Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cloudy day won't rain on laser communications

13.11.2006
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:
http://www.psu.edu

More articles from Physics and Astronomy:

nachricht Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)

nachricht Protecting the power grid: Advanced plasma switch for more efficient transmission
17.08.2018 | DOE/Princeton Plasma Physics Laboratory

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: It’s All in the Mix: Jülich Researchers are Developing Fast-Charging Solid-State Batteries

There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.

The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...

Im Focus: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Quantum bugs, meet your new swatter

20.08.2018 | Information Technology

A novel synthetic antibody enables conditional “protein knockdown” in vertebrates

20.08.2018 | Life Sciences

Metamolds: Molding a mold

20.08.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>