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comm.OQPSKModulator System object

Package: comm

Modulate using OQPSK method

Description

The OQPSKModulator object modulates using the offset quadrature phase shift keying method. The output is a baseband representation of the modulated signal.

To modulate a signal using offset quadrature phase shift keying:

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

  2. Call step to modulate the signal according to the properties of comm.OQPSKModulator. 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.OQPSKModulator creates a modulator System object, H. This object modulates the input signal using the offset quadrature phase shift keying (OQPSK) method.

H = comm.OQPSKModulator(Name,Value) creates an OQPSK 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.OQPSKModulator(PHASE,Name,Value) creates an OQPSK modulator object, H. This object has the PhaseOffset property set to PHASE and the other specified properties set to the specified values.

Properties

PhaseOffset

Phase of zeroth point of constellation from π4

Specify the phase offset of the zeroth point of the constellation shifted from π4, in radians, as a finite, real-valued scalar. The default is 0.

BitInput

Assume input is bits

Specify whether the input is bits or integers. The default is false. When you set this property to true, the inputs are bit representations of integers between 0 and 3. The input requires a column vector of bit values with length that is an integer multiple of two. When you set this property to false, the input requires a column vector of integer values between 0 and 3.

OutputDataType

Data type of output

Specify the output data type as double | single | Custom. The default is double.

 Fixed-Point Properties

Methods

cloneCreate OQPSK modulator 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
resetReset modulator state
stepModulate using OQPSK method

Examples

expand all

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

oqpskmod = comm.OQPSKModulator('BitInput',true);
oqpskdemod = comm.OQPSKDemodulator('BitOutput',true);
channel = comm.AWGNChannel('EbNo',4,'BitsPerSymbol',2);

Create an error rate calculator. Set the ReceiveDelay property to 2 to account for the delay between the modulator and demodulator.

errorRate = comm.ErrorRate('ReceiveDelay',2);

Main processing loop steps:

  • Generate 50 2-bit frames

  • OQPSK modulate

  • Pass through AWGN channel

  • OQPSK demodulate

  • Collect error statistics

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

Display the error statistics.

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

   4.0008e-04


numErrors =

     4


numBits =

        9998

Algorithms

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

Introduced in R2012a

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