Full-Duplex Wireless Communication

Current wireless devices operate in half-duplex - meaning they do not transmit and receive simultaneously in the same band - which results in inefficient use of the resources available for communication. But if devices could be full-duplex - meaning they both transmit and receive at the same time in the same band - wireless data rates would be much higher. The hurdle to full-duplex operation is self-interference (imagine tring to listen to a friend while you're shouting at the top of your lungs: you can't hear your friend because your own voice is so loud.) My research is focused on how we can suppress the self-interference and enable wireless full-duplex. Below are some research directions related to supressing self-interference and enabling wireless full duplex. Check out my talk below on wireless full-duplex that was delivered at the Rice Electrical and Computer Engineering Departemnts 2014 Corporated Affiliates Day.

Theory for wireless full-duplex (2014)

Full-duplex promises to transform today's wireless networks by letting base stations transmit and receive on the same frequency and at the same time. The challenge to full-duplex is the high-powered self-interference that swamps the receiver. Experiments at Rice have shown that proper antenna design is key to enabling full-duplex, and that isolating the receiver from self-interference backscattered from nearby objects is the biggest challenge. In my early Ph.D. work, I have developed a theory for wireless full-duplex that emphasizes backscattering by marrying antenna theory and information theory. Analysis using this theory proves that joint antenna and signal design can enable full-duplex even in high-scattering environments. Check out the paper, "A signal-space analysis of spatial self-interference isolation for full-duplex wireless," that we presented at the 2014 International Symposium on Information Theory.

Passive suppression for full-duplex (2012-2013)

In my Master's thesis work, I performed measurement-based study of the capabilities and limitations of three key mechanisms for passive self-interference suppression: directional isolation, absorptive shielding, and cross-polarization. The study demonstrates that more than 70 dB of passive suppression can be achieved in certain environments, but also establishes two results on the limitations of passive suppression: (1) environmental reflections limit the amount of passive suppression that can be achieved, and (2) passive suppression, in general, increases the frequency selectivity of the residual self-interference signal. These results suggest two design implications: (1) deployments of full-duplex infrastructure nodes should minimize near-antenna reflectors, and (2) active cancellation in concatenation with passive suppression should employ higher-order filters or per-subcarrier cancellation. See our paper, "Passive Self-Interference Suppression for Full-Duplex Infrastructure Nodes," in IEEE Transaction on Wireless Communication.

Structured signaling for full-duplex (2011)

Check out this video on our information theoretic approach to the problem of full-duplex communication in the presence of fading self-interference. It's a slightly modified version of the talk I gave at the 2011 Allerton Conference on Communication, Control, and Computing.