Communications Toolbox™

modem.oqpskmod - Construct OQPSK modulator object

Syntax

h = modem.oqpskmod(property1, value1, ...) h = modem.oqpskmod(OQPSKdemod_object) h = modem.oqpskmod(OQPSKdemod_object, property1, value1, ...) h = modem.oqpskmod

Description

The modem.oqpskmod function creates a modulator object that you can use with the modulate method to modulate a signal. To learn more about the process for modulating a signal, see Using Modem Objects.

h = modem.oqpskmod(property1, value1, ...) constructs an OQPSK modulator object h with properties as specified by the property/value pairs.

h = modem.oqpskmod(OQPSKdemod_object) constructs an OQPSK modulator object h by reading the property values from the OQPSK demodulator object, OQPSKdemod_object. The properties that are unique to the OQPSK modulator object are set to default values.

h = modem.oqpskmod(OQPSKdemod_object, property1, value1, ...) constructs an OQPSK modulator object h by reading the property values from the OQPSK demodulator object, OQPSKdemod_object. Additional properties are specified using property/value pairs.

h = modem.oqpskmod constructs an OQPSK modulator object h with default properties. This syntax is equivalent to:

h = modem.oqpskmod('PhaseOffset', 0, 'SymbolOrder', ...
  'binary', 'InputType', 'integer')

Note OQPSK modulators upsample by 2.

Modem Modulation Method

This object has a method modulate that is used to modulate signals.

The syntax is y = modulate(h, x), where h is the handle to a modulator object and x is a signal. This syntax outputs the baseband signal y.

x can be a multichannel signal. The columns of x are considered individual channels, while the rows are time steps.

When mapping input bits to symbols, the first bit is interpreted as the most significant bit.

For h.inputtype = ‘bit' (i.e., x represents binary input), nBits consecutive elements in each channel or column represent a symbol, where nBits = log₂(h.M). The number of elements in each channel must be an integer multiple of nBits, and elements of x must be 0 or 1. For an input x of size , an output y of size is computed.

For h.inputtype = ‘integer' (i.e., x represents symbol input), elements of x must be in the range [0, h.M-1]. For an input x of size , an output y of size is computed.

See Using Modem Objects for usage examples.

Properties

An OQPSK modulator object has the following properties. All the properties are writable unless explicitly noted otherwise.

Property	Description
`Type`	Type of modulation object. This is a fixed value, set to `'OQPSK Modulator'`.
`M`	M-ary value that is set to four and is not writable.
`PhaseOffset`	Phase offset of ideal signal constellation in radians.
`Constellation`	Ideal signal constellation. This property is not writable and is automatically computed based on `M` and `PhaseOffset`.
`SymbolOrder`	Type of mapping employed for mapping symbols to ideal constellation points. The choices are `'binary'` (binary mapping), `'gray'` (Gray mapping), and `'user-defined'` (custom mapping).
`SymbolMapping`	A list of integer values from 0 to `M`-1 that correspond to ideal constellation points. This property is writable only when `SymbolOrder` is set to `'user-defined'`. Otherwise, it is automatically computed.
`InputType`	Type of input to be processed by the OQPSK modulator object. The choices are `'bit'` (bit/binary output), and `'integer'` (integer/symbol output).

Methods

An OQPSK modulator object has the following functions for inspection, management, and simulation:

See Using Modem Objects for details and examples of their use.

Examples

% Construct a modulator object for OQPSK modulation
% with default constellation .
h = modem.oqpskmod
 
% Construct an object to modulate binary data using
% OQPSK modulation. The constellation has Gray mapping
% and is shifted by -pi/16 radians.
h = modem.oqpskmod('PhaseOffset', -pi/16, ...
  'SymbolOrder', 'Gray', 'InputType', 'Bit')
 
% Construct a modulator object from an existing demodulator
% object for OQPSK demodulation in order to modulate binary
% inputs.
demodObj = modem.oqpskdemod('PhaseOffset', pi/3)  
modObj = modem.oqpskmod(demodObj, 'InputType', 'Bit')