139 research outputs found

    Reducing false wake-up in contention-based wake-up control of wireless LANs

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    This paper studies the potential problem and performance when tightly integrating a low power wake-up radio (WuR) and a power-hungry wireless LAN (WLAN) module for energy efficient channel access. In this model, a WuR monitors the channel, performs carrier sense, and activates its co-located WLAN module when the channel becomes ready for transmission. Different from previous methods, the node that will be activated is not decided in advance, but decided by distributed contention. Because of the wake-up latency of WLAN modules, multiple nodes may be falsely activated, except the node that will actually transmit. This is called a false wake-up problem and it is solved from three aspects in this work: (i) resetting backoff counter of each node in a way as if it is frozen in a wake-up period, (ii) reducing false wake-up time by immediately putting a WLAN module into sleep once a false wake-up is inferred, and (iii) reducing false wake-up probability by adjusting contention window. Analysis shows that false wake-ups, instead of collisions, become the dominant energy overhead. Extensive simulations confirm that the proposed method (WuR-ESOC) effectively reduces energy overhead, by up to 60% compared with state-of-the-arts, achieving a better tradeoff between throughput and energy consumption

    Energy-efficient wireless communication

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    In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

    Energy-Efficient Data Collection Method for Sensor Networks by Integrating Asymmetric Communication and Wake-Up Radio

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    In large-scale wireless sensor networks (WSNs), nodes close to sink nodes consume energy more quickly than other nodes due to packet forwarding. A mobile sink is a good solution to this issue, although it causes two new problems to nodes: (i) overhead of updating routing information; and (ii) increased operating time due to aperiodic query. To solve these problems, this paper proposes an energy-efficient data collection method, Sink-based Centralized transmission Scheduling (SC-Sched), by integrating asymmetric communication and wake-up radio. Specifically, each node is equipped with a low-power wake-up receiver. The sink node determines transmission scheduling, and transmits a wake-up message using a large transmission power, directly activating a pair of nodes simultaneously which will communicate with a normal transmission power. This paper further investigates how to deal with frame loss caused by fading and how to mitigate the impact of the wake-up latency of communication modules. Simulation evaluations confirm that using multiple channels effectively reduces data collection time and SC-Sched works well with a mobile sink. Compared with the conventional duty-cycling method, SC-Sched greatly reduces total energy consumption and improves the network lifetime by 7.47 times in a WSN with 4 data collection points and 300 sensor nodes

    ACUTA Journal of Telecommunications in Higher Education

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    In This Issue Strategic Planning in the College and University Ecosystem Outlook 2012: Chickens or Eggs? lT Trends on Campus: 2012 Best Practices in Deploying a Successful University SAN Beyond Convergence: How Advanced Networking Will Erase Campus Boundaries Distributed Computing: The Path to the Power? Cell Phones on the University Campus: Adversary or Ally? lnstitutional Excellence Award Honorable Mention: Wake Forest University Interview President\u27s Message From the Executive Director Here\u27s My Advic

    Predictive Duty Cycling of Radios and Cameras using Augmented Sensing in Wireless Camera Networks

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    Energy efficiency dominates practically every aspect of the design of wireless camera networks (WCNs), and duty cycling of radios and cameras is an important tool for achieving high energy efficiencies. However, duty cycling in WCNs is made complex by the camera nodes having to anticipate the arrival of the objects in their field-of-view. What adds to this complexity is the fact that radio duty cycling and camera duty cycling are tightly coupled notions in WCNs. Abstract In this dissertation, we present a predictive framework to provide camera nodes with an ability to anticipate the arrival of an object in the field-of-view of their cameras. This allows a predictive adaption of network parameters simultaneously in multiple layers. Such anticipatory approach is made possible by enabling each camera node in the network to track an object beyond its direct sensing range and to adapt network parameters in multiple layers before the arrival of the object in its sensing range. The proposed framework exploits a single spare bit in the MAC header of the 802.15.4 protocol for creating this beyond-the-sensing-rage capability for the camera nodes. In this manner, our proposed approach for notifying the nodes about the current state of the object location entails no additional communication overhead. Our experimental evaluations based on large-scale simulations as well as an Imote2-based wireless camera network demonstrate that the proposed predictive adaptation approach, while providing comparable application-level performance, significantly reduces energy consumption compared to the approaches addressing only a single layer adaptation or those with reactive adaptation

