Thesis (M.S. in Computer Science)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Bert Lundy, Wen Su. Includes bibliographical references (p. 101-103). Also available online.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Xiaoping Yun, Fotis Papoulias. Includes bibliographical references (p. 81-82). Also available online.

Almost all mobile devices nowadays are enabled with IEEE 802.11 Wireless Local Area Network (WLAN), which is also known as WiFi. One of the most important considerations when choosing an 802.11 device is its battery life. To allow mobile devices to conserve energy, IEEE 802.11 standard specifies a power save mode (PSM). A station/device in PSM, i.e. PSM-STA, will wake up at a predefined listen interval (LI) to receive frames buffered at the access point (AP) while it is sleeping. In this thesis, we focus on enhancing the basic PSM mechanisms in the standard. In particular, two new power saving schemes, delayed wakeup and dynamic listen interval, are proposed. Unlike many existing schemes, our schemes are fully standard compliant, and legacy devices can support them via a firmware upgrade. In our delayed wakeup (DW) scheme, we assume that all PSM-STAs use the same listen interval of one. That is all PSM-STAs wake up at every beacon frame broadcast, or beacon interval (BI). From the traffic indication map (TIM) in the beacon, a PSMSTA learns if there are any buffered frames at AP. If yes, it will stay awake until all buffered frames are retrieved. This creates a rush hour on the shared channel right after a beacon broadcast. If the channel is congested, having all PSM-STAs staying awake will not improve the system delay performance but consume more power. Aiming at saving battery power while not affecting delay-throughput performance, our DWscheme divides a BI into n sub-BIs. Then based on the amount of buffered frames, AP identifies and instructs “excess” stations to sleep immediately and wake up at a non-congested sub-BI later on. “Instructions” are judiciously encoded inside the modified TIM. We show that our modifications are fully transparent to legacy stations. In order to more accurately identify the amount of excess stations, an analytical model is also constructed to derive the saturated throughput of a WLAN consisting of PSM-STAs. In our dynamic listen interval (DLI) scheme, we aim at minimizing unnecessary wakeups while without sacrificing delay performance. Note that when a PSM-STA wakes up to receive a beacon and found that there are no buffered frames at AP, the PSM-STA experiences an unnecessary wakeup. Accordingly, the associated mode transition energy is wasted. According to the IEEE 802.11 standard, each STA chooses its fixed LI at the time of association. If LI=1, a STA wakes up at every beacon interval (as that in DW scheme). Although packet delay is minimized in this case, the chance of unnecessary wakeups can be high. On the other hand, a larger LI can reduce the chance of unnecessary wakeups but the delay will be increased. Our DLI scheme addresses this problem by dynamically adjusting the LI value according to traffic load. Specifically, each unnecessary wakeup will increase a STA’s LI by one, and a necessary wakeup will immediately reset LI to one. Simulations show that when traffic is bursty, mode transition energy consumption can be reduced without noticeable degradation in delay performance. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Thesis (MTech. degree in Marketing)--Tshwane University of Technology, 2011. / Focuses primarily on the decision-making of students in the acquisition and usage of wireless internet products and services in the Tshwane Metropolitan area.

M. Tech. Electrical Engineering. / In a Wireless Local Area Network (WLAN), as the signal travels from the transmitter to the receiver, it experiences various forms of impairments that cause fading and path loss. To cater for this problem, monitoring the link between the transmitter and receiver becomes imperative. This study focuses on the design of a link adaptation algorithm that seeks to improve the quality of service delivery in IEEE 802.11n networks. From the results, it is shown that the Greedy Algorithm (GA) performed far better than that of Auto-Rate-Fallback (ARF) and it is also shown that the Optimal Algorithm (OA) approach outperformed GA and ARF in terms of throughput and efficiency. Simulations results of both proposed algorithms proved to be more efficient than the existing ARF algorithm. Thus, it is shown that the proposed algorithms have the potential of enhancing the quality of service in IEEE 802.11n network.

