The recent proliferation of Bluetooth Devices has caught the attention of hackers. With Bluetooth devices being put in everything from cell phones to PDAs to laptops, the abuse of this technology could have an even bigger impact than the viruses and malware running rampant on the internet. Bluetooth is a short range wireless technology intended to interconnect consumer electronics devices of all kinds. The same features that make Bluetooth so attractive to manufacturers, also makes it attractive to hackers. Bluetooth devices can quickly setup up ad-hoc networks with other, previously unknown devices. Hackers have started to take advantage of the ease with which a connection can be established along with the average user's lack of computer security knowledge to break into PDAs, cell phones to steal address books and credit card numbers. One of the largest obstacles that must be overcome in Bluetooth security is the mobility of devices and the relatively short duration of connections. In the Internet, threats can often be traced back to a source, and in many cases the source of the threat can be shut down. However, in a Bluetooth Network devices connect directly to one another, and there are no wires to follow to pinpoint the offending device. This thesis will explore the techniques for the location of Bluetooth Devices. An ideal position location system would be one that operates completely within the Bluetooth Specification. Such a system will be able to use any available Bluetooth Device to find the location of other devices. The primary focus of this thesis will be on such a system, with an overview of traditional radio position location techniques and Bluetooth so that we might gain some insight into how these techniques can be applied to Bluetooth. Data are presented from an extensive set of measurements to relate Bluetooth RSSI and distance on CSR BlueCore02 devices. Finally the results of the data are analyzed to give a rough estimate of the range error that would be incurred in the implementation of such a system. / Master of Science

Wireless communication has enjoyed explosive growth over the past decade. As demands for increased capacity and quality grow, improved methods for harnessing the multipath wireless channel must be developed. The use of adaptive antenna arrays is one area that shows promise for improving capacity of wireless systems and providing improved safety through position location capabilities. These arrays can be used for interference rejection through spatial filtering, position location through direction finding measurements, and developing improved channel models through angle of arrival channel sounding measurements. This thesis provides an overview of the technical challenges involved in position location of wireless users and details the hardware development of a multi-sensor testbed at the Mobile and Portable Radio Research Group at Virginia Tech. This testbed is to be used for position location experiments as well as a host of other adaptive signal processing applications. / Master of Science

Impulse-based Ultrawideband (UWB) is a form of signaling which uses streams of pulses of very short duration, typically on the order of a nanosecond. Impulse-based UWB systems possess the ability to fuse accurate position-location with low-data rate communication, and provide covertness for tactical applications and robustness in dense multipath propagation environments. These features can be leveraged in the design wireless ad hoc position-location networks (PoLoNets) for accurate location tracking and monitoring where GPS is not available, especially indoors. Location information is sequentially propagated through a network of reference nodes in order to create a framework for the tracking of mobile nodes, as well as a multi-hop message-passing infrastructure between mobile nodes and control nodes located outside the area of deployment. The applications of such networks include the location and command-and-control of fire-fighters in emergency scenarios, the location of military personnel deployed in urban or indoor environments, and the guidance of robots through large multi-room indoor environments. The main objective of this dissertation is to derive design principles, techniques and analytical models for UWB PoLoNets that are useful in the development of practical solutions. Some of the fundamental obstacles to obtaining accurate location information in indoor environments are non-line-of-sight (NLOS) signal propagation, limited connectivity between nodes, and the propagation of localization inaccuracies when using sequential estimation approaches in ad hoc scenarios. Several techniques and algorithms that mitigate these effects, thereby allowing the design of PoLoNets with requisite localization accuracy, are presented. Although these techniques are developed from the perspective of a UWB physical layer, the majority are applicable to generic PoLoNets. / Ph. D.

Position location has become one of the more important tasks for improving communication and networking performance for future commercial wireless systems. It is also the enabling technology for many control and sensing applications envisioned by the wireless sensor networks (WSN). Despite its meaningfulness and many algorithms being developed in the past several years, position location in harsh propagation environments remains to be a challenging issue, due mainly to the lack of sufficient infrastructure support and the prominent phenomenon of non-line-of-sight (NLOS) signal propagation. Recently, adopting the concept of collaborative position location has attracted much research interest due to its potential in overcoming the abovementioned two difficulties. In this work, we approach collaborative position location from two different angles. Specifically, we investigate the optimal performance of collaborative position location, which serves as a theoretical performance benchmark. In addition, we developed a computationally efficient algorithm for collaborative position location and incorporated an effective NLOS mitigation method to improve its performance in NLOS-dense environments. Overall, our work provides insight into both theoretical and practical aspects of collaborative position location. / Ph. D.

