Detection of selfish manipulation of carrier sensing in 802.11 networks

Recently, tuning the clear channel assessment (CCA) threshold in conjunction with power control has been considered for improving the performance of WLANs. However, we show that, CCA tuning can be exploited by selfish nodes to obtain an unfair share of the available bandwidth. Specifically, a selfish entity can manipulate the CCA threshold to ignore ongoing transmissions; this increases the probability of accessing the medium and provides the entity a higher, unfair share of the bandwidth. We experiment on our 802.11 testbed to characterize the effects of CCA tuning on both isolated links and in 802.11 WLAN configurations. We focus on AP-client(s) configurations, proposing a novel approach to detect this misbehavior. A misbehaving client is unlikely to recognize low power receptions as legitimate packets; by intelligently sending low power probe messages, an AP can efficiently detect a misbehaving node. Our key contributions are: 1) We are the first to quantify the impact of selfish CCA tuning via extensive experimentation on various 802.11 configurations. 2) We propose a lightweight scheme for detecting selfish nodes that inappropriately increase their CCAs. 3) We extensively evaluate our system on our testbed; its accuracy is 95 percent while the false positive rate is less than 5 percent. © 2012 IEEE

Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

Analysis and optimal configuration of distributed opportunistic scheduling techniques in wireless networks

The phenomenon of fading in wireless communications has traditionally been considered as a source of unreliability that needs to be mitigated. In contrast, Opportunistic Scheduling (OS) techniques exploit quick channel quality oscillations in fading links, during the assignment of transmission opportunities, to improve the performance of wireless networks. While centralized mechanisms rely on a central entity with global knowledge, Distributed Opportunistic Scheduling (DOS) techniques have recently been proposed to work in distributed networks, i.e., where either such a central entity is not available, or the communication overhead to feed timely information to this central entity is prohibitive. With DOS, each station contends for the channel with a certain access probability. If a contention is successful, the station measures the channel conditions and transmits if the channel quality is above a certain threshold. Otherwise, the station does not use the transmission opportunity, allowing all stations to recontend. Given the fact that different stations, in different time instances, experience different channel conditions, it is likely that the channel is used by a link with better conditions, improving overall performance. In this thesis we first propose ADOS, an adaptive mechanism that drives the system to an optimal allocation of resources in terms of proportional fairness. We show that this mechanism outperforms previous approaches, particularly in scenarios with non-saturated stations (that do not always have data to transmit). The distributed nature of DOS makes it particularly vulnerable to selfish users that seek to maximize their own performance at the expense of those that cooperate for the common welfare. We thus design a punishing mechanism, namely DOC, that (i) drives the system to the optimal point of operation when all stations follow the protocol, and (ii) removes any potential gain by deviating from it (and thus, the incentive to misbehave). Finally, we propose a novel allocation criterion, namely the EF criterion, to balance between the most energy-eficient configuration (where all resources are given to the most energy e cient devices) and the throughput-optimal allocation (where all devices evenly share the resources regardless of their power consumption). Due to the lack of models that accurately predict the power consumption behavior of wireless devices, we perform a thorough experimental study to devise a power consumption model that completes existing literature. Finally, we apply these findings to design an EF-optimal strategy in DOS networks. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------El fenómeno de "fading" o desvanecimiento en comunicaciones inalámbricas se ha considerado tradicionalmente como una fuente de problemas de fiabilidad que debe ser mitigada. En contraste, las técnicas de asignación de recursos oportunistas aprovechan las oscilaciones en la calidad de enlaces para mejorar el rendimiento global. Mientras que los mecanismos centralizados requieren una entidad central con información global, recientemente se han propuesto técnicas oportunistas distribuidas (DOS, por sus siglas en inglés) para operar en redes donde dicha entidad no está disponible, o donde el coste en la comunicación para proporcionarle información puntual es prohibitivo. Con DOS, cada estación contiende por el canal con una cierta probabilidad. Si la contienda resulta exitosa, la estación mide la calidad del canal y transmite si ésta supera un cierto umbral. De lo contrario, la estación no aprovecha esa oportunidad para transmitir, permitiendo a todas las estaciones contender de nuevo. Dado que estaciones diferentes, en distintas instancias de tiempo, experimentan diferentes condiciones de canal, es probable que un enlace con mejores condiciones use el canal, mejorando el rendimiento global. En esta tesis proponemos primero ADOS, un mecanismo adaptativo que lleva al sistema a un reparto óptimo de los recursos en términos de equidad proporcional. Mostramos que este mecanismo supera el rendimiento de trabajos previos, particularmente en escenarios con estaciones no saturados (que no siempre tienen datos que transmitir). La naturaleza distribuida de DOS lo hace particularmente vulnerable a usuarios egoístas que buscan maximizar su rendimiento a expensas de aquellos que cooperan por el bien común. Así, diseñamos un mecanismo, llamado DOC, que (i) optimiza el rendimiento si todos los nodos obedecen el protocolo, y (ii) elimina cualquier posible beneficio por desviarse del mismo (y así, el incentivo a no cooperar). Finalmente, proponemos un nuevo criterio de asignación de recursos, llamado EF, que supone un compromiso entre la configuración más eficiente energéticamente (donde todos los recursos se asignan a los nodos más eficientes) y una asignación donde todos comparten de forma equitativa los recursos sin tener en cuenta su consumo. Dada la falta de modelos para predecir de forma precisa el consumo de dispositivos inalámbricos, llevamos a cabo un estudio experimental que resulta en un modelo energético que completa a la literatura existente. Finalmente, aplicamos lo anterior para diseñar una estrategia que optimiza EF en redes basadas en DOS

