No description available.

Emerging body-wearable sensor devices for continuous health monitoring are severely energy constrained and yet required to offer high communication reliability under fluctuating channel conditions. This thesis aims at investigating the opportunities and challenges in the use of dynamic radio transmit power control for prolonging the lifetime of such devices. We first present extensive empirical evidence that the wireless link quality can change rapidly in body area networks, and a fixed transmit power results in either wasted energy (when the link is good) or low reliability (when the link is bad). We then propose a class of schemes feasible for practical implementation that adapt transmit power in real-time based on feedback information from the receiver. We show conservative, balanced, and aggressive adaptations of our scheme that progressively achieve higher energy savings of 14%-30% in exchange for higher potential packet losses (up to 10%). We also provide guidelines on how the parameters can be tuned to achieve the desired trade-off between energy savings and reliability within the chosen operating environment. Finally, we implement and profile our scheme on a MicaZ mote based platform, demonstrating that energy savings are achievable even with imperfect feedback information, and report preliminary results on the ultra-low-power integrated healthcare monitoring platform from our collaborating partner Toumaz Technology. In conclusion, our work shows adaptive radio transmit power control as a low-cost way of extending the battery-life of severely energy constrained body wearable devices, and opens the door to further optimizations customized for specific deployment scenarios.

Emerging body-wearable sensor devices for continuous health monitoring are severely energy constrained and yet required to offer high communication reliability under fluctuating channel conditions. This thesis aims at investigating the opportunities and challenges in the use of dynamic radio transmit power control for prolonging the lifetime of such devices. We first present extensive empirical evidence that the wireless link quality can change rapidly in body area networks, and a fixed transmit power results in either wasted energy (when the link is good) or low reliability (when the link is bad). We then propose a class of schemes feasible for practical implementation that adapt transmit power in real-time based on feedback information from the receiver. We show conservative, balanced, and aggressive adaptations of our scheme that progressively achieve higher energy savings of 14%-30% in exchange for higher potential packet losses (up to 10%). We also provide guidelines on how the parameters can be tuned to achieve the desired trade-off between energy savings and reliability within the chosen operating environment. Finally, we implement and profile our scheme on a MicaZ mote based platform, demonstrating that energy savings are achievable even with imperfect feedback information, and report preliminary results on the ultra-low-power integrated healthcare monitoring platform from our collaborating partner Toumaz Technology. In conclusion, our work shows adaptive radio transmit power control as a low-cost way of extending the battery-life of severely energy constrained body wearable devices, and opens the door to further optimizations customized for specific deployment scenarios.

Wireless Sensor Networks (WSNs) consist of Sensor Nodes (SNs) spatially removed from one another, that can monitor a variety of environmental conditions. SNs then collaboratively communicate the collected information to a central location, by passing along the data in a multi-hop fashion. SN energy resources are limited and energy monitoring and preservation in WSNs are therefore very important. Since multi-hop communication takes place, the routing protocol used may have a significant effect on the balanced use and preservation of energy in the WSN. A significant amount of research has been performed on energy efficient routing in WSNs, but the majority of these studies were only implemented in simulation. The simulation engines used to perform these studies do not take into account all of the relevant environmental factors affecting energy efficiency. In order to comment on the feasibility of a routing protocol meant to improve the energy efficiency of a WSN, it is important to test the routing scheme in a realistic environment. In this study, a SN specifically designed to be used in an energy consumption ascertaining WSN testbed was developed. This SN has a unique set of features which makes it ideal for this application. Each SN is capable of recording its own power consumption. The design also features a lithium battery charging circuit which improves the reusability of the SN. Each node has a detachable sensor module and transceiver module which enables the researcher to conduct experiments using various transceivers and sensors. Twenty of these SNs were then used to form an energy consumption ascertaining WSN testbed. This testbed was used to compare the energy consumption of a Minimum Total Transmission Power Routing (MTTPR) scheme to a shortest hop path routing scheme. The results show that each SN’s transmission power setting dependant efficiency has a significant effect on the overall performance of the MTTPR scheme. The MTTPR scheme might in some cases use more energy than a shortest hop path routing scheme because the transmission power setting dependant efficiency of the transceiver is not taken into account. The MTTPR scheme as well as other similar routing schemes can be improved by taking the transceiver efficiency at different transmission power settings into account. Simulation environments used to evaluate these routing schemes can also be improved by considering the transceiver efficiency at different transmission power settings. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

Wireless Sensor Networks (WSNs) consist of Sensor Nodes (SNs) spatially removed from one another, that can monitor a variety of environmental conditions. SNs then collaboratively communicate the collected information to a central location, by passing along the data in a multi-hop fashion. SN energy resources are limited and energy monitoring and preservation in WSNs are therefore very important. Since multi-hop communication takes place, the routing protocol used may have a significant effect on the balanced use and preservation of energy in the WSN. A significant amount of research has been performed on energy efficient routing in WSNs, but the majority of these studies were only implemented in simulation. The simulation engines used to perform these studies do not take into account all of the relevant environmental factors affecting energy efficiency. In order to comment on the feasibility of a routing protocol meant to improve the energy efficiency of a WSN, it is important to test the routing scheme in a realistic environment. In this study, a SN specifically designed to be used in an energy consumption ascertaining WSN testbed was developed. This SN has a unique set of features which makes it ideal for this application. Each SN is capable of recording its own power consumption. The design also features a lithium battery charging circuit which improves the reusability of the SN. Each node has a detachable sensor module and transceiver module which enables the researcher to conduct experiments using various transceivers and sensors. Twenty of these SNs were then used to form an energy consumption ascertaining WSN testbed. This testbed was used to compare the energy consumption of a Minimum Total Transmission Power Routing (MTTPR) scheme to a shortest hop path routing scheme. The results show that each SN’s transmission power setting dependant efficiency has a significant effect on the overall performance of the MTTPR scheme. The MTTPR scheme might in some cases use more energy than a shortest hop path routing scheme because the transmission power setting dependant efficiency of the transceiver is not taken into account. The MTTPR scheme as well as other similar routing schemes can be improved by taking the transceiver efficiency at different transmission power settings into account. Simulation environments used to evaluate these routing schemes can also be improved by considering the transceiver efficiency at different transmission power settings. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

