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How do I Create a Custom QAM Symbol Map Using Modulation Toolkit

Primary Software: LabVIEW Toolkits>>LabVIEW Modulation Toolkit
Primary Software Version: N/A
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
I need to use Modulation Toolkit to Create a Custom QAM Symbol Map for my application. What can I use to create this map?

Solution:
The Generate System Parameters VI in LabVIEW allows the user to either accept a default QAM symbol map, or to create a custom QAM symbol map in order to map bit patterns and IQ complex plane values differently.

This polymorphic VI has two options for each of the modulation schemes: M and Map. Use M to auto-generate the symbol map or use Map to define your own.

To find more information, right click this VI and select Help, then select the modulation type you would like to use. For example, selecting QAM symbol value array gives the following explanation:

This VI expects a two-dimensional, square array of integers as input for the symbol values control. 4-QAM expects a 2×2 array (2 rows, 2 columns), 16-QAM expects a 4×4 array, and so on. The integers 0 through (M–1) must all be included once (only) in the symbol values array, where M is the M-ary number of the modulation. The binary representation (LSB first convention) of the integers represents the bit pattern that is mapped to the corresponding symbol location in the symbol values array.

For example, for 4-QAM, if you specify the symbol values array as
[3 1]
[0 2],
the output QAM symbol map is [(–0.707 – 0.707i), (0.707 + 0.707i),
(0.707 – 0.707i), (–0.707 + 0.707i)].

In order to create a custom QAM symbol map that does not directly fit into a square 2 dimensional array, for example 32-QAM, you can set the additional spaces in the array to negative numbers. The negative number will not be considered as a part of the symbol map and will allow you to use the square array to represent your map.



There is a simple example attached to this knowledge base that illustrates this written example.
You can find more information about digital modulation in the attached link.

Related Links:
Developer Zone Tutorial: RF and Communications Fundamentals

Attachments:
custom_symbol_map with Constellation.vi




Report Date: 01/10/2007
Last Updated: 10/28/2008
Document ID: 459J9KJX

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