An Analytical Model of Packet Collisions in IEEE 802.15.4 Wireless Networks

Numerous studies showed that concurrent transmissions can boost wireless network performance despite collisions. While these works provide empirical evidence that concurrent transmissions may be received reliably, existing signal capture models only partially explain the root causes of this phenomenon. We present a comprehensive mathematical model that reveals the reasons and provides insights on the key parameters affecting the performance of MSK-modulated transmissions. A major contribution is a closed-form derivation of the receiver bit decision variable for arbitrary numbers of colliding signals and constellations of power ratios, timing offsets, and carrier phase offsets. We systematically explore the root causes for successful packet delivery under concurrent transmissions across the whole parameter space of the model. We confirm the capture threshold behavior observed in previous studies but also reveal new insights relevant for the design of optimal protocols: We identify capture zones depending not only on the signal power ratio but also on time and phase offsets.Comment: Accepted for publication in the IEEE Transactions on Wireless Communications under the title "On the Reception of Concurrent Transmissions in Wireless Sensor Networks.

Opportunistic nonorthogonal packet scheduling in fixed broadband wireless access networks

In order to mitigate high cochannel interference resulting from dense channel reuse, the interference management issues are often considered as essential part of scheduling schemes in fixed br

MAC protocols for wireless networks: Spatial-reuse and energy-efficiency

Master'sMASTER OF SCIENC

Towards next generation WLANs: exploiting coordination and cooperation

Wireless Local Area Networks (WLANs) operating in the industrial, scientific and medical (ISM) radio bands have gained great popularity and increasing usage over the past few years. The corresponding MAC/PHY specification, the IEEE 802.11 standard, has also evolved to adapt to such development. However, as the number of WLAN mobile users increases, and as their needs evolve in the face of new applications, there is an ongoing need for the further evolution of the IEEE 802.11 standard. In this thesis we propose several MAC/PHY layer protocols and schemes that will provide more system throughput, lower packet delivery delay and lessen the power consumption of mobile devices. Our work investigates three approaches that lead to improved WLAN performance: 1) cross-layer design of the PHY and MAC layers for larger system throughput, 2) exploring the use of implicit coordination among clients to increase the efficiency of random media access, and 3) improved packets dispatching by the access points (APs) to preserve the battery of mobile devices. Each proposed solution is supported by theoretical proofs and extensively studied by simulations or experiments on testbeds

Generative Connections: Affective Links in the Media Works of Cathy Sisler and Lindsay Seers

By looking at art by artists who manifest or who self-identify as having psycho-emotional disorders, connections between the artist and the world around them can be uncovered. The definitions of mental health versus mental illness are social and historical constructs. In this paper, the viewer’s perception of these artists and their art is contextualized. Current trauma theory refers to art not only as physical manifestations of trauma, but as transmissions of experience that open up spaces for interaction. This framework is applied to the media art of Cathy Sisler and Lindsay Seers who portray experiences of psychological and emotional disturbances. The writings of psychoanalysts, scientists, cognitive scientists, critical and cultural theorists, and art historians are applied to show the obvious and hidden modes through which Sisler and Seers communicate and how they forge empathetic, cognitive and intellectual bridges

Ubiquitous Interoperable Emergency Response System

In the United States, there is an emergency dispatch for fire department services more than once every second - 31,854,000 incidents in 2012. While large scale disasters present enormous response complexity, even the most common emergencies require a better way to communicate information between personnel. Through real-time location and status updates using integrated sensors, this system can significantly decrease emergency response times and improve the overall effectiveness of emergency responses. Aside from face-to-face communication, radio transmissions are the most common medium for transferring information during emergency incidents. However, this type of information sharing is riddled with issues that are nearly impossible to overcome on a scene. Poor sound quality, the failure to hear transmissions, the inability to reach a radio microphone, and the transient nature of radio messages illustrate just a few of the problems. Proprietary and closed systems that collect and present response data have been implemented, but lack interoperability and do not provide a full array of necessary services. Furthermore, the software and hardware that run the systems are generally poorly designed for emergency response scenarios. Pervasive devices, which can transmit data without human interaction, and software using open communication standards designed for multiple platforms and form factors are two essential components. This thesis explores the issues, history, design, and implementation of a ubiquitous interoperable emergency response system by taking advantage of the latest in hardware and software, including Google Glass, Android powered mobile devices, and a cloud based architecture that can automatically scale to 7 billion requests per day. Implementing this pervasive system that transcends physical barriers by allowing disparate devices to communicate and operate harmoniously without human interaction is a step towards a practical solution for emergency response management

