Communications Toolbox™

modem.pskmod - Construct PSK modulator object

Syntax

h = modem.pskmod(M) h = modem.pskmod(M, phaseoffset) h = modem.pskmod(property1, value1, ...) h = modem.pskmod(PSKdemod_object) h = modem.pskmod(PSKdemod_object, property1, value1, ...) h = modem.pskmod

Description

The modem.pskmod function (constructor) 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.pskmod(M) constructs a PSK modulator object h for M-ary modulation.

h = modem.pskmod(M, phaseoffset) constructs a PSK modulator object h whose constellation has a phase offset of phaseoffset radians.

h = modem.pskmod(property1, value1, ...) constructs a PSK modulator object h with properties as specified by the property/value pairs. If a property is not specified, it is assigned a default value. See the following section on properties.

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

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

h = modem.pskmod constructs a PSK modulator object h with default properties. It constructs a modulator object for BPSK modulation and is equivalent to:

h = modem.pskmod('M', 2, 'PhaseOffset', 0, 'SymbolOrder',...
    'binary', 'InputType', 'integer')

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

The following table describes the properties of the PSK modulator object.

Property	Description
`Type`	Type of modulation object. This property is a fixed value, set to `'PSK Modulator'`.
`M`	M-ary value. Default is `2`.
`PhaseOffset`	Phase offset of ideal signal constellation in radians. Default is `0`.
`Constellation`	Ideal signal constellation. This property is not writable and is automatically computed based on the `M` and `PhaseOffset` properties.
`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). Default is `'binary'`.
`SymbolMapping`	Symbol mapping values corresponding to ideal constellation points. This property is writable only when `SymbolOrder` is set to `'user-defined'`. Each element of the symbol mapping vector contains the symbol mapped to the corresponding element of the constellation vector. Thus, the first element of the symbol mapping vector contains the symbol mapped to the first element of the constellation vector, the second element contains the symbol mapped to the second element of the constellation vector, and so on.
`InputType`	Type of input to be processed by the PSK modulator object. The choices are `'bit'` (bit/binary output), and `'integer'` (integer/symbol output). Default is `'integer'`.

Methods

A General QAM 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 QPSK modulation.
h = modem.pskmod(4)
 
% Construct a modulator object for 8-PSK modulation with 
% constellation shifted by pi/8 radians.
h = modem.pskmod(8, pi/8)
 
% Construct an object to modulate binary data using 16-PSK .
% modulation. The constellation has Gray mapping and is 
% shifted by -pi/16 radians.
h = modem.pskmod('M', 16, 'PhaseOffset', -pi/16, ...
                 'SymbolOrder', 'Gray', 'InputType', 'Bit')