Advanced Mobile Phone System
Advanced Mobile Phone System
or AMPS is the analog mobile phone system
standard, introduced in the Americas during the
early 1980s. Though analog is no longer
considered advanced at all, the relatively
seamless cellular switching technology AMPS
introduced was what made the original mobile
radiotelephone practical, and was considered
quite advanced at the time.
Technology
It was a first-generation technology,
using FDMA which meant each cell site would
transmit on different frequencies, allowing many
cell sites to be build near each other. However
it had the disadvantage that each site did not
have much capacity for carrying calls. It also
had a poor security system which allowed people
to steal a phone's serial code to use for making
illegal calls. It was later replaced by the
newer Digital TDMA system which brought improved
security as well as increased capacity.
Frequency
bands
For each market area, there were to
be two licensee (networks). Each network is
authorized to use 416 channels in the 800 MHz
band. Each channel is composed of 2 frequencies.
416 of these are in the 824~849 MHz range for
transmissions from mobile stations to the base
stations, paired with 416 frequencies in the
869~894 MHz range for transmissions from base
stations to the mobile stations. Each cell site
will use a subset of these channels, and must
use a different set than neighboring cells to
avoid interference. This significantly reduces
the number of channels available at each site in
real-world systems. Each AMPS frequency is 30kHz
wide.
The AMPS band was taken from the same 806~890
MHz frequency band which was originally UHF TV
channels 70~83. This meant that these UHF
channels could not be used for UHF TV
transmission as these frequencies were to be
used for AMPS transmission.
Introduction
of digital TDMA
Later, many AMPS networks were
partially converted to what became (incorrectly)
known as TDMA, a digital, TDMA, based 2G
standard used mainly by Cingular Wireless (who
has purchased AT&T Wireless in October 2004) and
US Cellular. TDMA networks were backward
compatiable with AMPS. The mis-use of the term
TDMA (which is a type of channel sharing scheme)
to refer to a particular access protocol has
caused some confusion. The first version of the
TDMA standard was known as IS-54 and was
supplanted by IS-136.
Introduction
of GSM and CDMA
AMPS and TDMA are now being phased
out in favor of either CDMA and GSM which allow
for higher capacity data transfers which open
for gateway services over WAP and i-mode,
Multimedia Messaging Services (MMS), and
wireless Internet Access. The major difference
between the two options is that many CDMA phones
can fall-back on to AMPS networks if the phone
can not get a CDMA signal but can get a AMPS
signal. CDMA phones can not use TDMA, only AMPS.
GSM phones, being designed by Europeans who had
never intended that GSM be used in America, do
not normally support this feature. However there
are some phones capable of supporting AMPS, TDMA
and GSM all in one phone. However AMPS/CDMA
phones supports seamless handoffs between CDMA
and AMPS/TDMA while GSM phones can not.
Analog system
in Europe
Total Access Communication System or
TACS is the European version of AMPS. ETACS was
an extended version of TACS with more channels.
TACS and ETACS are now obsolete in Europe,
having been replaced by the more scalable and
all-digital GSM system.
Companies
using AMPS
Telecom New Zealand - Telecom
customers are in the process of migrating over
to the new CDMA service. The old AMPS/D-AMPS
system is due to be phased out in 2007. Since
the establishment of the AMPS service in 1987
the network had always had the largest coverage
of any network in New Zealand. However in recent
times Digital GSM and CDMA coverage has matured
enough to match or exceed AMPS coverage in many
areas.
Verizon Wireless - Although most Verizon
customers use digital services, the backup AMPS
network is the largest in the United States.
Bell Mobility, Telus Mobility and Rogers
Wireless all operate AMPS networks in Canada,
though they have since been overlaid with
digital services.
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