Cloudy Day Won't = Rain On Laser Communications

FeedsFarm.com > Cloudy Day Won't Rain On Laser=20 Communications

Source:

Lockergnome=20 Nexus

Language:

English

Domain:

http://www= .feedsfarm.com/s/site%3Awww.lockergnome.com

More feeds from lockergnome.co= m:

IT=20 Professionals=20
Linux=20 Fanatics=20
OS=20 X Fanatics=20
Search=20 Engineer=20
Web=20 Developers=20
Windows=20 Fanatics

Cloudy Day Won't Rain On Laser Communications

13th Nov 2006, = 19:00=20 GMT

Just as clouds block the sun, they interfere with = laser=20 communications systems, but Penn State researchers are using a = combination=20 of computational methods to find the silver lining and punch = through the=20 clouds. "Radio frequency communications are generally reliable and = well=20 understood, but cannot support emerging data rate needs unless = they use a=20 large portion of the radio spectrum," says Mohsen Kavehrad, the W. = L.=20 Weiss professor of electrical engineering and director, Penn State = Center=20 for Information and Communications Technology Research. "Free = space=20 optical communications offer enormous data rates but operate much = more at=20 the mercy of the environment." Laser light used in communications = systems=20 can carry large amounts of information, but, the dust, dirt, water = vapor=20 and gases in a fluffy cumulus cloud, scatter the light and create = echoes.=20 The loss of some light to scattering is less important than those = parts of=20 the beam that are deflected and yet reach their target, because = then,=20 various parts of the beam reach the endpoint at different times. = "All of=20 the laser beam photons travel at the speed of light, but different = paths=20 make them arrive at different times," says Kavehrad. "The Air = Force, which=20 is funding this project through the Defense Advanced Research = Projects=20 Agency, would like us to deliver close to 3 gigabytes per second = of data=20 over a distance of 6 to 8 miles through the atmosphere." That 6 to = 8 miles=20 is sufficient to cause an overlap of arriving data of hundreds of = symbols,=20 which causes echoes. The information arrives, but then it arrives = again=20 because the signal is distributed throughout the laser beam. In = essence,=20 the message is continuously being stepped on. Kavehrad and Sangwoo = Lee,=20 graduate student in electrical engineering, presented their = solutions to=20 the echo problem at the recent IEEE Military Communications = Conference in=20 Wash., D.C. "In the past, laser communications systems have been = designed=20 to depend on optical signal processing and optical apparatus," = says=20 Kavehrad. "We coupled state-of-the-art digital signal processing = methods=20 to a wireless laser communications system to obtain a reliable, = high=20 capacity optical link through the clouds." The researchers = developed an=20 approach called free-space optical communications that not only = can=20 improve air-to-air communications, but also ground-to-air links. = Because=20 their approach provides fiber optic quality signals, it is also a = solution=20 for extending fiber optic systems to rural areas without laying = cable and=20 may eventually expand the Internet in a third dimension allowing = airplane=20 passengers a clear, continuous signal. Using a computer simulation = called=20 the atmospheric channel model developed by Penn State's CICTR, the = researchers first process the signal to shorten the overlapping = data and=20 reduce the number of overlaps. Then the system processes the = remaining=20 signal, picking out parts of the signal to make a whole and = eliminate the=20 remaining echoes. This process must be continuous with overlap = shortening=20 and then filtering so that a high-quality, fiber optic caliber = message=20 arrives at the destination. All this, while one or both of the = sender and=20 receiver are moving. "We modeled the system using cumulus clouds, = the=20 dense fluffy ones, because they cause the most scattering and the = largest=20 echo," says Kavehrad. "Our model is also being used by Army = contractors to=20 investigate communications through smoke and gases and it does a = very good=20 job with those as well." The computer modeled about a half-mile = traverse=20 of a cumulus cloud. While the researchers admit that they could = simply=20 process the signal to remove all echoes, the trade-offs would = degrade the=20 system in other ways, such as distance and time. Using a two-step = process=20 provides the most reliable, high-quality data transfer. The system = also=20 uses commercially available off-the-shelf equipment and proven = digital=20 signal processing techniques.

View=20 full story at www.lockergnome.com

Cloudy Day Won't Rain On Laser = Communications=20 related news:

Extra-long=20 laser probe scans larger objects =E2=80=94 Monitoring,=20 Measurement and Quality latest news on Engineeringtalk=20
Dude,=20 No Way! Laser Shows Go Dark at Griffith =E2=80=94 NPR=20 Topics: People & Places=20
Wicked=20 Lasers Blu-ray Powered Laser =E2=80=94 Gizmodo=20
Permanent=20 Choice Laser Hair Removal Centers Now Offering Laser Skin=20 Treatments! =E2=80=94 PR=20 Leap - Advertising News Releases=20
New=20 Eye Implant Clears Cloudy Vision =E2=80=94 LiveScience.com=20
Laser=20 Design Expands Seattle Office (Laser Design) =E2=80=94 = CADwire.net=20 - Mechanical CAD industry news=20
Dell=20 Introduces Its First Color Laser AIO =E2=80=94 PC=20 Magazine's New Product Update=20
Blu-ray=20 Laser Gadget =E2=80=94 Slashdot=20
Technology=20 office expands in Seattle =E2=80=94 Monitoring,=20 Measurement and Quality latest news on Engineeringtalk=20
Laser=20 systems builder reports sales up by 12% =E2=80=94 Orders,=20 contracts, financial reports latest news on = Manufacturingtalk=20

Latest news from Lockergnome Nexus:

Don't=20 Get Over Committed=20
Cell=20 Phone Users - In Case of Emergency=20
PowerPoint=20 Tip: Play show while working=20
Reading=20 list: Part 2=E2=80=A6.=20
The=20 Basement Project Part Deux=20
Security=20 Updates as of 11/12/2006=20
Confessions=20 of a Zune preorderer=20
Finishing=20 a basement can be very messy!!!=20
New=20 faces in the crosshairs=20
California=20 boy to Missouri? Part #7=20

	News Feeds Tags Search=20 Shortcuts