THE MAGAZINE OF THE A. JAMES CLARK SCHOOL of ENGINEERING

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MoreChoicesCLARK SCHOOL RESEARCH BRINGS NEW COMMUNICATIONSCAPABILITIES TO PEOPLE AROUND THE WORLD

A n astounding 219 million Americans subscribed to a cell phone service in 2006.That’s 72 percent of the total U.S. population—up from 14.4 percent only 10years earlier, according to a nonprofit organization representing the wireless

industry. And that’s only in one country. “We’ve seen an explosion of wireless penetratingour lives,” notes Sennur Ulukus, an associate professor in electrical and computer engi-neering (ECE) and the Institute for Systems Research (ISR). “The next 10 years willbring unimaginable innovations.”

CLARK SCHOOL RESEARCH BRINGS NEW COMMUNICATIONSCAPABILITIES TO PEOPLE AROUND THE WORLD

By Beth PanitzPhotography by Mike Morgan

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Ulukus is one of a group of Clark School researchers, advisorsand corporate partners leading the wireless world forward in anumber of key areas: improving the speed of, and access to,current connections, enhancing the quality and security of datacommunications, creating ad hoc networks that are completelywire-free and developing networks of tiny sensing computersto communicate information from remote locations. Theirwork will give more communications options to more peoplearound the world than ever before, changing the way we live,work, play and relate to each other, and influencing the for-tunes of businesses and nations.

The most obvious example is the cell phone—“the onedevice that’s always with you,” according to Irwin Jacobs, co-founder of wireless technology giant QUALCOMM and arecent Whiting-Turner lecturer at the Clark School. Jacobs pre-dicts that a single cell phone will serve as a phone, watch, com-puter, television, personal digital assistant, wallet, global posi-tioning system, traffic monitoring system, MP3 player and

bio-sensing machine. Apple’s recently announced iPhone is onemore step toward that goal.

Such technologies break the boundaries between real andvirtual, face-to-face and online. “Your office will be with youall the time, in any location, once you get extremely fast broad-band access,” says Bahram Pourmand, executive vice presidentfor Hughes Communications and member of the Clark SchoolBoard of Visitors. Recent Whiting-Turner lecturer Kathy Hill,senior vice president, Ethernet & Wireless Technology Group,Cisco Systems, Inc., notes that mobility services are empower-ing new business capabilities. “Employees can do their jobsmore effectively and keep track of important assets through‘presence’ information provided by the wireless network,” shedescribes. In addition, response time greatly improves whenbusinesses have on-demand, real-time access to informationand supply chains can be more tightly managed.

In these and other exciting areas of communicationsresearch, the Clark School is leading the way.

Clark School researchers, from left, Prakash Narayan, Richard La, Anthony Ephremides, Sennur Ulukus, Gang Qu and K.J. Ray Liu.

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Making Cellular Faster, Clearer, More Secure The evolution of the next generation ofcellular networks, 4G, is being significantlyinfluenced by Rajiv Laroia, M.S. ’89 andPh.D. ’92, electrical engineering. (Seeevolution timeline, page 10.) Laroia, whowas recently inducted into the ClarkSchool Innovation Hall of Fame, has trans-formed the wireless world by co-inventingcellular data systems based on OrthogonalFrequency Division Multiplexing(OFDM), a technique for transmittinglarge amounts of digital data over a radiowave that makes broadband Internet accesspossible (see diagram above, related story,p. 9 and www.eng.umd.edu/ihof ). Wowedby the invention, industry leader QUAL-COMM acquired Laroia’s company,Flarion Technologies, in 2006 for $805million. OFDM, which sends multiple sig-nals by using different frequencies, is thebackbone for 4G technologies, such asQUALCOMM’s FLASH-OFDM and the

competing mobile WiMAX. The 4G network promises to bring

affordable broadband wireless capabilities tothe masses, providing access to the Internet,television and high-powered video capacitiesthrough cell phones and other handhelddevices. “Two technologies are about toconverge—mobile telecommunications andthe Internet,” says Sprint Nextel’s ChiefTechnology Officer Barry West, who spear-heads his company’s 4G network develop-ment. This expanded video capacity has thepotential to transform our lives, West notedat the Clark School’s White Symposium lastfall. (See related story, p.14 or watch thesymposium at www.eng.umd.edu/news/news_story.php?id=965)

Sprint Nextel’s 4G network will usemobile WiMAX, a high bandwidth data-centric wireless network that will accommo-date interactive multimedia applications andquadruple throughput performance.WiMAX chipsets soon will be embedded inlaptops, phones and other devices, providing

Internet access without the need to go to a“hot spot.” “We’re going to have the Internetalmost everywhere and in every device youcan imagine—from video cameras to gamingdevices,” says West. For example, your carnavigation system could access the Internetto provide videos of traffic conditions.

