No description available.

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: distributed beamforming; carrier synchronization. Includes bibliographical references (p.105-106).

Thesis (M.Eng.)(Computer Engineering)--University of Pretoria, 2005. / Title from opening screen (viewed March 20, 2006). Summaries in English and Afrikaans. Includes bibliographical references.

Thesis (Ph.D.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Richard Wolff. Includes bibliographical references.

As the demand for wireless communication systems grows, the need for spectrum grows accordingly. However, a large portion of the usable spectrum has already been exclusively licensed to various entities. This exclusive allocation method encourages spectrum to be left unused if the licensee has no need for that spectrum. In order to better utilize spectrum and formulate new approaches for greater spectrum use efficiency, it is imperative to possess a thorough understanding about how wireless spectrum behaves over time, frequency, and space. In this thesis, a practical, scalable, and low-cost wideband distributed spectrum sensing system is designed, implemented, and tested. The proposed system is made up of a collection of nodes that use general purpose, off-the-shelf computer hardware as well as a collection of inexpensive software-defined radio (SDR) equipment in order to collect and analyze spectrum data that varies across time, frequency, and space. The spectrum data the proposed system collects is the power present at a given frequency. The tools needed to analyze the gathered data are also created, including a periodogram and spectrogram function, which visualize average spectrum use over a period of time and as spectrum use varies with time, respectively. The proposed system also facilitates the testing of a spatio-spectrum characterization method using real data. This method has only been simulated up to this point. The characterization technique allows for spatially varying spectrum measurements to be visualized using heat maps.

"This thesis develops a system for synchronizing two wireless transmitters so that they are able to implement a distributed beamformer in several different channel models. This thesis considers a specific implementation of the system and proposes a metric to quantify its performance. The system's performance is investigated in single-path and multi-path time-invariant channel scenarios, as well as in single-path time-varying channel scenarios. Where prior systems have difficulty in implementing a distributed beamformer in multi-path channels and/or mobile scenarios, the results of this thesis show that the Round-Trip Time-Division distributed beamforming system is able to perform as a beamformer in all three of the channel models considered. "

As humans we find communicating natural and compelling. Over the centuries we have created many innovations which enable and improve communication between people; during the past decade mobile phone networks have brought about a technological revolution in this area. Never before have people been so connected to one another. Today we have the ability to communicate with almost anyone, anytime, anywhere. Our increased connectivity and reachability also leads to new issues and challenges that we need to deal with. When we phone someone we expect an instant connection, and when this does not occur it can be frustrating. On the other hand it is equally disruptive to receive a call when one is busy with an important task or in a situation where communication is inappropriate. Social protocol dictates that we try to minimize such situations for the benefit of others nearby and for ourselves. This management of communications is a constant and difficult task. Using presence – which signals a person’s availability and willingness to communicate – is a solution to this problem. Such information can benefit communication partners by increasing the likelihood of a successful connection and decreasing disruptions. This research addresses the problem of staying connected while keeping control over mobile communications. It adopts a design-science research paradigm, with the primary research artifact being a model for privacy-aware presence management in mobile communications. As part of the model development knowledge contributions are made in several ways. Existing knowledge about the problem area is extended through a quantitative analysis of mobile communications management. This analysis uses a novel survey, collecting useful empirical data for future research. This includes how people currently manage their communications and what features they expect from a potential “call management” system. The examination and use of presence standards, as a foundation for the model, provides a comparison of the main presence technologies available today. A focus on privacy features identifies several shortcomings in standards which, if addressed, can help to improve and make these standards more complete. The model stresses the privacy of potentially sensitive presence information. A unique perspective based on social relationship theories is adopted. The use of relationship groups not only makes logical sense but also assists in the management of presence information and extends existing standards. Finally, the evaluation of the model demonstrates the feasibility of a practical implementation as well the ability to extend the model in next generation mobile networks. Thus the model presents a solid foundation for the development of future services. In these ways the proposed model contributes positively towards balancing efficient mobile communications with the need for privacy-awareness.

Wireless communications have recently gained much popularity in various commercial applications. Because of the peculiar characteristic of radio channels, the ability for communicators to stand various kinds of interference in the open air is one of the most important issues in wireless communications. The focus of this dissertation is on the analysis and cancellation of narrowband interference (NBI) which is one very detrimental form of interference. To facilitate the analysis of SFH/DPSK under tone interfere, an analytical framework is developed for determination of the probability distribution of a corrupted differential phase. The concept of the phase characteristic function is introduced and its characterizations such as factorization are investigated. Based on it, expressions are derived for the general probability distribution of a received differential phase corrupted by signal tone interference and Gaussian noise under non-fading as well as different fading environments. Furthermore, we also derive the probability distribution of a received differential phase perturbed by multiple tone interference. Subsequently, an extensive analysis of SFH/DPSK is carried out in terms of bit error rate performance given different signalling schemes, fading environments and jamming strategies using band multitone and frequency jitter. Finally, we propose a new technique for rejection of narrowband interference based on multiple symbol detection of coherent or differential phase shift keying. We first show that the direct use of multiple symbol detection offers poor performance when narrowband interference is dominant. Our proposed technique employs a special signalling or coding scheme which is shown to be robust against narrowband interference. Our evaluation of bit error rate shows significant performance improvement in narrowband interference vis-a-vis direct multiple symbol detection. When viewed as a coding scheme, the proposed signalling scheme is significantly simpler for achieving the same coding gain than conventional error correction codes. / Graduate

Text communication is often perceived as lacking some components of communication that are essential in sustaining interaction or conversation. This interaction incoherency tends to make text communication plastic. It is traditionally devoid of intonation, pitch, gesture, facial expression and visual or auditory cues. Nevertheless, Instant Messaging (IM), a form of text communication is on the upward uptake both on PCs and on mobile handhelds. There is a need to rubberise this plastic text messaging to improve co-presence for text communications thereby improving synchronous textual discussion, especially on handheld devices. <br /> <br /> One element of interaction is gesture, seen as a natural way of conversing. Attaining some level of interaction naturalism requires improving synchronous communication spontaneity, partly achieved by enhancing input mechanisms. To enhance input mechanisms for interactive text-based chat on mobile devices, there is a need to facilitate gesture input. Enhancement is achievable in a number of ways, such as input mechanism redesigning and input offering adaptation. This thesis explores affective gesture mode on interface redesign as an input offering adaptation. This is done without a major physical reconstruction of handheld devices.<br /> <br /> This thesis presents a text only IM system built on Session Initiation Protocol (SIP) and SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE). It was developed with a novel user-defined hotkey implemented as a one-click context menu to &ldquo / fast-track&rdquo / text-gestures and emoticons.<br /> <br /> A hybrid quantitative and qualitative approach was taken to enable data triangulation. Results from experimental trials show that an Affective Gesture (AG) approach improved IM chat spontaneity/response. Feedback from the user trials affirms that AG hotkey improves chat responsiveness, thus enhancing chat spontaneity.

No description available.