(a) Refer to the differential encoder used in Figure a. Table 6.10 defines the phase changes induced in the V.32 modem by varying input debits. Expand this table by including the corresponding previous and current values of the differential encoder's output. Note that for every input debit there are four possible values for the differentially encoded debit and likewise for its previous value I1,n-1 I2,n-1.

(b) The current quad bit applied to the V.32 modem with non-redundant coding is 0001. The previous output of the modern is 01. Find the code word output produced by the modem and its coordinates.

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Least significant input dibit 16-point signal-space 16-QAM output mapper Qгл Most Read-only significant input dibit e1, memory 12,m-11,n-1| Differential encoder (T = symbol pericd) (a) Least significant input dibit 32-point Y2,n signal-space 32-QAM output 12,7 mapper Q2.r Convolutional encoder Most Read-only significant input dibit memory Yon Qл 2,m-11,n-1 т Differential encoder (T = symbol period) (b)