Associate Professor, Electrical Engineering
Full duplex wireless has attracted significant research attention in the last five years due to its ability to potentially double network capacity at the physical layer, while offering numerous benefits at the higher layers. The basic challenge in full duplex is the tremendous transmitter self-interference at the receiver, which can be one trillion times more powerful than the desired signal and must be dealt with in all domains. There has been significant work on prototype full-duplex radios using off-the-shelf components and showing the feasibility of self-interference cancellation, and on network-layer implications of full-duplex operation.
However, the implementation of integrated full-duplex radios in commercial CMOS processes, necessary for widespread deployment, particularly in small-form-factor devices, is fraught with several fundamental challenges. Integrated CMOS electronics typically exhibit much lower dynamic range than off-the-shelf components, leading to several challenges related to full-duplex operation, including noise and distortion added by the transceiver or by the cancellers, and the bandwidth associated with the cancellation. Furthermore, shared antenna interfaces for full-duplex, such as circulators, are either impossible to integrate on chip due to a reliance on magnetic (ferrite) materials, or exhibit prohibitive loss and/or linearity penalties.
This talk will introduce several generations of integrated full-duplex transceivers developed at Columbia University that address these problems. I will discuss RF self-interference cancellation concepts that add minimal noise and distortion penalty, and are able to achieve wideband cancellation across antenna interfaces with significant frequency selectivity. At the electromagnetic (i.e. antenna) interface, I will talk about our recent work on breaking Lorentz Reciprocity using time-variance to realize the first integrated magnetic-free non-reciprocal circulator. I will also discuss how polarization can be utilized to achieve robust self-interference suppression by embedding complex signal processing functionalities like wireless channel equalization in the antenna domain. Finally, I will discuss how joint self-interference suppression across the antenna, RF/analog and digital domains can enable achievement of the 90-100dB self-interference suppression levels in integrated full-duplex radios .