A Core Competence Product Evaluation
GSM: Global System For Mobile Communication
GSM is one of three digital cell phone technologies marketed in North America under the umbrella term PCS (Personal Communications Service). Just like plain old cellular, PCS operates over a wireless radio network. However, instead of modulating data for analog transmission, PCS encodes voice into a digital signal for improved sound quality and reliability. PCS offers circuit-switched data services that turn your phone into a wireless uplink for your laptop modem, supporting fax, email, web browsing, and file transfer applications. PCS Short Message Services (SMS) allow your phone to double as an alphanumeric pager by sending and receiving brief text messages without placing a call. Finally, the PCS digital air link that supports these services is encrypted to ensure privacy.
If you're confused by the alphabet soup of PCS, GSM, and SMS, not to mention related acronyms TDMA, CDMA, and CDPD, you're not alone. As digital cellular technologies have emerged, their names, frequencies, and even target markets have changed. Here's how the puzzle pieces fit together today...
AMPS refers to the plain old analog cellular service that is widely available today, operating at 800 Mhz in North America. Kind of noisy, with transient drop-offs in signal that are simply annoying for voice but downright hostile to data.
PCS refers collectively to three new digital cellular services (GSM, TDMA, and CDMA) now operating in North America at 1900 Mhz.
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TDMA (Time Division Multiple Access), also known as IS-136 or D-AMPS, is used
by North American carriers such as AT&T Wireless, BellSouth, and Southwestern Bell
to offer PCS services.
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CDMA (Code Division Multiple Access), also known as IS-95, is used by North American
carriers such as AirTouch, BellAtlantic/NYNEX, GTE, Primeco, and Sprint PCS to
offer PCS services.
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GSM, previously known as PCS 1900 or DCS 1900, originated in Europe but has since
become an international standard and is deployed in North America today by
Aerial Communications
Airadigm Communications
American Personal Communications
BellSouth Personal Communications
Conestoga Wireless
DigiPH
Omnipoint Communications
Pacific Bell Mobile Services
PCS One
Powertel
Southeast Telephone
Sprint Spectrum
Third Kentucky Cellular
Western Wireless
For more information about PCS and the differences between GSM, TDMA and CDMA, visit the PCS Data Knowledge Site. Of the three PCS technologies, only GSM offers global roaming. But because GSM operates at different frequencies in other countries, you can't just use your GSM 1900 phone in Europe. Instead, you must swap your own phone's SIM card into a loaner phone; SIM portability is a feature unique to GSM phones. Multi-frequency GSM phones that enable more transparent global roaming are being developed now. For detailed information about GSM carriers worldwide, including tariffs, services, roaming and coverage for over 215 operators in more than 100 countries, visit GSMInfo Online.
GSM was also the first PCS technology to offer data services - currently 9600 bps, expected to reach 14.4 Kbps later this year. PCS supports circuit-switched data, which means that digital data is exchanged by setting up a call (a "circuit") that dedicates a radio channel to your phone until you hang up, whether or not data is being transmitted. You may have also heard about packet-switched data services like CDPD (Cellular Digital Packet Data), ARDIS, RAM Mobile Data, and Metrocom Ricochet. Unlike PCS, these services do not establish private circuits to carry data. Instead, they transmit bursts of data (packets) over any available radio channel - somewhat analogous to the way in which shared Ethernet is used by all workstations on a hubbed LAN. Click here for more information about how packet data services compare to PCS. From a consumer viewpoint, one obvious difference is billing: with PCS, expect to be charged by connect time; with packet-switched data, expect to be charged by quantity of data sent and received.