    Energy-efficient MAC protocol for wireless sensor networks

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    A Wireless Sensor Network (WSN) is a collection of tiny devices called sensor nodes which are deployed in an area to be monitored. Each node has one or more sensors with which they can measure the characteristics of their surroundings. In a typical WSN, the data gathered by each node is sent wirelessly through the network from one node to the next towards a central base station. Each node typically has a very limited energy supply. Therefore, in order for WSNs to have acceptable lifetimes, energy efficiency is a design goal that is of utmost importance and must be kept in mind at all levels of a WSN system. The main consumer of energy on a node is the wireless transceiver and therefore, the communications that occur between nodes should be carefully controlled so as not to waste energy. The Medium Access Control (MAC) protocol is directly in charge of managing the transceiver of a node. It determines when the transceiver is on/off and synchronizes the data exchanges among neighbouring nodes so as to prevent collisions etc., enabling useful communications to occur. The MAC protocol thus has a big impact on the overall energy efficiency of a node. Many WSN MAC protocols have been proposed in the literature but it was found that most were not optimized for the group of WSNs displaying very low volumes of traffic in the network. In low traffic WSNs, a major problem faced in the communications process is clock drift, which causes nodes to become unsynchronized. The MAC protocol must overcome this and other problems while expending as little energy as possible. Many useful WSN applications show low traffic characteristics and thus a new MAC protocol was developed which is aimed at this category of WSNs. The new protocol, Dynamic Preamble Sampling MAC (DPS-MAC) builds on the family of preamble sampling protocols which were found to be most suitable for low traffic WSNs. In contrast to the most energy efficient existing preamble sampling protocols, DPS-MAC does not cater for the worst case clock drift that can occur between two nodes. Rather, it dynamically learns the actual clock drift experienced between any two nodes and then adjusts its operation accordingly. By simulation it was shown that DPS-MAC requires less protocol overhead during the communication process and thus performs more energy efficiently than its predecessors under various network operating conditions. Furthermore, DPS-MAC is less prone to become overloaded or unstable in conditions of high traffic load and high contention levels respectively. These improvements cause the use of DPS-MAC to lead to longer node and network lifetimes, thus making low traffic WSNs more feasible.Dissertation (MEng)--University of Pretoria, 2008.Electrical, Electronic and Computer EngineeringMEngUnrestricte

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

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    Master'sMASTER OF SCIENC

    Towards Secure, Power-Efficient and Location-Aware Mobile Computing

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    In the post-PC era, mobile devices will replace desktops and become the main personal computer for many people. People rely on mobile devices such as smartphones and tablets for everything in their daily lives. A common requirement for mobile computing is wireless communication. It allows mobile devices to fetch remote resources easily. Unfortunately, the increasing demand of the mobility brings many new wireless management challenges such as security, energy-saving and location-awareness. These challenges have already impeded the advancement of mobile systems. In this dissertation we attempt to discover the guidelines of how to mitigate these problems through three general communication patterns in 802.11 wireless networks. We propose a cross-section of a few interesting and important enhancements to manage wireless connectivity. These enhancements provide useful primitives for the design of next-generation mobile systems in the future.;Specifically, we improve the association mechanism for wireless clients to defend against rogue wireless Access Points (APs) in Wireless LANs (WLANs) and vehicular networks. Real-world prototype systems confirm that our scheme can achieve high accuracy to detect even sophisticated rogue APs under various network conditions. We also develop a power-efficient system to reduce the energy consumption for mobile devices working as software-defined APs. Experimental results show that our system allows the Wi-Fi interface to sleep for up to 88% of the total time in several different applications and reduce the system energy by up to 33%. We achieve this while retaining comparable user experiences. Finally, we design a fine-grained scalable group localization algorithm to enable location-aware wireless communication. Our prototype implemented on commercial smartphones proves that our algorithm can quickly locate a group of mobile devices with centimeter-level accuracy

