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Unformatted text preview: r technologies and offer data rates of several Mbps.
Local Multipoint Distribution Systems (LMDS)
LMDS is a technology for supporting point-to-multipoint applications. It uses a
28-31 GHz band with 1.3 GHz of spectrum allocated to it in the US and 3 GHz of
spectrum allocated to it in Canada. LMDS uses spread spectrum and microcell
technology that supports two-way data transfer rates of up to 1 Gbps. A drawback
of the LMDS technology is that signal propagation at the 28 GHz range requires a
direct line-of-sight path between the transmitter and receiver. Possible applications
of LMDS technology are high-speed Internet data, video conferencing, and cable
TV data transmission at several hundred Mbps.
Wireless Technologies and Standards
Over the years, several wireless technologies and standards have been introduced.
Out of these, some of the most popular ones are described below.
2G and 3G Technologies
The early mobile phones used first-generation technology, which was analog,
circuit-based, narrowband, and suitable only for voice communications. Then
came the second-generation wireless-networking technology (popularly known as
2G technology), which was digital, circuit-based, and narrowband but suitable for
voice and limited data communications. Currently, we have the third-generation wireless-networking technology (popularly known as 3G technology), which is
suitable for voice and advanced data applications, including online multimedia and
mobile e-commerce. Further details of the 2G and 3G technologies are given
As mentioned above, 2G technology is digital, circuit-based, narrowband, and
suitable for voice and limited data communications. It comprises of the following
three primary standards:
TDMA. The Time-Division-Multiple-Access (TDMA) technology does
time-division multiplexing of each cellular channel to handle multiple
communications simultaneously. In particular, TDMA technology divides each
cellular channel into three time slots, each of which handles a separate
The channel switches quickly from one time slot to another,
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- Spring '14