published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The frequency spectrum allocated to cellular mobile telephone systems is very limited. Efficient channel assignment schemes can significantly increase the utilization of the available frequency channels. Virtually Fixed Channel Assignment (VFCA) is a dynamic channel assignment method. The idea behind it is simple: each cell is allocated a set of nominal channels. A call request generated in a cell is assigned a nominal channel if one is available. Otherwise, a channel from an adjacent cell is borrowed to serve this call as long as frequency interference constraints are satisfied. VFCA is a promising method because (i) it is efficient in channel assignment, and (ii) it is relatively easy to implement compared to other dynamic channel assignment methods. VFCA has been analyzed based primarily on simulation studies in the past twenty years. In this thesis, we focus our study on development of new channel borrowing strategies and analytical models for VFCA. The contribution of this work is summarized as follows. (1) Development of an queuing model for performance analysis of VFCA. This model may also be used to conduct sensitivity analysis on some system parameters when VFCA is used. (2) Proposed a new channel reservation scheme for handoffs. (In a cellular system, when a call using a channel crosses a cell boundary, it needs to be handed off to a new channel in the new cell. This is called a handoff.) An optimization model for this channel reservation scheme is developed. (3) Applied the fluid-flow approach to modeling an integrated mobile cellular system that uses VFCA to estimate the distribution of data queue length in a cell of the system. These results are useful in the design, performance analysis and optimization of VFCA schemes.

Deaf people in South Africa are no longer a minority group and their needs regarding communication and interaction must therefore be taken into consideration. This demographic does not communicate and interact in the same way as hearing people, which means that any existing usability or accessibility guidelines do not apply. As a result, Deaf people do not have access to information in the same way that a hearing person does. Providing proper access to Information and Communications Technology services, which meet their particular needs, will help the hearing impaired to better integrate into society. The importance of demolishing the communication barrier between the hearing and the hearing impaired is very important. Many people assume that sign language is somehow based on oral language. However, this is not the case. Sign languages are natural visual-spatial languages, and form a contrast with spoken languages which are auditory-vocal based. Acknowledging this fact in 2008, the South African Sign Language Policy Implementation Conference together with several governmental bodies suggested that South African Sign Language should become recognized as the 12th official language of South Africa. Due to the fact that cell phone technology continues to evolve, it will remain a tool of communication upon which Deaf people heavily rely on. The cell phone fulfils a basic need for everyone, but especially for the Deaf demographic as they rely on the short message system to communicate. Deaf people are currently faced with a lack of appropriate mobile phone applications, which would allow them to communicate with hearing as well as deaf people. The primary objective of this research was therefore to make mobile technology equally accessible meaning usable to members of the Deaf demographic. The focus of the research was to investigate the communication barrier and a range of variables that can influence the deaf user’s experience. Topics such as user interface design, usability and interaction were investigated. The outcome of this research was to propose a set of guidelines that, when applied to the design of a website or to phone application accessibility, would ensure communication and interaction from a deaf user. The proposed set of guidelines was then applied to the design of the high fidelity prototype of a mobile phone application. The specific application is a messaging phone application that allows deaf users to communicate with other deaf and hearing users via short message system. A mobile phone application that allows Deaf people to send and receive messages based on the sign language alphabet. The application was named Signchat. Purpose of this was to visibly display how the guidelines were implemented in Signchat. While Signchat’s main purpose is to accommodate the needs of Deaf people, it is also a learning tool and an application that bridges the gap by allowing deaf and hearing users to communicate.

Interaction with mobile devices suffers from a number of shortcomings, most of which are linked to the small size of screens. Artificial tactile feedback promises to be particularly well suited to the mobile interaction context. To be practical, tactile transducers for mobile devices must be small and light, and yet be capable of displaying a rich set of expressive stimuli. This thesis introduces a tactile transducer for mobile interaction that is capable of distributed skin stimulation on the fingertip. The transducer works on a principle that was first investigated because of its potential application to the display of Braille. A preliminary study was conducted on an earlier version of the transducer. It concluded that subjects were able to identify simple Braille characters with a high rate of success. Then, a complete re-design of the transducer addressed the goal of integration in a handheld prototype for mobile interaction. The resulting device comprises a liquid crystal graphic display co-located with the miniature, low-power, distributed tactile transducer. Next, it was needed to measure the perceptual differences between the stimuli that the device could display. Our experiences with one evaluation approach raised questions relating to the methodology for data collection. Therefore, an analysis of the process was carried out using a stimulus set obtained with the device. By means of multidimensional scaling analysis, both the perceptual parameters forming the stimuli space and the evaluation technique were validated. Finally, two experiments were carried out with the objective to develop new mobile interactions paradigms that combined visual and tactile feedback. Both experiments modeled a list scrolling task on the device. The first experiment found a marginal improvement in performance when tactile feedback was employed. It also came at a higher attentional cost dedicated to operating the device. For the second experiment, the scrolling paradigm and the tactile feedback were improved. This lead to a decrease in the reliance on vision when tactile feedback was enabled. Results showed a 28% decrease in the number of key presses that controlled the visibility state of the scroll list.

