In a partially-coherent channel, the phase angle is not known, but it changes so slowly with respect to the bit rate that phase offset can be estimated from a long sequence of bits and can be corrected. However, there is a residual sign ambiguity if the modulation is BPSK because the phase estimate has a 180? ambiguity. Instead of using DPSK, it is proposed to use BPSK and to resolve this ambiguity by inserting a sequence of four ones after every 100 channel bits, and to use a data translation code to remove any sequence of four ones from the channel bit stream. (An example of such a code inserts in the encoder an artificial zero after every three consecutive ones and deletes in the decoder a zero after every three consecutive ones.)
a. Explain how this resolves the ambiguity.
b. By how much, in the best case, is the data rate reduced?
c. Sketch a copy of Figure 3.10 and on the sketch plot a curve for the proposed scheme. In the best case, what must be the change in Eb/N0 at a bit error rate of 10-5?