This thesis presents a new strategy in achieving highly reliable and accurate position solutions fulfilling the requirements of Location-Based Services (LBS) pedestrians’ applications. The new strategy is divided into two main parts. The first part integrates the available positioning technology within the surrounding LBS application context by introducing an adaptive LBS framework. The context can be described as a group of factors affecting the application behaviour; this includes environmental states, available resources and user preferences. The proposed adaptive framework consists of several stages, such as defining the contextual factors that have a direct effect on the positioning performance, identifying preliminary positioning performance requirements associated with different LBS application groups, and introducing an intelligent positioning services selection function. The second part of this work involves the design and development of a novel positioning model that is responsible for delivering highly reliable, accurate and precise position solutions to LBS users. This new model is based on the single frequency GPS Standard Positioning Service (SPS). Additionally, it is incorporated within the adaptive LBS framework while providing the position solutions, in which all identified contextual factors and application requirements are accounted. The positioning model operates over a client-server architecture including two main components, described as the Localisation Server (LS) and the Mobile Unit (MU). Hybrid functional approaches were developed at both components consisting of several processing procedures allowing the positioning model to operate in two position determination modes. Stand-alone mode is used if enough navigation information was available at the MU using its local positioning device (GPS/EGNOS receiver). Otherwise, server-based mode is utilised, in which the LS intervenes and starts providing the required position solutions. At the LS, multiple sources of GPS augmentation services were received using the Internet as the sole augmentation data transportation medium. The augmentation data was then processed and integrated for the purpose of guaranteeing the availability of valid and reliable information required for the provision of accurate and precise position solutions. Two main advanced position computation methods were developed at the LS, described as coordinate domain and raw domain. The positioning model was experimentally evaluated. According to the reported results, the LS through the developed position computation methods, was able to provide position samples with an accuracy of less than 2 meters, with high precision at 95% confidence level; this was achieved in urban, rural, and open space (clear satellite view) navigation environments. Additionally, the integrity of the position solutions was guaranteed in such environments during more than 90% of the navigation time, taking into consideration the identified integrity thresholds (Horizontal Alert Limits (HAL)=11 m). This positioning performance has outperformed the existing GPS/EGNOS service which was implemented at the MU in all scenarios and environments. In addition, utilising a simulation evaluation facility the developed positioning model performance was quantified with reference to a hybrid positioning service that will be offered by future Galileo Open Service (OS) along with GPS/EGNOS. Using the statistical t-test, it was concluded that there is no significant difference in terms of the position samples’ accuracy achieved from the developed positioning model and the hybrid system at a particular navigation environment described as rural area. The p-value was 0.08 and the level of significance used was 0.05. However, a significant difference in terms of the service integrity for the advantage of the hybrid system was experienced in all remaining scenarios and environments more especially the urban areas due to surrounding obstacles and conditions.