As redes de sensores sem fio (wsns) têm ganhado cada vez mais espaço no monitoramento e controle de processos na indústria. Dentro destas redes, os dispositivos são alimentados por baterias, e a comunicação é feita por radiofrequência. Por conta disto, os rádios dos dispositivos são responsáveis por consumir boa parte da energia armazenada nas suas baterias, e a comunicação dos dispositivos está sujeita à interferência provinda de outras redes e do maquinário industrial. Para sanar estes problemas podem ser empregadas técnicas de controle de potência de transmissão (cpt). Existem diversas técnicas de cpt na literatura, visando os mais diversos objetivos, desde economia de energia e redução de interferência, até controle da topologia da rede. Este trabalho apresenta uma proposta de emprego de (cpt) em uma rede de sensores sem fio através da utilização de controladores proporcionais-integrais (pi). Juntamente com a técnica proposta, são apresentados um procedimento para projeto dos controladores e alguns algoritmos desenvolvidos para o caso ideal e para os casos com saturação dos níveis de potência disponíveis. Este trabalho se diferencia dos trabalhos encontrados na literatura por apresentar uma técnica de controle linear e que depende apenas de informações já disponíveis em cada dispositivo cuja potência será ajustada. Deste modo, esta técnica pode ser empregada em conjunto com protocolos industriais mais restritivos quanto às informações que podem ser trocadas nas mensagens. Além disso, esta técnica reduz ainda mais o consumo e a interferência por evitar transmissões desnecessárias. A proposta apresentada foi validada através de simulações e de um experimento com dispositivos WirelessHART reais, apresentando bons resultados e provando que é possível controlar a potência sem a necessidade das informações extras. / Wireless sensor networks (wsns) are being increasingly adopted in monitor and control tasks in the industry. The devices within these networks are battery-powered, and they communicate through radio frequency. Therefore the radios of the devices account for the most of the consumption of the energy stored in the batteries, and the devices’ communication is subject to interference from other networks and industrial machinery. Transmission power control (tpc) techniques can be employed to cope with these problems. There are several tpc techniques in the literature, aiming at a wide range of objectives, from energy saving and interference reduction, to network topology control. This work presents the proposal of a (tpc) technique in a wireless sensor network that works by employing proportional-integral (pi) controllers. Besides the technique itself, a procedure is presented to design the controllers along some algorithms developed to the ideal case, and the case when there is saturation in the available power levels. This work, unlike the other works found in the literature, presents a linear technique that depends only on information that is already available in each device whose power needs to be adjusted. Therefore, the proposed technique can be employed together with more restrictive industrial protocols that limit the information that can be exchanged in the messages. Besides, it further reduces the power consumption and the interference by avoiding unnecessary transmissions. The proposal was validated through simulations and an experiment using real WirelessHART devices, presenting good results and proving that it is possible to adjust the transmission power without necessarily using the extra information.

The standard IEEE 802.11 MAC protocol assumes that each mobile host uses maximum transmission power for the transmission of each packet. However, energy is very valuable resources for mobile host in ad hoc wireless network. In the past, several researches about power control were proposed. These power control schemes use different power levels and one more separate power control channel in order to save energy, avoid occurrence of collision, and increase network channel utilization. But various power levels lead to each mobile host having different transmission power ranges, and cause the additional hidden terminal problem, namely heterogeneous power terminal problem. Therefore, in this paper, we propose a simple and efficient power control protocol that used dynamic adjustment transmission power ranges to reduce power consumption, avoid collision, increase the network channel utilization, and ease heterogeneous power terminal problem as well.

No description available.

The objective of the research is to develop a cost-effective, dynamic grid controller called the controllable network transformer (CNT) that can be implemented by augmenting existing load tap changing (LTC) transformers with an AC-AC converter. The concept is based on using a fractionally rated direct AC-AC converter to control the power through an existing passive LTC. By using a modulation strategy based on virtual quadrature sources (VQS), it is possible to control both the magnitude and the phase angle of the output voltage of the CNT without having any inter-phase connections. The CNT architecture has many advantages over existing power flow controllers, like absence of low frequency storage, fractional converter rating, retro-fitting existing assets and independent per-phase operation making it potentially attractive for utility applications. The independent control of the magnitude and the phase angle of the output voltage allow independent real and reactive power flow control through the CNT-controlled line. In a meshed network with asymmetric network stresses this functionality can be used to redirect power from critically loaded assets to other relatively under-utilized parallel paths. The power flow controllability of CNT can thus be used to lower the overall cost of generation of power. The solid state switches in the CNT with fast response capability enable incorporation of various additional critical functionalities like grid fault ride through, bypassing internal faults and dynamic damping. This bouquet of features makes the CNT useful under both steady state and transient conditions without compromising the grid reliability.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 41-44).