I worked on "Intelligent Antenna Sharing" schemes, where single antenna transceivers cooperate to improve the efficiency of wireless communication and scale of wireless networking. Specifically, I was interested in low complexity algorithms that utilize low cost radios and adapt reactively to the physics of wireless propagation. It was shown, under certain assumptions (limited csi, no "beamforming") the increase of spectral efficiency (in bps/Hz) or reduction in power in wireless communication of the proposed low complexity schemes, compared to traditional, point-to-point or even multihop communication. The benefits come from the exploitation of the wireless channel statistics, much the same way MIMO links work. Here, however the problem is harder since the antennas belong to different terminals and information is not a priori known.
There are similar ideas in the very recent literature. However, people overlook the amount of network coordination needed so that a set of terminals can cooperatively communicate. Also people usually confuse a MIMO link with the cooperative relay channel, studied in this work. The relay channel is much harder since distributed solutions are needed. Another common misconception regarding fundamental performance of relay networks comes from the "multihop" effect: choosing to communicate closer through an intermediate node provides energy gains, given that electromagnetic propagation is highly non-linear. What if all nodes where equidistant from each other? In that case, there is no "multihop" gain. Our cooperative, low complexity schemes increase outage rates for the same resources used (total tx power and bandwidth) compared to non-cooperative, direct or multi-hop communication, even when all nodes are equidistant. The benefits come from the richness of wireless propagation, much the same way as in MIMO links. The problem however is more complicated since now the whole network needs to react "fast" and in a distributed manner to wireless channel conditions.
this project we follow a top-bottom approach, by researching every detail
in all layers of communication: from routing (layer 3), to access (layer
2), to space-time coding (physical layer), to implementation in a real
world test bed. There is space for great improvements if networking is
viewed as a cooperative multipoint-to-multipoint communication problem
instead of a collection of competing point-to-point links. The goal is
to identify low complexity cooperative schemes, analyze them without oversimplified
assumptions and implement them in low-cost hardware.
Autonomous Time Keeping in Distributed Sensor Networks
We are addressing the problem in two orthogonal ways:
Approach B (Decentralized):
Network Beatles - Tabletop Location Estimation through Wireless Networking
Ultra-Wide Band (UWB) technologies will revolutionize indoor positioning
due to its inherent RADAR capabilities. Until UWB hardware is simplified
and miniaturized, there is an alternative approach for indoor sub-centimeter
accuracy, followed in this project: we used regular high frequency infrared
transceivers, for embedded wireless networking and at the same time, the
same transceivers were used for range estimation through received power
measurements. Triangulation was possible since multiple measurements were
made from neighboring nodes. In the above figure we see an experiment
of the above, were topology of the network is found through infrared received
power measurements and that information is passed through custom wireless
packet-based networking to the serial port and depicted at the pc.
LithoLab - Nanoscale Finger Control Interface
In this nanotechnology project, I was given a commercially available
Atomic Force Microscope and asked to reverse engineer it so as to create
a pick-and-drop nano-lithography tool. The software I developed provided
a text/script based command interface and at the same time could be used
for imaging puproses. It was called LithoLab and combined with the actuall
AFM, it was used from Brian Hubert for his Ph.D. project. That was work
done in Molecular Machines
group under prof. J. Jacobson, at the first year of my graduate studies
at MIT .
See the project
web site for more information.
Esopos - Hellenic Text-to-Speech
...last updae, September 2005