Theses: Signal Processing Techniques for Wireless Locationing
A. Urruela Planas

Abstract

 

Wireless positioning has received considerable attention during the last years due to the increasing number of deployed mobile devices, and the associated interest in obtaining the position of these devices. Multiple studies have shown the benefits and potential markets that will be realized once reliable location data on our PDAs, mobile cellular handsets, Bluetooth-enabled devices, etc is made available. To mention but a few possible applications that are highly sought after, we have locationing of emergency calls placed from mobile terminals, location-based advertisements, car routing, shopping routing in big supermarkets and more. Other applications, that are perhaps less spectacular and more of an academic interest, are the optimization of various networks based on the location of their nodes or social studies based on the movement of mobile devices.

A common property of all above mentioned mobile devices is that all of them transmit and receive some type of electromagnetic waveform in order to communicate with a fixed base station, or with another mobile device. This Thesis focuses on the type of system where one mobile unit communicates with a set of fixed base stations, but it also includes some brief treatment of the locationing of networked devices without fixed base stations, i.e., autonomous sensor networks. In particular, this Thesis studies the problem of computing the position of a mobile terminal that transmit and receive signals to or from a set of fixed base stations with known locations. The most representative application of the developments and findings in this Thesis is the locationing of emergency-callers in a cellular network for personal communications. Therefore, most simulations and evaluations in this work are made with this type of scenario in mind.

As discussed in the introduction to this document, a widely used and commonly accepted approach to the design of wireless positioning systems is to first obtain an estimate of the temporal propagation delays, and, then, process these estimates in order to obtain a position estimate. Therefore, one of the chapters in this work is focused on obtaining accurate time delay estimates in diffuse multipath environments. We also study some theoretical limits, in terms of the positioning accuracy of any unbiased positioning system based on estimates of time-delay. These theoretical limits will be used throughout the Thesis as benchmarks of comparison for the derived algorithms. The core of the Thesis is focused on obtaining closed-form solutions for time-delay based locationing and to mitigate the so-called Non Line of Sight effect. Finally, the last chapter of the Thesis is focused on wideband code division multiple access (CDMA) like systems. In this case, the employed medium access scheme changes the formulation of the positioning problem to some extent. We address differences and design a locationing estimator suitable for CDMA-like cellular systems. In conclusion, this Thesis proposes solutions for many signal processing problems that arise in the implementation of wireless positioning systems based on the estimates of signal delay between a set of base stations and a mobile device.

Wireless positioning has received considerable attention during the last years due to the increasing number of deployed mobile devices, and the associated interest in obtaining the position of these devices. Multiple studies have shown the benefits and potential markets that will be realized once reliable location data on our PDAs, mobile cellular handsets, Bluetooth-enabled devices, etc is made available. To mention but a few possible applications that are highly sought after, we have locationing of emergency calls placed from mobile terminals, location-based advertisements, car routing, shopping routing in big supermarkets and more. Other applications, that are perhaps less spectacular and more of an academic interest, are the optimization of various networks based on the location of their nodes or social studies based on the movement of mobile devices. A common property of all above mentioned mobile devices is that all of them transmit and receive some type of electromagnetic waveform in order to communicate with a fixed base station, or with another mobile device. This Thesis focuses on the type of system where one mobile unit communicates with a set of fixed base stations, but it also includes some brief treatment of the locationing of networked devices without fixed base stations, i.e., autonomous sensor networks. In particular, this Thesis studies the problem of computing the position of a mobile terminal that transmit and receive signals to or from a set of fixed base stations with known locations. The most representative application of the developments and findings in this Thesis is the locationing of emergency-callers in a cellular network for personal communications. Therefore, most simulations and evaluations in this work are made with this type of scenario in mind. As discussed in the introduction to this document, a widely used and commonly accepted approach to the design of wireless positioning systems is to first obtain an estimate of the temporal propagation delays, and, then, process these estimates in order to obtain a position estimate. Therefore, one of the chapters in this work is focused on obtaining accurate time delay estimates in diffuse multipath environments. We also study some theoretical limits, in terms of the positioning accuracy of any unbiased positioning system based on estimates of time-delay. These theoretical limits will be used throughout the Thesis as benchmarks of comparison for the derived algorithms. The core of the Thesis is focused on obtaining closed-form solutions for time-delay based locationing and to mitigate the so-called Non Line of Sight effect. Finally, the last chapter of the Thesis is focused on wideband code division multiple access (CDMA) like systems. In this case, the employed medium access scheme changes the formulation of the positioning problem to some extent. We address differences and design a locationing estimator suitable for CDMA-like cellular systems. In conclusion, this Thesis proposes solutions for many signal processing problems that arise in the implementation of wireless positioning systems based on the estimates of signal delay between a set of base stations and a mobile device.


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