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Cellular Networking Perspectives

Cellular Technologies


Cellular Networking Perspectives! analyzes and reports on AMPS cellular and PCS technology, including TDMA and CDMA digital as well as GSM and 3G technologies (CDMA2000 and Wideband-CDMA/UMTS). The original analog version of this wireless system was brought to commercial deployment by AT&T in 1983, prior to divestiture, based on the concept that higher capacity could be achieved by small (i.e. low power) cells, allowing frequencies to be reused. Other advantages, not known at the time, included the possibility of handheld phones and low terminal prices due to advances in electronics technology and the economies of scale of the mass market. Consequently, an industry that was estimated by optimists when the first systems in Chicago and Washington/Baltimore came online in 1983 as likely to serve 1 million subscribers in the US by the year 2000, is expected to be serving over 100 million by the end of 2000!

AMPS originally operated as an analog system in the 800 MHz frequency band using 30 kHz wide channels. A variant of AMPS, known as N-AMPS, uses 10 kHz wide channels and consequently has close to triple the capacity. AMPS is still in common use throughout the Americas, but is declining in the face of digital cellular standards.

Wireless carriers that began service with AMPS systems have generally turned to TDMA and CDMA digital operation in the 800 MHz cellular band. The 1800 MHz - 2200 MHz PCS frequency band has only ever used digital standards. Although the use of AMPS is declining, it is still retained for compatibility purposes, as many digital phones can fall back to analog operation if their digital mode is not available.

AMPS is defined not by a single standard, but by many standards. All the standards are developed by the TR-45 committee within the TIA (Telecommunications Industry Association). Even the radio interfaces are defined by several families of standards, one for each technology (Analog, NAMPS, TDMA and CDMA). Automatic roaming with a cellular phone is made possible by the TIA/EIA-41 standard that provides intersystem handoff, call delivery, remote feature control, short message delivery, validation and authentication through an intersystem messaging protocol. TIA/EIA-41, developed by the TIA TR-45.2 subcommittee, is often discussed in Cellular Networking Perspectives.

There are other forms of analog cellular in the world:

CDPD
Not really analog, but a digital packet data system that occupies a single 30 kHz AMPS channel, and provides 19.2 kbps shared bandwidth.
NAMPS
A version of AMPS that uses 10 kHz channels and, therefore, has about 3 times the capacity.
NMT
A Scandinavian 450/900 MHz analog cellular system, the closest thing in Europe to a standard prior to GSM. NMT systems have been installed in many countries outside Europe. Most NMT systems will eventually be displaced by GSM. NMT was originally implemented in the 450 MHz band using 25 kHz channels (known as NMT-450), but was later adapted for use in the 900 MHz band using 12.5 kHz channels, for about double the capacity.
TACS/ETACS
This standard is really AMPS, except that it operates in the 900 MHz frequency band. A version known as NTACS operates in a lower frequency band (860-870/915-925 MHz) using 12.5 kHz channels. A Japanese version known as JTACS is similar, but operates in other frequency bands

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© – Copyright Mon, May 14, 2007: Cellular Networking Perspectives Ltd.