As industry continues to search for waysto keep pace with the demand for higherspeeds and increasingly visual content,Laroia remains at the forefront. OFDM’scompatibility with advanced antenna tech-nology offers a promising way to expandnetwork capacity, he relates. Laroia is nowworking with multiple input/multiple out-put (MIMO) smart antenna technology toincrease the bits of information that can betransmitted per second.

Pushing the Limits

Emerging broadband applications demandreliable wireless communication at highertransmission speeds, a problem K.J. “Ray”Liu, professor of ECE and ISR, is solving

Engineering @ Maryland � Spring 2007

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with sophisticated methods. He developedcoding techniques to maximize performancein a MIMO-OFDM wireless system.“When you receive a communication, you’reactually receiving multiple signals, not justone,” explains Liu. “We looked at combin-ing signals in a constructive way. This is theonly code that can achieve the maximumdiversity in space, time and frequency andthat means maximum performance.”

Liu’s groundbreaking work was hon-ored with the university’s 2005 Inventionof the Year Award in the InformationScience category, and he is now collabo-rating with Mobitrum Corporation inSilver Spring, Md., to incorporate thepatent-pending invention into the compa-ny’s wireless technology.

In her Clark School laboratory, SennurUlukus is tackling a major communicationsnetwork problem: “How can we support themaximum number of people and the maxi-mum amount of data?” One technique she isresearching—power control—manages trans-mission power so that each wireless signal istransmitted at precisely the right strength,creating a more efficient network with lessinterference. She compares the technique tooptimizing the number of intelligible con-versations in a crowded room. “If you’re talking to someone next to you, you whisperjust enough to be heard. If you shout, you’regoing to create interference for someoneelse’s conversation.”

Another strategy—interference cancella-tion—helps a receiving device focus on itsintended signal, canceling other signals,explains Ulukus. She has developedsophisticated power-control and interfer-ence-cancellation algorithms that couldexpand wireless capacity to support anever-increasing amount of data.

Bill Witowsky, ECE Advisory Councilmember and chief technology officer forTexas Instruments Incorporated Systems andSoftware, Digital Signal Processing SystemsGroup, notes that “as we keep adding newfeatures to wireless devices, we are on aninnovation treadmill to reduce overall powerusage. Voice calls require one level of power,but if you start watching TV or participatein video-conferencing or other activities, thatrequires a lot more horsepower.”

“Two key components of any wirelessdevice are the battery and the antenna,” adds

Tom Scholl, a general partner with Bethesda,Md.-based Novak Biddle Venture Partnersand chair of the Clark School Board ofVisitors. “Industry giants as well as start-upsare trying to figure out how to extend bat-tery life and to make the antenna circuitrydynamically adaptive to the environment. Ifyou were to ask what technology couldchange the mobile industry overnight, itwould be in these areas,” he says. “Imaginehaving a battery you recharge once a yearinstead of daily.”

Playing It Safe

A pioneer in the field of wireless communi-cations, Anthony Ephremides, professor inECE and ISR, advocates developing anarsenal of tools to protect wireless networksfrom different security threats. Ephremides,who is the Cynthia Kim Eminent Professorof Information Technology, is designinganonymous routing protocols that hiderouting information so eavesdroppers can-not intercept messages. The challenge, henotes, is to develop a technique to identifymalicious users and prevent them fromexploiting the anonymous routing capability.His research is heavily supported by theArmy Research Office, which is developingsecure methods to communicate top-secretmilitary information.

His colleague Sennur Ulukus is “workingon improving security at the physical layer,which actually transmits the signal throughthe air,” by designing algorithms to mini-mize the capabilities of eavesdroppers andjammers who try to prevent communication.Her research involves coding the signal sothat only the intended receiver can under-stand it and switching transmission channelsto make it difficult for someone to track andjam a signal.

A new encryption technique to improvesecurity is under development by PrakashNarayan, professor in ECE and ISR, who isexploiting connections to data compressionalgorithms. “When you compress data asmuch as possible, it looks like noise,” heexplains. An eavesdropper cannot make senseof this noise, while a legitimate user will haveaccess to correlated data that will unlock theinformation, yielding a “secret key,” whichcan then be used for encryption and decryp-tion. Supplementing NSF support, industrialsponsor Interdigital Communications

A. JAMES CLARK SCHOOL OF ENGINEERING � GLENN L . MARTIN INST ITUTE OF TECHNOLOGY

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Laroia Joins Innovation Hall of FameRajiv Laroia, M.S. ’89 and Ph.D. ’92,electrical engineering, is the latestinductee into the Clark School’sInnovation Hall of Fame. Senior vicepresident of engineering for QUAL-COMM Flarion Technologies, Laroia washonored for his telecommunications con-tributions, including the co-invention ofOrthogonal Frequency DivisionMultiplexing (OFDM), a high-speed datatransmission technique that makesbroadband wireless Internet access possi-ble. The Hall of Fame was established in1986 to recognize individuals who havemade significant contributions to societythrough engineering innovation.

