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178 Chapter 7
Custom Real Time I/Q Baseband
Working with Differential Data Encoding
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.
The following illustration shows a 4QAM modulation I/Q State Map.
Differential Data Encoding
In real-time I/Q baseband digital modulation waveforms, data (1’s and 0’s) are encoded, modulated
onto a carrier frequency and subsequently transmitted to a receiver. In contrast to differential
encoding, differential data encoding modifies the data stream prior to I/Q mapping. Where
differential encoding encodes the raw data by using symbol table offset values to manipulate I/Q
1
2
3
4
1st Symbol
Data = 00000000
Distinct values: +1, +1
4th Symbol
Data = 00000011
Distinct values: +1, -1
2nd Symbol
Data = 00000001
Distinct values: -1, +1
3rd Symbol
Data = 00000010
Distinct values: -1, -1