Communications Toolbox™

modem.dpskdemod - Construct DPSK demodulator object

Syntax

h = modem.dpskdemod(property1, value1, ...) h = modem.dpskdemod(DPSKmod_object) h = modem.dpskdemod(DPSKmod_object, property1, value1, ...) h = modem.dpskdemod

Description

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

h = modem.dpskdemod(property1, value1, ...) constructs a DPSK demodulator object h with properties as specified by the property/value pairs.

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

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

h = modem.dpskdemod constructs a DPSK demodulator object h with default properties. It constructs a demodulator object for binary DPSK demodulation, and is equivalent to:

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

Modem Demodulation Method

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

The syntax is y = demodulate(h, x), where h is the handle to a demodulator object and x is a signal. This syntax processes the binary words (bits) or symbols (integers) in signal x with the demodulator object and output the baseband signal y.

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

The demodulator object's property DecisionType should be set depending on whether you want hard or soft (LLR or approximate LLR) decisions. To allow for soft decisions, the demodulator object's property OutputType must be set to 'bit'.

For h.outputtype = ‘bit', an output y of size is computed for an input x of size , where nBits = log₂(h.M).

For h.outputtype = ‘integer', an output y of size is computed for an input x of size .

See Using Modem Objects for usage examples.

Properties

A DPSK demodulator 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 Demodulator'`.
`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.
`OutputType`	Type of output to be computed by the DPSK demodulator object. The choices are `'bit'` (bit/binary output), and `'integer'` (integer/symbol output).
`DecisionType`	Type of output values to be computed by DPSK demodulator object. This property is set to `'hard decision'` and is not writable.
`InitialPhase`	Initial phase state of the DPSK demodulator. `InitialPhase` is used to calculate the first demodulated 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 demodulator object for 4-DPSK demodulation 
% with initial phase pi/4.
h = modem.dpskdemod('M', 4, 'InitialPhase', pi/4)
 
% Construct an object to compute hard bit decisions of a 
% baseband signal using 16-DPSK modulation. The modulated
% signal has a minimum phase rotation of pi/8 per symbol.
% The constellation has Gray mapping.  
h = modem.dpskdemod('M', 16, 'SymbolOrder', 'Gray', ...
                    'PhaseRotation', pi/8, 'OutputType', 'Bit') 
 
% Construct a demodulator object from an existing modulator
% object for DPSK modulation in order to make bit decision.
modObj = modem.dpskmod('M', 8, 'InputType', 'Bit')  
demodObj = modem.dpskdemod(modObj)