# Documentation

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# comm.DQPSKModulator System object

Package: comm

Modulate using DQPSK method

## Description

The DQPSKModulator object modulates using the differential quaternary phase shift keying method. The output is a baseband representation of the modulated signal.

To modulate a signal using differential quaternary phase shift keying:

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

2. Call step to modulate a signal according to the properties of comm.DQPSKModulator. The behavior of step is specific to each object in the toolbox.

 Note:   Starting in R2016b, instead of using the step method to perform the operation defined by the System object™, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

## Construction

H = comm.DQPSKModulator creates a modulator System object, H. This object modulates the input signal using the differential quadrature phase shift keying (DQPSK) method.

H = comm.DQPSKModulator(Name,Value) creates a DQPSK modulator 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.DQPSKModulator(PHASE,Name,Value) creates a DQPSK modulator 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 value. The default is pi/4. This value corresponds to the phase difference between previous and current modulated symbols when the input is zero. BitInput Assume bit inputs Specify whether the input is bits or integers. The default is false. When you set this property to true, the step method input must be a column vector of bit values. The length of this vector is an integer multiple of two. This vector contains bit representations of integers between 0 and 3. When you set this property to false, the step method input must be a column vector of integer symbol values between 0 and 3. SymbolMapping Constellation encoding Specify how the object maps an integer or group of two input 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 input integer m, between $0\le m\le 3$ shifts the output phase. This shift is (PhaseRotation + $2×\pi ×m}{4}$) radians from the previous output phase. The output symbol is exp(j$×$PhaseRotation + j$×$$2×\pi ×m}{4}$)$×$(previously modulated symbol). OutputDataType Data type of output Specify output data type as one of double | single. The default is double.

## Methods

 clone Create DQPSK modulator object with same property values getNumInputs Number of expected inputs to step method getNumOutputs Number of outputs from step method isLocked Locked status for input attributes and nontunable properties release Allow property value and input characteristics changes reset Reset states of DQPSK modulator object step Modulate using DQPSK method

## Examples

expand all

Create a DQPSK modulator and demodulator pair. Create an AWGN channel object having two bits per symbol.

dqpskmod = comm.DQPSKModulator('BitInput',true);
dqpskdemod = comm.DQPSKDemodulator('BitOutput',true);
channel = comm.AWGNChannel('EbNo',6,'BitsPerSymbol',2);

Create an error rate calculator. Set the ComputationDelay property to 1 to account for the one bit transient caused by the differential modulation

errorRate = comm.ErrorRate('ComputationDelay',1);

Main processing loop steps:

• Generate 50 2-bit frames

• 8-DPSK modulate

• Pass through AWGN channel

• 8-DPSK demodulate

• Collect error statistics

for counter = 1:100
txData = randi([0 1],100,1);
modSig = dqpskmod(txData);
rxSig = channel(modSig);
rxData = dqpskdemod(rxSig);
errorStats = errorRate(txData,rxData);
end

Display the error statistics.

ber = errorStats(1)
numErrors = errorStats(2)
numBits = errorStats(3)
ber =

0.0170

numErrors =

170

numBits =

9999

## Algorithms

This object implements the algorithm, inputs, and outputs described on the DQPSK Modulator Baseband block reference page. The object properties correspond to the block parameters.