Jelena Diakonikolas

Integrated Full Duplex Radios

Full duplex wireless has drawn significant interest in the recent past due to the potential for doubling network capacity in the physical layer and offering numerous other benefits at higher layers. However, the implementation of integrated full duplex radios is fraught with several fundamental challenges. Achieving the levels of self-interference cancellation required over the wide bandwidths mandated by emerging wireless standards is challenging in an integrated circuit implementation. The dynamic range limitations of integrated electronics restrict the transmitter power levels and receiver noise floor levels that can be supported in integrated full duplex radios. Advances in compact antenna interfaces for full duplex are also required. Finally, networks employing full duplex nodes will require a complete rethinking of the medium access control layer as well as cross-layer interaction and co-design. This article describes recent research results that address these challenges. Several generations of full duplex transceiver ICs are described that feature novel RF self-interference cancellation circuits, antenna cancellation techniques, and a non-magnetic CMOS circulator. Resource allocation algorithms and rate gain/improvement characterizations are also discussed for full duplex configurations involving IC-based nodes.

Accelerated Extra-Gradient Descent: A Novel Accelerated First-Order Method.

We provide a novel accelerated first-order method that achieves the asymptotically optimal convergence rate for smooth functions in the first-order oracle model. To this day, Nesterovs Accelerated Gradient Descent (AGD) and variations thereof were the only methods achieving acceleration in this standard blackbox model. In contrast, our algorithm is significantly different from AGD, as it relies on a predictor-corrector approach similar to that used by Mirror-Prox [Nemirovski, 2004] and Extra-Gradient Descent [Korpelevich, 1977] in the solution of convex-concave saddle point problems. For this reason, we dub our algorithm Accelerated Extra-Gradient Descent (AXGD). Its construction is motivated by the discretization of an accelerated continuous-time dynamics [Krichene et al., 2015] using the classical method of implicit Euler discretization. Our analysis explicitly shows the effects of discretization through a conceptually novel primal-dual viewpoint. Moreover, we show that the method is quite general: it attains optimal convergence rates for other classes of objectives (e.g., those with generalized smoothness properties or that are non-smooth and Lipschitz-continuous) using the appropriate choices of step lengths. Finally, we present experiments showing that our algorithm matches the performance of Nesterovs method, while appearing more robust to noise in some cases.

Demo abstract: Full-duplex with a compact frequency domain equalization-based RF canceller

This demonstration presents a practical real-time full-duplex wireless link consisting of two full-duplex transceivers. Our prototyped full-duplex transceiver contains a custom-designed RF self-interference canceller and a National Instruments (NI) Universal Software Radio Peripheral (USRP). The discrete-component-based RF self-interference canceller emulates a compact RFIC implementation, which uses programmable bandpass filters to achieve wideband cancellation through the technique of frequency domain equalization. We demonstrate self-interference suppression across the antenna, RF, and the digital domains through the NI LabVIEW interface.

On the Rate Regions of Single-Channel and Multi-Channel Full-Duplex Links

We study the achievable rate regions of full-duplex links in the single- and multi-channel cases (in the latter case, the channels are assumed to be orthogonal, e.g., OFDM). We present analytical results that characterize the uplink and downlink rate region and efficient algorithms for computing rate pairs at the region’s boundary. We also provide near-optimal and heuristic algorithms that “convexify” the rate region when it is not convex. The convexified region corresponds to a combination of a few full-duplex rates (i.e., to time sharing between different operation modes). The algorithms can be used for theoretical characterization of the rate region as well as for resource (time, power, and channel) allocation with the objective of maximizing the sum of the rates when one of them (uplink or downlink) must be guaranteed (e.g., due to QoS considerations). We numerically illustrate the rate regions and the rate gains (compared with time division duplex) for various channel and cancellation scenarios. The analytical results provide insights into the properties of the full-duplex rate region and are essential for future development of scheduling, channel allocation, and power control algorithms.