2008-2009

ECE Faculty Profile: Andrew Klein

Prof. Andrew Klein

Professor Andrew Klein is a new professor in the Department of Electrical & Computer Engineering at WPI, having joined the department in August 2007. Before coming to WPI he was conducting research outside Paris, France as a postdoctoral researcher at LSS/Supélec. The core of Professor Klein's research focuses on adaptive signal processing and parameter estimation to enable the next generation of wireless communications networks.

Prof. Klein's research blends digital signal processing and wireless communications principles. Within digital signal processing, he has a particular focus on adaptive signal processing. "Very often, particularly in mobile environments where things are moving around, the channel state is constantly changing. In such cases, we need to employ signal processing algorithms which are able to track or adapt to the changing conditions." While adaptive signal processing can be applied to a variety of applications, Prof. Klein focuses on wireless communications. Lately, he has developed a particular interest in multiple node wireless communications. "In most established wireless networks today -- whether it's your cell phone or the campus WiFi network -- the nodes only ever talk to a central base station; they typically do not talk to one another and they never go so far as to help one another." He is currently investigating how to use adaptive signal processing algorithms to combat a host of new issues that arise when wireless nodes cooperate. "Though my expertise is in signal processing and communication theory, I generally look for boundary-crossing research problems that brush up against related areas like information theory, RF circuits, or networking, perhaps even some aspects of security," adds Prof. Klein.

Current Research Topics

"There's a lot of focus right now on cooperative communication, but since the field is relatively recent, most of the current research assumes simple channel models to make the math tractable," claims Prof. Klein. The communication channel -- the medium used to convey information from sender to receiver -- undergoes several effects that impede reliable communications. Two key impediments are multipath fading and frequency selectivity. In wireless communications, the ground, buildings, trees, and atmosphere act as reflectors, and create multiple paths over which a signal propagates. Consequently, the receiver observes a superposition of multiple copies of the transmitted signal, each from a different path. Each signal copy undergoes differences in attenuation and phase change, which can result in interference, resulting in amplification or attenuation of the signal power at the receiver. "Though I don't recommend talking on your cellphone while driving, that is certainly a good example of where you may have seen fading firsthand -- either in the form of a dropped call, or a temporary loss in signal," says Prof. Klein.

Frequency selectivity is a problem that is most severe in wideband communication systems. This effect is also caused by the reflections in the communication channel. Again, while each signal copy undergoes attenuation and phase change, the affect of the attenuation and phase change may also be different at each frequency. "Probably the best example of observing a frequency selective channel is with acoustics. When a car drives by with its radio blaring, a lot of times you can only hear the bass. The channel between the car speaker and your ear -- which includes the effects of the car itself -- attenuates the higher frequencies. It makes all Reggaeton sound alike because all you can hear is that characteristic beat."

Fortunately, multipath fading and frequency selectivity in wireless systems can be combatted -- and even exploited -- using techniques from communications theory and adaptive signal processing. "Multipath fading and frequency selectivity have always been around. Cooperation helps solve the fading problem in the simplest of cases, but the question of how to combat or exploit frequency selectivity, and how to build practical cooperative systems in such scenarios is still an open problem."

Prof. Klein notes that his research blends elements of theory and practice, the heart of the WPI education tradition. "Often times we can derive the optimal receiver strategy for a given system, say, for combatting frequency selectivity -- but it may not be possible to build it with modern hardware. Pure theorists might be content to stop after having derived the 'optimal' receiver, but in this group we focus on strategies which can be implemented, which often means we are considering suboptimal strategies. While the research in our group is typically quite theoretical, the algorithms are meant to be deployed in real systems, with real hardware."

Arrival at WPI

"The ECE department at WPI has identified wireless communications as a key area, and has built up a solid group of professors who are recognized experts in wireless communications and related areas. That was certainly a big selling point for me in making the decision to come to WPI. Having so many experts in this area is very exciting because it fosters collaboration, or permits us to just bounce ideas off one another over lunch, and allows us to develop a richer offering of courses than might otherwise be possible. It is really an honor to be a part of this highly talented group of professors," says Prof. Klein. In addition, he cites the close interaction with students as one of the key differences of WPI. "While the graduate research going on at WPI is world-class, there is a unique commitment to undergraduate education. I have been very impressed by the level of interaction between students and professors which is made possible through programs like the IQP and MQP."

When asked what courses might be relevant to Prof. Klein's research, he said, "Certainly a solid understanding of probability and linear algebra. If you've never taken a course in mathematical analysis, I would highly suggest that. In ECE, I would recommend taking Estimation & Detection (531) in addition to the core graduate courses. Also, I had the chance to develop a course in information theory (5311) which was taught for the first time this spring. I'd definitely recommend taking that," he says with a grin.

Prof. Klein's webpage, which includes his publications, can be found here.

July 25, 2008