Problem: One technique used in mobile radio technologies to increase the data rate is to have the channel coding and modulation schemes adapt to changing channel conditions. In particular, the channel coding and modulation schemes are changed as the channel's signal to interference ratio (S/I) changes.
a). As the S/I ratio decreases, the channel coding is changed. What happens to the code rate as the S/I ratio decreases? Why? (Discuss)
b). One specific technology changes its modulation scheme between QPSK and 8-PSK as the S/I ratio changes. If the modulation scheme changes from 8-PSK to QPSK, has the S/I decreased or increased? Why? (Discuss)