First Generation Technology (1G) and AMPS

First Generation Technology (1G) and AMPS
First-generation wireless technology is based on analog signals. Analog signals are radio
transmissions sent in a wave-like form. A mobile device sends the waves to a base station
where they are processed to determine the signal’s next destination (i.e., another base station,
mobile phone, land-line phone etc.). Once the destination is determined, the signal is
reconstructed as accurately as possible into its original wave form by the base station. The
analog signal received by the end user may closely resemble the original transmission but
rarely duplicate it. Noticeable differences in quality and form occur due to recreation errors
of the signal wave (Fig. 10.1). Signal destruction (the signal is lost or damaged during
transmission), translation and interference problems threaten analog transmission to a
greater extent than their digital counterparts (digital signals are discussed Section 10.3).
Fig. 10.1 Analog signal before and after processing at the base station.
Many standards have evolved for analog cellular communications. The most notable
is Advanced Mobile Phone Service (AMPS), introduced in 1983.1 AMPS is still the most
widely used cellular technology in North America, though it is rarely used as a stand-alone
wireless communications standard (e.g., few systems rarely carry analog signals exclusively).
2 AMPS is primarily used to extend cellular network coverage through the use of
analog signals to include the few areas that do not support the more recent digital communications
systems. AMPS is also viewed as a backup or support system to digital communications
networks in case of system failures.
The compartments, or cells, of a honeycomb are comparable to the communication
areas of cellular networks like AMPS (Fig. 10.2).3 At the center of each cell is a base station,
which transmits analog signals to and from users within that cell. A base station cannot
communicate with users beyond the boundaries of its cell. If a mobile user passes through
a cell boundary, the signal must be passed to the base station of the cell the user has entered.
The transfer of signals from one base station to another is called a handoff. The handoff
Base Station
Original Signal Reproduced Signal
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© Copyright 1992–2002 by Deitel & Associates, Inc. All Rights Reserved. 6/19/01
allows mobile users to continue communications without disconnections or network interruptions
(Fig. 10.2).4
Fig. 10.2 Wireless communication networks demonstrating cells and handoffs
from base stations. (Courtesy of International Engineering Consortium:
www.iec.org).
Early AMPS systems and other analog-based networks had difficulty handing off cellular
transmissions effectively. Users could communicate with other users (i.e., mobile
phone users, landline phone users, etc.) only if the mobile phone user remained in one specific
cell. If a user moved to a different cell area, the call was often lost as handoffs would
not always occur correctly. Users often had to re-dial numbers or reconnect to the base station
in the new cell area.