563489578934

620
Wire and Wireless Communication Applications Chap. 8
Data in
Data out
Rx
Tx
Add/drop
terminal
Tx
Rx
Data in
Data out
Tx
Rx
Rx
Add/drop
terminal
Two-fiber cable
Tx
Data direction
Tx
Add/drop
terminal
Rx
Data in
Data out
Figure 8–28
Data direction
Optical-fiber ring system.
Specifications for a typical system are given in Table 8–6. This system has OC-48 capacity,
which is equivalent to 48 DS-3 circuits or 32,256 full-duplex VF circuits as described in Sec. 3–9.
(See Table 3–10.)
A link budget analysis for a typical line span operating at the 1.5 mm wavelength is given
in Table 8–7. It shows that a maximum line span of 92 km (57.5 miles) may be used between
optical repeaters (or adddrop terminals). Moreover, an optional lightwave booster amplifier
may be used at the transmitter end to increase the transmitted optical power and, consequently,
the line span.
8–8 CELLULAR TELEPHONE SYSTEMS
This section describes cellular telephone systems and includes standards for many analog and
digital systems.
Since the invention of wireless systems, the goal of telephone engineers has been to
provide telephone service to individuals by using radio systems to link phone lines with
persons in their cars or on foot. There is not enough spectral space to assign a permanent
radio channel for each phone subscriber to use over a wide geographical area. However, it
is possible to accommodate a large number of subscribers if each radio channel covers
only a small geographical area and if the channels are shared (via FDMA, TDMA, or
CDMA).