Advanced Mobile Phone System
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Advanced Mobile Phone System (AMPS) is the analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1983[1][2] It was the primary analog mobile phone system in North America (and other locales) through the 1980s and into the 2000s, and is still widely available today, although use has dropped considerably with the introduction of various digital standards.
Total Access Communication System (TACS) and ETACS are mostly-obsolete variants of AMPS which were used in some European countries (including the UK). TACS was also used in Japan under the name Japanese Total Access Communication (JTAC).[3][4]
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[edit] Technology
AMPS is a first-generation cellular technology that uses separate frequencies, or "channels", for each conversation (see FDMA). It therefore requires considerable bandwidth for a large number of users. In general terms, AMPS is very similar to the older "0G" IMTS service, but uses considerably more computing power in order to select frequencies, hand off conversations to POTS lines, and handle billing and call setup.
What really separates AMPS from older systems is the "back end" call setup functionality. In AMPS, the cell centers can flexibly assign channels to handsets based on signal strength, allowing the same frequency to be re-used in various locations without interference. This allowed a larger number of phones to be supported over a geographical area. AMPS pioneers fathered the term "cellular" because of its use of small hexagonal "cells" within a system.[5][6]
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 epidemic 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 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.
[edit] 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 1983, 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.
[edit] 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 in the United States, Rogers Wireless in Canada, and Movilnet in Venezuela.
[edit] 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).
[edit] The Future of AMPS
In 2002, the FCC decided to no longer require A and B carriers to support AMPS service as of February 18, 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.
Unlike in the United States, the CRTC and Industry Canada have not set any requirement for maintaining AMPS service in Canada. Rogers Wireless is in the process of dismantling their AMPS (along with IS-136) network, with full shutdown expected in May 2007. Bell Mobility and Telus Mobility, who also operate AMPS networks in Canada, have announced that they will observe the same timetable as outlined by the FCC in the United States, and as a result will not begin to dismantle their AMPS networks until after February 2008.[1]
OnStar relies heavily on North American AMPS service for its subscribers because, when the system was developed, AMPS offered the most comprehensive wireless coverage in the US. ADT recently asked the FCC to extend the AMPS deadline due to many of their alarm systems still using analog technology to communicate with the control centers.[7] Cellular companies who own an A or B license (such as Verizon and Alltel) must still provide analog service until February 18, 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 transitioning to digital service with the help of data transport technology developed by Airbiquity, but warns customers who cannot be upgraded to digital that their service will permanently expire on January 1, 2008.[8]
[edit] TACS, ETACS and JTAC variants
Total Access Communication System (or TACS) is a variant of AMPS developed by Motorola. It has been used in some European countries (including the UK), as well as Japan and Hong Kong.[9] (In Japan, it is known as Japanese Total Access Communication, or JTAC.)[3][4] ETACS was an extended version of TACS with more channels.
TACS and ETACS are now obsolete in Europe, having been replaced by the 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 except for limited use in rural areas due to its superior range.
[edit] Companies using AMPS
- Telecom New Zealand — Its customers are in the process of migrating over to the new CDMA service. The old AMPS/D-AMPS system is due to be turned off at the end of March 2007. Since the establishment of the AMPS service in 1987 the network had always had the largest coverage of any network in New Zealand. In recent times, however, Digital GSM and CDMA coverage has matured enough to match or exceed AMPS coverage in many areas. Unfortunately some areas may lose mobile phone service when the AMPS network goes offline.
- Verizon Wireless — Although most customers use digital services, the backup AMPS network is still in service. Verizon has noted that they are eager to quickly shut down the analog system when the FCC mandate allows.
- Bell Mobility, Telus Mobility and Rogers Wireless all operate AMPS networks in Canada, though they have since been overlaid with digital services. Rogers Wireless is currently in the process of decommissioning their AMPS network, will full shutdown expected to occur in May 2007. Both Bell Mobility and Telus Mobility have announced that they will observe the same shutdown guidelines as in the United States, and will not begin decommissioning their AMPS networks until after February 2008.[2]
- Alltel — In 2005 disclosed that only 15% of their total customer base are still using the existing analog network. The company has not made any official announcements as to when analog service will be discontinued. One plan involves only keeping analog service active in rural or outlying areas until digital service is fully developed. With the recent acquisition of Western Wireless, Alltel now takes the claim of the "largest network in America." The claim is true, oddly enough because of wide analog coverage in rural areas.
- Coastel Offshore Cellular — Operates an AMPS network in the Gulf of Mexico that stretches from south of Corpus Christi, TX to south of Gulf Shores, AL. As of 2006 Coastel is the only carrier in the US whose entire customer base is still 100% analog based.
- Moviline (Telefónica Servicios Uno since 1971, Moviline since 1994) - Has operated an ETACS 900 network in Spain. Since 31st December 2003, the system has been closed to new users, but existing suscribers can still use it. At that time, it covered 100% of Spanish population, but now some antennas have been given to GSM operators.[10]
[edit] References
- ^ Private Line.
- ^ MilestonesPast.
- ^ a b GSM Terma, volny.cz. Article retrieved 2006-01-19.
- ^ a b Japanese Total Access Communication (JTAC), mobiledia.com. Article retrieved 2007-01-19.
- ^ W. Rae Young, "AMPS: Introduction, Background, and Objectives", Bell System Technical Journal, vol. 58, 1, pages 1-14, January 1979. (Note: Young was the Bell Labs engineer who invented the hexagonal cell concept.)
- ^ Z. C. Fluhr and Philip T. Porter, "AMPS: Control Architecture", Bell System Technical Journal, vol. 58, 1, pages 1-14, January 1979. (Note: Porter was the Bell Labs engineer who invented call "handoff" for the cellular system, so that mobile phone calls from moving vehicles would be automatically handed off to the next base station with seamless connectivity and frequency changes.)
- ^ ITWorld.
- ^ OnStar.
- ^ Cellular Networks QuickStart: Getting up to Speed on Cellular, from 1G to 3G, devx.com. Article dated 2003-03-17, retrieved 2007-01-19.
- ^ Document covering end of Spanish analogue mobile telephone services (in Spanish), Ministerio de Industria, Turismo y Comercio (Spain). Article dated 2003-12-19, retrieved 2007-01-28.