Because of low-cost optical devices and virtually unlimited bandwidth, optical wireless communications (OWC) for indoor wireless local area networks (WLANs) have recently become an attractive alternative to radio frequency systems. Since optical signals cannot penetrate through walls or other opaque barriers, the security of infrared WLANs is very high and there is no interference between rooms. Subsequently, cell planning is simple and easy, and the potential capacity of an optical-based network in a building is extremely high. However, the system link is susceptible to path loss and multipath dispersion. In addition, the average transmit power is constrained by eye-safety regulations and power consumption concerns. Hence, most recent research deals with the physical layer aspects such as modulation, equalization and error-control coding in order to cope with these draw-backs, especially the effects of multipath dispersion. The objective of this thesis is to study practical signaling techniques capable of eliminating the effects of intersymbol interference (ISI). Regarding the drawbacks of OWC, modulation schemes which are power and band-width efficient are considered. Pulse-position modulation (PPM) has been employed for IrDA and IEEE802.11 standards because it offers high power efficiency. However, it re-quires high bandwidth so that its performance is considerably degraded when the channel is more corrupted by ISI. A number of modified PPM techniques have been proposed to improve bandwidth efficiency. This thesis introduces a hybrid between pulse-amplitude modulation (PAM) and differential pulse-position modulation (DPPM), named differential amplitude pulse-position modulation (DAPPM), in order to gain a better compromise be¬tween power and bandwidth efficiency. It yields better bandwidth and/or power efficiency than PAM, PPM and DPPM depending on the number of amplitude levels (A), and the maximum length (L) of a symbol. The channel capacity of PPM, DPPM and DAPPM systems is investigated. Since these modulation schemes over an ISI channel can be represented by a trellis diagram, their channel capacity is determined using a method for calculating the capacity of a Markov process channel. Over a soft-output channel, DAPPM achieves a higher capacity and is less sensitive to multipath dispersion than PPM and DPPM. Moreover, the comparison of hard-decision decoding (HDD) and soft-decision decoding (SDD) for PPM and DPPM systems shows that the performance of SDD is superior to that of HDD, especially when the channel is dispersive. Then, some soft-decision techniques for DPPM system are considered. Although maximum-likelihood sequence detection (MLSD) is the optimal SDD for DPPM system, its complexity is extremely high. This thesis examines SDDs which are less complex than MLSD, but have performance close to that with MLSD. As the DPPM system is a Markov pro¬cess, maximum a posteriori (MAP), Max-Log-MAP and the soft-output Viterbi algorithm (SOVA) are adopted. In addition, a novel very low complexity soft-decision decoding algorithm is introduced. The performance of the proposed algorithm is independent of the knowledge of the channel model, while the performance of the optimal and suboptimal MAP algorithms is impaired when the receiver has no information about the channel. Finally, to achieve lower power requirements, error-control coding in an OWC system is investigated. Because insertion and deletion errors exist in DPPM systems, conventional coding techniques cannot be used. This thesis presents the concatenation of marker and Reed-Solomon codes which is able to correct such errors. The coded systems with HDD and SDD are examined by analysis and simulation.

802.11-based wireless networking has invaded cities, offices, homes and coffee shops over the last five years, and has become a widely used and accepted technology. It has revolutionised computer networking and automation and added a social aspect to personal computing. Accompanying this widespread usage is the presence of crime; the more popular technology, the more opportunity exists for its misuse. / This dissertation studied 802.11-based wireless networking environment from a forensic computing perspective. It sought to understand the current state of wireless misuse: present misuses; potential forms of misuse involving 802.11-based wireless networks; and current tools and techniques used in its identification, containment and analysis. The research highlights the lack of current tools and procedures for forensic computing investigations that are able to effectively handle the presence of wireless devices and networks, and that there are forms of misuse that may escape detection by forensic investigation teams. This work was then developed into a taxonomy of wireless misuse. / Once the current state was known, this research sought to readdress the current state of forensic computing teams, through analysing the need for software tools and procedural changes to counter the misuses that this technology allows. Once software outcomes were developed, the legal and technical feasibility of their use was ascertained. Based on the outcomes of this work, a final set of software requirements was developed and the proposed methodology for their development was discussed. / A new series of procedures was also developed for forensic investigators to identify, contain and analyse sources of electronic evidence with 802.11-networking. Much of this work was based upon but extending current procedural guides for law enforcement. / The final outcome of this research was the development of a series of recommendations for forensic teams and research that incorporates short, medium and long term development for forensic teams as well as research and development. This work intended to provide mechanisms for future research that are jurisdictionally independent able to be adapted for each individual forensic team. The short term recommendations were primarily changes to procedure, whereas the medium and long terms changes sought to address the larger issues raised by wireless networking devices being the target of or involved in crime or misuse. / Much of this dissertation is exploratory in nature and much of its length is devoted to determining the current state of the misuse and current mechanisms employed to counter it. In such a rapidly developing field of study, this work will need constant revision as new technologies emerge and new forms of misuse take advantage of them. / Thesis (PhDInformationTechnology)--University of South Australia, 2007

The mobility of wireless users has created a number of technological challenges, especially when a Mobile Node (MN) changes the point of attachment to the network. In recent years, a great deal of research effort has been spent on the issue of mobility, and resulted in development of general frameworks as well as specific protocols supporting mobility. These frameworks and protocols are intended to solve the problem of IP routing (i.e. finding an IP path) to the MN. Typically, the access network may also establish and keep service state information (service context) necessary to process and forward packets in a way that suits specific service requirements. Context Transfer has been suggested as an alternative way of restoring the service context at the new access network. / Thesis (PhDTelecommunications)--University of South Australia, 2005.

