Free Space Optics Communication System Testing in Smoke and Fire Environments.
Free Space Optics Communication System Testing in Smoke
and Fire Environments.
(3319 K)
Maranghides, A.; Mell, W. E.; Walton, W. D.; Johnsson,
E. L.; Bryner, N. P.
NISTIR 7317; 48 p. April 2006.
Sponsor:
National Communications System
Keywords:
computer models; fire models; diesel fuels; fuel fires;
fire tests; free space optics; optical wireless; smoke
measurement; smoke obscuration; scenarios; experiments;
uncertainty
Abstract:
Free-Space Optics, also known as "FSO" or "Optical
Wireless", use laser light to transmit a digital signal,
data, voice, or video information, between two
transceivers. These laser-based systems require
unobstructed line of sight to properly operate. FSO
system performance, signal
intensity and integrity, is related to beam obscuration
from environmental conditions including the presence of
smoke and flames. The National Communications System
(NCS), the telecommunications sector specific agency
under the Department of Homeland Security is
interested in quantifying the performance of FSO units.
In order to assess whether smoke and flames affect FSO
performance, a preliminary evaluation was conducted by
NCS and the National Institute of Standards and
Technology (NIST). The evaluation used both computer
modeling and a limited set of indoor experiments.
Several obscuration scenarios based on the smoke from
realistic diesel fuel fires of varying sizes were
jointly developed. The NIST Fire Dynamics Simulator
(FDS), a computational fluid dynamics computer fire
model, was used to
predict the levels of smoke obscuration for the
different realistic fire scenarios at a specified
distance above the fire. The FDS predictions were used
to design the laboratory experiments. Even though the
laboratory fires were smaller than those in the original
scenarios, the laboratory configurations could produce
similar smoke concentrations. The fire experiments were
conducted in the NIST, Building and Fire Research
Laboratory, Large Fire Laboratory in Gaithersburg,
Maryland. NCS provided the FSO units and NIST set up
instrumentation to
characterize smoke obscuration. The smoke obscuration
measurements showed that the target transmittance levels
were achieved and that desired smoke obscurations could
be generated over prolonged durations. The performance
of the FSO units was assessed and reported by NCS.
