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Resources on Wireless PCS Technology |
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Wireless
and PCS Technology - Research
Wireless glossary, more wireless
history, PCS technologies, history of GSM, more digital cellular history,
CDMA vs TDM, history of the TCA, wireless communication standards, health
risks. |
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By
Mary
Bellis
PCS (Personal
Communication Services):
Used to describe a newer class of wireless
communications services recently authorized by the FCC. PCS systems use
a different radio frequency, the 1.9 GHz band, than cellular phones and
generally use all-digital technology for transmission and reception. (Definition
from the Wireless Advisor
glossary.)
After the Federal Communications
Commission (FCC) declared in 1987 that cellular licensees could employ
alternative cellular technologies in the 800 MHz band, the cellular industry
began to research new transmission technology as an alternative to AMPS
(Advanced Mobile Phone Service) that had been the industry standard since
1978.
In 1988, the Cellular
Technology Industry Association (CTIA) was established to work with
the cellular service operators and researchers to identify new technology
requirements and set goals. They wanted the new products and services introduced
by 1991, a 1000% percent increase in system capacity with both AMPS (analog)
and digital capability during transmission, and new data features such
as fax and messaging services.
The Telecommunications
Industry Association (TIA) created a standard specification based on
the requirements the CTIA had recommended. The TDMA Interim Standard 54
or TDMA IS-54 was released in early 1991. The technology was tested that
same year in Dallas and Sweden. In 1994, the FCC announced it was allocating
spectrum specifically for PCS technologies at the 1900 MHz band. Three
major standards have been released since 1991. All of these new digital
wireless standards are currently being used in PCS (Personal Communication
Services - see definition at top of page).
Wireless
Standards
Analog Service: A method of
modulating radio signals so that they can carry information such as voice
or data. Analog cellular phones work like a FM radio. The receiver and
transmitter are tuned to the same frequency, and the voice transmitted
is varied within a small band to create a pattern that the receiver reconstructs,
amplifies and sends to a speaker. The drawback of analog is the limitation
on the number of channels that can be used.
Digital Service: A method
of encoding information using a binary code of 0s and 1s. Most newer wireless
phones and networks use digital technology. In digital, the analog voice
signal is converted into binary code and transmitted as a series of on
and off transmissions. One of digital's drawbacks, is that there are three
digital wireless technologies, CDMA, TDMA and GSM. Phones that work with
one technology may not work on another.
TDMA
IS-136 (Time Division Multiple Access) is an update to TDMA IS-54,
also called Digital AMPS or D-AMPS. Released in 1994, TDMA IS-136 uses
the frequency bands available to the wireless network and divides them
into time slots with each phone user having access to one time slot at
regular intervals. TDMA IS-136 exists in North America at both the 800
MHz and 1900 MHz bands. Major US carriers using TDMA are AT&T Wireless
Services, Bell South and Southwestern Bell.
CDMA IS-95 (Code Division
Multiple Access) is based on a form of spread spectrum technology that
separates voice signals by assigning them digital codes within the same
broad spectrum. CDMA type technology dates back to the 1940s, when spread
spectrum technology was used in military communications systems because
it was resistant to interference from enemy signals. The
Qualcomm
corporation began developing a CDMA wireless system in the late 1980s that
was accepted as a standard in 1993 and went into operation by 1996. CDMA
also exists at both the 800 MHz and 1900 MHz bands. The major US carriers
using CDMA are Air Touch, Bell Atlantic/Nynex, GTE, Primeco and Sprint
PCS.
GSM (Global System for Mobile
Communications) is based on a improved version of TDMA technology. In 1982,
the Conference of European Posts and Telecommunications (CEPT) began the
process of creating a digital cellular standard that would allow users
to roam from country to country in Europe. By 1987, the GSM standard was
created based on a hybrid of FDMA (analog) and TDMA (digital) technologies.
GSM engineers decided to use wider 200 kHz channels instead of the 30 khz
channels that TDMA used, and instead of having only 3 slots like TDMA,
GSM channels had 8 slots. This allowed for fast bit rates and more natural-sounding
voice-compression algorithms. GSM is currently the only one of the three
technologies that provide data services such as email, fax, internet browsing,
and intranet/LAN wireless access, and it's also the only service that permits
users to place a call from either North America or Europe. The GSM standard
was accepted in the United States in 1995. GSM-1900 cellular systems have
been operating in the US since 1996, with the first network being in the
Washington, D.C. area. Major carriers of GSM 1900 include Omnipoint, Pacific
Bell, BellSouth, Sprint Spectrum, Microcell, Western Wireless, Powertel
and Aerial.
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