Association Control in Wireless Mesh Networks

Ph.DDOCTOR OF PHILOSOPH

Video QoS/QoE over IEEE802.11n/ac: A Contemporary Survey

The demand for video applications over wireless networks has tremendously increased, and IEEE 802.11 standards have provided higher support for video transmission. However, providing Quality of Service (QoS) and Quality of Experience (QoE) for video over WLAN is still a challenge due to the error sensitivity of compressed video and dynamic channels. This thesis presents a contemporary survey study on video QoS/QoE over WLAN issues and solutions. The objective of the study is to provide an overview of the issues by conducting a background study on the video codecs and their features and characteristics, followed by studying QoS and QoE support in IEEE 802.11 standards. Since IEEE 802.11n is the current standard that is mostly deployed worldwide and IEEE 802.11ac is the upcoming standard, this survey study aims to investigate the most recent video QoS/QoE solutions based on these two standards. The solutions are divided into two broad categories, academic solutions, and vendor solutions. Academic solutions are mostly based on three main layers, namely Application, Media Access Control (MAC) and Physical (PHY) which are further divided into two major categories, single-layer solutions, and cross-layer solutions. Single-layer solutions are those which focus on a single layer to enhance the video transmission performance over WLAN. Cross-layer solutions involve two or more layers to provide a single QoS solution for video over WLAN. This thesis has also presented and technically analyzed QoS solutions by three popular vendors. This thesis concludes that single-layer solutions are not directly related to video QoS/QoE, and cross-layer solutions are performing better than single-layer solutions, but they are much more complicated and not easy to be implemented. Most vendors rely on their network infrastructure to provide QoS for multimedia applications. They have their techniques and mechanisms, but the concept of providing QoS/QoE for video is almost the same because they are using the same standards and rely on Wi-Fi Multimedia (WMM) to provide QoS

An Efficient Uplink Multi-Connectivity Scheme for 5G mmWave Control Plane Applications

The millimeter wave (mmWave) frequencies offer the potential of orders of magnitude increases in capacity for next-generation cellular systems. However, links in mmWave networks are susceptible to blockage and may suffer from rapid variations in quality. Connectivity to multiple cells - at mmWave and/or traditional frequencies - is considered essential for robust communication. One of the challenges in supporting multi-connectivity in mmWaves is the requirement for the network to track the direction of each link in addition to its power and timing. To address this challenge, we implement a novel uplink measurement system that, with the joint help of a local coordinator operating in the legacy band, guarantees continuous monitoring of the channel propagation conditions and allows for the design of efficient control plane applications, including handover, beam tracking and initial access. We show that an uplink-based multi-connectivity approach enables less consuming, better performing, faster and more stable cell selection and scheduling decisions with respect to a traditional downlink-based standalone scheme. Moreover, we argue that the presented framework guarantees (i) efficient tracking of the user in the presence of the channel dynamics expected at mmWaves, and (ii) fast reaction to situations in which the primary propagation path is blocked or not available.Comment: Submitted for publication in IEEE Transactions on Wireless Communications (TWC