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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

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

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Agilent Technologies EXG Guida Utente Pagina 192