John C. McEachen

Shape-based tracking of left ventricular wall motion

An approach for tracking and quantifying the nonrigid, nonuniform motion of the left ventricular (LV) endocardial wall from two-dimensional (2-D) cardiac image sequences, on a point-by-point basis over the entire cardiac cycle, is presented. Given a set of boundaries, motion computation involves first matching local segments on one contour to segments on the next contour in the sequence using a shape-based strategy. Results from the match process are incorporated with a smoothness term into an optimization functional. The global minimum of this functional is found, resulting in a smooth flow field that is consistent with the match data. The computation is performed for all pairs of frames in the temporal sequence and equally sampled points on one contour are tracked throughout the sequence, resulting in a composite flow field over the entire sequence. Two perspectives on characterizing the optimization functional are presented which result in a tradeoff resolved by the confidence in the initial boundary segmentation. Experimental results for contours derived from diagnostic image sequences of three different imaging modalities are presented. A comparison of trajectory estimates with trajectories of gold-standard markers implanted in the LV wall are presented for validation. The results of this comparison confirm that although cardiac motion is a three-dimensional (3-D) problem, two-dimensional (2-D) analysis provides a rich testing ground for algorithm development.

Unconditionally secure communications over fading channels

In this paper, we propose a novel method for two communicates to exchange a secret over a public wireless fading channel. Unlike conventional computationally secure public key methods, this technique is information theoretic and unconditionally secure provided that a component of the reciprocal channel fading over time between the two communicates is statistically independent with the channel fading from either communicate to the eavesdropper. This technique may be particularly well suited to secure tactical mobile communications. A simple protocol suitable for a lognormal shadowed fading channel is described and its key exchange rate is derived.

Multiframe temporal estimation of cardiac nonrigid motion

A robust, flexible system for tracking the point to point nonrigid motion of the left ventricular (LV) endocardial wall in image sequences has been developed. This system is unique in its ability to model motion trajectories across multiple frames. The foundation of this system is an adaptive transversal filter based on the recursive least-squares algorithm. This filter facilitates the integration of models for periodicity and proximal smoothness as appropriate using a contour-based description of the objects boundaries. A set of correspondences between contours and an associated set of correspondence quality measures comprise the input to the system. Frame-to-frame relationships from two different frames of reference are derived and analyzed using synthetic and actual images. Two multiframe temporal models, both based on a sum of sinusoids, are derived. Illustrative examples of the systems output are presented for quantitative analysis. Validation of the system is performed by comparing computed trajectory estimates with the trajectories of physical markers implanted in the LV wall. Sample case studies of marker trajectory comparisons are presented. Ensemble statistics from comparisons with 15 marker trajectories are acquired and analyzed. A multiframe temporal model without spatial periodicity constraints was determined to provide excellent performance with the least computational cost. A multiframe spatiotemporal model provided the best performance based on statistical standard deviation, although at significant computational expense.

Evaluation of the XMesh Routing Protocol in Wireless Sensor Networks

The evaluation of a routing protocol developed by Crossbow Technologies called XMesh is presented. The main components of the routing protocol are described and the routing algorithm explained. Experiments were conducted to determine the connectivity ranges of motes in different transmission power settings. The relationship of mote transmission power and network connectivity is presented. An energy efficiency study looked at the means of extending the lifespan of the network. Although, packet losses during the period of a node failure were significant, the routing protocol showed that it was able to adapt and reorganize to provide reliable and stable routing in a network.

A New Method for Distributing Power Usage across a Sensor Network

We present a method for more uniformly distributing the energy burden across a wireless ground-based sensor network communicating with an overhead unmanned aerial vehicle (UAV). A subset of sensor nodes, termed a transmit cluster, receives and aggregates data gathered by the entire network, and forms a distributed antenna array, concentrating the radiated transmission into a narrow beam aimed towards the UAV. Because these duties are power-intensive, the role of transmit cluster must be shifted to different nodes as time progresses. We present an algorithm to reassign the transmit cluster, specifying the time that should elapse between reassignments and the number of hops that should be placed between successive transmit clusters in order to achieve three competing goals: first, we wish to better and more broadly spread the energy load across the sensor network while, second, minimizing the energy expended in moving the transmit cluster, all the while, third, reducing to the extent practicable the time to bring the UAV and the sensor networks beam into alignment. The algorithm thus extends the lifetime of the sensor network while meeting system-level performance objectives

A Distributed Approach to Beamforming in a Wireless Sensor Network

A beamforming approach can be used in a wireless sensor network (WSN) to increase the effective communication range of the network. In this paper, the impact on array performance of node position deviations with respect to the ideal array element locations is examined and a distributed beamforming algorithm is proposed to compensate for these position deviations. Simulation results are provided to demonstrate that the proposed solution closely approximates the performance of an ideal uniform linear array.

