## Answer 6.8

####

1. Both four-level bipolar and polar baseband signalling occupy the same bandwidth, and have a bandwidth efficiency of 2 bits/second/Hz. Thus for a 256 kbps data signal the bandwidth required (minimum) is 128 kHz.
2. See a above.
3. BPSK is a binary bandpass modulation format with a bandwidth efficiency of only 1 bit/second/Hz maximum. Hence 256 kHz of bandwidth is required to support 256 kbps.
4. QPSK is a bandpass modulation format with four symbol states. This has a bandwidth efficiency of 2 bits/second/Hz requiring 128 kHz of bandwidth.
5. 64-QAM conveys 6 bits per symbol [log2(64) = 6] compared with 2 bits per symbol for QPSK. The bandwidth required is thus reduced by a factor of three compared with QPSK to 42.667 kHz.