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| − | [[Category:Block Docs]]
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| − | 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:
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| − | 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)]
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| − | Symbol Map = [0, 4, 12, 8, 1, 5, 13, 9, 3, 7, 15, 11, 2, 6, 14, 10]
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| − | 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.
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| | See [https://www.gnuradio.org/doc/doxygen/page_digital.html] for more info. | | See [https://www.gnuradio.org/doc/doxygen/page_digital.html] for more info. |
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| − | == Parameters ==
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| − | ; Constellation Type
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| − | : Type of modulation scheme. Choose Variable Constellation for more control.
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| − | ; Soft Decisions Precision
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| − | : Specifies how accurate the look up table (LUT) is to a given number of bits.
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| − | ; Soft Decisions LUT
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| − | : Vector of floating point tuples that acts as the look up table (LUT). Can be set to 'auto' for GNU Radio to populate it.
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| − | ; Symbol Map
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| − | : (Available when using Variable Constellation) Manually specify the symbol map, in list form.
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| − | ; Constellation Points
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| − | : (Available when using Variable Constellation) Manually specify the constellation points, using a list of complex numbers.
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| − | ; Rotational Symmetry
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| − | : (Available when using Variable Constellation) The number of rotations per 360 degrees that the constellation is symmetric, which is 4 for the common constellations.
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| − | ; Dimensionality
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| − | : (Available when using Variable Constellation) The number of dimensions, typically set to 1.
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| | == Example Flowgraph == | | == Example Flowgraph == |
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| − | 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.
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| − | [[File:constellation_soft_decoder_ex.png|800px]]
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| − | == Source Files ==
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| − | ; C++ files
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| − | : [https://github.com/gnuradio/gnuradio/blob/0fa281fd7369348dbdeadcecfebb20b73082e93e/gr-digital/lib/constellation.cc see middle of this page]
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| − | ; Header files
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| − | : [https://github.com/gnuradio/gnuradio TODO]
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| − | ; Public header files
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| − | : [https://github.com/gnuradio/gnuradio/blob/0fa281fd7369348dbdeadcecfebb20b73082e93e/gr-digital/include/gnuradio/digital/constellation.h Here]
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| − | ; Block definition
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| − | : TODO
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