Medium access control mechanisms for high speed metropolitan area networks

In this dissertation novel Medium Access Control mechanisms for High Speed Metropolitan Area networks are proposed and their performance is investigated under the presence of single and multiple priority classes of traffic. The proposed mechanisms are based on the Distributed Queue Dual Bus network, which has been adopted by the IEEE standardization committee as the 802.6 standard for Metropolitan Area Networks, and address most of its performance limitations. First, the Rotating Slot Generator scheme is introduced which uses the looped bus architecture that has been proposed for the 802.6 network. According to this scheme the responsibility for generating slots moves periodically from station to station around the loop. In this way, the positions of the stations relative to the slot generator change continuously, and therefore, there are no favorable locations on the busses. Then, two variations of a new bandwidth balancing mechanism, the NSW_BWB and ITU_NSW are introduced. Their main advantage is that their operation does not require the wastage of channel slots and for this reason they can converge very fast to the steady state, where the fair bandwidth allocation is achieved. Their performance and their ability to support multiple priority classes of traffic are thoroughly investigated. Analytic estimates for the stations\u27 throughputs and average segment delays are provided. Moreover, a novel, very effective priority mechanism is introduced which can guarantee almost immediate access for high priority traffic, regardless of the presence of lower priority traffic. Its performance is thoroughly investigated and its ability to support real time traffic, such as voice and video, is demonstrated. Finally, the performance under the presence of erasure nodes of the various mechanisms that have been proposed in this dissertation is examined and compared to the corresponding performance of the most prominent existing mechanisms

Security Improvements for the S-MIM Asynchronous Return Link

S-MIM is a hybrid terrestrial and satellite system that enables efficient and high-performance communication in the return link. For communication to be possible between a device and the satellite, a preamble has to be established. Some parameters to generate the preamble are broadcasted by the satellite without protection. It is very important to protect the preamble, because if an attacker knows the preamble he could avoid the communication. This project presents a method without the necessity of establishing the preamble in a way that ensures the communication. However, to achieve this security the trade-off is degradation of throughput and a delay in communication

Coordination and Interference in 802.11 Networks: Inference, Analysis and Mitigation

In the last decade, 802.11 wireless devices data-rates have increased by three orders of magnitude, while communications experiencing low throughput are still largely present. Such throughput loss is a fundamental problem of wireless networking that is difficult to diagnose and amend. My research addresses two key causes of throughput loss: MAC layer protocol overhead and destructive link interference. First, I design WiFi-Nano reducing the channel access overhead by an order of magnitude leveraging an innovative speculative technique to transmit preambles. This new concept is based on simultaneous preamble transmission and detection via a self-interference cancellation design, and paves the way to the realization of the collision detection paradigm in wireless networks. Next, I propose 802.11ec (Encoded Control), the first 802.11-based protocol that eliminates the overhead of control packets. Instead, 802.11ec coordinates node transmissions via a set of predefined pseudo-noise codewords, resulting in the dramatic increase of throughput and communication robustness. Finally, I design MIDAS, a model-driven network management tool that alleviates low throughput wireless links identifying key corrective actions. MIDAS' key contribution is to reveal the fundamental role of node transmission coordination in characterizing destructive interference. I implement WiFi-Nano, 802.11ec, and MIDAS using a combination of WARP FPGA-based radio boards, custom emulation platforms, and network simulators. The results obtained show that WiFi-Nano increases the network throughput by up to 100%, 802.11ec improves network access fairness by up to 90%, and MIDAS identifies corrective actions with a prediction error as low as 20%

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC

Embracing interference in wireless systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2013."February 2013." Cataloged from PDF version of thesis.Includes bibliographical references (p. 169-183).The wireless medium is a shared resource. If nearby devices transmit at the same time, their signals interfere, resulting in a collision. In traditional networks, collisions cause the loss of the transmitted information. For this reason, wireless networks have been designed with the assumption that interference is intrinsically harmful and must be avoided. This dissertation takes an alternate approach: Instead of viewing interference as an inherently counterproductive phenomenon that should to be avoided, we design practical systems that transform interference into a harmless, and even a beneficial phenomenon. To achieve this goal, we consider how wireless signals interact when they interfere, and use this understanding in our system designs. Specifically, when interference occurs, the signals get mixed on the wireless medium. By understanding the parameters of this mixing, we can invert the mixing and decode the interfered packets; thus, making interference harmless. Furthermore, we can control this mixing process to create strategic interference that allow decodability at a particular receiver of interest, but prevent decodability at unintended receivers and adversaries. Hence, we can transform interference into a beneficial phenomenon that provides security. Building on this approach, we make four main contributions: We present the first WiFi receiver that can successfully reconstruct the transmitted information in the presence of packet collisions. Next, we introduce a WiFi receiver design that can decode in the presence of high-power cross-technology interference from devices like baby monitors, cordless phones, microwave ovens, or even unknown technologies. We then show how we can harness interference to improve security. In particular, we develop the first system that secures an insecure medical implant without any modification to the implant itself. Finally, we present a solution that establishes secure connections between any two WiFi devices, without having users enter passwords or use pre-shared secret keys.by Shyamnath Gollakota.Ph.D

