Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Multi-rate laser pulses could boost outdoor optical wireless performance

27.10.2004


Multi-rate, ultra-short laser pulses -- with wave forms shaped like dolphin chirps -- offer a new approach to help optical wireless signals penetrate clouds, fog and other adverse weather conditions, say Penn State engineers.



The new approach could help bring optical bandwidth, capable of carrying huge amounts of information, to applications ranging from wireless communication between air and ground vehicles on the battlefield to short links between college campus buildings to metropolitan area networks that connect all the buildings in a city.

Dr. Mohsen Kavehrad, the W. L. Weiss professor of electrical engineering and director of the Center for Information and Communications Technology Research, leads the study. He says, "The multi-rate approach offers many advantages. For example, lower rate signals can get through clouds or fog when high rate signals can’t. By sending the same message at several different rates, one of them can probably get through."


Rather than slowing communication down, the multi-rate approach has been shown in tests to achieve an average bit rate higher than conventional optical wireless links operating at 2.5 Gbps as well as providing an increased level of communication reliability by maintaining a minimum of one active link throughout channel conditions, he adds.

Kavehrad outlined his team’s new approach at the Optics East 2004 Conference in Philadelphia, Oct. 27, in a paper, "Ultra-short Pulsed FSO Communications System with Wavelet Fractal Modulation." He will also describe the system at the IEEE MILCOM conference in Monterey, California, on Nov. 1. His co-author is Belal Hamzeh, doctoral candidate in electrical engineering.

In optical wireless systems, also known as free-space optics (FSO), voice, video and/or data information is carried on line-of-sight, point-to-point laser beams. Outdoor FSO systems have been in use for over 30 years but are hampered by weather and other obstructions that prevent the transmitter and receiver from "seeing" each other.

Kavehrad explains that clouds and fog often clear abruptly providing brief windows for transmission, making pulsed delivery better suited to FSO. The new Penn State approach embeds data in ultra-short pulses of laser light, shaped via fractal modulation as wavelets, and then transmits the wavelets at various rates.

Belal says the wavelets are easy to generate. "We use holography to generate and separate the wavelets. You just generate the mother wavelet and then the others can be generated as a fraction of the transmission bit rate of the mother. They can all co-exist in the channel without interference," he notes.

The wavelets used by the Penn State team are Meyer’s Type which look like dolphin chirps. The wavelets minimize bandwidth waste and the ultra-short pulses are less likely to interact with rain or fog that could degrade the signal.

The researchers note that their proposed system ensures on-the-fly operation without the need for significant electronic processing. The project is supported by the Air Force Research Laboratory.

Barbara Hale | EurekAlert!
Further information:
http://www.psu.edu

All articles from Information Technology >>>

The most recent press releases about innovation >>>

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

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

Im Focus: Skyrmions like it hot: Spin structures are controllable even at high temperatures

Investigation of the temperature dependence of the skyrmion Hall effect reveals further insights into possible new data storage devices

The joint research project of Johannes Gutenberg University Mainz (JGU) and the Massachusetts Institute of Technology (MIT) that had previously demonstrated...

Im Focus: Making the internet more energy efficient through systemic optimization

Researchers at Chalmers University of Technology, Sweden, recently completed a 5-year research project looking at how to make fibre optic communications systems more energy efficient. Among their proposals are smart, error-correcting data chip circuits, which they refined to be 10 times less energy consumptive. The project has yielded several scientific articles, in publications including Nature Communications.

Streaming films and music, scrolling through social media, and using cloud-based storage services are everyday activities now.

Im Focus: New synthesis methods enhance 3D chemical space for drug discovery

After helping develop a new approach for organic synthesis -- carbon-hydrogen functionalization -- scientists at Emory University are now showing how this approach may apply to drug discovery. Nature Catalysis published their most recent work -- a streamlined process for making a three-dimensional scaffold of keen interest to the pharmaceutical industry.

"Our tools open up whole new chemical space for potential drug targets," says Huw Davies, Emory professor of organic chemistry and senior author of the paper.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

 
Latest News

"Make two out of one" - Division of Artificial Cells

19.02.2020 | Life Sciences

High-Performance Computing Center of the University of Stuttgart Receives new Supercomuter "Hawk"

19.02.2020 | Information Technology

A step towards controlling spin-dependent petahertz electronics by material defects

19.02.2020 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>