N5161A/62A/81A/82A/83A MXG Signal Generators User's Guide

Custom Digital Modulation (Option 431)Differential EncodingThe following illustration shows a 4QAM modulation I/Q State Map.2nd SymbolData = 00000001Distinct values: –1, +11st SymbolData = 00000000Distinct values: +1, +1213 43rd SymbolData = 00000010Distinct values: –1, –14th SymbolData = 00000011Distinct values: +1, –1Differential encoding employs relative offsets between the states in the symbol table to encodeuser–defined modulation schemes. The Differential State Map table editor is used to introducesymbol table offset values which in turn cause transitions through the I/Q State Map based on theirassociated data value. Whenever a data value is modulated, the offset value stored in the DifferentialState Map is used to encode the data by transitioning through the I/Q State Map in a direction anddistance defined by the symbol table offset value.Entering a value of +1 will cause a 1–state forward transition through the I/Q State Map, as shownin the following illustration.NOTEThe following I/Q State Map illustrations show all of the possible state transitions using aparticular symbol table offset value. The actual state–to–state transition would depend uponthe state in which the modulation had started.As an example, consider the following data/symbol table offset values.Table 11-2DataOffset Value00000000 +100000001 –1288 Agilent N5161A/62A/81A/82A/83A MXG Signal Generators User’s Guide