280 research outputs found

    Doctor of Philosophy

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    dissertationDevice-free localization (DFL) and tracking services are important components in security, emergency response, home and building automation, and assisted living applications where an action is taken based on a person's location. In this dissertation, we develop new methods and models to enable and improve DFL in a variety of radio frequency sensor network configurations. In the first contribution of this work, we develop a linear regression and line stabbing method which use a history of line crossing measurements to estimate the track of a person walking through a wireless network. Our methods provide an alternative approach to DFL in wireless networks where the number of nodes that can communicate with each other in a wireless network is limited and traditional DFL methods are ill-suited. We then present new methods that enable through-wall DFL when nodes in the network are in motion. We demonstrate that we can detect when a person crosses between ultra-wideband radios in motion based on changes in the energy contained in the first few nanoseconds of a measured channel impulse response. Through experimental testing, we show how our methods can localize a person through walls with transceivers in motion. Next, we develop new algorithms to localize boundary crossings when a person crosses between multiple nodes simultaneously. We experimentally evaluate our algorithms with received signal strength (RSS) measurements collected from a row of radio frequency (RF) nodes placed along a boundary and show that our algorithms achieve orders of magnitude better localization classification than baseline DFL methods. We then present a way to improve the models used in through-wall radio tomographic imaging with E-shaped patch antennas we develop and fabricate which remain tuned even when placed against a dielectric. Through experimentation, we demonstrate the E-shaped patch antennas lower localization error by 44% compared with omnidirectional and microstrip patch antennas. In our final contribution, we develop a new mixture model that relates a link's RSS as a function of a person's location in a wireless network. We develop new localization methods that compute the probabilities of a person occupying a location based on our mixture model. Our methods continuously recalibrate the model to achieve a low localization error even in changing environments

    CUSTARD (Cranfield University Space Technology Advanced Research Demonstrator) - A Micro-System Technology Demonstrator Nanosatellite. Summary of the Group Design Project MSc in Astronautics and Space Engineering. 1999-2000, Cranfield University

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    CUSTARD (Cranfield University Space Technology And Research Demonstrator) was the group design project for students of the MSc in Astronautics and Space Engineering for the Academic Year 1999/2000 at Cranfield University. The project involved the initial design of a nanosatellite to be used as a technology demonstrator for microsystem technology (MST) in space. The students worked together as one group (organised into several subgroups, e.g. system, mechanical), with each student responsible for a set of work packages. The nanosatellite designed had a mass of 4 kg, lifetime of 3 months in low Earth orbit, coarse 3-axis attitude control (no orbit control), and was capable of carrying up to 1 kg of payload. The electrical power available was 18 W (peak). Assuming a single X-band ground station at RAL (UK), a data rate of up to 1 M bit s-1 for about 3000 s per day is possible. The payloads proposed are a microgravity laboratory and a formation flying experiment. The report summarises the results of the project and includes executive summaries from all team members. Further information and summaries of the full reports are available from the College of Aeronautics, Cranfield University

    Doctor of Philosophy

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    dissertationThe wireless radio channel is typically thought of as a means to move information from transmitter to receiver, but the radio channel can also be used to detect changes in the environment of the radio link. This dissertation is focused on the measurements we can make at the physical layer of wireless networks, and how we can use those measurements to obtain information about the locations of transceivers and people. The first contribution of this work is the development and testing of an open source, 802.11b sounder and receiver, which is capable of decoding packets and using them to estimate the channel impulse response (CIR) of a radio link at a fraction of the cost of traditional channel sounders. This receiver improves on previous implementations by performing optimized matched filtering on the field-programmable gate array (FPGA) of the Universal Software Radio Peripheral (USRP), allowing it to operate at full bandwidth. The second contribution of this work is an extensive experimental evaluation of a technology called location distinction, i.e., the ability to identify changes in radio transceiver position, via CIR measurements. Previous location distinction work has focused on single-input single-output (SISO) radio links. We extend this work to the context of multiple-input multiple-output (MIMO) radio links, and study system design trade-offs which affect the performance of MIMO location distinction. The third contribution of this work introduces the "exploiting radio windows" (ERW) attack, in which an attacker outside of a building surreptitiously uses the transmissions of an otherwise secure wireless network inside of the building to infer location information about people inside the building. This is possible because of the relative transparency of external walls to radio transmissions. The final contribution of this dissertation is a feasibility study for building a rapidly deployable radio tomographic (RTI) imaging system for special operations forces (SOF). We show that it is possible to obtain valuable tracking information using as few as 10 radios over a single floor of a typical suburban home, even without precise radio location measurements

