Shiow-Fen Hwang

A study of recent research trends and experimental guidelines in mobile ad-hoc network

This work investigates and analyzes recent research trends and presents experimental guidelines on MANETs. More than 1,300 MANET related papers in IEEE/IEE Electronic Library (IEL Online) from 1998 to 2003 were collected and surveyed. The research trends, qualitative analysis and simulation guidelines from fifteen major MANET issues are investigated to assist the user in conducting MANET research. Based on recent six year trends we found that some issues such as routing and power management attracted much attention. We also found that some issues have potential study value, such as IP addressing and fault tolerance. In the qualitative analysis, we found that some factors such as scalability, stability, and reliability attracted much attention in major MANET issues. The essential simulation metrics for various MANET issues are identified and listed for experimental guidelines. The analysis results demonstrate the utilization trends for various MANET simulators.

An efficient multi-source multicast routing protocol in mobile ad hoc networks

Mobile ad hoc networks are organized by a collection of wireless devices. Any pre-established wired or wireless infrastructure or centralized administration is unnecessary. Thus, ad hoc wireless networks are particularly useful in regions such as battle-fields or disaster areas. There are numerous applications, such as video conferencing, distance learning and video on-demand relay on multicast routing. Most existing multicast routing protocols in ad hoc networks consider only one source in a multicast group, resulting in large overhead when the system is extended to multi-source multicasting. In this paper, we propose a cluster-based multi-source multicast routing protocol to provide efficient multicasting in the multi-source multicast environment. Simulation results show that the proposed protocol generates low overhead without dropping the delivery ratio in the multi-source multicast environment.

A Cluster-Based Coverage-Preserved Node Scheduling Scheme in Wireless Sensor Networks

Wireless sensor networks consist of a large number of low-power, small-scale sensors with limited processing and communication capabilities. Such networks are usually applied to gather data from interested area or specific environment and deliver to remote users for analyzing or monitoring. Because of sensing devices are usually powered by batteries, it is a great challenge to meet the performance of long system lifetime required by different applications under limited power. In the densely deployed sensor networks, the area or data sensed by neighboring sensors may overlap. In recent researches, coverage preserved node scheduling has been proposed to conserve power and provide sensing reliability. By selecting appropriate sensors into sleep state, the system lifetime can be extended without losing coverage. In this paper, we propose a duster-based coverage-preserved node scheduling scheme. We divide sensors into clusters and group cluster members into sponsor sets based on neighbor information. The proposed approach distributes the workloads among sponsor set nodes and ensures sufficient coverage as long as possible

HarpiaGrid: A Geography-Aware Grid-based Routing Protocol for Vehicular Ad Hoc Networks

Vehicular Ad Hoc Network (VANET) is a research field attracting growing attention. Current routing protocols in VANETs usually use route discovery to forward data packets to the destination. In addition, if vehicle density is low in the network, there might not be vehicles available to deliver the packet. This paper proposes HarpiaGrid, a geography-aware grid-based routing protocol for VANETs. The protocol uses map data to generate a shortest transmission grid route, effectively trades route discovery communication overhead with insignificant computation time. By restricting packets in grid sequences rather than blindly greedy search and making use of route cache approach, HarpiaGrid reduces many unnecessary transmissions, thus greatly improving routing efficiency. Moreover, in the route maintenance, this work proposes a local recovery scheme and uses backtracking techniques to generate a new grid forwarding route, providing superior fault-tolerance capability. Experiments were conducted, and the results demonstrated that the proposed scheme is indeed more efficient than other protocols.

An efficient traffic control system using dynamic thresholding techniques in wireless mesh networks

Wireless mesh networks (WMNs) depend on a resilient and high-performance infrastructure to provide users pervasive Internet access. In WMNs, all Internet traffic will be forwarded to the Internet gateways. Hence, these gateways are generally bottleneck nodes. This work proposes a traffic control technique to reduce the bottleneck problem and increase the utilization of network resources. Our approach provides a traffic control strategy that exploits dynamic techniques to adjust the threshold according to the traffic load of each gateway. The base threshold is defined in order to effectively control the traffic. When the current load exceeds the threshold of a gateway, the traffic redirection strategy is implemented by switching border nodes. The service regions can be adjusted for each gateway based on the traffic load. Furthermore, the proposed dynamic thresholding approaches can distribute the workloads of gateways and maintain the thresholds of any two gateways within a level range, making an in-band balance of load. Thus, our proposed scheme can handle the unnecessary traffic redirection and reduce the traffic control overhead for various distributions of traffic. Experimental results demonstrate that our scheme outperforms other schemes in terms of packet delivery ratio and efficiency, especially in bursty traffic environments. Copyright

