Chapter 7 195
Custom Real Time I/Q Baseband
Working with Differential Data Encoding
For a bit–by–bit illustration of the encoding process, see the following illustration:
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.
1
01 00 1 100
11
0
raw (unencoded) data
differentially encoded data
11
11
1
1
1
111
0
0
0
change =
no change =
0
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