563489578934

624
Wire and Wireless Communication Applications Chap. 8
enough space in this book to describe details of all the systems that are listed in Table 8–9;
however, a few of them will be described in the following sections. Standards are also evolving
on a daily basis, so it is not possible to cover today’s developments in a book. The reader
is encouraged to read about these developments. They are posted on many Web sites, such as
the system descriptions on Wikipedia.
The following section describes some 1G systems. The 1G systems are analog circuitswitched
systems.
First Generation (1G)—The AMPS Analog
Circuit-switched System
As shown in Table 8–10, the first generation (1G) cellular telephone system used in the
United States was the Advanced Mobile Phone System (AMPS), which was developed by
AT&T and Motorola. It is an analog system, since it uses the VF audio signal to frequency
modulate (FM) a carrier. To implement this AMPS concept in the United States, the FCC had
to find spectral space for assignment. It did so by using the 806- to 890-MHz band that was
once assigned to TV channels 70 to 83 (see Table 8–13), but discontinued in 1974. Part of this
band was assigned for cellular service, as shown in Table 8–10. Historically, the FCC decided
to license two competing cell systems in each geographical area; one licensed to a conventional
telephone company and another to a nontelephone company common carrier. The nontelephone
system is called the A service, or nonwireline service, and the telephone company
system is called the B service, or wireline service. Thus, subscribers to a 1G cellular system
have the option of renting service from the wireline company or the nonwireline company. In
addition, as shown in the Table 8–10, the standards provide for full duplex service. That is,
one carrier frequency is used for mobile to cell base-station transmission, and another carrier
frequency is used for base-station to mobile transmission. Control is provided by FSK signaling.
Of the 416 channels that may be used by a cellular service licensee, 21 are used for
paging (i.e., control) with FSK signaling. FSK signaling is also used at the beginning and end
of each call on a VF channel. When a cellular telephone is turned on, its receiver scans the
paging channels looking for the strongest cell-site signal and then locks onto it. The cell site
transmits FSK data continuously on a paging channel, and, in particular, it sends control
information addressed to a particular cellular phone when a call comes in for it. That is, the
FSK control signal tells the phone which channel to use for a call.
Each cellular telephone contains a PROM (programmable read-only memory) or
EPROM (erasable programmable read-only memory)—called a numeric assignment module
(NAM). The NAM is programmed to contain the telephone number—also called the
mobile identification number (MIN)—of the phone. The phone also contains its electronic
service number (ESN) which is a unique identification number embedded in the phone by
the manufacturer.
When the phone is ”on the air” it automatically transmits its serial number to the MSC.
The serial number is used by the MSC to lock out phone service to any phone that has been
stolen. This feature, of course, discourages theft of the units. The MSC uses the telephone
number of the unit to provide billing information. When the phone is used in a remote city, it
can be placed in the roam mode, so that calls can be initiated or received, but still allow the
service to be billed via the caller’s “hometown” company.