Special feature
Camera phone showdown
|
|
AMPS(Advanced Mobile Phone System)
AMPS(Advanced Mobile Phone System) is the analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1984. 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
AMPS is a first-generation cellular technology. Since AMPS uses FDMA which means each conversation is divided simply by using a different channel, it seemed a lot like the older 0G IMTS service. However, AMPS exceled over older technologies because of its use of computerized management of not only frequencies, but individual handset transmitter power, and call setup. AMPS fathered the term "cellular" because of its use of small "cells" within a system. These cells are what made the AMPS system successful because they allowed for frequency reuse so that many people could reuse the same channel in different parts of the system without interference. It suffered from some downfalls when compared to today's digital technologies. Since it is an analog standard, it is very susceptible to static and noise and has no protection from eavesdropping using an illegal scanner. In the 1990's, "cloning" was an epedemic that cost the industry millions of dollars. An unscrupulous eavesdropper with specialized equipment can intercept a handset's NAM (Number Assignment Module). A Number Assignment Module is a packet of data which is sent by the handset to the cellular system for billing purposes. The system then allows or disallows calls and or features based on its customer file. If a NAM is intercepted, it could then be cloned onto a different phone and used in other areas for making calls without paying. The problem became so large that some carriers required the use of a PIN number before making calls. Though cloning is still possible even with digital technologies, the cost of wireless service is so low that the problem has virtually disappeared. AMPS has been replaced by newer digital standards, such as Digital AMPS, GSM, and CDMA which brought improved security as well as increased capacity.
AMPS was originally standardized by ANSI as EIA/TIA/IS-3. This was later superseded by EIA/TIA-553 and TIA interim standard IS-91.
Frequency bands
AMPS cellular service operates in the 800 MHz "Cellular" FM band. For each market area, the Federal Communications Commission (FCC) allowed two licensee (networks) known as "A" and "B" carriers. Each carrier within a market uses a specified "block" of frequencies consisting of 21 control channels and 395 voice channels. Originally, the B (wireline) side license was usually owned by the local phone company such as a "Baby Bell" (Ameritech), and the A (non-wireline) license was made available to private companies such as Cellular One. At the inception of cellular in 1984, the FCC had granted each carrier within a market 333 channels (666 channels total). By the late 1980's, the cellular industry's subscriber base had grown into the millions across America and it became necessary to add channels for additional capacity. In 1989, the FCC granted carriers an expansion from the current 666 channels to the now 832 (416 per carrier). The additional frequency was available in the upper 800 MHz band which also was home to UHF channels 70-83. This meant that these UHF channels could no longer be used for UHF TV transmission as these frequencies were to be used for AMPS transmission.
The anatomy of 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.
Introduction of digital TDMA
Later, many AMPS networks were partially converted to D-AMPS, often referred to as TDMA (though TDMA is a generic term that applies to many cellular systems). D-AMPS is a digital, 2G standard used mainly by Cingular Wireless and U.S. Cellular.
Introduction of GSM and CDMA
AMPS and D-AMPS ("TDMA") are now being phased out in favor of either CDMA2000 or GSM which allow for higher capacity data transfers for services such as WAP, Multimedia Messaging System (MMS), and wireless Internet access. There are some phones capable of supporting AMPS, D-AMPS and GSM all in one phone (using the GAIT standard).
The Future of AMPS
In 2002, the FCC decided to no longer require A and B carriers to support AMPS service as of March 1, 2008. Since the AMPS standard is analog technology, it suffers from an inherently inefficient use of the frequency spectrum. All AMPS carriers have converted most of their consumer base to a digital standard such as CDMA2000 or GSM and continue to do so at a rapid pace. Digital technologies such as GSM and CDMA2000 support multiple voice calls on the same channel and offer enhanced features such as two-way text messaging and data services.
OnStar still heavily relies on North American AMPS service for its subscribers because, when the system was developed, AMPS offered the most comprehensive wireless coverage in the US. Thankfully, cellular companies who own an A or B license (such as Verizon and Alltel) must still provide analog service until March 1, 2008. After that point, however, most cellular companies will be eager to shut down AMPS and use the remaining channels for digital services. OnStar is currently in a digital transition but warns customers who cannot be upgraded to digital that their service will permanently expire on February 1, 2008.
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 GSM system. In the United Kingdom, the last ETACS service operated by Vodafone was discontinued on 31 May 2001, after sixteen years of service. ETACS is however still in use in a handful of countries elsewhere in the world. NMT is another analog cellular standard that was widely used in Europe, mainly in the Nordic countries, which has now been fully replaced by GSM.
|
|
Put Your ads here
|
 |