A Comparison of Optimized Link State Routing with Traditional Routing Protocols in Marine Wireless Ad-hoc and Sensor Networks

The performance of mobile ad-hoc networks (MANET) is related to the efficiency of the routing protocols in adapting to frequently changing network topology and link status. This paper addresses the issue by comparing the relative performance of three key ad-hoc routing protocols: destination-sequenced distance vector (DSDV), ad-hoc on-demand distance vector (AODV) and optimized link state routing (OLSR). The protocols are tested based on two scenarios, namely, tactical networks for ships and sensor-based network nodes. Four performance metrics were measured by varying the maximum speed of mobile hosts, network size and traffic load, to assess the routing capability and protocol efficiency. The simulation results indicate that AODV performs better than OSLR and DSDV in the first scenario. Although OLSR also performed relatively well, the associated high routing overhead is the dominant reason for not choosing it. On the other hand, OLSR emerged as the protocol of choice for sensor networks, where the high routing overhead is counteracted by consistently better performance in all other metrics. Due to the slow evolution of the sensor network topology, OLSR performed satisfactorily for best effort traffic but needed subtle adjustments to balance between latency and bandwidth to meet the requirements of delay-sensitive applications

A Beamforming Approach for Distributed Wireless Sensor Networks

We present an energy-aware approach for enabling communication between a wireless ground-based sensor network, and an overhead unmanned aerial vehicle (UAV). Specifically, we present a technique for assembling a subset of sensor nodes into a distributed antenna array useful for beamforming. A small subset of sensor nodes receives and aggregates information gathered by the network, and forms a distributed antenna array, concentrating the radiated transmission into a narrow beam aimed towards the UAV. Although, in general, the relative orientations of the elements in a distributed antenna array have an effect on antenna performance, our proposed approach can be employed in scenarios where the individual sensor nodes do not have knowledge of their location within an absolute coordinate system.

RF Characteristics of Mica-Z Wireless Sensor Network Motes

The RF characteristics of Mica-Z wireless unattended sensor motes were evaluated for military and commercial applications. The Mica-Z motes propagation characteristics and network performance were measured under near free- space, indoor and outdoor environments to provide a comprehensive perspective of typical sensor network characteristics. Link break distance and re-association distance with their corresponding RF power measurements were recorded to determine the Mica-Zs range characteristics under different operating environments. Power Loss exponents were also estimated to provide Mica-Z users a faster and more convenient way to estimate operating ranges in the different environments. A graphical numeric electromagnetic code (GNEC) simulation was also used to investigate some of the possible improvements that could be made to the existing Mica- Z antenna design to enhance the performance of the sensor network. This paper substantiates the difficulties of operating such sensor networks in the most hostile environments. Although the analyses demonstrate that controlled deployment was possible to some extent, the effectiveness of random deployment remains challenging.

Geolocation of LTE subscriber stations based on the timing advance ranging parameter

This paper investigates geolocating a Long Term Evolution (LTE) subscriber station based on the timing advance ranging parameter within the network signal internals. The basic approach to geolocation based on radial distances from multiple base stations is outlined. Specifics of the timing parameters used during LTE network entry are examined as they relate to calculating these distances. Computer simulation is used to demonstrate expected geolocation accuracy in multiple base station networks when estimating likely locations of subscriber stations on a two-dimensional coordinate mapping system. Computer simulation is further refined to demonstrate expected geolocation accuracy in multiple base station networks when estimating likely locations of subscriber stations on a three-dimensional coordinate mapping scheme. Results show the possibility of fixes with ten times greater accuracy than in previous results in the literature when applying timing advance techniques to Global System for Mobile communications networks when using a two-dimensional coordinate mapping scheme, and accuracy approaching fifty centimeters when using a three-dimensional coordinate mapping scheme, accuracy that is comparable to the accuracy in Global Positioning System technologies.