Optical flow switched networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 253-279).In the four decades since optical fiber was introduced as a communications medium, optical networking has revolutionized the telecommunications landscape. It has enabled the Internet as we know it today, and is central to the realization of Network-Centric Warfare in the defense world. Sustained exponential growth in communications bandwidth demand, however, is requiring that the nexus of innovation in optical networking continue, in order to ensure cost-effective communications in the future. In this thesis, we present Optical Flow Switching (OFS) as a key enabler of scalable future optical networks. The general idea behind OFS-agile, end-to-end, all-optical connections-is decades old, if not as old as the field of optical networking itself. However, owing to the absence of an application for it, OFS remained an underdeveloped idea-bereft of how it could be implemented, how well it would perform, and how much it would cost relative to other architectures. The contributions of this thesis are in providing partial answers to these three broad questions. With respect to implementation, we address the physical layer design of OFS in the metro-area and access, and develop sensible scheduling algorithms for OFS communication. Our performance study comprises a comparative capacity analysis for the wide-area, as well as an analytical approximation of the throughput-delay tradeoff offered by OFS for inter-MAN communication. Lastly, with regard to the economics of OFS, we employ an approximate capital expenditure model, which enables a throughput-cost comparison of OFS with other prominent candidate architectures. Our conclusions point to the fact that OFS offers significant advantage over other architectures in economic scalability.(cont.) In particular, for sufficiently heavy traffic, OFS handles large transactions at far lower cost than other optical network architectures. In light of the increasing importance of large transactions in both commercial and defense networks, we conclude that OFS may be crucial to the future viability of optical networking.by Guy E. Weichenberg.Ph.D

International Conference on Civil Infrastructure and Construction (CIC 2020)

This is the proceedings of the CIC 2020 Conference, which was held under the patronage of His Excellency Sheikh Khalid bin Khalifa bin Abdulaziz Al Thani in Doha, Qatar from 2 to 5 February 2020. The goal of the conference was to provide a platform to discuss next-generation infrastructure and its construction among key players such as researchers, industry professionals and leaders, local government agencies, clients, construction contractors and policymakers. The conference gathered industry and academia to disseminate their research and field experiences in multiple areas of civil engineering. It was also a unique opportunity for companies and organizations to show the most recent advances in the field of civil infrastructure and construction. The conference covered a wide range of timely topics that address the needs of the construction industry all over the world and particularly in Qatar. All papers were peer reviewed by experts in their field and edited for publication. The conference accepted a total number of 127 papers submitted by authors from five different continents under the following four themes: Theme 1: Construction Management and Process Theme 2: Materials and Transportation Engineering Theme 3: Geotechnical, Environmental, and Geo-environmental Engineering Theme 4: Sustainability, Renovation, and Monitoring of Civil InfrastructureThe list of the Sponsors are listed at page 1

Enabling Efficient, Robust, and Scalable Wireless Multi-Hop Networks: A Cross-Layer Approach Exploiting Cooperative Diversity