The ability to find the location of a mobile user has become of utmost importance. The demands of first responders necessitates the ability to accurately identify the location of an individual who is calling for help. Their response times are directly influenced by the ability to locate the caller. Thus, applications such as Enhanced 911 and other location-based services warrant the ability to quickly and accurately calculate location. The FCC has also put in place a timeline for indoor location accuracy requirements that must be met by the mobile communications service providers. In order to meet these requirements, there are many means of performing indoor geolocation that require research; in this thesis two specific methods of identifying the location of a user will be investigated. In the first part, the indoor localization of a target, whose exact location is unknown, in a LTE network is studied. In this problem the time difference of arrival of the LTE uplink signals sent from the target to an observer are used as the means to estimate the target position. The two-dimensional location of a user is then estimated through the use of a nonlinear least-squares algorithm. To improve this approach, a cooperative localization technique in uplink LTE is proposed in which the User Equipment (UE) communicates with base stations as well as other handsets. Through simulated results it is shown that utilizing collaboration can improve location estimation and outperform non-collaborative localization. In the second part, the indoor localization of a target, focusing on its third dimension or elevation, is studied through the use of barometric pressure sensors in mobile handsets. Finding the third dimension of location, or the correct height above the ground level which equates to the floor in a building that a UE is on, cannot be performed with two-dimensional measurement models. For this problem, the pressure sensors are used to accurately find an immediate pressure measurement and allow for the altitude of a handset to be calculated. This altitude can be translated into an estimation for a specific floor of a building given the use of a ground floor pressure reference. Through simulation results it is then shown that the accuracy of third dimension or indoor-floor localization can be improved with the use of collaborative pressure sensors of other mobile handsets. / Master of Science

This thesis focuses on the least-squares formulation of the non-collaborative and collabo- rative position location problems. For the non-collaborative problem, characterization encompassing the number of minima and the causes thereof is provided. Based on these efforts, we propose an improvement to the existing modified parallel projection method (MPPM), the reflected parallel projection method (RPPM). We show that the global minimum to the non-collaborative objective function can nearly always be found using the non-optimal reflected parallel projection method (RPPM). For the collaborative position location problem, we provide a characterization that shows a heavy tail of root-mean-square (RMS) error due to a small percentage of simulated node/anchor layouts when solved by the iterative parallel projection method (IPPM). We provide an identification technique that successfully identifies most layouts that show large RMS error followed by a proposed solution to improve the accuracy in those problematic layouts. Finally, we report the findings of a measurement campaign that validates our Gaussian model for line-of-sight (LOS) noise and shows that, for these particular measurements, non-line-of-sight (NLOS) noise is difficult to accurately model and can be very large. This research was supported by a Bradley Fellowship from Virginia Tech's Bradley Department of Electrical and Computer Engineering, made possible by an endowment from the Harry Lynde Bradley Foundation. / Master of Science

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This project investigates the feasibility of position detection in an office or industrial setting. The objective is to design a low-cost positioning system that uses the unlicensed 5.7 GHz ISM band, with centimeter accuracy and limited range. During the conceptual design phase of the system, indoor channel models will be investigated to determine which of a variety of architectures will be useful. For triangulating the position, an array of widely spaced stationary receivers and a mobile transmitter is proposed.