    Characterizing Multiple Wireless Sensor Networks for Large-Scale Radio Tomography

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    Radio Tomographic Imaging (RTI) is an emerging Device-Free Passive Localization (DFPL) technology that uses a collection of cheap wireless transceivers to form a Wireless Sensor Network (WSN). Unlike device-based active localization, DFPL does not require a target of interest to be wearing any kind of device. The basic concept of RTI utilizes the changes in Received Signal Strength (RSS) between the links of each transceiver to create an attenuation image of the area. This image can then be used for target detection, tracking, and localization. Each transceiver in the WSN must transmit sequentially to prevent collisions. This is not a problem when the number of transceivers in the WSN are small. However, large-scale RTI with a large number of transceivers suffer from high computational complexity, low frame rates, and physical distance limitations on the range of the transceivers. The goal of this research is to determine the applicability and characterize the feasibility of using multiple WSNs to address the limitations with a large-scale RTI network. The concept to this new variant of RTI, called Multiple-Networks RTI (mnRTI), is to divide the transceivers into multiple WSNs as opposed to using one WSN. Analytical, simulated, and experimental data are computed, collected, and compared between a RTI network with one WSN to a mnRTI network with two WSNs. The WSN(s) comprise a total of 70 wireless transceivers covering an area of no more than 19 ft x 16 ft. Simulated and experimental results are presented from a series of stationary and moving target data collection. Preliminary results demonstrate multiple WSNs can potentially provide similar or better results than the traditional RTI method with one WSN. Multiple WSNs have higher frame rates and lower computational complexity. Also, position estimation accuracy are comparable, if not better, than the traditional RTI method with one WSN

    Target detection in urban scenarios using netted radar multipath signals

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    Abstract In urban environments, multipath and obscuration by buildings decreases the ability of radar systems to detect targets and also increases the number of false alarms caused by image artefacts. To reduce these problems this paper proposes a network of low-cost easilydeployable radar sensors that are set up in a multiple-input multiple-output (MIMO) radar configuration. An analysis is given of the signal processing required to combine the data from several co-operating radar sensors while using building information and including the effects of multipath propagation. The key part of this idea is that the known building positions from a database are used to determine the origin of multipath signals. This process enables the removal of artefacts and allows the sensors to "see around the corner" of buildings

    A high bit rate flexible MAC protocol for monitoring applications using 60ghz radio technology

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    In recent years there has been a growing trend in optical wireless convergence. One particular aspect of this is 60 GHz radio-over-fiber technology. It is intended for use in wireless personal area networks. However, we think that the same technology could be used for monitoring applications in the indoor environment. It could be used to detect emergency situations or to detect intruders. We shall examine reasons why this choice might be a suitable one. We shall then propose a MAC layer protocol to accomplish this task. Since in case of emergency we might require to obtain data from only one node for an extended duration, flexibility in implementation is required. We shall develop an adaptive MAC protocol where this would be possible. We accomplish this by including two protocol modes called the Icarus mode, which is to be used in case of an emergency and the Resync mode which is used when normality is restored. A significant problem at high frequencies is that the beam becomes increasingly narrow and behaves more in a ray like condition. This implies that particularly in an indoor environment it is possible that the beam may be accidentally blocked. In this case the node must be able shift the beam in order to enable communication. We demonstrate three such strategies and offer a comparative analysis.M.S.Committee Chair: Chang, Gee-Kung; Committee Member: Barry , John; Committee Member: Gaylord, To

    Exploitation and Mitigation of Multipath in Complex Wave Propagation Environments for Target Detection, Tracking, and Communication.