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Acoustic networks of autonomous underwater vehicles (AUVs) show great promise, but a lack of simulation tools and reliance on protocols originally developed for terrestrial radio networks has hindered progress. This work addresses both issues. A new simulator of underwater communication among AUVs provides accurate communication modeling and flexible vehicle behavior, while a new routing protocol, location-aware source routing (LASR) provides superior network performance. The new simulator was used to evaluate communication without networking, and then with networking using the coding or dynamic source routing (DSR) protocols. The results confirmed that a network was essential to ensure effective fleet-wide communication. The flooding protocol provided extremely reliable communication but with low message volumes. The DSR protocol, a popular routing protocol due to its effectiveness in terrestrial radio networks, proved to be a bad choice in an acoustic environment: in most cases, it suffered from both poor reliability and low message volumes. Due to the high acoustic latency, even moderate vehicle speeds caused the network topology to change faster than DSR could adapt. DSR's reliance on shortest-path routing also proved to be a significant disadvantage. Several DSR optimizations were also tested; most proved to be unhelpful or actually harmful in an underwater acoustic network. LASR was developed to address the problems noted in flooding and DSR. LASR was loosely derived from DSR, most significantly retaining source routes and the reply/request route discovery technique. However, LASR added features which proved, in simulation, to be significant advantages -- two of the most effective were a link/route metric and a node tracking system. To replace shortest-path routing, LASR used the expected transmission count (ETX) metric. / This allowed LASR to make more informed routing decisions which greatly increased performance compared to DSR. The node tracking system was the most novel addition: using only implicit communication coupled with the use of time-division multiple access (TDMA), the tracking system provided predicted node locations. These predictions made it possible for LASR to proactively respond to topology changes. In most cases, LASR outperformed flooding and DSR in message delivery reliability and message delivery volume. / by Edward A. Carlson. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

Controlling the cooperative behaviors of a fleet of autonomous underwater vehicles in a stochastic, complex environment is a formidable challenge in artificial intelligence. The complexity arises from the challenges of limited navigation and communication capabilities of underwater environment. A time critical cooperative operation by acoustic networks of Multiple Cooperative Vehicles (MCVs) necessitates a robust task allocation mechanism and an efficient path planning model. In this work, we present solutions to investigate two aspects of the cooperative schema for multiple underwater vehicles under realistic underwater acoustic communications: a Location-aided Task Allocation Framework (LAAF) algorithm for multi-target task assignment and a mathematical programming model, the Grid-based Multi-Objective Optimal Programming (GMOOP), for finding an optimal vehicle command decision given a set of objectives and constraints. We demonstrate that, the location-aided auction strategies perform significantly better than the generic auction algorithm in terms of effective task allocation time and information bandwidth requirements. In a typical task assignment scenario, the time needed in the LAAF algorithm is only a fraction compared to the generic auction algorithm. On the other hand; the GMOOP path planning technique provides a unique means for multi-objective tasks by cooperative agents with limited communication capabilities. Under different environmental settings, the GMOOP path planning technique is proved to provide a method with balance of sufficient expressive power and flexibility, and its solution algorithms tractable in terms of mission completion time, with a limited increase of overhead in acoustic communication. Prior to this work, existing multi-objective action selection methods were limited to robust networks where constant communication available. / The dynamic task allocation, together with the GMOOP path planning controller, provides a comprehensive solution to the search-classify tasks for cooperative AUVs. / by Yueyue Deng. / Thesis (Ph.D.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Vision based technology such as motion detection has long been limited to the domain of powerful processor intensive systems such as desktop PCs and specialist hardware solutions. With the advent of much faster mobile phone processors and memory, a plethora of feature rich software and hardware is being deployed onto the mobile platform, most notably onto high powered devices called smart phones. Interaction interfaces such as touchscreens allow for improved usability but obscure the phone’s screen. Since the majority of smart phones are equipped with cameras, it has become feasible to combine their powerful processors, large memory capacity and the camera to support new ways of interacting with the phone which do not obscure the screen. However, it is not clear whether or not these processor intensive visual interactions can in fact be run at an acceptable speed on current mobile handsets or whether they will offer the user a better experience than the current number pad and direction keys present on the majority of mobile phones. A vision based finger interaction technique is proposed which uses the back of device camera to track the user’s finger. This allows the user to interact with the mobile phone with mouse based movements, gestures and steering based interactions. A simple colour thresholding algorithm was implemented in Java, Python and C++. Various benchmarks and tests conducted on a Nokia N95 smart phone revealed that on current hardware and with current programming environments only native C++ yields results plausible for real time interactions (a key requirement for vision based interactions). It is also shown that different lighting levels and background environments affects the accuracy of the system with background and finger contrast playing a large role. Finally a user study was conducted to ascertain the overall user’s satisfaction between keypad interactions and the finger interaction techniques concluding that the new finger interaction technique is well suited to steering based interactions and in time, mouse style movements. Simple navigation is better suited to the directional keypad.