Chang Wu Yu

Expected k-coverage in wireless sensor networks

We are concerned with wireless sensor networks where n sensors are independently and uniformly distributed at random in a finite plane. Events that are within a fixed distance from some sensor are assumed to be detectable and the sensor is said to cover that point. In this paper, we have formulated an exact mathematical expression for the expected area that can be covered by at least k out of n sensors. Our results are important in predicting the degree of coverage a sensor network may provide and in determining related parameters (sensory range, number of sensors, etc.) for a desired level of coverage. We demonstrate the utility of our results by presenting a node scheduling scheme that conserves energy while retaining network coverage. Additional simulation results have confirmed the accuracy of our analysis. � 2005 Elsevier B.V. All rights reserved.

A distributed and cooperative black hole node detection and elimination mechanism for ad hoc networks

A mobile node in ad hoc networks may move arbitrarily and acts as a router and a host simultaneously. Such a characteristic makes nodes in MANET vulnerable to potential attacks. The black hole problem, in which some malicious nodes pretend to be intermediate nodes of a route to some given destinations and drop any packet that subsequently goes through it, is one of the major types of attack. In this paper, we propose a distributed and cooperative mechanism to tackle the black hole problem. The mechanism is distributed so that it can fit with the ad hoc nature of network, and nodes in the protocol work cooperatively together so that they can analyze, detect, and eliminate possible multiple black hole nodes in a more reliable fashion. Simulation results show that our method achieves a high black hole detection rate and good packet delivery ratio, while the overhead is comparatively lower as the network traffic increases.

A low overhead dynamic route repairing mechanism for mobile ad hoc networks

Ad hoc networks are wireless networks with no fixed infrastructure. Each mobile node in the network functions as a router that discovers and maintains routes for other nodes. These nodes may move arbitrarily, therefore network topology changes frequently and unpredictably. Many routing protocols have been designed for ad hoc networks. However, most of these kinds of protocols are not able to react fast enough to maintain routing. In this paper, we propose a new protocol that repairs the broken route by using information provided by nodes overhearing the main route communication. When links go down, our protocol intelligently replaces these failed links or nodes with backup ones that are adjacent to the main route. Theoretical analysis reveals that, in a given circumstance, our proposed protocol can find a backup route in more than 60% of time. Simulation results also demonstrate that our protocol achieves better (or as good) in terms of the packet delivery rate, control packet overhead and communication delay than the major ad hoc routing protocols under light and moderate traffic conditions.

Link probability, network coverage, and related properties of wireless ad hoc networks

This paper has analyzed link probability, expected node degree, expected number of links, and expected area collectively covered by a finite number of nodes in wireless ad hoc networks. Apart from the formulation of exact mathematical expressions for these properties, we have disclosed two fundamental results: (1) Every possible link has an equal probability of occurrence. (2) It is the border effects that makes two links probabilistically dependent. Simulation results show that our analysis predicts related measure with accuracy.

Clustering and splitting charging algorithms for large scaled wireless rechargeable sensor networks

Merging and clustering charging algorithms named HCCA and HCCA-TS are proposed for WRSN.HCCA combines K-means clustering and hierarchical clustering for enhancing charging efficiency.HCCA-TS optimizes the performance of HCCA from a task splitting view. As the interdiscipline of wireless communication and control engineering, the periodical charging issue in Wireless Rechargeable Sensor Networks (WRSNs) is a popular research problem. However, existing techniques for periodical charging neglect to focus on the location relationship and topological feature, leading to large charging times and long traveling time. In this paper, we develop a hybrid clustering charging algorithm (HCCA), which firstly constructs a network backbone based on a minimum connected dominating set built from the given network. Next, a hierarchical clustering algorithm which takes advantage of location relationship, is proposed to group nodes into clusters. Afterward, a K-means clustering algorithm is implemented to calculate the energy core set for realizing energy awareness. To further optimize the performance of HCCA, HCCA-TS is proposed to transform the energy charging process into a task splitting model. Tasks generated from HCCA are split into small tasks, which aim at reducing the charging time to enhance the charging efficiency. At last, simulations are carried out to demonstrate the merit of the schemes. Simulation results indicate that HCCA can enhance the performance in terms of reducing charging times, journey time and average charging time simultaneously. Moreover, HCCA-TS can further improve the performance of HCCA.

