research activities in 2007 - CSEM

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Exploiting Directive Antennas for Wireless Sensor Networks L. von Allmen, P. Dallemagne, Q. Xu, J. R. Farserotu CSEM identified and characterized a number of applications using wireless sensor networks that would benefit from directive antennas. The goal is to reduce the power consumption of the communication system, while preserving or even improving the quality of service. CSEM is investigating energy saving techniques using directive antennas for wireless communication devices [1] in specific applications. The use of directive antennas offers the potential for improved overall system performance. For example, one measure of performance is the environmental impact of the radio-communication system, which may be reduced by lowering the emissions, which in turn translates into power savings, as well as, improved coexistence. Further, the use of directive antennas offers the potential for reducing the overall power consumption of the communication system; especially, in high density networks, where the number of transmitting devices can be large. Reducing the radiated power also improves spatial re-use, global reduction of the electro-smog and implicit improvement of the end user privacy by focusing and segmentation. Ultimately, this relates to the broadening of the concept of quality of service by involving factors like environmental-friendliness, compliance to more stringent standards – related to communication as well as safety – and operational conditions, or even transparency to the user. In radio communication systems, energy may be wasted in the following situations, some of which directional antennas can help mitigate: Idle listening − A node is turning on its radio to listen, but there is no transmitter in the receiving range. Directional antennas do not bring a solution to idle listening. In fact this could even make the situation worse if there is no way to change the beam orientation when the antenna is incorrectly oriented (pointing to an area without nodes). “Crying in the wilderness” − A node is sending when there is no destination present. This cannot be solved by smart antennas. Overhearing − A node receives a radio signal but the content is not addressed to it. In this case smart antennas will reduce overhearing. Collisions − Smart antennas could offer an improvement in the case where collisions occur between traffic from pair-wise communications; i.e. the traffic between A and B is in collision with the traffic between C and D. With directive antennas, the benefitt is due to improved spatial usage. Range − To reach long range requires more energy than short distance to transmit information with the same quality. In this situation, adaptable directive antennas, in combination with a suitable MAC protocol, can enhance performance by concentrating the energy in the direction of the destination. As such, for the same radio energy consumption, radio directional antennas yield a longer range. Potential applications that can benefit from using directional antennas are (names are taken from the terminology defined in the IST project e-SENSE): • Wireless hospital • Sub-network interconnection • Store of the future • Entertainment In order to identify applications that would benefit from directive antennas, the study considered the scenarios (see Figure°1) elaborated within the e-SENSE project. Figure 1: Application spaces, Use Cases, Applications and Scenarios within e-SENSE Each scenario has been analyzed with regards to the applicability and potential benefits of using directional antennas. The analysis highlighted for instance that scenarios involving mobility during communication are difficult if not impossible to benefit from directional antennas. However, the use of directional and automatically reconfigurable (smart) antennas would help in this regard. The analysis has also shown that in applications where directional antennas add benefits, the main benefits expected are: • Energy use improvement on both terminal and base • Spatial reuse and system capacity improvement • Extension of range Another point linked to the use of directional antennas is the need for dedicated or modified MAC (Medium Access Control) protocols (i.e., for adaptation and control of directivity). The study added a review of the state of the art and a classification of MAC protocols using directional antennas. This work classifies the typical MAC protocol algorithms with respect to the constraints and specifics brought by directional antennas, so that the most adequate algorithm can be chosen given the application properties. This work was partly funded by IST project e-SENSE. CSEM thanks them for their support. [1] Q. Xu, et al., “UWB Antenna with Improved Bandwidth and Spatial Diversity using RF-MEMS Switches”, in this report, page 80 83
A MAC Protocol for UWB-IR Wireless Sensor Networks J. Rousselot, A. El-Hoiydi, J.-D. Decotignie WideMac, a novel MAC protocol designed for wireless sensor networks using ultra wide band impulse radio transceivers, is compared with state of the art low power protocols. It compares favourably with the best while offering additional services such as rapid discovery of neighbors and positioning. These features are of high interest for distributed routing and for mobility enabled networks. Furthermore, contrary to the best known protocols, it operates without requiring special modulation types. Wireless sensor networks (WSN) are collections of small electronic devices which communicate together wirelessly and are equipped with one or more sensors, whose choice depends on the application domain. They are often deployed in environmental monitoring scenarios and must be able to run on battery for months or years. The management of the radio transceiver performed by the Medium Access Control protocol has an important impact on power consumption. Ultra Wide Band Impulse Radio (UWB-IR) is a communication technique based on a time-domain approach. It offers robustness to multipath propagation and to multi user interference and allows accurate ranging. These properties, associated with ultra low power consumption, make UWB-IR a good candidate for WSN platforms. Numerous low power Medium Access Control (MAC) protocols for WSN have been proposed in the last few years. All attempt to reduce four sources of energy waste: collisions, overhearing, idle listening and overhead. Introducing an UWB- IR physical layer has an impact on MAC protocol power consumption and may even make some implementations unusables. For example, the detection of an ongoing transmission poses challenges with respect to implementation with a UWB-IR radio. The best low-power MAC protocols therefore require a modification of the UWB-IR modulation to enable effective operation. Figure 1: WideMac operation WideMac is a novel MAC protocol designed specifically for UWB-IR sensor networks. It operates as follows: each node periodically transmits a beacon message announcing its presence, and then listens for a brief period of time to detect any incoming transmission. A node with a message to transmit first listens until it receives the beacon of the destination node, after which it can safely transmit the message. The next time a message must be exchanged between the two nodes, the time spent listening for the beacon message can be greatly reduced because the destination wake up time will be known. Figure 1 illustrates the operation principle of WideMac. WideMac power consumption was compared with state of the art WSN MAC protocols (WiseMac and optimal preamble sampling, SCP-Mac, Crankshaft) using mathematical models. The results presented in Figure 2 show that WideMac was able to match the performance of the best known protocols. 84 Remarkably, it is the only one to reach this efficiency without a modification of the modulation scheme. Figure 2: WideMac power consumption WideMac also offers unique additional capabilities such as rapid discovery of neighbours, ranging and positioning. This is of special interest for distributed networks which require ad hoc routing, and for mobility enabled networks such as large scale environmental monitoring, herd control, vehicles tracking, warehouse inventory or elderly care.
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CONTENTS PREFACE 5 RESEARCH ACTIVIT
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PREFACE Dear Reader, In this report
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TissueOptics - Portable SpO2 Monito
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Counterfeit - Machine Readable Cove
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ArrayFM - An Atomic Force Microscop
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Encoder - Nanometric Optical Absolu
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PackTime - Zero-Level Packaging of
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TissueOptics - Portable SpO2 Monito
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spectrometer applications so CSEM h
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As a first step, CSEM is building s
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Data Fusion for Wireless Distribute
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A High-Performance 2.4 GHz RF Front
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Quasi-Harmonic Quadrature CMOS Rela
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icycam, a System-On Chip (SoC) for
Page 34 and 35: PHOTONICS Nicolas Blanc The Photoni
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