308 Keysight EXG and MXG X-Series Signal Generators User’s GuideUsing Custom Digital Modulation for N5172B/82B with Option 431 and 653/655/656/657Differential EncodingWhen applied to the user–defined default 4QAM I/Q map, starting from the 1st symbol (data 00),the differential encoding transitions for the data stream (in 2–bit symbols) 0011100001 appear inthe following illustration.As you can see from the previous illustration, the 1st and 4th symbols, having the same data value(00), produce the same state transition (forward 1 state). In differential encoding, symbol values donot define location; they define the direction and distance of a transition through the I/Q StateMap.Using Differential EncodingThe signal generator’s Differential State Map table editor enables you to modify thedifferential state map associated with user–defined I/Q and user–defined FSK modulations. In thisprocedure, you create a user–defined I/Q modulation and then configure, activate, and applydifferential encoding to the user–defined modulation. For more information, see “DifferentialEncoding” on page 305.Configuring User–Defined I/Q Modulation1. Press Preset.2. Perform the following keypress sequence required for your format type.For Custom ARB FormatPress Mode > ARB Custom Modulation > Single Carrier Setup > Modulation Type > Select >More 1 of 2 > Define User I/Q > More > Load Default I/Q Map > QAM > 4QAM.Or this alternate sequence:Data Value Symbol Table Offset00011011+1–1+2+0Data = 0011100001{{{{{5th Symbol1st Symbol 3rd Symbol4th Symbol2nd Symbol1st2nd3rd5th 4th
