Constellation Object

From GNU Radio
Jump to: navigation, search

GNU Radio supports the creation and use of Constellation objects for many of its digital communications needs. We define these constellations with a set of constellation points in complex space and the symbol mappings to those points. For a constellation that has 4 symbols, it then has log2(4) = 2 bits/symbol. We define this constellation with a list of Constellation Points and Symbol Map. For example, 16QAM would have:

Constellation Points = [(-3-3j), (-1-3j), (1-3j), (3-3j), (-3-1j), (-1-1j), (1-1j), (3-1j), (-3+1j), (-1+1j), (1+1j), (3+1j), (-3+3j), (-1+3j), (1+3j), (3+3j)]
Symbol Map = [0, 4, 12, 8, 1, 5, 13, 9, 3, 7, 15, 11, 2, 6, 14, 10]

The mapping is a 1-to-1 for the items in both lists. The symbols are referred to as the 'pre_diff_code' since this is the mapping before the application of differential modulation, if used.

See [1] for more info.

Parameters[edit]

Constellation Type
Type of modulation scheme. Choose Variable Constellation for more control.
Soft Decisions Precision
Specifies how accurate the look up table (LUT) is to a given number of bits.
Soft Decisions LUT
Vector of floating point tuples that acts as the look up table (LUT). Can be set to 'auto' for GNU Radio to populate it.
Symbol Map
(Available when using Variable Constellation) Manually specify the symbol map, in list form.
Constellation Points
(Available when using Variable Constellation) Manually specify the constellation points, using a list of complex numbers.
Rotational Symmetry
(Available when using Variable Constellation) The number of rotations per 360 degrees that the constellation is symmetric, which is 4 for the common constellations.
Dimensionality
(Available when using Variable Constellation) The number of dimensions, typically set to 1.

Example Flowgraph[edit]

This flowgraph generates symbols using a chosen modulation scheme, runs the signal through a channel model, and then simulates a receiver by synchronizing to the signal and performing soft decoding.

Constellation soft decoder ex.png

Source Files[edit]

C++ files
see middle of this page
Header files
TODO
Public header files
Here
Block definition
TODO