Communications Toolbox™

modem.pammod - Construct PAM modulator object

Syntax

h = modem.pammod(property1, value1, ...) h = modem.pammod(PAMdemod_object) h = modem.pammod(PAMdemod_object, property1, value1, ...) h = modem.pammod

Description

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

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

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

h = modem.pammod constructs a PAM modulator object h with default properties. It constructs a modulator object for BPAM modulation, and is equivalent to:

h = modem.pammod('M', 2, '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

A PAM 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 `'PAM Modulator'`.
`M`	M-ary value.
`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 PAM modulator object. The choices are `'bit'` (bit/binary output), and `'integer'` (integer/symbol output).

Methods

A PAM 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 4-PAM modulation.
h = modem.pammod('M', 4)
 
% Construct an object to modulate binary data using
% 16-PAM modulation.
% The constellation has Gray mapping.
h = modem.pammod('M', 16, 'SymbolOrder', 'Gray', ...
                 'InputType', 'Bit')
 
% Construct a modulator object from an existing
% demodulator object for PAM demodulation in order to
% modulate binary inputs.
demodObj = modem.pamdemod('M', 8)
modObj   = modem.pammod(demodObj, 'InputType', 'Bit')