The availability of location estimates of mobile devices (MDs) is vital for several important applications such as law enforcement, disaster management, battlefield operations, vehicular communication, traffic safety, emergency response, and preemption. While global positioning system (GPS) is usually sufficient in outdoor clear sky conditions, its functionality is limited in urban canyons and indoor locations due to the absence of clear line-of-sight between the MD to be localized and a sufficient number of navigation satellites. In such scenarios, the ubiquitous nature of cellular networks makes them a natural choice for localization of MDs. Traditionally, localization in cellular networks has been studied using system level simulations by fixing base station (BS) geometries. However, with the increasing irregularity of the BS locations (especially due to capacity-driven small cell deployments), the system insights obtained by considering simple BS geometries may not carry over to real-world deployments. This necessitates the need to study localization performance under statistical (random) spatial models, which is the main theme of this work.
In this thesis, we use powerful tools from stochastic geometry and point process theory to develop a tractable analytical model to study the localizability (ability to get a location fix) of an MD in single-tier and heterogeneous cellular networks (HetNets). More importantly, we study how availability of information about the location of proximate BSs at the MD impacts localizability. To this end, we derive tractable expressions, bounds, and approximations for the localizability probability of an MD. These expressions depend on several key system parameters, and can be used to infer valuable system insights. Using these expressions, we quantify the gains achieved in localizability of an MD when information about the location of proximate BSs is incorporated in the model. As expected, our results demonstrate that localizability improves with the increase in density of BS deployments. / Master of Science / Location based services form an integral part of vital day-to-day applications such as traffic control, emergency response, and navigation. Traditionally, users have relied on the global positioning system system (GPS) for localizing a device. GPS systems rely on the availability of clear line-of-sight between the devices to be localized and a sufficient number of navigation satellites. Since it is not possible to have these line-of-sight links, especially in urban canyons and indoor locations, the ubiquity of cellular networks makes them a natural choice for localization. Typically, localization using cellular networks is studied using simulations, which are carried out by fixing the network configuration including the geometry of the base stations (BSs) as well as the number of BSs that participate in localization. This limits the scope of the results obtained since a change in the network configuration would mean that one must do another set of time consuming simulations with the new network parameters. This motivates the need to develop an analytical model to study the impact of fundamental system-design factors such as BS geometries, number of participating BSs, propagation effects, and channel conditions on localization in cellular networks. Such analysis would make it convenient to infer how changing these system parameters affects localization.
In this thesis, we develop a general analytical model to study the localizability (ability of get a location fix) of a device in a cellular network. In particular, we study how information about the location of BSs in the proximity of the device to be localized affects localizability. We derive expressions for metrics such as the localizability probability of a device. Our results help quantify the gains achieved in localizability performance when information about the location of BSs in the vicinity of the device to be localized is available at the device. Our results concretely demonstrate that including this additional information significantly improves the localizability performance, especially in regions with dense BS deployments.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/78664 |
| Date | 03 August 2017 |
| Creators | Bhandari, Tapan |
| Contributors | Electrical and Computer Engineering, Dhillon, Harpreet Singh, MacKenzie, Allen B., Buehrer, R. Michael |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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