Jong-Shin Chen

Efficient Cluster Head Selection Methods for Wireless Sensor Networks

The past few years have witnessed increased in the potential use of wireless sensor network (WSN) such as disaster management, combat field reconnaissance, border protection and security surveillance. Sensors in these applications are expected to be remotely deployed in large numbers and to operate autonomously in unattended environments. Since a WSN is composed of nodes with nonreplenishable energy resource, elongating the network lifetime is the main concern. To support scalability, nodes are often grouped into disjoint clusters. Each cluster would have a leader, often referred as cluster head (CH). A CH is responsible for not only the general request but also assisting the general nodes to route the sensed data to the target nodes. The power-consumption of a CH is higher then of a general (non-CH) node. Therefore, the CH selection will affect the lifetime of a WSN. However, the application scenario contexts of WSNs that determine the definitions of lifetime will impact to achieve the objective of elongating lifetime. In this study, we classify the lifetime into different types and give the corresponding CH selection method to achieve the life-time extension objective. Simulation results demonstrate our study can enlarge the life-time for different requests of the sensor networks.

Energy-Aware Data Aggregation for Grid-Based Wireless Sensor Networks with a Mobile Sink

Wireless sensor networks (WSNs) are made up of many small and highly sensitive nodes that have the ability to react quickly. In WSNs, sink mobility brings new challenges to large-scale sensor networks. Almost all of the energy-aware routing protocols that have been proposed for WSNs aim at optimizing network performance while relaying data to a stationary gateway (sink). However, through such contemporary protocols, mobility of the sink can make established routes unstable and non-optimal. The use of mobile sinks introduces a trade-off between the need for frequent rerouting to ensure optimal network operation and the desire to minimize the overhead of topology management. In this paper, in order to reduce energy consumption and minimize the overhead of rerouting frequency, we propose an energy-aware data aggregation scheme (EADA) for grid-based wireless sensor networks with a mobile sink. In the proposed scheme, each sensor node with location information and limited energy is considered. Our approach utilizes location information and selects a special gateway in each area of a grid responsible for forwarding messages. We restrict the flooding region to decrease the overhead for route decision by utilizing local information. We conducted simulations to show that the proposed routing scheme outperforms the coordination-based data dissemination scheme (CODE) (Xuan, H. L., & Lee, S. Proceedings of the Sensor Networks and Information Processing Conference, pp. 13–18, 2004).

Performance Enhancement of TCP in Dynamic Bandwidth Wired and Wireless Networks

In this paper, we propose a scheme that dynamically adjusts the slow start threshold (ssthresh) of TCP. The ssthresh estimation is used to set an appropriate ssthresh. A good ssthresh would improve the transmission performance of TCP. For the congestion avoidance state, we present a mechanism that probes the available bandwidth. We adjust the congestion window size (cwnd) appropriately by observing the round trip time (RTT) and reset the ssthresh after quick retransmission or timeout using the ssthresh estimation. Then the TCP sender can enhance its performance by using the ssthresh estimation and the observed RTT. Our scheme defines what is considered an efficient transmission rate. It achieves better utilization than other TCP versions. Simulation results show that our scheme effectively improves TCP performance. For example, when the average bottleneck bandwidth is close to 30% of the whole network bandwidth, our scheme improves TCP performance by at least 10%.

Analysis of using the tongue deviation angle as a warning sign of a stroke

BackgroundThe symptom of tongue deviation is observed in a stroke or transient ischemic attack. Nevertheless, there is much room for the interpretation of the tongue deviation test. The crucial factor is the lack of an effective quantification method of tongue deviation. If we can quantify the features of the tongue deviation and scientifically verify the relationship between the deviation angle and a stroke, the information provided by the tongue will be helpful in recognizing a warning of a stroke.MethodsIn this study, a quantification method of the tongue deviation angle was proposed for the first time to characterize stroke patients. We captured the tongue images of stroke patients (15 males and 10 females, ranging between 55 and 82 years of age); transient ischemic attack (TIA) patients (16 males and 9 females, ranging between 53 and 79 years of age); and normal subjects (14 males and 11 females, ranging between 52 and 80 years of age) to analyze whether the method is effective. In addition, we used the receiver operating characteristic curve (ROC) for the sensitivity analysis, and determined the threshold value of the tongue deviation angle for the warning sign of a stroke.ResultsThe means and standard deviations of the tongue deviation angles of the stroke, TIA, and normal groups were: 6.9 ± 3.1, 4.9 ± 2.1 and 1.4 ± 0.8 degrees, respectively. Analyzed by the unpaired Student’s t-test, the p- value between the stroke group and the TIA group was 0.015 (>0.01), indicating no significant difference in the tongue deviation angle. The p- values between the stroke group and the normal group, as well as between the TIA group and the normal group were both less than 0.01. These results show the significant differences in the tongue deviation angle between the patient groups (stroke and TIA patients) and the normal group. These results also imply that the tongue deviation angle can effectively identify the patient group (stroke and TIA patients) and the normal group. With respect to the visual examination, 40% and 32% of stroke patients, 24% and 16% of TIA patients, and 4% and 0% of normal subjects were found to have tongue deviations when physicians “A” and “B” examined them. The variation showed the essentiality of the quantification method in a clinical setting. In the receiver operating characteristic curve (ROC), the Area Under Curve (AUC, = 0.96) indicates good discrimination. The tongue deviation angle more than the optimum threshold value (= 3.2°) predicts a risk of stroke.ConclusionsIn summary, we developed an effective quantification method to characterize the tongue deviation angle, and we confirmed the feasibility of recognizing the tongue deviation angle as an early warning sign of an impending stroke.

