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15 March 2016 Characterization of modems and error correcting protocols using a scintillation playback system
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The performance of free space optical (FSO) communication systems is strongly affected by optical scintillation. Scintillation fades can cause errors when the power on a detector falls below its noise floor, while surges can overload a detector. The very long time scale of scintillation compared to a typical bit in an FSO link means that error-correcting protocols designed for fiber optic links are inappropriate for FSO links.

Comparing the performance effects of different components, such as photodetectors, or protocols, such as forward error correction, in the field is difficult because conditions are constantly changing. On the other hand, laboratory-based turbulence simulators, often using hot plates and fans, do not really simulate the effects of long-range propagation through the atmosphere.

We have investigated a different approach. Scintillation has been measured during field tests using FSO terminals by sending a continuous wave beam through the atmosphere. A high dynamic range photodetector was digitized at a 10 KHz rate and files of the intensity variations were saved. Many hours of scintillation data under different environmental conditions and at different sites have been combined into a library of data.

A fiber-optic based scintillation playback system was then used in the laboratory to test modems and protocols with the recorded files. This allowed comparisons using the same atmospheric conditions allowing optimization of such parameters as detector dynamic range. It also allowed comparison and optimization of different error correcting protocols.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
William S. Rabinovich, Rita Mahon, Mike S. Ferraro, James L. Murphy, and Christopher I. Moore "Characterization of modems and error correcting protocols using a scintillation playback system", Proc. SPIE 9739, Free-Space Laser Communication and Atmospheric Propagation XXVIII, 97390M (15 March 2016);

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