Jim Mee Ng

Efficient Load-Balanced Clustering Algorithms for wireless sensor networks

Wireless sensor networks have been receiving increasing attention in recent years due to their potential applications in the establishment of dynamic communications for emergency/rescue operations, disaster relief efforts, and military networks. In this paper, we investigate the problem of grouping the sensor nodes into clusters to enhance the overall scalability of the network. A selected set of nodes, known as gateway nodes, will act as cluster-heads for each cluster and the objective is to balance the load among these gateways. Load-Balanced Clustering increases system stability and improves the communication between the various nodes in the network. We call the problem addressed in this paper as the Load-Balanced Clustering Problem (LBCP). We first show that a special case of LBCP (whereby the traffic load contributed by all sensor nodes are the same) is optimally solvable in polynomial time. We next prove that the general case of LBCP is NP-hard. We then proposed an efficient 32-approximation algorithm for the problem.

A distributed group mobility adaptive clustering algorithm for mobile ad hoc networks

This paper proposes a distributed group mobility adaptive (DGMA) clustering algorithm for mobile ad hoc networks (MANETs) on the basis of a revised group mobility metric, linear distance based spatial dependency (LDSD), which is derived from the linear distance of a nodes movement instead of its instantaneous speed and direction. In particular, it is suitable for group mobility pattern where group partitions and mergence are prevalent behaviors of mobile groups. The proposed clustering scheme aims to form more stable clusters by prolonging cluster lifetime and reducing the clustering iterations even in highly dynamic environment. Simulation results show that the performance of the proposed framework is superior to two widely referenced clustering approaches, the Lowest-ID clustering scheme and the mobility based clustering algorithm MOBIC, in terms of average clusterhead lifetime, average resident time, average number of clusterhead changes, and average number of cluster reaffiliations.

A Distributed Group Mobility Adaptive Clustering Algorithm for Mobile Ad Hoc Networks

This paper proposes a distributed group mobility adaptive (DGMA) clustering algorithm for mobile ad hoc networks (MANETs) on the basis of a revised group mobility metric, spatial dependency, which is derived from the linear distance of a nodes movement instead of its instantaneous speed and direction. In particular, it is suitable for reflecting group mobility pattern where group partitions and mergence are prevalent behaviors of mobile groups. The proposed clustering scheme aims to form stable clusters by prolonging cluster lifetime and reducing the clustering iterations even in a highly dynamic environment. Simulation results show that the performance of the proposed framework is superior to another widely used clustering approach, the Lowest-ID clustering scheme, in terms of average clusterhead lifetime, average resident time and number of cluster reaffiliations.

Reference region group mobility model for ad hoc networks

In this paper, we propose a novel group mobility model, called reference region group mobility (RRGM) model, which can be used in the description of a group motion behavior as well as individual movement. This model is designed to be applicable to many different scenarios, such as military operation, search and rescue, exhibition hall visiting, building search, etc., where a group may be partitioned into a number of smaller groups and groups may merge whenever necessary. The groups may move independently towards their own destinations. Moreover, by using the density-based approach, our model can control the size of the region to be covered by a group. Our main contribution is on the effectiveness of modeling application scenarios, which are most likely to be deployed in ad hoc networks by including group partitioning and merging processes in group mobility.

A Mobility Model with Group Partitioning for Wireless Ad Hoc Networks

In this paper, we propose a novel group mobility model, called reference region group mobility (RRGM) model, which can be used in the description of group motion behavior as well as individual movement. This model is designed to be applicable to many different scenarios, such as military operation, search and rescue, exhibition hall visiting, building search, etc., where a group may be partitioned into a number of smaller groups and groups may merge whenever necessary. Moreover, by using the density-based approach, our model can control the size of the region to be covered by a group. Our main contribution is on the effectiveness of modeling group mobility scenarios with group partitioning and merging, which are most likely to be found in ad hoc networks

Low-power authenticated group key agreement for heterogeneous wireless networks

Heterogeneous wireless networks are gaining popularity as users can be connected to these networks without any cables and even when they are mobile. The high power nodes in heterogeneous wireless networks do not have energy constraints but the user nodes, which can be large in numbers, are usually low power energy constrained devices. Therefore, the GKA protocol used to secure group communications in these networks has to take into consideration both the low power nature of the user nodes and the network size. In this paper, we present an energy efficient and scalable authenticated GKA protocol, which uses our proposed Contributory Ring-Centralised (ContRi-Central) group model. Besides providing complexity analysis, we also show the computational and communication energy consumption costs analysis of all nodes running our proposed scheme and four other efficient GKA protocols. Both the complexity analysis and energy consumption costs analysis indicate that our proposed scheme is more efficient and suitable for heterogeneous wireless networks.

On-demand QoS multicast routing and reservation protocol for MANETs

We proposed a routing and resource reservation protocol that support both unicasting and multicasting for mobile ad hoc network (MANET). Unlike the wired network where the network topology is rather static, the topology of a MANET changes regularly depending on the mobility of the network nodes. Hence, integrating the resource reservation protocol into an on-demand routing protocol would be an efficient means to search for a path with the required bandwidth. Resources are temporarily reserved on the feasible paths during the path searching, and are committed only when the path is selected. Two reservation styles are supported which allow the sharing of resources by multiple data sources if needed.

Multiuser collaborative work in virtual environment based CASE tool

Abstract VRCASE is a virtual environment based Computer Aided Software Engineering (CASE) tool. It provides a 3D multiuser collaborative software modeling environment with automatic object-class abstraction, class diagram generation, and C++ skeleton generation facilities for assisting Object-Oriented software development. It allows multiple concurrent users to model software system collaboratively. To achieve efficient collaborative software development in VRCASE, we have proposed and implemented a Fine-grained locking and notification mechanism together with visual indicators to maintain system consistency among multiple concurrent users. The system evaluation shows that our approach can effectively support multiuser collaborative software design in VRCASE.

Dynamic group multicast routing with bandwidth reservations

Multicasting refers to the transmission of data from a source node to multiple destination nodes in a network. Group multicasting is a generalization of multicasting whereby every member of a group is allowed to multicast messages to other members that belong to the same group. The routing problem in this case involves the construction of a set of low cost multicast trees with bandwidth requirements, one for each member of the group for multicasting messages to other members of the group. In this paper, we examine this routing problem with an additional requirement that member nodes are allowed to join and leave the multicasting group anytime during a session. We call this problem, the dynamic group multicast routing problem (DGMRP). In this paper, we proposed three heuristic algorithms to generate a set of low cost multicast trees with dynamic group membership. Results from our empirical study shows that the one of the proposed algorithms, called Maximum bandwidth bottleneck path selection algorithm (MBBPS), achieves better utilization of bandwidth resources as compared with the other two algorithms which are based on a greedy approach. In addition MBBPS performs better in terms of cost when the bandwidth is not sufficient in the network. Copyright

An efficient algorithm for the video server selection problem

This paper addresses the problem of video server selection in a distributed video-on-demand system. The objective of the problem is to balance the load among video servers and to minimize the delay for the video requests to be served. In order to achieve this objective, a near optimal assignment algorithm is proposed for video server selection. Empirical study shows that our proposed algorithm is able to achieve good load balancing performance as compared to some landmark algorithms.