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Service, Department of the Treasury, and
other civilian agencies). The APCO Project-25 process has
encouraged an unprecedented level of cooperation among municipal
7. These activities are carried out by the
ITU Radiocommunication Sector (ITU-R) Working Party 8/13, later
renamed ITU-R Task Group 8/1.
8. The implementation of standards based
on IMT-2000 in Japan clearly would give Japanese companies early
experience with the technology and perhaps position them to
dominate future world markets for IMT-2000 products.
9. Although optical communications systems
are not addressed in detail in this report, in large part because
the commercial research focuses on indoor applications, the
advantages of laser systems need to be mentioned. A laser produces
optical radiation by stimulating emissions from an electronic or
chemical material. Unlike light produced by incandescent or
fluorescent sources, the resultant beam is coherent and exhibits
extremely low angular divergence, properties that enable
transmissions spanning great distances (i.e., thousands of miles).
The data, voice, images, or other signals are modulated on a beam
of light, which is detected by an optical receiver and decoded. The
transmitter and receiver need to be in direct visual contact, and
so the laser beam is steered in the appropriate direction using
mirrors or other optical elements. Laser communications systems
offer several advantages over RF systems. The main advantage is
high capacity: Systems now under development will support
transmissions in the range of hundreds of megabits per second, with
systems under consideration attaining the gigabits-per-second
range. Another advantage is the low power requirement for
point-to-point communications (orders of magnitude lower than RF
systems). All the energy is focused into a very narrow beam because
the physical dispersion of a laser beam in space is minimal.
Furthermore, laser communications systems offer security benefits
because almost no energy is diffused outside the laser beam, which
is therefore not easily detected by an adversary. This combination
of features makes laser communications systems attractive for
secure transmissions between hub points in mobile, dynamically
changing environments (e.g., between base stations on
vehicle-mounted switching facilities). However, laser systems are
sensitive to interference from other light sources, such as the
sun, and any obstructions of the visual link by dust, rain, or fog.
There is also a risk of damage to the eyes of unprotected
observers. Finally, components for laser-based systems are much
more expensive than those for RF systems and therefore are unlikely
to penetrate the commercial market for some time.
10. These activities are carried out by
the ITU Telecommunications Sector, Study Group 11.
11. The ISM bands (at 902–928 MHz,
2400–2483 MHz, and 5700–5850 MHz) are available for any
wireless device that uses less than 1 watt of transmit power.
12. The United States participates in the
IMT-2000 process in Task Group 8/1 through a delegation led by the