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    This thesis introduces novel wave propagation models and RF based techniques for detection, tracking, and communication in highly cluttered environments. The applications of interest include localization of deeply submerged targets such as UXO and clandestine tunnels, real-time positioning and tracking of small robotic platforms for search and rescue missions, and enhanced situational awareness in urban warfare. First, an accurate near-ground wave propagation model for indoor and urban scenarios that is based on a hybrid physical optics and asymptotic expansion of dyadic Green's function for a half-space dielectric medium is presented. This model and other full-wave solvers are then used to: 1) investigate direction finding in highly cluttered environments, and 2) analyze the performance of compact antenna diversity systems. Second, a novel sub-wavelength RF source tracking system for applications in GPS-denied environments is realized and measured. The system utilizes a highly miniaturized transmit antenna and a biomimetic circuit that mimics the hearing mechanism of a fly to achieve a compact system. It is shown that tracking with absolute positioning of better than 70cm in complex buildings through multiple layers of walls is achievable from outside in a standoff distance. The third part of the work focuses on a physics-based analysis technique for compact and co-located antenna diversity systems that takes into account the complex radiation pattern of the diversity antennas in conjunction with an accurate near-ground propagation model. A co-located, co-polarized radiation pattern diversity system prototype is realized and characterized. Based on the above analysis technique and measurement results, a diversity gain of 8dB is achieved. In the last part of the work, a subsurface imaging radar system based on distributed near-ground sensor networks that utilize ultra-wideband waveforms in the VHF range is described. Numerical models and laboratory scale model measurements are used to demonstrate high resolution synthetic aperture imaging of deeply submerged targets under a layered medium using an ad hoc network of mobile transceivers.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/96112/1/fikadu_1.pd

    Device-Free, Radio-based Activity Recognition using Smart Home Wireless Communication Technologies

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    This dissertation demonstrates the use of received signal strength to infer human activities. It has the following contributions: 1) Reference design of a device-free, 2.4GHz IEEE 802.15.4-based sensor system for Activity Recognition; 2) Fundamental description of influences affecting Activity Recognition performance; 3) Software design pattern for device-free, radio-based Inference Systems; 4) Development and characterization of three specialized device-free, radio-based Inference System

    Pointing, Acquisition, and Tracking Systems for Free-Space Optical Communication Links

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    Pointing, acquisition, and tracking (PAT) systems have been widely applied in many applications, from short-range (e.g. human motion tracking) to long-haul (e.g. missile guidance) systems. This dissertation extends the PAT system into new territory: free space optical (FSO) communication system alignment, the most important missing ingredient for practical deployment. Exploring embedded geometric invariances intrinsic to the rigidity of actuators and sensors is a key design feature. Once the configuration of the actuator and sensor is determined, the geometric invariance is fixed, which can therefore be calibrated in advance. This calibrated invariance further serves as a transformation for converting the sensor measurement to actuator action. The challenge of the FSO alignment problem lies in how to point to a 3D target by only using a 2D sensor. Two solutions are proposed: the first one exploits the invariance, known as the linear homography, embedded in the FSO applications which involve long link length between transceivers or have planar trajectories. The second one employs either an additional 2D or 1D sensor, which results in invariances known as the trifocal tensor and radial trifocal tensor, respectively. Since these invariances have been developed upon an assumption that the measurements from sensors are free from noise, including the uncertainty resulting from aberrations, a robust calibrate algorithm is required to retrieve the optimal invariance from noisy measurements. The first solution is suffcient for most of the PAT systems used for FSO alignment since a long link length constraint is generally the case. Although PAT systems are normally categorized into coarse and fine subsystems to deal with different requirements, they are proven to be governed by a linear homography. Robust calibration algorithms have been developed during this work and further verified by simulations. Two prototype systems have been developed: one serves as a fine pointing subsystem, which consists of a beam steerer and an angular resolver; while the other serves as a coarse pointing subsystem, which consists of a rotary gimbal and a camera. The average pointing errors in both prototypes were less than 170 and 700 micro-rads, respectively. PAT systems based on the second solution are capable of pointing to any target within the intersected field-of-view from both sensors because two sensors provide stereo vision to determine the depth of the target, the missing information that cannot be determined by a 2D sensor. They are only required when short-distance FSO communication links must be established. Two simulations were conducted to show the robustness of the calibration procedures and the pointing accuracy with respect to random noise
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