Cellular Phone Technology

Analog Service is similar to FM radio in that modulating radio signals carry information such as voice or data. The receiver and transmitter must be tuned to the same frequency within a small band width for the receiver to rebuild the signal, amplify it, and send it to the speaker. There are limitations on the number of channels that can be used making this technology soon to be outlived. Effective February 2008, many wireless providers will be discontinuing support of this service.

Digital Service is a method similar to computers, in that it uses binary code of Os and 1s. Most new wireless phones and networks use digital technology. The analog signal in Digital is converted into binary code and transmitted as a series of on and off transmissions. There are three digital wireless technologies, CDMA, TDMA and GSM and I will explain these three as phones that work with one may not work on another.

TDMA (Time Division Multiple Access) was released in 1994; it uses the frequency bands available to the wireless network and divided them into time slots with each phone user having access to one time slot at regular intervals. In North America TDMA uses both 800 MHz and 1900 MHz bands. Most of the major wireless carriers use TDMA.

CDMA (Code Division Multiple Access) technology dates back to the 1940’s, when it was developed for military use because it was resistant to interference from enemy signals. Known as spread spectrum technology this technology was restricted to military use and top secret during World War 2. In the 1980’s the commercial use of this technology was realized after a 1976 publication of Spread Spectrum Systems by Robert Dixon was published.

Previous publications were classified military reports or narrow subtopics on academic papers. By 1993 CDMA was accepted as a standard and went into operation in 1996. CDMA also exists at both the 800 MHz and 1900 MHz band, and is used by the major carriers.

GSM (Global System for Mobile Communications) is based upon an improved version of TDMA technology. In 1982, a conference in Europe created a digital standard to allow users to roam from country to country in Europe. By 1987, the GSM standard was created based upon both analog and TDMA digital technologies. Using wider 200 kHz channels instead of the 30 kHz channels TDMA used along with other modifications they were able to speed up the bit rate with a more natural sounding voice-compression algorithm.

This also enabled GSM to provide such other data services as email, fax, internet browsing, and internet/LAN wireless access. The GSM standard was accepted in the United States in 1995 and is the only phone that can be used around the world. This technology will be the bases of future growth in the wireless phone industry as it offers the multifunction capabilities today’s users require.

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