|
|
|
| |
|
|
|
| |
The
PCS Technology |
|
|
| |
|
|
|
| |
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. |
| |
| |
| Source: http://inventors.about.com/library/weekly |
| |
| |
|
Site
designed and developed by DDA Infotech
|
|
