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CHAPTER 4
Digital Transmission
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. The three different techniques described in this chapter are line coding, block cod-
ing, and scrambling.
3. The data rate defines the number of data elements (bits) sent in 1s. The unit is bits
per second (bps). The signal rate is the number of signal elements sent in 1s. The
unit is the baud.
5. When the voltage level in a digital signal is constant for a while, the spectrum cre-
ates very low frequencies, called DC components, that present problems for a sys-
tem that cannot pass low frequencies.
7. In this chapter, we introduced unipolar, polar, bipolar, multilevel, and multitran-
sition coding.
9. Scrambling, as discussed in this chapter, is a technique that substitutes long zero-
level pulses with a combination of other levels without increasing the number of
bits.
11. In parallel transmission we send data several bits at a time. In serial transmission
we send data one bit at a time.
Exercises
13. We use the formula s = c × N × (1/r) for each case. We let c = 1/2.
a. r = 1 → s = (1/2) × (1 Mbps) × 1/1 = 500 kbaud
b. r = 1/2 → s = (1/2) × (1 Mbps) × 1/(1/2) = 1 Mbaud
c. r = 2 → s = (1/2) × (1 Mbps) × 1/2 = 250 Kbaud
d. r = 4/3 → s = (1/2) × (1 Mbps) × 1/(4/3) = 375 Kbaud
15. See Figure 4.1 Bandwidth is proportional to (3/8)N which is within the range in
Table 4.1 (B = 0 to N) for the NRZ-L scheme.
17. See Figure 4.2. Bandwidth is proportional to (12.5 / 8) N which is within the range
in Table 4.1 (B = N to B = 2N) for the Manchester scheme.
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