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Advanced Mobile Phone System
Advanced Mobile Phone System or AMPS 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.
It was a first-generation technology, using FDMA which meant each cell site would transmit on different frequencies, allowing many cell sites to be built 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 systems, such as Digital AMPS and GSM, which brought improved security as well as increased capacity.
AMPS cellular service operates in the 800 MHZ FM band. For each market area, the 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 Federal Communications Commission 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 Federal Communications Commission 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 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 U.S. Cellular. The misuse 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 or GSM which allow for higher capacity data transfers for services such as WAP, Multimedia Messaging System (MMS), and wireless Internet Access. The major difference between the two options is that CDMA has a much higher capacity then GSM, as well as some other features (i.e. being able to talk to six different cell sites simultaneously, and a higher bitrate Vocoder). There are some phones capable of supporting AMPS, TDMA and GSM all in one phone (using the GAIT standard; see the Nokia 6340, for example); however, AMPS/CDMA phones supports nearly seamless roaming between CDMA and AMPS (with the loss of some features when in AMPS mode, such as text messaging) while GAIT phones cannot.
The Future of AMPS
AMPS is the most extensive and reliable wireless coverage available for nationwide service. Even today, analog continues to provide the widest range of coverage across the U.S. and Canada. However, in 2002, the FCC made the drastic desicion to no longer require A and B carriers to support AMPS cellular 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 CDMA or GSM and continue to do so at a rapid pace. Digital technologies such as CDMA support multiple voice calls on the same channel, superior call qualiy, enhanced features such as two-way text messaging, voicemail indicator, internet, and GPS services; whereas, AMPS can only support one call per channel and a short message service.
OnStar still heavily relies on North American AMPS service for its subscribers because it provides the best and most reliable coverage and their entire system was built around analog cellular technology. Thankfully, cellular companies who own an A or B license (such as Verizon and Alltel) must still provide reliable analog service until March 1, 2008. However after that point, most cellular companies will be eager to shut down AMPS and use the remaining channels for even more capacity and enhanced data services. OnStar is currently in a digital transition but warns customers who cannot be upgraded to digital that their service will permanetly 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 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. 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 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.
Alltel - Alltel (a North American AMPS/CDMA carrier) stated in 2005 that only 15% of their total customer base still uses the existing analog network. According to an Alltel spokesman, 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.