Communications Toolbox™

modem.dpskmod - Construct DPSK modulator object

Syntax

h = modem.dpskmod(property1, value1, ...) h = modem.dpskmod(DPSKdemod_object) h = modem.dpskmod(DPSKdemod_object, property1, value1, ...) h = modem.dpskmod

Description

The modem.dpskmod 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.dpskmod(property1, value1, ...) constructs a DPSK modulator object h with properties as specified by the property/value pairs.

h = modem.dpskmod(DPSKdemod_object) constructs a DPSK modulator object h by reading the property values from the DPSK demodulator object, DPSKdemod_object. The properties that are unique to the DPSK modulator object are set to default values.

h = modem.dpskmod(DPSKdemod_object, property1, value1, ...) constructs a DPSK modulator object h by reading the property values from the DPSK demodulator object, DPSKdemod_object. Additional properties are specified using property/value pairs.

h = modem.dpskmod constructs a DPSK modulator object h with default properties. It constructs a modulator object for binary DPSK modulation, and is equivalent to:

h = modem.dpskmod('M', 2, 'PhaseRotation', 0, ...
                  'SymbolOrder', 'binary', ...
                  'InputType', 'integer', 'InitialPhase', 0)

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

A DPSK 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 `'DPSK Modulator'`.
`M`	Constellation size.
`PhaseRotation`	Specifies the phase rotation (rad) of the modulation. In this case, the total per-symbol phase shift is the sum of `PhaseRotation` and the phase generated by the differential modulation.
`Constellation`	Ideal signal constellation. This property is not writable and is automatically computed based on `M`.
`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 DPSK modulator object. The choices are `'bit'` (bit/binary output), and `'integer'` (integer/symbol output).
`InitialPhase`	Initial phase state of the DPSK modulator. `InitialPhase` is used to calculate the first modulated symbol.

Methods

A DPSK demodulator object has the following four functions for inspection, management, and simulation:

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

Examples

% Construct a modulator object for 4-DPSK modulation
% with initial phase pi/4.
h = modem.dpskmod('M', 4, 'InitialPhase', pi/4)
 
% Construct an object to modulate binary data using 
% 16-DPSK modulation with pi/8 degrees minimum phase 
% rotation per symbol. The constellation has Gray mapping.
h = modem.dpskmod('M', 16, 'SymbolOrder', 'Gray', ...
                  'PhaseRotation', pi/8, 'InputType', 'Bit')
 
% Construct a modulator object from an existing demodulator
% object for DPSK demodulation in order to modulate binary
% inputs.
demodObj = modem.dpskdemod('M', 8)  % existing DPSK 
                                    % demodulator object
modObj = modem.dpskmod(demodObj)