    Smart-antenna techniques for energy-efficient wireless sensor networks used in bridge structural health monitoring

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    Abstract: It is well known that wireless sensor networks differ from other computing platforms in that 1- they typically require a minimal amount of computing power at the nodes; 2- it is often desirable for sensor nodes to have drastically low power consumption. The main benefit of the this work is a substantial network life before batteries need to be replaced or, alternatively, the capacity to function off of modest environmental energy sources (energy harvesting). In the context of Structural Health Monitoring (SHM), battery replacement is particularly problematic since nodes can be in difficult to access locations. Furthermore, any intervention on a bridge may disrupt normal bridge operation, e.g. traffic may need to be halted. In this regard, switchbeam smart antennas in combination with wireless sensor networks (WSNs) have shown great potential in reducing implementation and maintenance costs of SHM systems. The main goal of implementing switch-beam smart antennas in our application is to reduce power consumption, by focusing the radiated energy only where it is needed. SHM systems capture the dynamic vibration information of a bridge structure in real-time in order to assess the health of the structure and to predict failures. Current SHM systems are based on piezoelectric patch sensors. In addition, the collection of data from the plurality of sensors distributed over the span of the bridge is typically performed through an expensive and bulky set of shielded wires which routes the information to a data sink at one end of the structure. The installation, maintenance and operational costs of such systems are extremely high due to high power consumption and the need for periodic maintenance. Wireless sensor networks represent an attractive alternative, in terms of cost, ease of maintenance, and power consumption. However, network lifetime in terms of node battery life must be very long (ideally 5–10 years) given the cost and hassle of manual intervention. In this context, the focus of this project is to reduce the global power consumption of the SHM system by implementing switched-beam smart antennas jointly with an optimized MAC layer. In the first part of the thesis, a sensor network platform for bridge SHM incorporating switched-beam antennas is modelled and simulated. where the main consideration is the joint optimization of beamforming parameters, MAC layer, and energy consumption. The simulation model, built within the Omnet++ network simulation framework, incorporates the energy consumption profiles of actual selected components (microcontroller, radio interface chip). The energy consumption and packet delivery ratio (PDR) of the network with switched-beam antennas is compared with an equivalent network based on omnidirectional antennas. In the second part of the thesis, this system model is leveraged to examine two distinct but interrelated aspects: Gallium Arsenide (GaAs) based solar energy harvesting and switched-beam antenna strategies. The main consideration here is the joint optimization of solar energy harvesting and switchedbeam directional antennas, where an equivalent network based on omnidirectional antennas acts as a baseline reference for comparison purposes.Il est bien connu que les rĂ©seaux de capteurs sans fils diffĂšrent des autres plateformes informatiques Ă©tant donnĂ© 1- qu’ils requiĂšrent typiquement une puissance de calcul minimale aux noeuds du rĂ©seau ; 2- qu’il est souvent dĂ©sirable que les noeuds capteurs aient une consommation d’énergie dramatiquement faible. La principale retombĂ©e de