Application acceleration for wireless and mobile data networks

This work studies application acceleration for wireless and mobile data networks. The problem of accelerating application can be addressed along multiple dimensions. The first dimension is advanced network protocol design, i.e., optimizing underlying network protocols, particulary transport layer protocol and link layer protocol. Despite advanced network protocol design, in this work we observe that certain application behaviors can fundamentally limit the performance achievable when operating over wireless and mobile data networks. The performance difference is caused by the complex application behaviors of these non-FTP applications. Explicitly dealing with application behaviors can improve application performance for new environments. Along this overcoming application behavior dimension, we accelerate applications by studying specific types of applications including Client-server, Peer-to-peer and Location-based applications. In exploring along this dimension, we identify a set of application behaviors that significantly affect application performance. To accommodate these application behaviors, we firstly extract general design principles that can apply to any applications whenever possible. These design principles can also be integrated into new application designs. We also consider specific applications by applying these design principles and build prototypes to demonstrate the effectiveness of the solutions. In the context of application acceleration, even though all the challenges belong to the two aforementioned dimensions of advanced network protocol design and overcoming application behavior are addressed, application performance can still be limited by the underlying network capability, particularly physical bandwidth. In this work, we study the possibility of speeding up data delivery by eliminating traffic redundancy present in application traffics. Specifically, we first study the traffic redundancy along multiple dimensions using traces obtained from multiple real wireless network deployments. Based on the insights obtained from the analysis, we propose Wireless Memory (WM), a two-ended AP-client solution to effectively exploit traffic redundancy in wireless and mobile environments. Application acceleration can be achieved along two other dimensions: network provision ing and quality of service (QoS). Network provisioning allocates network resources such as physical bandwidth or wireless spectrum, while QoS provides different priority to different applications, users, or data flows. These two dimensions have their respective limitations in the context of application acceleration. In this work, we focus on the two dimensions of overcoming application behavior and Eliminating traffic redundancy to improve application performance. The contribution of this work is as follows. First, we study the problem of application acceleration for wireless and mobile data networks, and we characterize the dimensions along which to address the problem. Second, we identify that application behaviors can significantly affect application performance, and we propose a set of design principles to deal with the behaviors. We also build prototypes to conduct system research. Third, we consider traffic redundancy elimination and propose a wireless memory approach.Ph.D.Committee Chair: Sivakumar, Raghupathy; Committee Member: Ammar, Mostafa; Committee Member: Fekri, Faramarz; Committee Member: Ji, Chuanyi; Committee Member: Ramachandran, Umakishor

Mitigating the Impact of Physical Layer Capture and ACK Interference in Wireless 802.11 Networks

Ph.DDOCTOR OF PHILOSOPH

Decoding the Public Service Announcements (PSAs) of HIV/AIDS: Evaluating Botswana\u27s AIDS Messages and Their Impact on 15 - 24 Ages

The study is grounded in the concept of “Start where the people are” (Nyswander, 1956) which suggests that effective health campaigns that promote prevention strategies to enhance the quality of life for those targeted must be rooted in the prevalent cultural practices and religious values of the receivers of the slogans, themes, and taglines. Health campaigns that superimpose the values of the outsiders promoted as universalized solutions have limited effectiveness. Sub-Saharan Africa has only 1.3 billion people out of an estimated eight billion of which China and India each recording above two billion, cumulatively accounting for more than half of the world population. Yet sub-Saharan Africa is the epicenter of HIV infections with more than 68% (avert.org), or nearly 26 million out of almost 38 million people living with HIV, globally. This scenario demands that global citizens should foster effective collaborations to end human suffering. Among the ten nations in the world hardest hit by HIV, seven of them are in the southern African region where Botswana, in position three at 18.6% is trailing her next-door neighbors, Lesotho (20.9%) and Eswatini (formerly Swaziland) which leads the pack with 27.9% (UNAIDS Report 2022). This study, therefore, focuses on children and adolescents between 15 and 24 in Botswana. According to a surveillance report (Botswana AIDS Impact Survey 2021) covering the period from March to August, adolescents and youths in Botswana are a source of concern. The report puts the national prevalence at 20.8% or 329,000 persons of the reproductive population (15-49 ages) are living with HIV. This sobering picture is despite the free availability of treatment drugs at no cost since 2002, when Botswana became the first African nation to roll out antiretroviral treatment (HAART interchangeably called ARVs) that was adapted as Masa – ‘a ray of hope of a new dawn’ in 2002. Further, the continued increase in new HIV infections among people of ages 15 to 24 since 2010 is recorded amid major prevention campaigns sponsored through global health partnerships, translating into billions of U S dollars. Numerous HIV prevention strategies developed in the West using empirical data and technology include condom use, antiretroviral regimens known as pre-exposure prophylaxis (PrEP), and treatment as prevention popularized as undetectable equals untransmissible (U = U). Social media channels like Facebook, TikTok, YouTube, Snapchat, and Instagram are awash with these HIV prevention strategies, and the adolescent population of Botswana consumes information about everything, including these HIV prevention campaigns. These mentioned strategies seem to provide effective barriers against the intrusion of HIV in the “key populations,” a United Nations preferred term to refer to members of the lesbian, gay, bisexual, transgender, queer and intravenous drug users (LGBTQI) communities in the Western nations. However, these strategies require major adjustments when launched in sub-Saharan Africa, this study’s results show, or they are the right message targeted to the wrong audience, mainly because of a lack of cultural representation in the nuanced taglines, headlines, slogans, and themes. The study suggests that for HIV to be eliminated, participatory research and co-learning where Western science and technology on one hand, and African indigenous knowledge, on the other hand, can fuse in the design of strategies should be prioritized as an emergency