The localization of wireless devices, e.g. mobile phones, laptops, and handheld GPS receivers, has gained much interest due to the benefits it provides, including quicker emergency personnel dispatch, location-aided routing, as well as commercial revenue opportunities through location based services.  GPS is the dominant position location system in operation, with 31 operational satellites producing eight line of sight satellites available to users at all times making it very favorable for system implementation in all wireless networks.  Unfortunately when a GPS receiver is in a challenging environment, such as an urban or indoor scenario, the signal quality often degrades causing poor accuracy in the position estimate or failure to localize altogether due to satellite availability. Our goal is to introduce a new solution that has the ability to overcome this limitation by improving the accuracy and availability of a GPS receiver when in a challenging environment.  To test this theory we created a simulated GPS receiver using a MATLAB simulation to mimic a standard GPS receiver with all 31 operational satellites.  Here we are able to alter the environment of the user and examine the errors that occur due to noise and limited satellite availability.  Then we introduce additional user(s) to the GPS solution with the knowledge (or estimate) of the distances between the users.  The new solutions use inter-receiver distances along with pseudoranges to cooperatively determine all receiver location estimates simultaneously, resulting in improvement in both the accuracy of the position estimate and availability. / Master of Science

The Federal Communications Commission (FCC) that regulates all wireless communication service providers has issued modified regulations that all service providers must select a method for providing position location (PL) information of a user, requesting for E-911 service, by October 2000. The wireless 911 rules adopted by the FCC are aimed both for improving the reliability of the wireless 911 services and for providing the enhanced features generally available for wireline calls. From the service providers' perspective, effective position location technologies must be utilized to meet the FCC rules. The Time-of-Arrival (TOA) and the Time-Difference-of-Arrival (TDOA) methods are the technology that can provide accurate PL information without necessitating excessive hardware or software changes to the existing cellular/PCS infrastructure. The TOA method works well when the mobile station (MS) is located close to the controlling base station. With certain corrections applied, the TOA method can perform reliably even in the presence of Non-Line-of-Sight (NLOS) condition. The TDOA method performs better when the MS is located at a significant distance from the controlling base station. However, under the NLOS environmental condition, the performance of the TDOA method degenerates significantly. The fusion of TOA and the TDOA method exhibits certain advantages that are not evident when only one of the methods is applied. This thesis investigates the performance of data fusion techniques for a PL system, that are able to merge independent estimates obtained from TOA and TDOA measurements. A channel model is formulated for evaluating PL techniques within a NLOS cellular environment. It is shown that NLOS propagation can introduce a bias into TDOA measurements. A correction method is proposed for removing this bias and new corrected data fusion techniques are compared with previous techniques using simulation method, yielding favorable results. / Master of Science

Determining the locations of devices in mobile ad-hoc networks (MANETs), wireless sensor networks (WSNs), and cellular networks has many important applications. In MANETs, which are useful in disaster recovery, rescue operations, and military communications, location information is used to enable location-aided routing and geodesic packet forwarding. In WSNs, whose applications include environmental monitoring (e.g., for precision agriculture) and asset tracking in warehouses, not only is location information useful for the self-organization of the network, but in addition, tying locations to the sensor observations is crucial for adding meaning to the sensed data. In cellular networks, location information is used to provide subscribers with location-based services in addition to providing public service answering points with potentially life-saving location information during emergency calls. These applications are largely not new, which is evidenced by the fact that the literature is quite rich with localization studies presented over the span of many years. Because of this, it may be surprising to learn that there is a lack of analyses concerning the fundamental factors impacting localization performance. Fundamentally, localization performance depends upon three factors: (i) the number of devices participating in the localization procedure, (ii) the locations of the participating devices, and (iii) the quality of the positioning observations gathered from the participating devices. For the most part, these factors cannot reasonably be considered deterministic. Instead, at any point in time, random effects within a network and its surroundings will determine these factors for individual positioning scenarios. Unfortunately, there are currently no analytical approaches for characterizing localization performance over these random factors. Instead, researchers either provide analytical results for a deterministic set of factors or use complex system-level simulations to obtain general performance insights. While the latter certainly averages over the random factors, the validity of the results is limited by the simulation assumptions. Any change in a network parameter requires running a new time-consuming simulation. In this dissertation, we address current deficiencies in several ways. We present a new model for tractably analyzing network localization fundamentals. This is demonstrated through fundamental analyses of hearability and geometry. Further, collaboration among non-reference devices has recently garnered increasing interest from the research community as a means to (i) improve positioning accuracy and (ii) improve positioning availability. We present fundamental analyses of both of these potential benefits. As a result of our work, we not only characterize several key performance metrics, we also demonstrate that there exist new tractable ways to analyze localization performance. / Ph. D.