“The real expertise in industry is sys-tems expertise,” Laroia noted in hisacceptance speech, emphasizing thattoday’s technological innovators need tocoordinate complex systems. Laroia citedhis experience at the Clark School’sSystems Research Center (now theInstitute for Systems Research) as criticalto his success.

As a student, Laroia worked closelywith his advisor, now Clark School DeanNariman Farvardin. Together with ECEProfessor Steven Tretter, they received apatent in 1995 for a data transmissionmechanism. “There is nothing more grati-fying,” said Farvardin, “than to see a stu-dent like Rajiv succeed brilliantly andreturn to inspire Clark School students andfaculty to contribute as he has to the goodof society.”

To learn more about the InnovationHall of Fame, see www.eng.umd.edu/ihof.

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Corporation is working with Narayan andAlexander Barg, professor in ECE and ISR,to incorporate this technique into a suite ofalgorithms for network security.

Extending Telecommunicationsto Everyone For all of the wonders of today’s cellular net-works, these systems are still, for the mostpart, wired. Enter the ad hoc wireless net-work. “It’s like a mini Internet, but trulywireless,” says Ephremides. “You have many,many nodes—computers and cell phones—that work without any infrastructure.”

With funding from the Department ofDefense, Ephremides is hoping to make adhoc networks perform as smoothly as thosewith infrastructure. “These networks are sub-ject to interference and obstacles at everystage,” he notes. “To counter those impair-ments, the design must be much moresophisticated.” These true wireless networkscould serve as tremendous military assets,allowing for instant communication net-works in the remotest of areas. In the civilian

world, they could link residents in rural areasto a cellular infrastructure or could be usedin emergency situations if the infrastructureis destroyed, adds Ephremides.

Finding the Fastest Route on the

Network Highway

Routing a message in this completely wirelessenvironment is challenging, says Richard La,an assistant professor in ECE and ISR, whois developing more efficient routing proto-cols. With NSF funding, he designed analgorithm to find the most stable multi-hoppath between two points, ensuring that datagets to its destination reliably. Finding thebest path gets complicated in a network withmoving nodes that might suddenly be out oftransmission range, creating what comparesto an unexpected road closure.

In simulation tests, La’s algorithm yieldeda 40 to 60 percent increase in the durationof workable paths. The results are even bet-ter when combined with a “local recoveryalgorithm” he developed that creates adetour when a link in the path becomesunavailable, similar to an alternate path adetoured driver may choose.

La, along with Ephremides and Ulukus, isalso refining media access control (MAC)protocols, the rules that determine wheneach transmitter in a network can access ashared channel. “Designing an efficientMAC protocol is crucial for improving thethroughput of a mobile ad hoc network,”explains La.

Additionally Ephremides is exploring anew technique called network coding thatcould substantially increase networkthroughput. Network coding offers thepossibility of more throughput by com-bining, or “carpooling,” messages thatcurrently travel on their own networks.For example, when two messages arrive at

a node from different sources, they wouldbe combined into one packet.

With funding from the U.S. ArmyResearch Laboratory and the Office of NavalResearch, Ephremides’s team is the first tostudy this breakthrough idea in the wirelessenvironment. “No one would have anticipat-ed that garbling packets together wouldimprove performance,” says Ephremides,who is searching for efficient ways to sepa-rate the packet information to ensure thatthe correct data reaches each destination.

Tying Transmission Techniques

Prakash Narayan is investigating the possi-bility of a hybrid communication systemthat optimizes performance in wireless adhoc networks by drawing on the best oftwo current communication techniques—radio frequency (RF) transmission andoptical beaming. Though commonly used,RF transmission is plagued with interfer-ence problems. Optical beaming offershigher speeds and less interference, but theoptical beam fades as it travels through theair due to turbulence.

Cellular Service Evolves 1980s: 1G, Analog CellularService for Voice OnlyMobile phone users cancarry conversations seam-lessly as they move fromcell to cell. A digital systemis launched in Europe forvoice only.

1990s: 2G, Digital CellularService with Limited DataDigital transmissions allowfor more phone conversa-tions in the same amountof spectrum and lay thegroundwork for servicesbeyond simple voice telephone calls.

