A number of techniques for indoor and outdoor WiFi localization using received signal strength (RSS) signatures have been published. Little work has been performed to characterize the RSS signatures used by these WiFi localization techniques or to assess the accuracy of current channel models to represent the signatures. Without accurate characterization and models of the RSS signatures, a large amount of empirical data is needed to evaluate the performance of the WiFi localization techniques. The goal of this research is to characterize the RSS signatures, propose channel model improvements based on the characterization, and study the performance of channel models for use in WiFi localization simulations to eliminate the need for large amounts of empirical data measurements. In this thesis, we present our empirical database of RSS signatures measured on the Worcester Polytechnic Institute campus. We use the empirical database to characterize the RSS signatures used in WiFi localization, showing that they are composed of connective segments and influenced by the access point (AP) location within a building. From the characterization, we propose improving existing channel models by building partitioning the signal path-loss using site-specific information from Google Earth. We then evaluate the performance of the existing channel models and the building partitioned models against the empirical data. The results show that using site-specific information to building partition the signal path-loss a tighter fit to the empirical RSS signatures can be achieved.

Internet security (Network security) is a big topic that is very important in our society communication system, but it is extremely dynamic and wide in scope. This is the reason that many companies and organizations invest heavily in a dedicated infrastructure security and highly trained specialists.The aim of security monitoring and preventing the network from cyber threats requires vigilance over the network equipment. The case study of this thesis is to provide the possible solution to the problems encountered by the namely network users such as: Internet Game Center (Centrum Halmstad, Sweden) and, the Blueville Internet Cafe (Ede, Nigeria).Our research and information collected over the telephone and a visit at the nearest office. We concluded that both companies mentioned above experienced similar cyber threats. The two companies have internal and external threats such as accessing the network via ssh by using it brute force attack, network war-driver, the installation of spyware, password sniffer, viruses, SQL injection and PHP attacks (web attacks) on the networks. The cyber threats virus and spyware are among the big internet threat to users, organization and companies.We carry out experiments in the lab to tests for threats such as brute force (ssh) attack, password sniffer and war-driver in the Wireless environment. From the results, we are able to the select WPA2 using 802.1x as the best possible way to limit and reduce the strength of cyber-attacks, and as a suggested solution to the namely café problems in our report. We also list different suggestion and solution to the cyber café attacks from our research papers and information gathers from different sources such as library, internet, seminar and textbooks.

One of the primary sources of inefficiency in today's wireless networks is the half-duplex constraint - the assumption that nodes cannot transmit and receive simultaneously in the same band. The reason for this constraint and the hurdle to full-duplex operation is self-interference: a node's transmit signal appears at its own receiver with very high power, desensitizing the receiver electronics and precluding the reception of a packet from a distant node. Recent research has demonstrated that full-duplex can indeed be feasible by employing a combination of analog and digital self-interference cancellation mechanisms. However, two glaring limitations remain. The first is that the full-duplex state-of-the-art requires at least two antennas and extra RF resources that space-constrained mobile devices may not be able to accommodate. The second limitation is range: current full-duplex demonstrations have been for ranges less than 10~m. At longer distances nodes must transmit with higher power to overcome path loss, and the power differential between the self-interference and the signal-of-interest becomes more that the current cancellation mechanisms can handle. We therefore present engineering solutions for answering the following driving questions: (a) can we leverage full-duplex in a network consisting mostly of half-duplex mobiles? and (b) can we extend the range of full-duplex by achieving self-interference suppression sufficient for full-duplex to outperform half-duplex at ranges exceeding 100 m? In answer to the first question, we propose moving the burden of full-duplexing solely to access points (APs), enabling the AP to boost network throughput by receiving an uplink signal from one half-duplex mobile, while simultaneously transmitting a downlink signal to another half-duplex mobile in the same band. In answer to the second question we propose an AP antenna architecture that uses a careful combination of three mechanisms for passive suppression of self-interference: directional isolation, absorptive shielding, and cross-polarization. Results from a 20 MHz OFDM prototype demonstrate that the proposed AP architecture can achieve 90+ dB total self-interference suppression, enabling >50% uplink rate gains over half-duplex for ranges up to 150 m.

No description available.

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

Multipath TCP (MPTCP) is a new modification of TCP protocol which enables a client to transfer data over multiple paths simultaneously under a single TCP connection, for improved throughput and fault resilience. However, MPTCP is susceptible to some major drawbacks when applied in a wireless network. We found several cases where, despite improving individual MPTCP clients throughput, MPTCP reduces the capacity of the overall wireless network due to the mac level fairness and contention-based access schemes. Additionally, even if the bandwidth improves, employing Multipath TCP (MPTCP) in wireless networks can be energy inecient due to additional energy consumption by multiple interfaces. This creates a dilemma between bandwidth improvement and energy efficiency. This thesis research aims to solve these important issues for MPTCP in the wireless environment. We analyzed the root cause of these drawbacks and identified instances where they can arise. Two novel schemes denoted MPWiFi and kMPTCP, are developed to solve the bandwidth degradation and energy efficiency issues respectively, while maintaining the promised benefitts of MPTCP. The MPWiFi assigns dierent priorities to the subflows and aggressively suppresses some of them based on some design logic. Similarly, kMPTCP adds an additional multipath subflow only if the bandwidth requirement can't be fulllled by single path and the new subflow meets the data rate and signal strength condition. Moreover, kMPTCP keeps additional subflows as long as the signal strength remains in good range and this subflow remain mandatory to provide the necessary bandwidth to the application. These two schemes have been implemented along with Linux Kernel MPTCP implementation. Extensive real-world deployment and NS3 simulation show that the proposed schemes can eectively alleviate the adverse impacts of the MPTCP based multipath access in Wireless networks.

