Modulation Symbol Demapper (DEMAP) - INTERCONNECT Element – Ansys Optics

INTERCONNECT

The symbol demapper takes constellation points and generates appropriate consecutive bits

Keywords

digital, electrical, unidirectional

Ports

Name	Type
input I	Electrical Signal
input Q	Electrical Signal
output	Digital Signal

Properties

General Properties

Name	Default value	Default unit	Range
name Defines the name of the element.	Modulation Symbol Demapper	-	-
annotate Defines whether or not to display annotations on the schematic editor.	true	-	[true, false]
enabled Defines whether or not the element is enabled.	true	-	[true, false]
type Defines the element unique type (read only).	Modulation Symbol Demapper	-	-
description A brief description of the elements functionality.	The symbol demapper takes constellation points and generates appropriate consecutive bits	-	-
prefix Defines the element name prefix.	DEMAP	-	-
model Defines the element model name.	-	-	-
library Defines the element location or source in the library (custom or design kit).	-	-	-
local path Defines the local path or working folder $LOCAL for the element.	-	-	-
url An optional URL address pointing to the element online help.	-	-	-

Standard Properties

Name	Default value	Default unit	Range
configuration Defines whether or not to enable I and Q ports.	dual input	-	[dual input, single input
bitrate Defines the input signal bitrate.	%bitrate%	bits/s	[1, +∞)
bitrate mode Controls whether the output signal bitrate varies with modulation order (variable) or remains constant (fixed). Variable mode maintains constant symbol period; fixed mode maintains constant bitrate.	variable	-	[variable, fixed
synchronization delay I The time delay to apply to the input signal.	0	s	[0, +∞)
synchronization delay Q The time delay to apply to the input signal.	0	s	[0, +∞)
decision method Defines the decision method. Methods include 'hard decision', 'log-likelihood ratio' and 'approximate log-likelihood ratio'.	hard decision	-	[hard decision, log likelihood ratio, approximate log likelihood ratio
noise variance I The noise variance or the noise power.	0	W	[0, +∞)
noise variance Q The noise variance or the noise power.	0	W	[0, +∞)
decision point Defines whether or not to automatically determine the decision point for the constellation diagram.	automatic	-	[automatic, user defined
decision instant Defines the time instant for the constellation diagram detection decision points.	20e-012	s	(-∞, +∞)
scale factor I The scale factor for the symbol map IQ values.	1	-	(0, +∞)
scale factor Q The scale factor for the symbol map IQ values.	1	-	(0, +∞)
rotation The rotation angle rotates the symbol map IQ values.	0	rad	(-∞, +∞)
load map from file Defines whether or not to load IQ values from an input file or to use the currently stored values.	false	-	[true, false]
symbol map filename The file containing user defined IQ values. Refer to the Implementation Details section for the format expected.	-	-	-
modulation type Defines the input signal modulation scheme. The user can choose between different standard modulation schemes.	2PAM	-	[user defined, 2PAM, 4PAM, 8PAM, 16PAM, BPSK, QPSK, 8PSK, 8QAM, 16QAM, 32QAM, 64QAM, 128QAM, 256QAM
symbol map table The table allows the user to read or modified a symbol map by changing the position of one or more symbols.	<2,2> [-1, 1, 0,...]	-	-

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Implementation Details

The modulation symbol demapper demodulates constellation points and outputs the corresponding bit sequence. It supports all standard modulation types (PAM, PSK, QAM families) and can be configured for single or dual port output depending on whether the input is real (I) or complex (I/Q) modulation.

For accurate bit recovery, both the modulation type and bitrate mode must match between the mapper and demapper. The Bitrate mode property (default: variable mode) determines whether the demapper maintains a constant symbol rate (variable bitrate mode) or constant bitrate (fixed bitrate mode)—this critical setting must align with the mapper to ensure correct timing and bit recovery. Mismatched bitrate modes between mapper and demapper will result in timing misalignment and incorrect output.

Please see the example file Demapper.icp, attached to this article, for detailed information.

In this example, a 16QAM modulated electrical signal is generated by the modulation symbol mapper, then demodulated by the modulation symbol demapper. When the demapper's modulation type and bitrate mode both match the mapper's settings, the original transmitted bit sequence is correctly recovered. This demonstrates the importance of configuration alignment between mapper and demapper—mismatched settings, whether in modulation type or bitrate mode, will result in incorrect bit recovery.

The first figure demonstrates correct operation with matched mapper and demapper settings (modulation type and bitrate mode). The second figure shows the consequences of mismatched modulation type, resulting in incorrect bit recovery. For correct demodulation, both modulation type and bitrate mode must match.

Modulation Symbol Demapper (DEMAP) - INTERCONNECT Element