186 research outputs found

    Improvement of strength and water absorption of Interlocking Compressed Earth Bricks (ICEB) with addition of Ureolytic Bacteria (UB)

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    Interlocking Compressed Earth Brick (ICEB) are cement stabilized soil bricks that allow for dry stacked construction. This characteristic resulted to faster the process of building walls and requires less skilled labour as the bricks are laid dry and lock into place. However there is plenty room for improving the interlocking bricks by increase its durability. Many studies have been conducted in order to improve the durability of bricks by using environmentally method. One of the methods is by introducing bacteria into bricks. Bacteria in brick induced calcite precipitation (calcite crystals) to cover the voids continuously. Ureolytic Bacteria (UB) was used in this study as a partial replacement of limestone water with percentage of 1%, 3% and 5%. Enrichment process was done in soil condition to ensure the survivability of UB in ICEB environment. This paper evaluates the effect of UB in improving the strength and water absorption properties of ICEB and microstructure analysis. The results show that addition of 5% UB in ICEB indicated positive results in improving the ICEB properties by 15.25% in strength, 14.72% in initial water absorption and 14.68% reduction in water absorption. Precipitation of calcium carbonate (CaCo3) in form of calcite can be distinguish clearly in microstructure analysis

    Cognitive routing models

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    This paper investigates the effect of introducing cognitive mechanisms in the routing module of a wireless network. A routing cost function that incorporates measurements of both internal network status and instantaneous behavior of external world is described. The proposed cost function is analyzed by simulation in the framework of IEEE 802.1.5.4a-like low data rate and low cost networks for mixed indoor/outdoor communications. The analysis focuses on the impact of MUI modeling on network performance. Results indicate that MUI-awareness, as provided by the proposed cognitive cost function, may improve network performance in terms of network lifetime. Based on this analysis, a mechanism for learning from previous routing decisions and adapting the routing cost function to MUI conditions is introduced

    Analysis of the IEEE 802.15.4a ultra wideband physical layer through wireless sensor network simulations in OMNET++

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    Wireless Sensor Networks are the main representative of pervasive computing in large-scale physical environments. These networks consist of a large number of small, wireless devices embedded in the physical world to be used for surveillance, environmental monitoring or other data capture, processing and transfer applications. Ultra wideband has emerged as one of the newest and most promising concepts for wireless technology. Considering all its advantages it seems a likely communication technology candidate for future wireless sensor networks. This paper considers the viability of ultra wideband technology in wireless sensor networks by employing an IEEE 802.15.4a low-rate ultra wideband physical layer model in the OMNET++ simulation environment. An elaborate investigation into the inner workings of the IEEE 802.15.4a UWB physical layer is performed. Simulation experiments are used to provide a detailed analysis of the performance of the IEEE 802.15.4a UWB physical layer over several communication distances. A proposal for a cognitive, adaptive communication approach to optimize for speed and distance is also presented. AFRIKAANS : Draadlose Sensor Netwerke is die hoof verteenwoordiger vir deurdringende rekenarisering in groot skaal fisiese omgewings. Hierdie tipe netwerke bestaan uit ’n groot aantal klein, draadlose apparate wat in die fisiese wĂȘreld ingesluit word vir die doel van bewaking, omgewings monitering en vele ander data opvang, verwerk en oordrag applikasies. Ultra wyeband het opgestaan as een van die nuutste en mees belowend konsepte vir draadlose kommunikasie tegnologie. As al die voordele van diĂ© kommunikasie tegnologie in ag geneem word, blyk dit om ’n baie goeie kandidaat te wees vir gebruik in toekomstige draadlose sensor netwerke. Hierdie verhandeling oorweeg die vatbaarheid van die gebruik van die ultra wyeband tegnologie in draadlose sensor netwerke deur ’n IEEE 802.15.4a lae-tempo ultra wyeband fisiese laag model in die OMNET++ simulasie omgewing toe te pas. ’n Breedvoerige ondersoek word geloots om die fyn binneste werking van die IEEE 802.15.4a UWB fisiese laag te verstaan. Simulasie eksperimente word gebruik om ’n meer gedetaileerde analiese omtrent die werkverrigting van die IEEE 802.15.4a UWB fisiese laag te verkry oor verskillende kommunikasie afstande. ’n Voorstel vir ’n omgewings bewuste, aanpasbare kommunikasie tegniek word bespreek met die doel om die spoed en afstand van kommunikasie te optimiseer.Dissertation (MEng)--University of Pretoria, 2011.Electrical, Electronic and Computer Engineeringunrestricte

