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The Naval Research Laboratory’s Chesapeake Bay (CBD) Lasercom Test Facility (LCTF) maintains a full suite of optical instruments characterizing a path that goes 16 km across Chesapeake Bay. In addition, a 100 Mbps FSO link is continuously run to gather link quality statistics.
In this work we examine data from CBD including scintillation index, transmission, and packet error rate, as well as local weather data. With this data, as well as link models, we determine to what extent we can predict the actual link availability at CBD and at other locations.
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.
Multiple quantum well-based modulating retroreflectors for inter- and intra-spacecraft communication
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