Mary Ann Weitnauer

On Using Cooperative Routing for Lifetime Optimization of Multi-Hop Wireless Sensor Networks: Analysis and Guidelines

Theoretically optimal performance and behavior of a routing protocol are very important because they can be used to guide the design of practical protocols. Motivated by the promising lifetime performance of an existing suboptimal cooperative transmission (CT) routing protocol for wireless sensor networks, we formulate the lifetime-optimization problem using linear programming (LP), which requires considerations of CTs unique characteristics and sophisticated variable definitions. By evaluating LP for various cases, we show the effectiveness of cooperative routing by comparing it with the non-CT case. Also, by analyzing the LP solution, we identify some important factors and behaviors of optimal cooperative routing. More specifically, we conclude that (i) matching the rate of doing CT and matching the candidate pools of cooperators to the LP solution are important factors to achieve near-optimal lifetime performances, and, (ii) for small multi-hop networks, the design of cooperative routing can be simplified because one may use the sink node as a single VMISO receiver and rely on the existing energy-aware routing for the primary routing.

Achieving Undetectable Communication

In this paper we consider the problem of achieving a positive error-free communications rate without being detected by an eavesdropper-we coin this the privacy rate. Specifically, we analyze the privacy rate over additive white Gaussian Noise (AWGN) channels with finite and infinite number of samples and Rayleigh single input-single (SISO) and multiple input-multiple output (MIMO) channels with infinite samples when an eavesdropper employs a radiometer detector and has uncertainty about his noise variance. Leveraging recent results on the phenomenon of a signal-to-noise ratio (SNR) wall when there is eavesdropper noise power measurement uncertainty, we show that a nonzero privacy rate is possible. We also show that in this scenario, the detector should not necessarily take as many samples as possible.

Distributed extremum seeking and formation control for nonholonomic mobile network

a b s t r a c t In this paper, an integrated control and optimization problem is studied in the context of formation and coverage of a cluster of nonholonomic mobile robots. In particular, each communication channel is mod- eled by its outage probability, and hence, connectivity is maintained if the outage probability is less than a certain threshold. The objective of the communication network is to not only maintain resilient commu- nication quality but also extend the network coverage. An information theory based performance index is defined to quantify this control objective. Unlike most of the existing results, the proposed coopera- tive control design does not assume the knowledge of any gradient (of the performance index). Rather, a distributed extremum seeking algorithm is designed to optimize the connectivity and coverage of the mobile network. The proposed approach retains all the advantages of cooperative control, and it can not only perform extremum seeking individually, but also ensures a consensus of estimates between any pair of connected systems. Simulation results demonstrate effectiveness of the proposed methodology.

Multi-Packet Opportunistic Large Array Transmission on Strip-Shaped Cooperative Routes or Networks

The Opportunistic Large Array (OLA) is one type of cooperative transmission, which provides fast and reliable broadcasts and unicasts in multi-hop networks. While the existing literature on OLAs assumes one-shot transmission with a single packet, we analyze multi-packet OLA transmission within a single flow along strip-shaped networks or OLA-based cooperative routes. When multiple packets are transmitted from the same source using the same channel before the previous packet has cleared the network, which is called spatial pipelining, intra-flow interference is produced by OLAs transmitting co-channel packets. Using the continuum assumption (approximated by high density networks), the authors optimize the throughput. This paper theoretically shows spatial pipelining over strip networks is always feasible for path loss exponent α≥2, which is not true for disk-shaped networks. Moreover, the impacts of system parameters are analyzed, and the upper bound of the optimal packet spacing (the lower bound of the optimal throughput) is derived. Also, spatial pipelining in finite networks is studied with numerical results, which confirm the theoretical analysis.

On cooperative transmission range extension in multi-hop wireless ad-hoc and sensor networks

Range extension is a promising feature offered by cooperative transmission (CT), also known as virtual multiple-input-single-output (VMISO). Many authors have considered how the diversity and array gains from CT may benefit a wireless multi-hop network, when the gains are used for increasing link reliability and reducing transmit power. However, relatively less attention has been given to the benefits of CT range extension and few testbed implementations of CT have been demonstrated. In this paper, we focus on how CT range extension can impact the lower three layers, especially medium access control (MAC) and routing for ad hoc and sensor multi-hop networks (AHSMNs). We assume cooperators decode and forward the packets. Various analytical models, performance analyses, and experimental results using software-defined radios in an indoor office environment are discussed. For wireless sensor networks (WSNs), we review CT range extension at the network layer, to eliminate the energy hole that forms around sink nodes in non-CT networks, and we review cooperator selection and duty cycle scheduling algorithms at Layer 2, to maximize the lifetime of a multi-hop WSN. For ad hoc networks, we emphasize a family of lightweight broadcasting and unicasting protocols based on a simple form of CT called the opportunistic large array (OLA). Experimental results, including OLA-based unicast routing and diversity order effects in two-hop CT networks, are discussed.

Harmonic Path (HAPA) algorithm for non-contact vital signs monitoring with IR-UWB radar

We introduce the Harmonic Path (HAPA) algorithm for estimation of heart rate (HR) and respiration rate (RR) with Impulse Radio Ultrawideband (IR-UWB) radar. A well known result is that a periodic movement, such as the lung wall or heart wall movement, induces a fundamental frequency and its harmonics. IR-UWB enables capture of these spectral components and frequency domain processing enables a low cost implementation. Most existing methods try to identify the fundamental component to estimate the HR and/or RR. However, often the fundamental is distorted or cancelled by interference, such as RR harmonics interference on the HR fundamental, leading to significant error for HR estimation. HAPA is the first reported algorithm to take advantage of the HR harmonics, where there is less interference, to achieve more reliable and robust estimation of the fundamental frequency. Example experimental results for HR estimation demonstrate how our algorithm eliminates errors caused by interference.

