Chapter 7 193
Custom Real Time I/Q Baseband
Working with Differential Data Encoding
This section provides information about the following:
• Understanding Differential Encoding
• “Using Differential Encoding” on page 197
Understanding Differential Encoding
Differential encoding is a digital–encoding technique whereby a binary value is denoted by a signal
change rather than a particular signal state. Using differential encoding, binary data in any
user–defined I/Q or FSK modulation can be encoded during the modulation process via symbol table
offsets defined in the Differential State Map.
For example, consider the signal generator’s default 4QAM I/Q modulation. With a user–defined
modulation based on the default 4QAM template, the I/Q Values editor contains data that represent
four symbols (00, 01, 10, and 11) mapped into the I/Q plane using two distinct values, 1.000000 and
–1.000000. These four symbols can be differentially encoded during the modulation process by
assigning symbol table offset values associated with each data value. Figure 7- 3 on page 193 shows
the 4QAM modulation in the I/Q Values editor.
Figure 7-3
NOTE The number of bits per symbol can be expressed using the following formula. Because the
equation is a ceiling function, if the value of x contains a fraction, x is rounded up to the
next whole number.
Where x = bits per symbol, and y = the number of differential states.
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