Cellular mobile
radio systems aim to provide high-mobility, wide-ranging, two-way wireless voice
communications. These systems accomplish their task by integrating wireless access
with large-scale networks, capable of managing mobile users. Cellular radio technology
generally uses transmitter power at a level around 100 times that used by a cordless
telephone (approximately 2 W for cellular).
Standards Cellular
radio has evolved into digital radio technologies, using the systems standards
of GSM (at 900 and 1800 MHz) in Europe, PDC in Japan, and IS-136A and IS-95A in
the United States. Third-generation systems, such as wideband code division multiple
access (WCDMA) and cdma2000, are currently under development.
Design
Considerations One of the most significant consideration in designing digital
systems is the high cost of cell sites. This has motivated system designers to
try to maximize the number of users per megahertz, and users per cell site. Another
important consideration is maintaining adequate coverage in areas of varying terrain
and population density. For example, in order to cover sparsely populated regions,
system designers have retained the high-power transmission requirement to provide
maximum range from antenna locations. Communications engineers have also been
developing very small coverage areas, or microcells. Microcells provide increased
capacity in areas of high user density, as well as improved coverage of shadowed
areas. Some microcell base stations are installed in places of high user concentrations,
such as conference center lobbies.