comm.OQPSKDemodulator System object

Package: comm

Demodulate using OQPSK method

Description

The `OQPSKDemodulator` object demodulates a signal that was modulated using the offset quadrature phase shift keying method. The input is a baseband representation of the modulated signal.

To demodulate a signal that was modulated using offset quadrature phase shift keying:

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

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

Construction

`H = comm.OQPSKDemodulator` creates a demodulator System object™, `H`. This object demodulates the input signal using the offset quadrature phase shift keying (OQPSK) method.

`H = comm.OQPSKDemodulator(Name,Value)` creates an OQPSK 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.OQPSKDemodulator(PHASE,Name,Value)` creates an OQPSK demodulator 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 $\pi }{4}$ Specify the phase offset of the zeroth point of the constellation shifted from $\pi }{4}$, in radians, as a finite, real-valued scalar. The default is `0`. `BitOutput` Output data as bits Specify whether the output consists of groups of bits or integer values. The default is `false`. When you set this property to `true` the `step` method outputs a column vector of bit values. The vector length must equal to twice the number of demodulated symbols. When you set this property to `false`, the `step` method outputs a column vector. The length of this vector equals to the number of demodulated symbols that contain integer values between `0` and `3`. The object produces one output demodulated symbol for each pair of input samples. `OutputDataType` Data type of output Specify output data type as `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 `step` method output inherits the data type from the input. When the input is of `single` or `double` data, the `step` method outputs the same data type as the input. When the input data is of a fixed-point type, then the `step` method outputs the same data type as if you set the `OutputDataType` property to `Smallest unsigned integer`. When you set the `BitOutput` property to `true`, the `logical` data type becomes a valid option. 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.

Methods

 clone Create OQPSK demodulator object with same property values constellation Calculate or plot ideal signal constellation 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 demodulator state step Demodulate using OQPSK method

Examples

Modulate and demodulate a signal using OQPSK modulation with a constellation with pi/8 radians of phase offset.

``` hMod = comm.OQPSKModulator(pi/8); hAWGN = comm.AWGNChannel('NoiseMethod', ... 'Signal to noise ratio (SNR)','SNR',6); hDemod = comm.OQPSKDemodulator(pi/8); % Create an error rate calculator, account for the one symbol delay hError = comm.ErrorRate('ReceiveDelay',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 OQPSK Demodulator Baseband block reference page. The object properties correspond to the block parameters.