802.11-based wireless networking has invaded cities, offices, homes and coffee shops over the last five years, and has become a widely used and accepted technology. It has revolutionised computer networking and automation and added a social aspect to personal computing. Accompanying this widespread usage is the presence of crime; the more popular technology, the more opportunity exists for its misuse. / This dissertation studied 802.11-based wireless networking environment from a forensic computing perspective. It sought to understand the current state of wireless misuse: present misuses; potential forms of misuse involving 802.11-based wireless networks; and current tools and techniques used in its identification, containment and analysis. The research highlights the lack of current tools and procedures for forensic computing investigations that are able to effectively handle the presence of wireless devices and networks, and that there are forms of misuse that may escape detection by forensic investigation teams. This work was then developed into a taxonomy of wireless misuse. / Once the current state was known, this research sought to readdress the current state of forensic computing teams, through analysing the need for software tools and procedural changes to counter the misuses that this technology allows. Once software outcomes were developed, the legal and technical feasibility of their use was ascertained. Based on the outcomes of this work, a final set of software requirements was developed and the proposed methodology for their development was discussed. / A new series of procedures was also developed for forensic investigators to identify, contain and analyse sources of electronic evidence with 802.11-networking. Much of this work was based upon but extending current procedural guides for law enforcement. / The final outcome of this research was the development of a series of recommendations for forensic teams and research that incorporates short, medium and long term development for forensic teams as well as research and development. This work intended to provide mechanisms for future research that are jurisdictionally independent able to be adapted for each individual forensic team. The short term recommendations were primarily changes to procedure, whereas the medium and long terms changes sought to address the larger issues raised by wireless networking devices being the target of or involved in crime or misuse. / Much of this dissertation is exploratory in nature and much of its length is devoted to determining the current state of the misuse and current mechanisms employed to counter it. In such a rapidly developing field of study, this work will need constant revision as new technologies emerge and new forms of misuse take advantage of them. / Thesis (PhDInformationTechnology)--University of South Australia, 2007

802.11-based wireless networking has invaded cities, offices, homes and coffee shops over the last five years, and has become a widely used and accepted technology. It has revolutionised computer networking and automation and added a social aspect to personal computing. Accompanying this widespread usage is the presence of crime; the more popular technology, the more opportunity exists for its misuse. / This dissertation studied 802.11-based wireless networking environment from a forensic computing perspective. It sought to understand the current state of wireless misuse: present misuses; potential forms of misuse involving 802.11-based wireless networks; and current tools and techniques used in its identification, containment and analysis. The research highlights the lack of current tools and procedures for forensic computing investigations that are able to effectively handle the presence of wireless devices and networks, and that there are forms of misuse that may escape detection by forensic investigation teams. This work was then developed into a taxonomy of wireless misuse. / Once the current state was known, this research sought to readdress the current state of forensic computing teams, through analysing the need for software tools and procedural changes to counter the misuses that this technology allows. Once software outcomes were developed, the legal and technical feasibility of their use was ascertained. Based on the outcomes of this work, a final set of software requirements was developed and the proposed methodology for their development was discussed. / A new series of procedures was also developed for forensic investigators to identify, contain and analyse sources of electronic evidence with 802.11-networking. Much of this work was based upon but extending current procedural guides for law enforcement. / The final outcome of this research was the development of a series of recommendations for forensic teams and research that incorporates short, medium and long term development for forensic teams as well as research and development. This work intended to provide mechanisms for future research that are jurisdictionally independent able to be adapted for each individual forensic team. The short term recommendations were primarily changes to procedure, whereas the medium and long terms changes sought to address the larger issues raised by wireless networking devices being the target of or involved in crime or misuse. / Much of this dissertation is exploratory in nature and much of its length is devoted to determining the current state of the misuse and current mechanisms employed to counter it. In such a rapidly developing field of study, this work will need constant revision as new technologies emerge and new forms of misuse take advantage of them. / Thesis (PhDInformationTechnology)--University of South Australia, 2007