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Free Space Optics Communication System Testing in Smoke and Fire Environments.


pdf icon 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.