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Chapter 7 163
Custom Real Time I/Q Baseband
Working with Differential Data Encoding
How Differential Encoding Works
Differential encoding employs offsets in the symbol table to encode user-defined modulation schemes. The
Differential State Map editor is used to introduce symbol table offset values, which in turn cause
transitions through the I/Q State Map based on their associated data value. Whenever a data value is
modulated, the offset value stored in the Differential State Map is used to encode the data by transitioning
through the I/Q State Map in a direction and distance defined by the symbol table offset value.
Entering a value of +1 causes a 1-state forward transition through the I/Q State Map. As an example,
consider the following data/symbol table offset values. These symbol table offsets result in one of the
transitions shown.
NOTE The following I/Q State Map illustrations show all possible state transitions using a
particular symbol table offset value. The actual state-to-state transition depends on the state
in which the modulation starts.
Example 2
transition 1 state backward
Example 1
transition 1 state forward
Example 3
transition 2 states forward
Example 4
no transition
xx
Example Data Offset
Value
1 00000000 +1
2 00000001 −1
3 00000010 +2
4 00000011 0