Multi-Packet Interference in Opportunistic Large Array Broadcasts over Disk Networks

The Opportunistic Large Array (OLA) is a simple form of cooperative transmission, in which a group of single-antenna nodes decode the same packet, then a short time later relay the packet simultaneously in orthogonal or space-time coded channels. The authors have previously shown that OLA transmissions can be adequately synchronized so they appear to a receiver as having come from a conventional array with co-located antennas doing transmit diversity. OLAs have been considered as a basis for rapid single-packet broadcasting in multi-hop networks, however, there are few studies that consider OLA broadcasting of multiple co-channel packets. Using the continuum assumption (approximated by high density networks), we focus on broadcast throughput optimization, as determined by the packet insertion rate at the source. We consider spatial pipelining, which means broadcasting a packet before the previous co-channel packet has cleared the network. We show theoretically that for infinitely large networks the feasibility of spatial pipelining depends on the path loss exponent. For finite networks, we study the propagation behavior of spatially pipelined packets using numerical analysis.

Towards Sleep Apnea Screening with an Under-the-Mattress IR-UWB Radar Using Machine Learning

In this work, we apply machine learning to investigate the effectiveness of an Impulse Radio Ultra-Wide Band (IR-UWB) radar panel, in an under-the-mattress configuration, for detecting apnea events in subjects known to have obstructive sleep apnea (OSA). We consider a collection of features, some novel and some inspired by features that worked well for sleep apnea detection using other types of sensors (i.e., not IR-UWB). To extract the features, we collected a total of 25 hours of data from four subjects as they slept through the night. The data included digitized samples of the IR-UWB radar return signal and the scored polysomnograph (PSG), which is the gold standard and measures a large number of physiological parameters in a well-equipped sleep laboratory. Normal and apnea epochs were extracted from the IR-UWB data corresponding to normal and apnea epochs in the PSG data. Statistical features were derived from these extracted epochs and a Linear Discriminant classifier was trained. Using cross-validation, we found that the classifier had an accuracy of around 70% in detection of apnea and normal epochs. The novel aspect of this project involves processing and investigation of different methods for feature extraction on data obtained from real apnea subjects and suggests that the radar, when paired with other under-the-mattress sensors might provide an effective screening device in a convenient form factor.

Aggregated Packet Transmission in Duty-Cycled WSNs: Modeling and Performance Evaluation

Duty cycling (DC) is a popular technique for energy conservation in wireless sensor networks (WSNs) that allows nodes to wake up and sleep periodically. Typically, a single-packet transmission (SPT) occurs per cycle, leading to possibly long delay. With aggregated packet transmission (APT), nodes transmit a batch of packets in a single cycle. The potential benefits brought by an APT scheme include shorter delay, higher throughput, and higher energy efficiency. In the literature, different analytical models have been proposed to evaluate the performance of SPT schemes. However, no analytical models for the APT mode on synchronous DC medium access control (MAC) mechanisms exist. In this paper, we first develop a 3-D discrete-time Markov chain (DTMC) model to evaluate the performance of an APT scheme with packet retransmission enabled. The proposed model captures the dynamics of the state of the queue of nodes and the retransmission status and the evolution of the number of active nodes in the network, i.e., nodes with a nonempty queue. We then study the number of retransmissions needed to transmit a packet successfully. Based on the observations, we develop another less-complex DTMC model with infinite retransmissions, which embodies only two dimensions. Furthermore, we extend the 3-D model into a 4-D model by considering error-prone channel conditions. The proposed models are adopted to determine packet delay, throughput, packet loss, energy consumption, and energy efficiency. Furthermore, the analytical models are validated through discrete-event-based simulations. Numerical results show that an APT scheme achieves substantially better performance than its SPT counterpart in terms of delay, throughput, packet loss, and energy efficiency and that the developed analytical models reveal precisely the behavior of the APT scheme.

Towards robust estimation of systolic time intervals using head-to-foot and dorso-ventral components of sternal acceleration signals

Continuous measurement of cardiac time intervals throughout normal activities of daily living is of interest for both chronic disease management and preventive wellness monitoring. Systolic time intervals in particular - i.e., pre-ejection period (PEP) and left ventricular ejection time (LVET) - have been shown to be relevant to assessing myocardial health and performance, but are challenging to measure with wearable sensors. In this paper, we present novel methods for estimating PEP and LVET from a single three-axis accelerometer placed at the sternum, based on the measurement of cardiogenic vibrations: seismocardiography (SCG) and ballistocardiography (BCG). Although such signals have been examined in the existing literature, the analysis and interpretation has focused mainly on the dorso-ventral components only in the context of systolic time interval estimation. In this paper, we find that features extracted from the head-to-foot accelerations yield better correlations to PEP measured from impedance cardiogram (ICG) than standard approaches based on dorso-ventral components. Additionally, we examine the effects of postural variations on the correlation between PEP estimated from accelerometer and ICG signals and also on correlation between LVET estimated from both sensors. We determine that such correlations are robust to postural changes. Based on these findings, we anticipate that wearable, accelerometer based vibration measurements from standing subjects can be used for robust systolic time interval estimation in a variety of ubiquitous cardiovascular health and fitness sensing applications.