## Answer 5.9

#### The minimum bandwidth required to support BPSK is twice that for a binary baseband channel which, as we saw in chapter 3, is one half of the symbol rate. The minimum bandwidth for BPSK is thus equal to the symbol rate and the maximum bandwidth efficiency for BPSK is thus 1 bit/second/Hz.
For a non-ideal filter, the bandwidth must be increased by a factor (1 + a), and the bandwidth efficiency is thus reduced by a factor (1 + a). Thus, for an a = 0.5, the bandwidth efficiency is reduced to 0.75 bits/second/Hz.