Dazhi Chen

A survey of void handling techniques for geographic routing in wireless networks

Communications voids, where geographic greedy forwarding fails to move a packet further towards its destination, are an important issue for geographic routing in wireless networks. This article presents an overview of the void problem and surveys the currently available void-handling techniques (as of July 2006) for geographic routing. In the survey, we classify these void-handling techniques into six categories, each designed with a different approach, that is, planar-graph-based, geometric, flooding-based, costbased, heuristic, and hybrid. For each category, we present its basic principle and illustrate some classic techniques as well as the latest advances. We also provide a qualitative comparison of these techniques and discuss some possible directions of future research.

Selection of a Forwarding Area for Contention-Based Geographic Forwarding in Wireless Multi-Hop Networks

Contention-based geographic forwarding (CGF) is a state-free forwarding technique. In this paper, we develop a general analytical framework to evaluate the performance of CGF with different forwarding areas in wireless multi-hop networks. In particular, we compare the performance of CGF for three typical forwarding areas, analytically and by extensive simulations. We further investigate the impact of several important assumptions on our analytical results. Our study provides guidelines regarding the selection of a specific forwarding area during the design phase of a CGF protocol. It also serves as a general performance evaluation framework for CGF protocols as well as traditional geographic forwarding protocols.

On-demand Geographic Forwarding for data delivery in wireless sensor networks

A purely on-demand network protocol, called On-demand Geographic Forwarding (OGF), is proposed for data delivery in large-scale and resource-constrained static wireless sensor networks with unreliable sensors. OGF is a cross-layer protocol that employs (i) an explicit contention scheme to establish a next-hop node in a distributed fashion, (ii) a simple scheme using a forwarding table to maintain the learned next-hop information, and (iii) a novel partial source routing scheme to handle communication voids. The operation of our protocol is based on the actual demands of the application, data traffic, and network dynamics. Packet-level simulations show that OGF exhibits a superior performance in terms of energy consumption, scalability, and void handling. Our study demonstrates that OGF is viable for efficient data delivery in the targeted sensor networks.

A state-free data delivery protocol for multihop wireless sensor networks

A novel, state-free, and competition-based data delivery protocol, called state-free implicit forwarding (SIF), is proposed for multihop wireless sensor networks. The SIF protocol assumes moderate node density and distance-to-sink awareness. The state-free feature of SIF makes it robust to high network dynamics. SIF also combines the tasks of routing and MAC, via cross-layer design, to simplify the complexity of the protocol stack in sensors and to save precious network resources. Simulation results are presented to show that SIF performs better than some previously proposed protocols for data delivery in terms of communication overhead, packet delivery ratio, and average packet delay.

On the forwarding area of contention-based geographic forwarding for ad hoc and sensor networks

Contention-based Geographic Forwarding (CGF) is a state-free communication paradigm for information delivery in multihop ad hoc and sensor networks. Ap rioriselection of the forwarding area impacts its overall network performance and the design of the CGF protocol as well. In this work, we study the fundamental problem of defining the forwarding area ap riorifor CGF and determine its impact on the performance. We model CGF without void (i.e., absence of a next-hop node in the forwarding area) handling as a 3-step forwarding strategy. Based on this model and given a random distribution of network nodes, we develop a general mathematical analysis technique to evaluate the performance of CGF with different forwarding areas, in terms of the performance metric average single-hop packet progress. Further, we introduce two state-free void handling schemes, i.e., active exploration and passive participation, for CGF and study their performance in depth. Our theoretical analysis and numerically evaluated results, validated by extensive simulations, provide a guideline regarding the selection of specific forwarding areas for the design of a practical CGF protocol. It also serves as a general performance evaluation framework for the existing CGF protocols.

Distributed in-network path planning for sensor network navigation in dynamic hazardous environments

Wireless sensor networks can be employed to provide distributed real-time navigation instructions to users attempting to travel in hazardous environments. In this work, we propose a distributed path planning algorithm for sensor network navigation in dynamic hazardous environments. Using geographic or virtual coordinates of sensors and based on a partial reversal method for directed acyclic graphs (DAG), our algorithm constructs a distributed in-network directed navigation graph, where each source sensor is guaranteed to have at least one desired directed path to one destination sensor. When the hazardous environment changes due to its dynamic nature, path replanning does not need to reconfigure most of the directed links in the graph unaffected by the changes. Correctness of our algorithm is proved and extensive simulation results demonstrate that the constructed navigation graph provides near-optimal navigation paths for users, successfully adapts to dynamic hazardous environments, and requires very low communication overhead for maintenance, when compared to other navigation graphs constructed by existing algorithms that use frequent or periodic flooding. Copyright

Geographic Routing in Wireless Ad Hoc Networks

Geographic routing has become an efficient solution for communications and information delivery in wireless ad hoc networks where the position information of nodes is available. This chapter provides a comprehensive overview of basic principles, classical techniques, as well as latest advances in geographic routing. The chapter first presents in detail the topic of geographic unicast routing, where the presentation is focused on two operation modes of geographic forwarding, that is, greedy forwarding and void handling. The chapter also briefly introduces three advanced topics in geographic routing: geographic multicast, geocast, and trajectory-based forwarding. Finally, the chapter makes some comments on the practical aspects of geographic routing for practitioners and discusses the directions for further research with a list of open issues in the area of geographic routing.

In-network path planning for distributed sensor network navigation in dynamic environments

We propose a set of distributed algorithms for in-network path planning that enables a distributed sensor network navigation service in dynamic environments. Different from existing algorithms that use frequent or periodic flooding, our algorithms exploit geographic information of sensors to construct and maintain navigation links. Based on a partial reversal method of directed acyclic graphs, our algorithms ensure that each source sensor has at least one safe navigation path to one of the multiple destination sensors.