The practical performance in terms of throughput, robustness, and scalability of traditional Wireless Multihop Networks (WMNs) is limited. The key problem is that such networks do not allow for advanced physical layers, which typically require (a) spatial diversity via multiple antennas, (b) timely Channel State Information (CSI) feedback, and (c) a central instance that coordinates nodes. We propose Corridor-based Routing to address these issues. Our approach widens traditional hop-by-hop paths to span multiple nodes at each hop, and thus provide spatial diversity. As a result, at each hop, a group of transmitters cooperates at the physical layer to forward data to a group of receivers. We call two subsequent groups of nodes a stage. Since all nodes participating in data forwarding at a certain hop are part of the same fully connected stage, corridors only require one-hop CSI feedback. Further, each stage operates independently. Thus, Corridor-based Routing does not require a network-wide central instance, and is scalable. We design a protocol that builds end-to-end corridors. As expected, this incurs more overhead than finding a traditional WMN path. However, if the resulting corridor provides throughput gains, the overhead compensates after a certain number of transmitted packets. We adapt two physical layers to the aforementioned stage topology, namely, Orthogonal Frequency-Division Multiple Access (OFDMA), and Interference Alignment (IA). In OFDMA, we allocate each subchannel to a link of the current stage which provides good channel conditions. As a result, we avoid deep fades, which enables OFDMA to transmit data robustly in scenarios in which traditional schemes cannot operate. Moreover, it achieves higher throughputs than such schemes. To minimize the transmission time at each stage, we present an allocation mechanism that takes into account both the CSI, and the amount of data that each transmitter needs to transmit. Further, we address practical issues and implement our scheme on software-defined radios. We achieve roughly 30% average throughput gain compared to a WMN not using corridors. We analyze OFDMA in theory, simulation, and practice. Our results match in all three domains. Further, we design a physical layer for corridor stages based on IA in the frequency domain. Our practical experiments show that IA often performs poorly because the decoding process augments noise. We find that the augmentation factor depends only on the channel coefficients of the subchannels that IA uses. We design a mechanism to determine which transmitters should transmit to which receivers on which subchannels to minimize noise. Since the number of possible combinations is very large, we use heuristics that reduce the search space significantly. Based on this design, we present the first practical frequency IA system. Our results show that our approach avoids noise augmentation efficiently, and thus operates robustly. We observe that IA is most suitable for stages with specific CSI and traffic conditions. In such scenarios, the throughput gain compared to a WMN not using corridors is 25% on average, and 150% in the best case. Finally, we design a decision engine which estimates the performance of both OFDMA and IA for a given stage, and chooses the one which achieves the highest throughput. We evaluate corridors with up to five stages, and achieve roughly 20% average throughput gain. We conclude that switching among physical layers to adapt to the particular CSI and traffic conditions of each stage is crucial for efficient and robust operation

Systematic Approaches for Telemedicine and Data Coordination for COVID-19 in Baja California, Mexico

Conference proceedings info: ICICT 2023: 2023 The 6th International Conference on Information and Computer Technologies Raleigh, HI, United States, March 24-26, 2023 Pages 529-542We provide a model for systematic implementation of telemedicine within a large evaluation center for COVID-19 in the area of Baja California, Mexico. Our model is based on human-centric design factors and cross disciplinary collaborations for scalable data-driven enablement of smartphone, cellular, and video Teleconsul-tation technologies to link hospitals, clinics, and emergency medical services for point-of-care assessments of COVID testing, and for subsequent treatment and quar-antine decisions. A multidisciplinary team was rapidly created, in cooperation with different institutions, including: the Autonomous University of Baja California, the Ministry of Health, the Command, Communication and Computer Control Center of the Ministry of the State of Baja California (C4), Colleges of Medicine, and the College of Psychologists. Our objective is to provide information to the public and to evaluate COVID-19 in real time and to track, regional, municipal, and state-wide data in real time that informs supply chains and resource allocation with the anticipation of a surge in COVID-19 cases. RESUMEN Proporcionamos un modelo para la implementación sistemática de la telemedicina dentro de un gran centro de evaluación de COVID-19 en el área de Baja California, México. Nuestro modelo se basa en factores de diseño centrados en el ser humano y colaboraciones interdisciplinarias para la habilitación escalable basada en datos de tecnologías de teleconsulta de teléfonos inteligentes, celulares y video para vincular hospitales, clínicas y servicios médicos de emergencia para evaluaciones de COVID en el punto de atención. pruebas, y para el tratamiento posterior y decisiones de cuarentena. Rápidamente se creó un equipo multidisciplinario, en cooperación con diferentes instituciones, entre ellas: la Universidad Autónoma de Baja California, la Secretaría de Salud, el Centro de Comando, Comunicaciones y Control Informático. de la Secretaría del Estado de Baja California (C4), Facultades de Medicina y Colegio de Psicólogos. Nuestro objetivo es proporcionar información al público y evaluar COVID-19 en tiempo real y rastrear datos regionales, municipales y estatales en tiempo real que informan las cadenas de suministro y la asignación de recursos con la anticipación de un aumento de COVID-19. 19 casos.ICICT 2023: 2023 The 6th International Conference on Information and Computer Technologieshttps://doi.org/10.1007/978-981-99-3236-