    On the Trade-off Between Accuracy and Delay in Cooperative UWB Navigation

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    In ultra-wide bandwidth (UWB) cooperative navigation, nodes estimate their position by means of shared information. Such sharing has a direct impact on the position accuracy and medium access control (MAC) delay, which needs to be considered when designing UWB navigation systems. We investigate the interplay between UWB position accuracy and MAC delay for cooperative scenarios. We quantify this relation through fundamental lower bounds on position accuracy and MAC delay for arbitrary finite networks. Results show that the traditional ways to increase accuracy (e.g., increasing the number of anchors or the transmission power) as well as inter-node cooperation may lead to large MAC delays. We evaluate one method to mitigate these delays

    UWB Technology for WSN Applications

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    Ultra Low Power Communication Protocols for UWB Impulse Radio Wireless Sensor Networks

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    This thesis evaluates the potential of Ultra Wideband Impulse Radio for wireless sensor network applications. Wireless sensor networks are collections of small electronic devices composed of one or more sensors to acquire information on their environment, an energy source (typically a battery), a microcontroller to control the measurements, process the information and communicate with its peers, and a radio transceiver to enable these communications. They are used to regularly collect information within their deployment area, often for very long periods of time (up to several years). The large number of devices often considered, as well as the long deployment durations, makes any manual intervention complex and costly. Therefore, these networks must self-configure, and automatically adapt to changes in their electromagnetic environment (channel variations, interferers) and network topology modifications: some nodes may run out of energy, or suffer from a hardware failure. Ultra Wideband Impulse Radio is a novel wireless technology that, thanks to its extremely large bandwidth, is more robust to frequency dependent propagation effects. Its impulsional nature makes it robust to multipath fading, as the short duration of the pulses leads most multipath components to arrive isolated. This technology should also enable high precision ranging through time of flight measurements, and operate at ultra low power levels. The main challenge is to design a system that reaches the same or higher degree of energy savings as existing narrowband systems considering all the protocol layers. As these radios are not yet widely available, the first part of this thesis presents Maximum Pulse Amplitude Estimation, a novel approach to symbol-level modeling of UWB-IR systems that enabled us to implement the first network simulator of devices compatible with the UWB physical layer of the IEEE 802.15.4A standard for wireless sensor networks. In the second part of this thesis, WideMac, a novel ultra low power MAC protocol specifically designed for UWB-IR devices is presented. It uses asynchronous duty cycling of the radio transceiver to minimize the power consumption, combined with periodic beacon emissions so that devices can learn each other's wake-up patterns and exchange packets. After an analytical study of the protocol, the network simulation tool presented in the first part of the thesis is used to evaluate the performance of WideMac in a medical body area network application. It is compared to two narrowband and an FM-UWB solutions. The protocol stack parameters are optimized for each solution, and it is observed that WideMac combined to UWB-IR is a credible technology for such applications. Similar simulations, considering this time a static multi-hop network are performed. It is found that WideMac and UWB-IR perform as well as a mature and highly optimized narrowband solution (based on the WiseMAC ULP MAC protocol), despite the lack of clear channel assessment functionality on the UWB radio. The last part of this thesis studies analytically a dual mode MAC protocol named WideMac-High Availability. It combines the Ultra Low PowerWideMac with the higher performance Aloha protocol, so that ultra low power consumption and hence long deployment times can be combined with high performance low latency communications when required by the application. The potential of this scheme is quantified, and it is proposed to adapt it to narrowband radio transceivers by combining WiseMAC and CSMA under the name WiseMAC-HA

    Autonomous optimization of UWB link access

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    We present a novel approach for interference management in low data rate IR-UWB networks that enables concurrent transmissions at full power while allows each source to independently adapt its pulse rate (transmitted pulses per second) to mitigate multi-user interference. The work is motivated by the fact that the distributed adaptation of IR-UWB pulse rate has not been sufficiently addressed in the literature before. Existing approaches rely on the presence of a central authority or assume a definite receiver technique. Our approach enables users to share the communication medium in an efficient way compatible with individual QoS requirements and it is independent of any particular modulation scheme or receiver technique

    A Three-Tiered Architecture for Large-Scale Wireless Hospital Sensor Networks

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    International audienceThe Utra Wide Band physical layer specified by the IEEE 802.15.4a standard [1] presents numerous advantages comparing with its original IEEE 802.15.4 standard, namely high accuracy positioning ability, high data rate up to 27 mbps, extended communication range, low power consumption and low complexity. Actually, many research and development activities focus on the design of UWB sensor nodes entities. However nodes interactions or network configuration are neglected. For that, we propose in this paper to investigate the use of UWB for large scale Wireless Hospital Sensor Networks (WHSNs) to benefit from the advantages offered by the UWB technology. This evolving networking paradigm promises to revolutionize healthcare by allowing inexpensive, non-invasive, pervasive and ubiquitous, ambulatory health monitoring. We present the design of new system architecture, based on IEEE 802.15.4a compliant sensors, suitable for health monitoring application in high dense hospital environment. The proposed system architecture is intended to support large-scale deployment and to improve the network performance in terms of energy efficiency, real-time guarantees and Quality-of-Service (QoS)
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