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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