A Density-Based Algorithm for Redundant Reader Elimination in a RFID Network

Radio frequency identification (RFID) technology has become more sophisticated in recent years and is being developed rapidly for a variety of applications. The problem of eliminating redundant readers has been reduced to the minimum cover problem and proved to be NP-hard. In this paper, a density-based redundant reader elimination algorithm (DRRE) is presented; DRRE eliminates the redundant readers without influencing the number of usable tags. Simulation results demonstrate that the DRRE algorithm performed better in all instances in a variety of environments compared with other algorithms. In a densely deployed RFID network, the DRRE algorithm detected 85% more redundant readers than others.

TADP: Enabling temporal and distantial priority scheduling for on-demand charging architecture in wireless rechargeable sensor Networks

Abstract Recently, adopting mobile energy chargers to replenish the energy supply of sensor nodes in wireless sensor networks has gained increasing attentions from the research community. The utilization of the mobile energy chargers provides a more reliable energy supply than systems harvesting dynamic energy from the surrounding environment. Wireless power transfer technique provides a new alternative for solving the limited power capacity problem for so many popular mobile wireless devices, and makes wireless rechargeable sensor networks (WRSNs) promising. However, mainly due to the underestimate of the unbalanced influences of spatial and temporal constraints posed by charging requests, traditional scheduling strategies for on-demand WRSNs architecture achieve rather low charging request throughput or successful rate, posing as a major bottleneck for further improvements. In this paper, we propose a T empor A l & D istantial P riority charging scheduling algorithm (TADP), which takes both the distance between nodes and the mobile charger and the arrival time of charging requests into consideration, and quantizes these two factors step by step. TADP forms a mixed priority queue which directs mobile charger to replenish the energy for nodes. At last extensive simulations are conducted to demonstrate the advantages of TADP. Simulation results reveal that TADP can achieve better scheduling performance in guaranteeing the scheduling success of the high-priority tasks and improving stability of the system.

GTCharge: A game theoretical collaborative charging scheme for wireless rechargeable sensor networks

Abstract Collaborative charging schemes are indeed helpful for energy replenishment. However, classic and traditional collaborative charging schemes are still suffering from a series of severe problems, which are almost neglected. The lack of homogeneity and dynamic charging decisions on collaborative charging schemes in Wireless Rechargeable Sensor Networks (WRSN) deteriorate the charging efficiency. To enhance charging performance, especially in terms of charging efficiency, in this paper, a game theoretical collaborative charging scheme, namely GTCharge is devised. The charging process is converted into a collaborative game taken between wireless charging vehicles (WCVs). We investigate the functionalities of contribution degree, charging priority and profits. Then GTCharge is demonstrated in detail, in which each WCV seeks for the maximum profit when fulfilling charging tasks. The conditions including all WCVs’ charging strategies are proven to reach a Nash Equilibrium point. Finally, extensive simulations are conducted to show the advantages of the proposed scheme. Simulation results demonstrate the merits of the proposed scheme in terms of charging efficiency.

An Ad Hoc Routing Protocol with Multiple Backup Routes

Numerous routing protocols have recently been developed for ad hoc mobile networks. Routing protocols to date can be categorized as either ‘table-driven’ or ‘on-demand’. Many of the proposed routing protocols take the on-demand approach because this does not require keeping lots of routing information. However, these kinds of protocols are not able to react fast enough to maintain routing. In this paper, we propose a new protocol to improve existing on-demand routing protocols by constructing multiple backup routes; when the network topology changed, the proposed protocol could transmit data packets dynamically through backup routes. We then developed an analytic model to estimate the reconnection probability of the proposed algorithm. We also examined the performance by simulating the protocol using ns2. The experimental results showed that the protocol had fewer control packages, lower routing packet overhead, and a higher receiving ratio than others.

Efficient parallel algorithms for doubly convex-bipartite graphs

Abstract Suppose that G = (S, T, E) is a bipartite graph. An ordering of S(T) has the adjacency property if for each vertex in T(S), its adjacent vertices in S(T) are consecutive in the ordering. If there exist orderings of S and T which have the adjacency property, G is called a doubly convex-bipartite graph. In this paper, a parallel algorithm is proposed to recognize a doubly convex-bipartite graph. The algorithm runs in O(log n) time using O( n 3 log n ) processors on the CRCW PRAM, or O(log2 n) time using O( n 3 log 2 n) processors on the CREW PRAM.