An Efficient Forward and Backward Fault-Tolerant Mobile Agent System

Mobile agent is a special program and it can switch and execute the task of user commands among the networks and hosts. During the task executing, the mobile agent can convey the data, state and program code to another host in order to autonomously execute and continue the task in another host. While the mobile agent is executing the task at any of the software and hardware fault incurred or network problems, there will be two conditions as following lists: 1. Users continuously wait the reply from the agent, but users will never have the reply because of the some faults incurred to the agent in the networks or hosts. 2. Users assign a new agent as the former agent has been lost to restart the former task, but the former agent only congested the delay problem of the network or host. This causes that these two agents have the same task to be executed. Therefore, the fault detecting and recovering of the mobile agent are important issues to be discussed. However, this paper propose a front behind failure detection and recovery method that the task agent has to report the task process at the present stage to the former and latter agent and agents will exchange their messages for the present stage. This is more accurate than the method in for the task at present because it can reduce the loading of the task fault report from the network congested.

An Efficient Cluster Head Selection Strategy for Wireless Sensor Network

A wireless sensor network can be divided into several clusters. Each cluster has a number of sensors nodes and one of the nodes is elected as the coordinator, termed as head. The head is responsible for not the general mission but also collecting the sensed data of other nodes and routing to the sink. Accordingly, the energy-consumption is higher than other nodes. Therefore, the head selection will affect the life-time of a network. In this study, we consider the factor of energy consumption to determine the head. Simulation results demonstrate our study can enlarge the life time for wireless sensor networks.

A Distributed Fault-tolerant Resource Planning Scheme for Wireless Networks

Efficient management of wireless channels is critical for the performance of cellular systems. Resource planning represents the allocations of system channels into cells. Accordingly, channel assignment strategies respond for using the allocated channels of cells to provide communication services in cells. However, a cellular system that experiences the varying of traffic distributions and the mobile service stations (MSSs) failing to provide communication services or recovered from failures will lessen the utilization of channels to provide communication services. In this paper, we present a distributed fault-tolerant resource planning scheme that can adaptively allocate channels to cells according to above variations in cellular systems. When the MSS of a cell fails to provide communications, its allocated channels can be reallocated to other non-failed MSSs. Our scheme has the advantages of low message overhead and low time delay. Moreover, freedom from deadlock is ensured. Simulation results, which are observed from reducing the overall average call blocking probability and the message overhead with and without applying our resource planning scheme to various channel assignment strategies, demonstrate that our algorithm is very efficient.

The Hamiltonian connectivity of rectangular supergrid graphs

Abstract A Hamiltonian path of a graph is a simple path which visits each vertex of the graph exactly once. The Hamiltonian path problem is to determine whether a graph contains a Hamiltonian path. A graph is called Hamiltonian connected if there exists a Hamiltonian path between any two distinct vertices. In this paper, we will study the Hamiltonian connectivity of rectangular supergrid graphs. Supergrid graphs were first introduced by us and include grid graphs and triangular grid graphs as subgraphs. The Hamiltonian path problem for grid graphs and triangular grid graphs was known to be NP-complete. Recently, we have proved that the Hamiltonian path problem for supergrid graphs is also NP-complete. The Hamiltonian paths on supergrid graphs can be applied to compute the stitching traces of computer sewing machines. Rectangular supergrid graphs form a popular subclass of supergrid graphs, and they have strong structure. In this paper, we provide a constructive proof to show that rectangular supergrid graphs are Hamiltonian connected except one trivial forbidden condition. Based on the constructive proof, we present a linear-time algorithm to construct a longest path between any two given vertices in a rectangular supergrid graph.

An adaptive capacity enhancement strategy for sector-based cellular systems

Sector-based cellular systems that are more flexible to enhance the system capacity will be the mainstream for wireless networks. In this framework, each base station (BS) has a number of antennas and each antenna responds for providing wireless communication services to the mobile hosts in a partial region, termed as a sector. However, the architecture generates a high ratio of overlapped area, which is partitioned into several subareas. An overlapped region means the region which more than one antenna can cover. Therefore, the overlapped region allocation to antennas will impact the traffic loads among the antennas and the capacity of the BS. Therefore, this study will present an area allocation strategy for sector-based cellular systems. This strategy considers the traffic loads to allocate the overlapped regions to antennas. Simulation results demonstrate our strategy can greatly enhance the system capacity.

An Efficient Cluster Construction Strategy for Wireless Sensor Networks

Wireless sensor networks consist of small battery powered devices with limited energy resources. The energy efficiency is key design that needs to be enhanced in order to improve the life-time of the network. However, the conventional cluster constructions are difficult to control the geographical area of a cluster. The methods usually generate long-distance intra-cluster routing and can not keep the energy efficiency. This paper presents an efficient cluster construction strategy that can handle the geographical area of a cluster. Accordingly, the numbers of sensor nodes of clusters are balanced and long-distance intra-cluster data delivery can be avoided.