The Holes Problem in Wireless Sensor Networks

Several anomalies can occur in wireless sensor networks that impair their desired functionalities i.e., sensing and communication. Different kinds of holes can form in such networks creating geographically correlated problem areas such as coverage holes, routing holes, jamming holes, sink/black holes and worm holes, etc. We detail in this paper different types of holes, discuss their characteristics and study their effects on successful working of a sensor network. We present state-of-the-art in research for addressing the holes related problems in wireless sensor networks and discuss the relative strengths and short-comings of the proposed solutions for combating different kinds of holes. We conclude by highlighting future research directions.

The recent advances in the MEMS (Micro-ElectroMechanical Systems) technology has augmented research in wireless sensor networks. A wireless sensor network is composed of tiny sensor nodes each capable of sensing some phenomenon, doing some limited data processing and communicating with each other . These tiny sensor nodes are deployed in the target field in large numbers and they collaborate to form an adhoc network capable of reporting the phenomenon to a data collection point called sink or base station. These networked sensors have many potential civil and military applications i.e., they can be utilized for object tracking, intrusion detection, habitat and other environmental monitoring, disaster recovery, hazard and structural monitoring, traffic control, inventory management in factory environment and health related applications etc. [2], [3]. These myriad of applications present various design, operational, and management challenges for wireless sensor networks. The challenges become even more demanding if we consider the constraints of wireless sensor networks such as low processing power and bandwidth, limited battery life, and short radio ranges. Wireless sensor networks differ from ad-hoc networks in several ways. One of the distinguishing features is the introduction of the sensing component in sensor networks. A node in a sensor network is thus performing two demanding tasks simultaneously, sensing and communicating. To accomplish these NICTA is funded through the Australian Government’s Backing Australia’s Ability initiative, in part through the Australian Research Council tasks, we normally assume that the node not only performs required sensing of the phenomenon but is also able to communicate with neighbors for onward transmission of the sensed data to sink. But this assumption is often not true in real world deployment scenarios. Several anomalies can occur in the wireless sensor network that can impair their functionality. The target field that is supposed to be 100% covered by the densly deployed nodes may have coverage holes, areas not covered by any node, due to random aerial deployment creating voids, presence of obstructions, and, more likely, node failures etc. Similarly, nodes may not be able to communicate correctly if routing holes, areas devoid of any nodes, exist in the deployed topology. Thus the network fails to achieve its objectives if some of the nodes cannot sense or report the sensed data. Some of these anomalies may be deliberately created by adversaries that are trying to avoid the sensor network. These malicious nodes can jam the communication to form jamming holes or they can overwhelm regions in the sensor network by denial of service attacks such as sink/black/worm holes to hinder their operation normally based on trus

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