Agilent Technologies E8247C PSG CW, E8267C PSG, E8257C PSG Transmittedbiti = databiti 1 ⊕ databiti

Custom Real Time I/Q Baseband

Working with Differential Data Encoding

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 mapping at the point of modulation, differential data encoding uses the transition from one bit value to another to encode the raw data.

Differential data encoding modifies the raw digitized data by creating a secondary, encoded data stream that is defined by changes in the digital state, from 1 to 0 or from 0 to 1, of the raw data stream. This differentially encoded data stream is then modulated and transmitted.

In differential data encoding, a change in a raw data bit’s digital state, from 1 to 0 or from 0 to 1, produces a 1 in the encoded data stream. No change in digital state from one bit to the next, in other words a bit with a value of 1 followed by another bit with a value of 1 or a bit with a value of 0 followed by the same, produces a 0 in the encoded data. For instance, differentially encoding the data stream containing 01010011001010 renders 1111010101111.

Differential data encoding can be described by the following equation:

transmittedbit(i )= databit(i – 1 ) ⊕ databit(i)

For a bit-by-bit illustration of the encoding process, see the following illustration:

0 1 0 1 0 0 1 1 0 0 1 0 1

raw (unencoded) data

change = no change =

1 1 1 1 0 1 0 1 0 1 1 1 1

differentially encoded data

162 Chapter 7