Mobile Access to
Modern cellular phones provide an incredible set of functions, and new functionalities
are being added at a startling pace. Phones can be used to store contact information, make
task or to-do lists, keep track of appointments and set reminders, provide access to calcula-
tors, send and receive e-mail, download information (e.g. news, entertainment, stock
quotes) from the Internet, enable users to play games, take pictures with in-built cameras
and send them via the Web, and integrate with other devices such as PDAs, MP3 players
and GPS receivers.
In terms of architecture, cellular phones comprise a circuit board containing analogue-
to-digital (for the incoming signal) and digital-to-analogue (for the outgoing signal)
converters, the digital signal processor, memory (ROM and Flash), the radio frequency
and power components, radio frequency amplifiers, a keypad, a display, a speaker, and a
Cellular phones are sophisticated radio devices, the cellular approach having been intro-
duced as a successor to radio-telephone systems.This relies on the division of geographic
areas into cells (typically sized at about twenty-six square kilometres, although in densely
populated urban areas the cells can be smaller), analogous to a collection of hexagons on a
large hexagonal grid. Each cell is equipped with a base station, comprising a tower with
antennae and corresponding radio equipment. A unique set of frequencies and correspon-
ding voice and data channels are used within each cell, thus avoiding collisions between
adjacent cells. Additionally, cell phones and base stations use low-power transmitters and
the same frequencies can be reused in non-adjacent cells. Each provider employs a Mobile
Telephone Switching Office (MTSO) from which all phone connections to the normal
land-based phone system and all of the base stations in the region are controlled. Mobile
phones have special codes associated with them which can be used to identify the phone,
its owner, and the service provider.The connection of each phone to the network and the
logs of cell phone movement from one cell to another are controlled by the MTSO and
the corresponding base stations.
There are two basic categories of cell phones analogue and digital.The analogue cell-
phone standard called the Advanced Mobile Phone System (AMPS) was launched in 1983.
Digital cell phones use the same radio technology as analogue phones, but they use it in a
different way digital signals can be compressed and manipulated in order to transmit
more channels within a given bandwidth.
Three common technologies are used by cellular phone networks for transmitting
information: frequency division multiple access (FDMA), time division multiple access
(TDMA), and code division multiple access (CDMA). FDMA is used for analogue trans-
mission, and although digital information can be carried using this standard it is not very
efficient.TDMA acts as the access technology for Global System for Mobile
Communications (GSM) systems, which use encryption to make phone calls more secure.
CDMA systems allow multiple calls to share the same channel involving GPS technology.
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