U.S. Army researchers are exploring the use of ultraviolet optical communications in battlefield situations because, under the right circumstances, the technology might support links that are undetectable to the enemy.
One thing the researchers looked at was the effects of attenuation, the natural phenomenon of the signals getting weaker over distance. They wanted to know whether there was a distance range in which the signals were weak enough that adversaries likely couldn’t detect them, but still be strong enough that friendly receivers could. They say they observed that to be the case, but the research paper about their work doesn’t say what those distances are.
According to an army press release, “ultraviolet communication has unique propagation characteristics that not only allow for a novel non-line-of-sight optical link, but also imply that the transmissions may be harder for an adversary to detect.”
The main thrust of the study by the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory was to develop a framework for future research that could quantify the circumstances under which ultraviolet communications could be both useful to friendly forces and undetectable to hostiles. In the course of that research they gleaned two other important insights:
- The worst case scenario – when the enemy detector is in direct line-of-sight with the transmitter and the friendly receiver is not – isn’t as big a concern as might be feared.
- Steering the signal of the UV transmitter doesn’t seem to be an effective way to mitigate detection of the signal by an adversary.
The researchers plan to analyze four scenarios involving the placement of the UV transmitter, the intended receiver and the enemy detector:
- The friendly receiver and the adversary detector are both in line-of-sight with the transmitter.
- The friendly receiver is in line-of-sight but the adversary detector is not. (Best case)
- The adversary’s detector is in line-of-sight but the friendly receiver is not. (Worst case)
- Neither the friendly receiver nor adversary detector is in line-of-sight.
The assumption is that an opponent would try to count photons over time to detect a coherent transmission signal that would indicate that communication was underway.
The scientists accept the fact that close-in to the transmitter, the signal is easy to detect, so effective use of the UV transmissions would rely on having a good sense of where the opposing detectors are located.
“Our work provides a framework enabling the study of the fundamental limits of detectability for an ultraviolet communication system meeting desired communication performance requirements,” said Dr. Robert Drost, one of the researchers.
“Our research is ensuring that the community has the fundamental understanding of the potential for and limitations of using ultraviolet wavelengths for communications, and I am confident that this understanding will inform the development of future Army networking capabilities.”
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