2000 to present: 3G,Broadband CellularServiceBroadband capabilitiesprovide the ability to trans-fer simultaneously bothvoice data and non-voicedata, including limitedInternet access.

Anticipated 2008:4G, High-speedBroadband ServiceThese speeds enable high-quality, real-timevideo transmission andrapid download of largemusic files.

Sennur Ulukus

Cynthia Kim Eminent Professor of

Information Technology, Anthony Ephremides

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“There are pros and cons to each,” saysNarayan. With NSF funding, “we are devel-oping a hybrid system that would knowwhen to use each method.” When a signal issent to the receiver, it would send feedbackto the transmitter to help it select the appro-priate option. The technology could be usedin ad hoc networks, such as robots manufac-turing car components. The robots couldcommunicate with each other in harshindustrial environments—switching seam-lessly between RF and optical beaming toexchange information. In crowded urbanareas with plenty of RF congestion, opticalbeaming between rooftops could provide analternate transmission method.

Transmitting Opportunities and Dangers Imagine thousands of sensors throughout a subway system, each device quietly monitoring for a chemical terrorist attack.Through a wireless network, these sensorsalert security personnel to the presence ofdangerous chemicals.

Ephremides and a multidisciplinary teamof Clark School researchers are busy refiningsensor networks that may one day become aprevalent way of collecting data on every-thing from terrorist threats to temperatures.Wireless sensor networks operate like ad hocnetworks, with data traveling in many hopsfrom node to node to its final destination,

explains Ephremides. A sensor networkcould be deployed in the ocean to monitorpollution levels, in a battlefield to detecttroop movement or in a forest to identifyfires. Based on collected data, sensor net-works could trigger actuators to respondappropriately, from a simple security systemthat detects movement and triggers lights toa sophisticated command-and-control mili-tary system.

The energy issue is crucial in sensor net-works where sensor nodes are difficult toretrieve and recharge. “If you put sensornodes in the enemy’s battlefield, you can’tgo back and replace the batteries,” notesGang Qu, an associate professor of ECE.“When the battery dies, so does the sensor.As more sensors die, the network eventuallybecomes inoperable.”

At the Clark School’s new wireless sensorlab, filled with off-the-shelf sensors andcomputers, researchers are improving energyefficiency in everything from hardware tonetwork protocol design, says Qu. The teamis exploring trade-offs between a node’s threemain energy-consuming functions: data collection, data processing and data trans-mission. For example, a network might exertminimal energy in data processing, but con-sequently require more energy to transmitthe overwhelming amount of raw data. Quemphasizes the importance of tackling theenergy issue from a systems approach, not-ing that “a sensor network is like a smallcommunity, and together the sensors com-plete the task.”

Jeong Kim, president of Bell Labs and aprofessor of practice in the Clark School,speaks to the future significance of sensornetworks, noting that Bell Labs is alreadyproducing sensors with a wireless range ofone-half of a kilometer and a target weightof only 35 grams (about the weight of sixU.S. quarters). He fully expects that futuresensors may be as small as grains of sand.

“Sensor networks will generate a huge vol-ume of information,” he says, pointing tothe radio frequency identification (RFID)sensor network already being used by retailgiant Wal-Mart to track inventory. “Downthe road, don’t be surprised if there are radiofrequency implants in children for identifica-tion purposes that may offer an improve-ment over the fingerprinting ID programsthat are popular today.”

A Powerful VoiceThe wireless revolution promises to offermore people more ways to access and sendunprecedented amounts of non-voice andvoice data and visuals, anywhere, anytime.While the technology can provide wonderfulopportunities, it’s yet to be seen whether thechanges will all be for the good, says BarryWest, who questions if literacy will decreaseas access to visual-centric media increases.“Why will we even bother to learn to readand write?” he questions.

Others are more optimistic. Hughes’sPourmand sees wireless technology opening a sea of information—written, verbal andvisual—to people in developing countrieslacking wired infrastructure. “You make itpossible to provide education to way morepeople, increasing their standard of living.”

Matt Kirschenbaum, associate directorof the university’s Maryland Institute forTechnology in the Humanities, is confidentthat these new technologies will onlyenhance communication at every level.“Current wireless technologies rely heavilyon language with e-mail, chat rooms, texting,” he notes. “The powerful, creativecombination of words and images willdemand even higher levels of thinkingfrom users.”

Beth Panitz is a freelance writer based in Rockville, Md. A gradu-ate of the University of Maryland College of Journalism, she previ-ously served as senior editor of ASEE Prism, the magazine of theAmerican Society for Engineering Education.

From left, K.J. Ray Liu discusses research

with Gang Qu and Prakash Narayan.

Richard La