Tingjun Chen

Outage Minimization for a Fading Wireless Link With Energy Harvesting Transmitter and Receiver

This paper studies online power control policies for outage minimization in a fading wireless link with energy harvesting transmitter and receiver. The outage occurs when either the transmitter or the receiver does not have enough energy, or the channel is in outage, where the transmitter only has the channel distribution information. Under infinite battery capacity and without retransmission, we prove that threshold-based power control policies are optimal. We thus propose disjoint/joint threshold-based policies with and without battery state sharing between the transmitter and receiver, respectively. We also analyze the impact of practical receiver detection and processing on the outage performance. When retransmission is considered, policy with linear power levels is adopted to adapt the power thresholds per retransmission. With finite battery capacity, a three dimensional finite state Markov chain is formulated to calculate the optimal parameters and corresponding performance of proposed policies. The energy arrival correlation between the transmitter and receiver is addressed for both finite and infinite battery cases. Numerical results show the impact of battery capacity, energy arrival correlation and detection cost on the outage performance of the proposed policies, as well as the tradeoff between the outage probability and the average transmission times.

Panda: Neighbor Discovery on a Power Harvesting Budget

Object tracking applications are gaining popularity and will soon utilize Energy Harvesting (EH) low-power nodes that will consume power mostly for Neighbor Discovery (ND) (i.e., identifying nodes within communication range). Although ND protocols were developed for sensor networks, the challenges posed by emerging EH low-power transceivers were not addressed. Therefore, we design an ND protocol tailored for the characteristics of a representative EH prototype: the TI eZ430-RF2500-SEH. We present a generalized model of ND accounting for unique prototype characteristics (i.e., energy costs for transmission/reception, and transceiver state switching times/costs). Then, we present the Power Aware Neighbor Discovery Asynchronously (Panda) protocol in which nodes transition between the sleep, receive, and transmit states. We analyze Panda and select its parameters to maximize the ND rate subject to a homogeneous power budget. We also present Panda-D, designed for non-homogeneous EH nodes. We perform extensive testbed evaluations using the prototypes and study various design tradeoffs. We demonstrate a small difference (less then 2%) between experimental and analytical results, thereby confirming the modeling assumptions. Moreover, we show that Panda improves the ND rate by up to 3x compared to related protocols. Finally, we show that Panda-D operates well under non-homogeneous power harvesting.

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.

Full-duplex wireless based on a small-form-factor analog self-interference canceller: demo

A demonstration of a real-time full-duplex wireless link is presented, in which a pair of full-duplex transceivers perform simultaneous transmission and reception on the same frequency channel. A full-duplex transceiver is composed of a custom-designed small-form-factor analog self-interference canceller, and a digital self-interference cancellation implementation is integrated with the National Instruments Universal Software Radio Peripheral (USRP). An adaptive analog self-interference canceller tuning mechanism adjusts to environmental changes. We demonstrate the practicality and robustness of the full-duplex wireless link through the National Instruments LabVIEW interface.

Power control policies for a wireless link with energy harvesting transmitter and receiver

This paper addresses the outage minimization problem for a wireless link where both the transmitter and the receiver are powered by harvested energy, and the energy arrival processes of both nodes are correlated. We propose three power control policies to minimize the outage probability, including threshold-based On-Off policy, joint scheduling policy, and linear power levels policy. With infinite battery capacity, we analyze the optimality of the thresholds with different correlations between energy arrivals at the transmitter and the receiver. With finite battery capacity, we use finite state Markov chain (FSMC) to obtain the optimality of our policies and also numerically evaluate their performance. The optimal thresholds for minimum outages are derived according to the average energy arrival rate and the system parameters. The numerical results show the performance gains using different policies, as well as the tradeoff between the minimum outage probabilities and the average transmission times.

Panda: Neighbor discovery on a power harvesting budget

Object tracking applications are gaining popularity and will soon utilize Energy Harvesting (EH) low-power nodes that will consume power mostly for Neighbor Discovery (ND) (i.e., identifying nodes within communication range). Although ND protocols were developed for sensor networks, the challenges posed by emerging EH low-power transceivers were not addressed. Therefore, we design an ND protocol tailored for the characteristics of a representative EH prototype: the TI eZ430-RF2500-SEH. We present a generalized model of ND accounting for unique prototype characteristics (i.e., energy costs for transmission/reception, and transceiver state switching times/costs). Then, we present the Power Aware Neighbor Discovery Asynchronously (Panda) protocol in which nodes transition between the sleep, receive, and transmit states. We analyze Panda and select its parameters to maximize the ND rate subject to a homogeneous power budget. We also present Panda-D, designed for non-homogeneous EH nodes. We perform extensive testbed evaluations using the prototypes and study various design tradeoffs. We demonstrate a small difference (less then 2%) between experimental and analytical results, thereby confirming the modeling assumptions. Moreover, we show that Panda improves the ND rate by up to 3x compared to related protocols. Finally, we show that Panda-D operates well under non-homogeneous power harvesting.

Full-duplex in a hand-held device — From fundamental physics to complex integrated circuits, systems and networks: An overview of the Columbia FlexICoN project

Full-duplex wireless is an exciting emerging wireless communication paradigm that also poses tremendous challenges at virtually every layer: from the antenna interface and integrated circuits (ICs) and systems to the network layer. This paper covers recent advances at Columbia University across all these dimensions. Several potential full-duplex system architectures that are appropriate for different application spaces are discussed. Specific research advances include (i) a novel integrated CMOS non-reciprocal circulator that utilizes time-variance to break Lorentz reciprocity, (ii) a polarization-based antenna cancellation technique that achieves very wideband isolation that can be reconfigured as the environment changes, (iii) several generations of RF and analog self-interference cancellation circuits that combat noise, distortion and bandwidth limitations, (iv) higher-layer resource allocation algorithms that evaluate full-duplex rate gains given realistic physical layer models, and (v) demonstrations of full-duplex operation using realistic IC-based nodes.

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.

Power-Aware Neighbor Discovery for Energy Harvesting Things: Demo Abstract

Object tracking applications are gaining popularity and will soon utilize energy harvesting low-power wireless nodes where power is mostly consumed for neighbor discovery. Such applications require the design and experimentation with low-power neighbor discovery protocols. We demonstrate the Panda protocol [4, 5] implementation using commercial off-the-shelf energy harvesting devices, based on the TI eZ430-RF2500-SEH prototype. The prototypes harvest indoor light energy to perform power-aware neighbor discovery, while maintaining a power budget. A custom-designed online monitoring system interactively demonstrates the network dynamics, including the energy storage levels of the devices, the neighbor discovery events, and aggregate discovery statistics.

Performance Evaluation of Energy-Constrained Broadcast (EconCast) in Wireless Networks

Wireless object tracking applications are gaining popularity and will soon utilize emerging ultra-low-power device-to- device communication. However, severe energy constraints require much more careful accounting of energy usage than what prior art provides. To address these challenges, in [1] we focused on maximizing broadcast throughput between a set of heterogeneous ultra-low-power devices and presented the Energy-Constrained Broadcast (EconCast) protocol. EconCast is a simple asynchronous distributed protocol that can operate in groupput and anyput modes to respectively maximize two alternative throughput measures. In this paper, we evaluate the throughput performance of EconCast numerically and via extensive simulations in various heterogeneous and homogeneous networks. We also evaluate the latency performance of EconCast and compare its throughput-delay tradeoffs when operating in groupput and anyput modes.