The use of wireless ad hoc and sensor networks is steadily increasing from general networking applications to more specialised areas such as environmental monitoring, health care, logistics, military and surveillance. Theory, design and deployment of those networks are subject to many constraints and challenges, most of which differ from those encountered in traditional wired networks. These challenges are addressed through efforts of many research groups from both academia and industry all around the world, and many conferences and symposia are devoted to the presentation and dissemination of their research results.
One of such conferences is the highly successful series of workshops on Wireless Ad hoc and Sensor Networks (WWASN) held in conjunction with previous ICDCS conferences in Providence, RI; Tokyo, Japan; Columbus, OH; Lisbon, Portugal; Toronto, ON; Beijing, China; and, most recently, Montreal, Canada. The Sixth International Workshop on Ad hoc and Sensor Wireless Networks (WWASN2009), held in Montreal on June 2009, has attracted no less than 37 paper submissions, out of which a total of 18 were selected for presentation at the workshop. While the acceptance rate has remained more or less at the same level over the years, the quality of submitted papers has steadily increased. We have also noticed that, while the well-established areas of topology, routing and performance still attract a lot of attention, an increasing number of papers dealt with emerging areas of energy efficiency, security, underwater/medical sensor networks, opportunistic spectrum access and data caching and storage in ad hoc and sensor networks. The scope and number of submissions indicate that the field of wireless ad hoc and sensor networks is alive and healthy and that research-oriented workshops such as this one are the primary outlet needed to disseminate the latest advances in the state of the art in modelling, design and deployment of such networks.
Extended versions of five of the best papers from the workshop are presented in this special issue.
The first paper, by Akkaya, Guneydas and Bicak, deals with sensor–actor network in which sensors and actors collaborate to facilitate autonomous actor positioning and thus reduce the need for human intervention or eliminate it altogether. The paper presents a location-matching algorithm that assigns actors to appropriate clusterheads with the goal of minimising both message overhead (born by the sensors) and travel distance of individual actors. Simulation results show that the proposed approach can give satisfactory results with very little overhead, while not requiring centralised control and knowledge of all actor and clusterhead positions.
The paper by Li focuses on multihop wireless networks with multiple channels and attempts to solve the transmission time minimisation problem. While the problem itself is NP-hard, a number of heuristic algorithms that approach the lower bound of the minimum transmission time are described and analysed. The performance of proposed algorithms for undirected networks is significantly better than the pipelined breadth-first search tree algorithm that is commonly used, mostly on account of exploiting more transmission concurrency.
The third paper, by Du, Kranakis and Nayak, describes a novel geometric localised routing protocol in disruption- or delay-tolerant networks. Local distributed solutions to extract spanning trees from local Delaunay triangulation graphs are described which allow packet delivery with high probability and very low delay, while requiring less storage on each intermediate node than comparable protocols, including the ubiquitous epidemic routing protocol.
The paper by Raman and Gupta provides an overview of several broadcast mechanisms in wireless sensor networks, covering the well-known approaches such as flooding, site and bond percolation and others. Different network topologies, including random, grid and clustered ones, are considered. The results show that flooding has the lowest latency but consumes the most energy, whereas site percolation offers improved performance, especially energy wise, in some important special cases.
The last paper, by Zhuang, Pan and Wu, deals with clustering techniques in order to accommodate limited resources – in particular, limited onboard energy supply – of wireless sensor motes. An energy-optimal grid clustering techniques is proposed, and its performance with respect to energy efficiency, network lifetime, data aggregation and other relevant parameters is evaluated. Furthermore, a randomised technique for extending the network lifetime is proposed and evaluated.
Overall, the papers presented here demonstrate the breadth and diversity of research in the field of wireless ad hoc and sensor network. We wish to thank both authors and reviewers for their hard work and the effort they have invested in producing this special issue. We would also like to express our sincere gratitude to the Editor-in-Chief, Professor Ivan Stojmenovic and the Editorial Staff at the Taylor & Francis Group for giving us this opportunity and for their continuous support and professionalism.