abstract: The purpose of this paper is to introduce a new method of dividing wireless communication (such as the 802.11a/b/g/n and cellular UMTS MAC protocols) across multiple unreliable communication links (such as Ethernet). The purpose is to introduce the appropriate hardware, software, and system architecture required to provide the basis for a wireless system (using a 802.11a/b/g/n and cellular protocols as a model) that can scale to support thousands of users simultaneously (say in a large office building, super chain store, etc.) or in a small, but very dense communication RF region. Elements of communication between a base station and a Mobile Station will be analyzed statistically to demonstrate higher throughput, fewer collisions and lower bit error rates (BER) with the given bandwidth defined by the 802.11n wireless specification (use of MIMO channels will be evaluated). A new network nodal paradigm will be presented. Alternative link layer communication techniques will be recommended and analyzed for the affect on mobile devices. The analysis will describe how the algorithms used by state machines implemented on Mobile Stations and Wi-Fi client devices will be influenced by new base station transmission behavior. New hardware design techniques that can be used to optimize this architecture as well as hardware design principles in regard to the minimal hardware functional blocks required to support such a system design will be described. Hardware design and verification simulation techniques to prove the hardware design will accommodate an acceptable level of performance to meet the strict timing as it relates to this new system architecture. / Dissertation/Thesis / JMP Analysis Files / Defense Presentation / M.S. Electrical Engineering 2014

No description available.

Magíster en Ciencias, Mención Computación / A partir del surgimiento de la computación móvil, la necesidad de conocer la ubicación de recursos y/o personas ha sido imperante en el desarrollo de nuevas tecnologías y de soluciones que emplean este paradigma de computación. En particular, los sistemas de localización en tiempo real cobran cada día más importancia. Típicamente, este tipo de sistemas persiguen objetivos que están orientados a la seguridad, optimización y administración del uso de los recursos. Una gran cantidad de áreas de aplicación aprovechan cada vez más las ventajas de estas tecnologías y las incorporan en su plan de negocios. Estas aplicaciones van desde el seguimiento de activos dentro de un recinto cerrado, hasta el control de flota en empresas de transporte. El presente trabajo desarrolló un modelo predictivo para la estimación de la posición de los recursos en escenarios cerrados (indoor). Este modelo fue luego implementado a través en una aplicación de software que funciona en dispositivos móviles. La aplicación permite estimar la posición tanto del usuario local como de otros usuarios que están alrededor de él. Aunque el margen de error de la estimación es aún importante (del orden de 4-5 metros), el modelo predictivo cumple con el objetivo para el cual fue diseñado. Ese objetivo es que dos o más usuarios de la aplicación puedan encontrarse entre sí cara-a-cara, en base a la información entregada por la aplicación. La información necesaria para realizar la estimación de la posición de un recurso se obtiene de contrastar un modelo del espacio físico pre-cargado en la memoria del dispositivo, contra las señales inalámbricas observadas en tiempo-real. Se requiere que el entorno en el cual se desea implantar esta solución cuente con distintos puntos de accesos WiFi, los cuales puedan ser usados como referencia. La aplicación desarrollada permite construir de manera expedita y con la mínima información el modelo del decaimiento de las señales WiFi para toda la zona objetivo. La estimación de posición se realiza usando conjuntamente las redes WiFi escaneadas, y la información proporcionada por los sensores de movimiento de cada dispositivo. El intercambio de información con el resto de los usuarios se realiza a través de protocolos ad-hoc implementados sobre una red MANET, formada por los usuarios presentes en el recinto. La solución implementada se adapta fácilmente ante cambios en las referencias del recinto y permite que un mismo modelo funcione en distintos dispositivos con un leve cambio en la configuración. La calidad de la estimación es proporcional a la densidad de señales WiFi del ambiente. La versión actual del sistema permite, en un ambiente con densidad moderada, obtener márgenes de error aceptables para que un humano pueda encontrar a otra persona usando inspección visual.

IEEE 802.11 (a.k.a. WiFi) is a popular wireless LAN specification. This thesis documents implementation of this standard within the experimental operating system HelenOS which differs from conventional operating systems with its microkernel-based design. First, the basic concepts of WiFi technology are described. Description of external tools used during development is following. Together with that, the chosen method of integrating the wireless framework into existing system is depicted. In the next chapter we analyse the implementation details of the work. There is thoroughly explained the structure of the driver for selected WiFi device and also the functionality of resulting IEEE 802.11 library. In the end of the thesis there is an evaluation of the features of final work and comparison of enclosed implementation with existing solutions.