ce travail rĂ©side en la durĂ©e de vie allongĂ©e du rĂ©seau avant que les piles ne doivent ĂȘtre remplacĂ©es ou, alternativement, la capacitĂ© de fonctionner indĂ©finiment Ă  partir de modestes sources d’énergie ambiente (glĂąnage d’énergie). Dans le contexte du contrĂŽle de la santĂ© structurale (CSS), le remplacement de piles est particuliĂšrement problĂ©matique puisque les noeuds peuvent se trouver en des endroits difficiles d’accĂšs. De plus, toute intervention sur un pont implique une perturbation de l’opĂ©ration normale de la structure, par exemple un arrĂȘt du traffic. Dans ce contexte, les antennes intelligentes Ă  commutation de faisceau en combinaison avec les rĂ©seaux de capteurs sans fils ont dĂ©montrĂ© un grand potentiel pour rĂ©duire les coĂ»ts de rĂ©alisation et d’entretien de systĂšmes de CSS. L’objectif principal de l’intĂ©gration d’antennes Ă  commutation de faisceau dans notre application rĂ©side dans la rĂ©duction de la consommation Ă©nergĂ©tique, rĂ©alisĂ©e en concentrant l’énergie radiĂ©e uniquement lĂ  oĂč elle est nĂ©cessaire. Les systĂšmes de CSS capturent l’information dynamique de vibration d’une structure de pont en temps rĂ©el de maniĂšre Ă  Ă©valuer la santĂ© de la structure et prĂ©dire les failles. Les systĂšmes courants de CSS sont basĂ©s sur des senseurs piĂ©zoĂ©lectriques planaires. De plus, la collecte de donnĂ©es Ă  partir de la pluralitĂ© de senseurs distribuĂ©s sur l’étendue du pont est typiquement effectuĂ©e par le biais d’un ensemble coĂ»teux et encombrant de cĂąbles blindĂ©s qui vĂ©hiculent l’information jusqu’à un point de collecte Ă  une extremitĂ© de la structure. L’installation, l’entretien, et les coĂ»ts opĂ©rationnels de tels systĂšmes sont extrĂȘmement Ă©levĂ©s Ă©tant donnĂ© la consommation de puissance Ă©levĂ©e et le besoin d’entretien rĂ©gulier. Les rĂ©seaux de capteurs sans fils reprĂ©sentent une alternative attrayante, en termes de coĂ»t, facilitĂ© d’entretien et consommation Ă©nergĂ©tique. Toutefois, la vie de rĂ©seau en termes de la durĂ©e de vie des piles doit ĂȘtre trĂšs longue (idĂ©alement de 5 Ă  10 ans) Ă©tant donnĂ© le coĂ»t et les problĂšmes liĂ©s Ă  l’intervention manuelle. Dans ce contexte, ce projet se concentre sur la rĂ©duction de la consommation de puissance globale d’un systĂšme de CSS en y intĂ©grant des antennes intelligentes Ă  commutation de faisceau conjointement avec une couche d’accĂšs au mĂ©dium (couche MAC) optimisĂ©e. Dans la premiĂšre partie de la thĂšse, une plateforme de rĂ©seau de capteurs sans fils pour le CSS d’un pont incorporant des antennes Ă  commutation de faisceaux est modĂ©lisĂ© et simulĂ©, avec pour considĂ©ration principale l’optimisation des paramĂštres de sĂ©lection de faisceau, de la couche MAC et de la consommation d’énergie. Le modĂšle de simulation, construit dans le logiciel de simulation de rĂ©seaux Omnet++, incorpore les profils de consommation d’énergie de composants rĂ©els sĂ©lectionnĂ©s (microcontrĂŽleur, puce d’interface radio). La consommation d’énergie et le taux de livraison de paquets du rĂ©seau avec antennes Ă  commutation de faisceau est comparĂ© avec un rĂ©seau Ă©quivalent basĂ© sur des antennes omnidirectionnelles. Dans la deuxiĂšme partie de la thĂšse, le modĂšle systĂšme proposĂ© est mis Ă  contribution pour examiner deux aspects distrincts mais interreliĂ©s : le glĂąnage d’énergie Ă  partir de cellules solaire Ă  base d’arsĂ©niure de Gallium (GaAs) et les stratĂ©gies liĂ©es aux antennes Ă  commutation de faisceau. La considĂ©ration principale ici est l’optimisation conjointe du glĂąnage d’énergie et des antennes Ă  commutation de faisceau, en ayant pour base de comparaison un rĂ©seau Ă©quivalent Ă  base d’antennes omnidirectionnelles
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