by Leung Wing Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 73-75). / Abstract --- p.i / Acknowledgements --- p.iii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Background --- p.7 / Chapter 2.1 --- What is Mobile Computing? --- p.7 / Chapter 2.1.1 --- Applications of Mobile Computing --- p.8 / Chapter 2.1.2 --- New Challenges of Mobile Computing --- p.9 / Chapter 2.2 --- Related Work --- p.12 / Chapter 2.2.1 --- Lazy Replicated File Service --- p.12 / Chapter 2.2.2 --- Dividing the Database into Clusters --- p.14 / Chapter 2.2.3 --- Applying Causal Consistency --- p.15 / Chapter 2.3 --- Summary --- p.16 / Chapter 2.4 --- Serializability and Concurrency Control --- p.17 / Chapter 3 --- System Model and Suggested Protocol --- p.20 / Chapter 3.1 --- System Model --- p.20 / Chapter 3.2 --- Cache Management --- p.21 / Chapter 3.2.1 --- Version Control Mechanism --- p.22 / Chapter 3.2.2 --- Cache Consistency --- p.22 / Chapter 3.2.3 --- Request Data from Servers --- p.25 / Chapter 3.2.4 --- Invalidation Report --- p.27 / Chapter 3.2.5 --- Data Broadcasting --- p.30 / Chapter 4 --- Simulation Study --- p.32 / Chapter 4.1 --- Physical Queuing Model --- p.32 / Chapter 4.2 --- Logical System Model --- p.33 / Chapter 4.3 --- Parameter Setting --- p.34 / Chapter 4.4 --- The Significance of the Length of Invalidation Range --- p.37 / Chapter 4.4.1 --- Performance with Different Invalidation Range --- p.38 / Chapter 4.4.2 --- Increasing the Update Frequency --- p.40 / Chapter 4.4.3 --- Impact of Piggybacking Popular Data --- p.41 / Chapter 4.4.4 --- Increasing the Disconnection Period --- p.42 / Chapter 4.5 --- Comparison of the Proposed Protocol with the Amnesic Terminal Protocol --- p.44 / Chapter 4.5.1 --- Setting a Short Timeout Period --- p.45 / Chapter 4.5.2 --- Extending the Timeout Period --- p.46 / Chapter 4.5.3 --- Increasing the Frequency of Temporary Disconnection --- p.48 / Chapter 4.5.4 --- Increasing the Frequency of Crossing Boundaries --- p.49 / Chapter 4.6 --- Evaluate the Performance Gain with Piggybacking Message --- p.50 / Chapter 4.6.1 --- Adding Piggybacking Messages --- p.51 / Chapter 4.6.2 --- Reducing the Number of Popular Data --- p.52 / Chapter 4.6.3 --- Increasing the Frequency of Updates --- p.53 / Chapter 4.7 --- Behaviour of the Proposed Protocol --- p.54 / Chapter 4.7.1 --- Finding Maximum Number of Mobile Computers --- p.54 / Chapter 4.7.2 --- Interchanging the Frequency of Read-Only and Update Transactions --- p.55 / Chapter 5 --- Partially Replicated Database System --- p.57 / Chapter 5.1 --- Proposed Amendments --- p.57 / Chapter 5.1.1 --- Not Cache Partially Replicated Data ( Method 1 ) --- p.58 / Chapter 5.1.2 --- Drop Partially Replicated Data ( Method 2 ) --- p.59 / Chapter 5.1.3 --- Attaching Server-List ( Method 3 ) --- p.59 / Chapter 5.2 --- Experiments and Interpretation --- p.60 / Chapter 5.2.1 --- Partially Replicated Data with High Accessing Probability --- p.61 / Chapter 5.2.2 --- Reducing the Cache Size --- p.64 / Chapter 5.2.3 --- Partially Replicated Data with Low Accessing Probability --- p.65 / Chapter 6 --- Conclusions and Future Work --- p.70 / Chapter 6.1 --- Future Work --- p.72 / Bibliography --- p.73 / Chapter A --- Version Control Mechanism for Servers --- p.76

Thesis (M.S.)--Georgia State University, 2004. / Title from title screen. Sushil K. Prasad, committee chair; Anu Bourgeois, Alex Zelikovsky, committee members. Description based on contents viewed Feb. 26, 2007. Includes bibliographical references (p. 55-59). Source code: p. 75-123.

With the advances of technology and the popularization of mobile devices, the need of researching and discussing subjects related to mobile devices has raised. One of the subjects that needs to be further analyzed is data replication. This study investigates data replication on mobile devices focusing on power consumption. It presents four different scenarios that propose, describe, apply and evaluate data replication mechanisms, with the purpose of finding the best scenario that presents less energy consumption. In order to make the experiments, Sun SPOT was chosen as a mobile device. This device is fully programmed in a java environment. A different software was created in each scenario in order to verify the performance of the mobile devices regarding energy saving. The results found did not meet the expectations. While trying to find the best scenario a hardware limitation was found. Although software can be easily changed to fix errors, hardware cannot be changed as easily. The implications for the hardware limitation found in this study prevented the results to be optimal. The results found also imply that new hardware should be used in further experimentation. As this study proved to be limited, it suggests that additional studies should be carried out applying the new version of the hardware used in this study.

