Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Cloudy day won't rain on laser communications

Just as clouds block the sun, they interfere with laser communications systems, but Penn State researchers are using a combination of computational methods to find the silver lining and punch through the clouds.

"Radio frequency communications are generally reliable and well understood, but cannot support emerging data rate needs unless they use a large portion of the radio spectrum," says Mohsen Kavehrad, the W. L. Weiss professor of electrical engineering and director, Penn State Center for Information and Communications Technology Research. "Free space optical communications offer enormous data rates but operate much more at the mercy of the environment."

Laser light used in communications systems can carry large amounts of information, but, the dust, dirt, water vapor and gases in a fluffy cumulus cloud, scatter the light and create echoes. The loss of some light to scattering is less important than those parts of the beam that are deflected and yet reach their target, because then, various parts of the beam reach the endpoint at different times.

"All of the laser beam photons travel at the speed of light, but different paths make them arrive at different times," says Kavehrad. "The Air Force, which is funding this project through the Defense Advanced Research Projects Agency, would like us to deliver close to 3 gigabytes per second of data over a distance of 6 to 8 miles through the atmosphere."

That 6 to 8 miles is sufficient to cause an overlap of arriving data of hundreds of symbols, which causes echoes. The information arrives, but then it arrives again because the signal is distributed throughout the laser beam. In essence, the message is continuously being stepped on.

Kavehrad and Sangwoo Lee, graduate student in electrical engineering, presented their solutions to the echo problem at the recent IEEE Military Communications Conference in Wash., D.C.

"In the past, laser communications systems have been designed to depend on optical signal processing and optical apparatus," says Kavehrad. "We coupled state-of-the-art digital signal processing methods to a wireless laser communications system to obtain a reliable, high capacity optical link through the clouds."

The researchers developed an approach called free-space optical communications that not only can improve air-to-air communications, but also ground-to-air links. Because their approach provides fiber optic quality signals, it is also a solution for extending fiber optic systems to rural areas without laying cable and may eventually expand the Internet in a third dimension allowing airplane passengers a clear, continuous signal.

Using a computer simulation called the atmospheric channel model developed by Penn State's CICTR, the researchers first process the signal to shorten the overlapping data and reduce the number of overlaps. Then the system processes the remaining signal, picking out parts of the signal to make a whole and eliminate the remaining echoes. This process must be continuous with overlap shortening and then filtering so that a high-quality, fiber optic caliber message arrives at the destination. All this, while one or both of the sender and receiver are moving.

"We modeled the system using cumulus clouds, the dense fluffy ones, because they cause the most scattering and the largest echo," says Kavehrad. "Our model is also being used by Army contractors to investigate communications through smoke and gases and it does a very good job with those as well."

The computer modeled about a half-mile traverse of a cumulus cloud. While the researchers admit that they could simply process the signal to remove all echoes, the trade-offs would degrade the system in other ways, such as distance and time. Using a two-step process provides the most reliable, high-quality data transfer.

The system also uses commercially available off-the-shelf equipment and proven digital signal processing techniques.

A'ndrea Elyse Messer | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht 'Frequency combs' ID chemicals within the mid-infrared spectral region
16.03.2018 | American Institute of Physics

nachricht Fraunhofer HHI have developed a novel single-polarization Kramers-Kronig receiver scheme
16.03.2018 | Fraunhofer-Institut für Nachrichtentechnik, Heinrich-Hertz-Institut, HHI

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

Im Focus: Radar for navigation support from autonomous flying drones

At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.

Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

International Virtual Reality Conference “IEEE VR 2018” comes to Reutlingen, Germany

08.03.2018 | Event News

Latest News

Wandering greenhouse gas

16.03.2018 | Earth Sciences

'Frequency combs' ID chemicals within the mid-infrared spectral region

16.03.2018 | Physics and Astronomy

Biologists unravel another mystery of what makes DNA go 'loopy'

16.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>