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Baseband Pulse and Digital Signaling Chap. 3
4
2
T s
T 0
w 3 (t)
0
T b
–2
–4
0
1
2 3 4
t(ms)
5 6 7 8
(a) Rectangular Pulse Shape T b =1 ms
4
2
w 4 (t)
0
–2
–4
0 1 2 3
(b) sin(x)/x Pulse Shape, T b =1 ms
t(ms)
5 6 7 8
Mid-symbol
sampling
Figure 3–14
L = 4-level signaling (computed). (See Example3_08.m.)
In the next section, exact formulas are obtained for the power spectral density of binary
and multilevel signals.
3–5 LINE CODES AND SPECTRA
Binary Line Coding
Binary 1’s and 0’s, such as in PCM signaling, may be represented in various serial-bit signaling
formats called line codes. Some of the more popular line codes are shown in Fig. 3–15. †
There are two major categories: return-to-zero (RZ) and nonreturn-to-zero (NRZ). With RZ
coding, the waveform returns to a zero-volt level for a portion (usually one-half) of the bit
interval. The waveforms for the line code may be further classified according to the rule that
is used to assign voltage levels to represent the binary data. Some examples follow.
† Strictly speaking, punched paper tape is a storage medium, not a line code. However, it is included for historical
purposes to illustrate the origin of the terms mark and space. In punched paper tape, the binary 1 corresponds
to a hole (mark), and a binary 0 corresponds to no hole (space).