Improving Multi-storey Building Sensor Network with an External Hub

Abstract

Abstract —Monitoring and automatic control of building environ-ment is a crucial application of Wireless Sensor Network (WSN)in which maximizing network lifetime is a key challenge. Previousresearch into the performance of a network in a building environmenthas been concerned with radio propagation within a single floor. Weinvestigate the link quality distribution to obtain full coverage ofsignal strength in a four-storey building environment, experimentally.Our results indicate that the transitional region is of particular concernin wireless sensor network since it accommodates high varianceunreliable links. The transitional region in a multi-storey buildingis mainly due to the presence of reinforced concrete slabs at eachstorey and the fac¸ade which obstructs the radio signal and introducesan additional absorption term to the path loss. Keywords —Wireless sensor networks, radio propagation, buildingmonitoring I. I NTRODUCTION T ODAY environmental monitoring is considered as one ofthe principle application for sensor networks [16]. Oneof the earliest known civil applications of sensor networksis in ecological habitat monitoring. A team from Universityof California Berkeley [14], [17], [18] used a wireless sensornetwork to observe birds on an island, using a base stationconnected over the web via a satellite communication link.This kind of “unattended” monitoring minimizes disruption tothe objects of study by an observer walking around the islandto collect data.A sensor network is a computer network of many, spatiallydistributed devices using sensors to monitor conditions atdifferent locations, such as temperature, sound, vibration,pressure, motion or pollutants. Usually these devices are smalland inexpensive, so that they can be produced and deployedin large numbers, and so their resources in terms of energy,memory, computational speed and bandwidth are severelyconstrained. Various research problems of sensor networkssuch as data aggregation or fusion [3], [4], packet size optimi-sation [15], cluster formation [6], [7], target localisation [21],battery management [5], network protocols [10], [11], [19]are discussed in the literature with respect to crucial energylimitations. Efficient battery management for sensor lifetime[5] and guidelines for efficient and reliable sensor networkdesign is investigated in [8]. Commercial radio technologyhas advanced and commercial standards such as Bluetooth,developed by the Bluetooth consortium [1], have started toappear. Ad hoc networks have been gaining popularity formilitary, space, biomedical and manufacturing applicationsin recent years because their easy deployment and lack ofinfrastructure requirements. Unlike cellular wireless networks,adhocwireless networksdonot needanyfixedcommunicationinfrastructure. Three main networking protocols are knownin wireless communications: direct communication, multi-hopcommunication and clustering. The routes can be single ormulti-hop and the nodes which may be heterogeneous andcommunicate via packet radio. The heterogeneity of the nodeswould allow some nodes to be servers and others to beclients. The ability of an ad hoc node to act as a serveror service provider will depend on its energy, memory andcomputational capacities. Each node should estimate its ownbattery life before committing to a task. Even relaying packetsfor others may result in deteriorating its own limited batterypower, and the node may not accept the task when it isdevoted to another important activity. There is a fundamental,incompatiblefeatures between computersimulation and exper-imental evaluation of sensor networks. On one hand, computersimulations provide complete control and transparent intoexperiments, but, on the other hand, they cannot reproduce,trustworthy, all the parameters that affect a live system [16].In this paper, we performed experimental study to investi-gate link quality distribution in sensor network deployment forbuilding environment. This experiment will leverage queriesin real sensor network and also will drive development ofnetwork architecture. Both man-made hazards such as crimeand terrorism as well as natural hazards such as earthquakes,tsunamis and winds can cause damages to building. Sensornetworks can be effectively used to reduce the impact ofsuch hazards through early detection. Therefore, monitoringand automatic control of building environment is a crucialapplication of Wireless Sensor Network (WSN) in whichmaximizing network lifetime is a key challenge. We havepreviously investigated the link quality distribution to obtainfull coverage of signal strength in a single floor of buildingenvironment. Our results confirmed the transitional region isparticular concern in wireless sensor network since it accom-modates high variance unreliable links. The reason due to thistransitional region in inside building environment could bethe obstacles including concrete/brick walls, partitions, officefurniture and other items affect as additional absorption termto the path loss. We now extend the experimental work toexplore the performance of a sensor network that is deployedinto a four-storey building with a network hub located at mid-height on an adjacent building. This configuration allows the