H. This object has the PhaseRotation property set to PHASE and the other specified properties set to the specified values.

Properties

PhaseRotation

Additional phase shift

Specify the additional phase difference between previous and current modulated symbols in radians as a real scalar. The default is pi/4. This value corresponds to the phase difference between previous and current modulated symbols when the input is zero.

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 twice the number of demodulated symbols. When you set this property to false, the step method outputs a column vector, of length equal to the input data vector, that contains integer symbol values between 0 and 3.

SymbolMapping

Constellation encoding

Specify how the object maps an integer or group of 2 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 maps to the current symbol as exp(j PhaseRotation + j ) (previously modulated symbol).

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 the output has the same data type as that of the input. In this case, the input data type is single- or double-precision value. When you set the BitOutput property to true, logical data type becomes a valid option.

Methods

cloneCreate DQPSK demodulator object with same property values
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
resetReset states of DQPSK demodulator object
stepDemodulate using DQPSK method

Examples

Modulate and demodulate a signal using DQPSK modulation.

    hMod = comm.DQPSKModulator(pi/8);
    hAWGN = comm.AWGNChannel('NoiseMethod', ...
                         'Signal to noise ratio (SNR)','SNR',15);
    hDemod = comm.DQPSKDemodulator(pi/8);
% Create an error rate calculator, account for the one symbol transient caused by the differential modulation
    hError = comm.ErrorRate('ComputationDelay',1);
    for counter = 1:100
% Transmit a 50-symbol frame
        data = randi([0 3],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 DQPSK Demodulator Baseband block reference page. The object properties correspond to the block parameters.

See Also

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