A Distributed Virtual Backbone Development Scheme for Ad-Hoc Wireless Networks

The virtual backbone is an approach for solving routing problems in ad-hoc wireless networks. The virtual backbone approach features low latency, moderate routing overhead and is a hybrid scheme that uses the table-driven and on-demand routing protocols. This work presents a distributed virtual backbone development scheme for ad-hoc wireless networks. Using clustering, distributed labeling and heuristic Steiner tree techniques, our scheme outperforms other schemes in terms of the size and stability of the virtual backbone and the virtual backbone change rate. Experimental results demonstrate that our scheme has lower overhead than traditional table-driven and on-demand routing schemes.

An energy-efficient routing protocol in wireless sensor networks with holes

In wireless sensor networks, holes may exist due to uneven deployment, energy exhaustion and physical obstacles. How to establish the energy-efficient routing mechanism in wireless sensor networks with holes is a practical and challenging issues. Many researches employ hole detection algorithm to determine boundary nodes, and then the holes are covered by some virtual shapes such as circles and ellipses. This usually leads to longer path length and more energy exhaustion. In this paper, we propose an energy-efficient routing protocol in wireless sensor networks with holes. Only a few nodes need to determine whether it is a boundary node and a few anchor nodes are used to record the information of holes, thus reducing the energy consumption. In addition, the anchor nodes will be replaced when their residual energy is less than a threshold to prolong the network lifetime. Simulation results demonstrate that our proposed scheme has good performance in terms of energy consumption, control overhead and path length.

Hierarchical multicast in wireless sensor networks with mobile sinks

In most studies of wireless sensor networks (WSNs), sensor nodes and sinks are typically stationary. However, mobile sinks are required in various applications of real-life environments, and delivering sensed data to mobile sinks using ordinary routing protocols is very inefficient. Multicasting is an important process in the minimization of the number of transmissions in WSNs. Since sensor nodes have limited resources, many studies have focused on how to send data to specific receivers efficiently. This work presents a grid-based hierarchical multicast (HM) routing protocol for WSNs with mobile sinks. Location servers (LSs) are adopted to manage the information about the locations of receivers and then a multicast tree is constructed distributively to reduce the update cost and energy consumed by sink mobility. The multicast tree can be shared by multiple sources, reducing the path construction overhead. Furthermore, effective maintenance mechanisms that make the multicast tree more stable and robust are presented. Finally, the performance of the proposed HM is investigated by simulation. Simulation results demonstrate that the proposed protocol has a lower energy consumption and higher multicast efficiency than distributed multicast routing protocol (DMRP) and hierarchical geographic multicast routing (HGMR), especially when many sources and receivers are involved. Copyright

A Cluster-Based Approach for Efficient Multi-Source Multicasting in MANETs

A mobile ad hoc network (MANET) is a distributed wireless network. The characteristics such as free mobility, self configuration, and fast deployment make MANETs suitable for various tasks. Multicasting can efficiently support a variety of applications and services. Most of existing multicast routing protocols in MANETs consider only one source in a multicast group and become inefficient when the protocol is extended to multi-source multicasting. In this paper, we propose a cluster-based multi-source multicast routing protocol to provide efficient multicasting in the multi-source multicast environment. The proposed shared forwarding cluster and cluster-based routing preserve forwarding efficiency as well as robustness. Simulation results show that the proposed protocol maintains the delivery ratio without losing efficiency in the multi-source multicast environment.

A Scalable and Reliable Multicast Routing Protocol for Ad-hoc Wireless Networks

Multicasting is an essential service for ad-hoc wireless networks. In a multicasting environment with multiple senders, receivers or meeting members, traditional multicast routing protocols must pay great overhead for multiple multicast sessions. This work presents a scalable and reliable multicasting protocol for ad-hoc wireless networks. A virtual backbone is used as a shared structure for multiple sessions. A clustering scheme is used to reduce the routing path length. A novel scheme is developed to effectively multicast packets using forwarding gates. Furthermore, a lost packet recovery scheme is developed for reliable packet transmission. This scheme can be used to improve the reliability of traditional non-acknowledged multicasting approach. Experiments were conducted to evaluate the proposed multicasting scheme and the results demonstrate that our scheme outperforms other schemes in terms of packet delivery ratio, packet delivery time, control overhead, multicast efficiency, and cost effect. Furthermore, our approach is stable for networks with high mobility and the lost packet recovery scheme is cost-effective.