Techn. Universiẗat, Diss. u.d.T.:Blankenbach, Jörg: Architektur und Umsetzung mobiler standortbezogener Anwendungen und Dienste unter Berücksichtigung von Interoperabilität--Darmstadt, 2006.

Cloud computing becomes popular nowadays. It allows applications to use the enormous resources in the clouds. With the combination of mobile computing, mobile cloud computing is evolved. With the use of clouds, mobile applications can offload tasks to clouds in client-server model. For cloud computing, migration is an important function for supporting elasticity. Lightweight and portable task migration support allows better resource utilization and data access locality, which are essentials for the success of cloud computing. Various migration techniques are available, such as process migration, thread migration, and virtual machine live migration. However, for these existing migration techniques, migrations are too coarse-grained and costly, and this offsets the benefits from migration. Besides, the migration path is monotonic, and mobile and clouds resources cannot be utilized. In this study, we propose a new computation migration technique called stack-on-demand (SOD). This technique is based on the stack structure of tasks. Computation migration is carried out by exporting parts of the execution state to achieve lightweight and flexible migration. Compared to traditional task migration techniques, SOD allows lightweight computation migration. It allows dynamic execution flows in a multi-domain workflow style. With its lightweight feature, tasks of a large process can be migrated from clouds to small-capacity devices, such as iPhone, in order to use the unique resources, such as photos, found in the devices. In order to support its lightweight feature, various techniques have been introduced. To allow efficient access to remote objects in task migration, we propose an object faulting technique for efficient detection of remote objects. This technique avoids the checking of object status. To allow portable, lightweight application-level migration, asynchronous migration technique and twin method hierarchy instrumentation technique are proposed. This allows lightweight task migration from mobile device to cloud nodes, and vice versa. We implement the SOD concept as a middleware in a mobile cloud environment to allow transparent execution migration of Java programs. It has shown that SOD migration cost is pretty low, comparing to several existing migration mechanisms. We also conduct experiments with mobile devices to demonstrate the elasticity of SOD, in which server-side heavyweight processes can run adaptively on mobile devices to use the unique resources in the devices. On the other hand, mobile devices can seamlessly offload tasks to the cloud nodes to use the cloud resources. In addition, the system has incorporated a restorable communication layer, and this allows parallel programs to communicate properly with SOD migration. / published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Computer Science and Information Systems / Master / Master of Philosophy

With the popularity of portable computers and the proliferation of wireless networking interfaces, there is currently a great deal of interest in providing IP networking support for host mobility using the Internet as a foundation for wireless networking. Most proposed solutions depend on a default route through the mobile host's horne address, which makes for unnecessarily long routes. The major problem that this gives rise to is that of finding an efficient way of locating and routing that allows datagrams to be delivered efficiently to moving destinations whilst limiting costly Internet-wide location updates as much as possible. Two concepts - "local region" and "patron service" - are introduced based on the locality features of the host movement and packet traffic patterns. For each mobile host, the local region is a set of designated subnetworks within which a mobile host often moves, and the patrons are the hosts from which the majority of traffic for the mobile host originated. By making use of the hierarchical addressing and routing structure of Internet, the two concepts are used to confine the effects of a host moving, so location updates are sent only to a designated host moving area and to those hosts which are most likely to call again, thus providing nearly optimal routing for most communication. The proposed scheme was implemented as an IP extension using a network simulator and evaluated from a system performance point of view. The results show a significant reduction in the accumulated communication time along with improved datagram tunneling, as compared with its extra location overhead. In addition, a comparison with another scheme shows that our functionality is more effective both for location update and routing efficiency. The scheme offers improved network and host scalability by isolating local movement from the rest of the world, and provides a convenient point at which to perform administration functions.

Teilw. zugl.: Darmstadt, Techn. Univ., Diss., 2006 u.d.T.: Blankenbach, Jörg: Architektur und Umsetzung mobiler standortbezogener Anwendungen und Dienste unter Berücksichtigung von Interoperabilität

Zugl.: Berlin, Freie Univ., Diplomarbeit, 2007