Penn State Live

From: Subject: Penn State Live Date: Fri, 10 Nov 2006 13:45:41 -0500 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_002C_01C704CE.832DCF20" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2962 This is a multi-part message in MIME format. ------=_NextPart_000_002C_01C704CE.832DCF20 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://live.psu.edu/story/20743 Penn State Live

=20

Home

Press Pass

Subscribe Live Calendar

PSU e-Mall Video/Photo Archives Contact Us =20

Home Subscribe Calendar=20 Video/Photo=20 Archives PSU e-Mall Contact Press Pass =

State of the University
2006 State of the University = Address=20 =

Lion=20 Cam
Live Video Larger = View (Problems viewing=20 video?)=20

In=20 Motion - Channel 1
=20 PSU Employee Tells of Breast = Cancer=20 Battle Watch video now=20 =

In=20 Motion - Channel 2
=20 Students videotape Homecoming = highlights=20 Watch video now=20 =

In=20 Motion - Channel 3
<= IMG=20 height=3D120 = src=3D"http://live.psu.edu/in_motion/labgirl.jpg"=20 width=3D144 border=3D0>=20 2006 Teen Campaign = Commercial <= FONT=20 size=3D1>Watch video now=20 =

Weather World
Download Media = Player: <= B>Windows=20 or Mac=20

WPSU-TV
Pennsylvania = Inside=20 Out Talk=20 Tuesday

On=20 the Air
=20 Listen to = WPSU-FM Penn=20 State's NPR and PRI affiliate public broadcasting=20 station Listen=20 to ComRadio AP=20 News feed, College of Communications = programming=20

Hot=20 Topics
National = security and=20 defense=20 Budget and=20 appropriation=20 Environmental=20 conservation=20 Board of = Trustees=20 actions and reports=20 Alcohol=20 awareness =

PSU=20 News
=20 Faculty/Staff Off-Campus Student = Science & Technology = Sports Student=20

Campus News
=20 Beaver Berks Dickinson School of Law = DuBois Erie Fayette Harrisburg Hershey Lehigh Valley McKeesport Mont Alto =20 = Schuylkill Shenango York=20

Other News
Admissions=20 Alumni=20 Arts and = Entertainment=20 Cancer=20 Institute=20 Diversity=20 Engineering=20 Greek=20 Health = &=20 Wellness=20 Off-Campus=20 Student=20 Outreach=20 Penn = State=20 Press=20 Penn = State Public=20 Broadcasting=20 University=20 Libraries =

Recent Headlines

Text=20 only

Recent Headlines

Cloudy day = won't rain=20 on laser communications
Friday,=20 November 10, 2006

=20

University Park, Pa. =96 Just as = clouds=20 block the sun, they interfere with laser = communications=20 systems, but Penn State researchers are using a = combination of=20 computational methods to find the silver lining and = punch=20 through the clouds.

"Radio frequency = communications are=20 generally reliable and well understood, but cannot = support=20 emerging data rate needs unless they use a large = portion of=20 the radio spectrum," says Mohsen Kavehrad, the W. L. = Weiss=20 professor of electrical engineering and director, Penn = State=20 Center for Information and Communications Technology = Research.=20 "Free space optical communications offer enormous data = rates=20 but operate much more at the mercy of the=20 environment."

Laser light used in = communications=20 systems can carry large amounts of information, but, = the dust,=20 dirt, water vapor and gases in a fluffy cumulus cloud, = scatter=20 the light and create echoes. The loss of some light to = scattering is less important than those parts of the = beam that=20 are deflected and yet reach their target, because = then,=20 various parts of the beam reach the endpoint at = different=20 times.

"All of the laser beam photons travel at = the=20 speed of light, but different paths make them arrive = at=20 different times," says Kavehrad. "The Air Force, which = is=20 funding this project through the Defense Advanced = Research=20 Agency, would like us to deliver close to 3 gigabytes = per=20 second of data over a distance of 6 to 8 miles through = the=20 atmosphere."

That 6 to 8 miles is sufficient to = cause=20 an overlap of arriving data of hundreds of symbols, = which=20 causes echoes. The information arrives, but then it = arrives=20 again because the signal is distributed throughout the = laser=20 beam. In essence, the message is continuously being = stepped=20 on.

Kavehrad and Sangwoo Lee, graduate student = in=20 electrical engineering, presented their solutions to = the echo=20 problem at the recent IEEE Military Communications = Conference=20 in Wash., D.C.

"In the past, laser = communications=20 systems have been designed to depend on optical signal = processing and optical apparatus," says Kavehrad. "We = coupled=20 state-of-the-art digital signal processing methods to = a=20 wireless laser communications system to obtain a = reliable,=20 high capacity optical link through the = clouds."

The=20 researchers developed an approach called free-space = optical=20 communications that not only can improve air-to-air=20 communications, but also ground-to-air links. Because = their=20 approach provides fiber optic quality signals, it is = also a=20 solution for extending fiber optic systems to rural = areas=20 without laying cable and may eventually expand the = Internet in=20 a third dimension allowing airplane passengers a = clear,=20 continuous signal.

Using a computer simulation = called=20 the atmospheric channel model developed by Penn = State's CICTR,=20 the researchers first process the signal to shorten = the=20 overlapping data and reduce the number of overlaps. = Then the=20 system processes the remaining signal, picking out = parts of=20 the signal to make a whole and eliminate the remaining = echoes.=20 This process must be continuous with overlap = shortening and=20 then filtering so that a high-quality, fiber optic = caliber=20 message arrives at the destination. All this, while = one or=20 both of the sender and receiver are moving.

"We = modeled=20 the system using cumulus clouds, the dense fluffy = ones,=20 because they cause the most scattering and the largest = echo,"=20 says Kavehrad. "Our model is also being used by Army=20 contractors to investigate communications through = smoke and=20 gases and it does a very good job with those as=20 well."

The computer modeled about a half-mile = traverse=20 of a cumulus cloud. While the researchers admit that = they=20 could simply process the signal to remove all echoes, = the=20 trade-offs would degrade the system in other ways, = such as=20 distance and time. Using a two-step process provides = the most=20 reliable, high-quality data transfer.

The = system also=20 uses commercially available off-the-shelf equipment = and proven=20 digital signal processing techniques.

Email=20 this story to a friend
Printer-friendly=20 version

Contact
A'ndrea=20 Messer
aem1@psu.edu
=20 http://live.psu.edu
= 814-865-9481

Contact
Vicki=20 Fong
vfong@psu.edu
=20 http://live.psu.edu
=20 = 814-865-9481

The=20 Pennsylvania State = University =A9 2006

Penn State: Making Life Better

Have a question? See our list = of=20 contacts.

=20