Wireless PCS
Technology
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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