Yong-hwan Kim

Centroid-Based Movement Assisted Sensor Deployment Schemes in Wireless Sensor Networks

Efficient deployment of sensors is an important issue in wireless sensor networks. If we deploy sensors randomly by our hands or carriers only, some unlucky places are not covered forever. In this paper, we propose distributed self-deployment schemes of mobile sensors. At first, sensors are deployed randomly. They then calculate the next positions locally by utilizing the proposed schemes and move to them. The locations of the sensors are adjusted round by round so that the coverage is gradually improved. By using Voronoi diagram and centroid (geometric center), we design two schemes, named Centroid (centroid-based scheme) and Dual-Centroid (dual-centroid based scheme). We also measure the performance of the proposed schemes and the existing schemes, and show that the proposed schemes get better results.

Lifetime maximization considering target coverage and connectivity in directional image/video sensor networks

A directional sensor network consists of a large number of directional sensors (e.g., image/video sensors), which have a limited angle of sensing range due to technical constraints or cost considerations. In such directional sensor networks, the power saving issue is a challenging problem. In this paper, we address the Directional Cover and Transmission (DCT) problem of organizing the directional sensors into a group of non-disjoint subsets to extend the network lifetime. One subset in which the directional sensors cover all the targets and forward the sensed data to the sink is activated at one time, while the others sleep to conserve their energy. For the DCT problem proven to be the NP-complete problem, we present a heuristic algorithm called the Shortest Path from Target to Sink (SPTS)-greedy algorithm. To verify and evaluate the proposed algorithm, we conduct extensive simulations and show that it can contribute to extending the network lifetime to a reasonable extent.

Regular sensor deployment patterns for p-coverage and q-connectivity in wireless sensor networks

In this paper, we study the regular sensor deployment patterns to achieve p-coverage and q-connectivity (q ≤ 6) under different ratios of sensor nodes communication range (rc) to their sensing range (rs) for wireless sensor networks. In particular, we propose the triangular lattice, square grid, and hexagon deployment patterns to achieve p-coverage and q-connectivity. To form such regular deployment patterns for given p and q values, we present the distance between sensor nodes as well as the relationship between rc and rs. We will get this information by using the inverse method of the proposed theorems which estimate the coverage level of the target region when sensors are deployed. We also compare the efficiency of the proposed regular deployment patterns in terms of the number of sensors needed to provide p-coverage and q-connectivity.

An energy-efficient self-deployment with the centroid-directed virtual force in mobile sensor networks

The deployment of sensors at their intended locations enables not only adequate sensing coverage of the area of interest, but also efficient sensor resource management. However, for static wireless sensor networks, it is sometimes impossible to manually deploy the sensors in those locations as they can be distributed in unexploited, hostile, or disaster areas. Nevertheless, if each sensor has locomotive capability, they can re-deploy themselves using the location information of neighboring sensors. In particular, in our previous study, we showed that the coverage area can be efficiently expanded by having sensors move to the centroids of their Voronoi polygon generated using the location information of neighboring sensors. In this paper, we present an energy-efficient self-deployment scheme to utilize the attractive force generated from the centroid of a sensor’s local Voronoi polygon as well as the repulsive force frequently used in self-deployment schemes using the potential field. We also provide the design and implementation of the simulator used to analyze the performance of the proposed approach as compared with existing self-deployment schemes. The simulation results show that our scheme can achieve a higher coverage and enables less sensor movements in shorter times than self-deployment schemes using the traditional potential field.

Betweenness of Expanded Ego Networks in Sociality-Aware Delay Tolerant Networks

Recently, the consideration of social characteristics present a new angle of view in the design of data routing and dissemination in delay tolerant networks. Many social network studies have been undertaken using a ego network because it has the benefit of simplicity in data collection and gives statistically significant features about the entire network in many cases. In this paper, we newly define the expanded ego network by comprising the ego’s 2-hop neighbor nodes as well as the ego’s 1-hop ones. In delay tolerant networks, the expended ego network can be easily self-configured at a node and it can contain more network information than the ego network. Therefore, it is expected that the effectiveness of the expanded ego network will be higher than the one of the ego network in terms of data routing and dissemination. We examine that the relationship among the expanded ego betweenness, the ego betweenness, and the betweenness of the entire network for a node. By a simulation study, we show that the expanded ego betweenness is highly correlated with the betweenness of the entire network when the network is dense and its nodes are highly inter-related.

An Energy-Efficient Self-Deployment Scheme in Intelligent Mobile Sensor Networks

In traditional static wireless sensor networks, it is sometimes impossible to deploy the sensors manually when they are distributed in unexploited, hostile, or disaster areas. If each sensor has the locomotion capability, it can re-deploy itself using the location information of neighbor sensors. In our previous study, we showed that moving sensors to the centroids of their Voronoi polygon generated by the location information of neighbor sensors is efficient for expanding the coverage area. In this paper, we present an improved potential-field-based selfdeployment scheme to utilize the attractive force generated from the centroid of a sensors local Voronoi polygon as well as the repulsive force usually used in the traditional potential-fieldbased scheme. Simulation results show that our scheme can achieve higher coverage and less movement in shorter time than the traditional potential-field-based scheme.

A scheduling algorithm for connected target coverage under probabilistic coverage model

Connected Target Coverage (CTC) problem [8], covering given targets fully with the deployed sensors and also guaranteeing connectivity to a sink node, is a challenging scheduling problem. In this paper, unlike the existing heuristic algorithms, we adopt the probabilistic coverage model to solve the problem and develop a heuristic algorithm called CWGC-PM (Communication Weighted Greedy Cover-Probabilistic Model) to extend the network lifetime while such coverage and connectivity constraints are satisfied. Simulation results are presented to evaluate the performance of the proposed algorithm and they show that the probabilistic coverage model can capture the diverse sensing characteristics of sensor nodes in the real world.

A SDN-based distributed mobility management in LTE/EPC network

As smart phones have rapidly proliferated over the past few years, LTE operators endeavor to cope with large mobile data traffic volumes. To solve such problems, we propose a new distributed LTE/EPC network architecture based on SDN, NFV, and cloud computing supporting distributed P-GWs and centralized control plane in LTE/EPC networks. It is designed considering the three requirements: (1) distributing P-GWs closer to the user equipments, (2) virtually centralizing control plane, and (3) control and data plane separation. Next, we present a new SDN-based distributed mobility management (SDMM) which confirms to the proposed architecture. Based on the SDMM, the location and handover management are then presented. For enhancing network performance more, we also propose a route optimization strategy for internal traffic exchanged between LTE UEs. The proposed solutions are compared with the conventional LTE/EPC network’s scheme in terms of the gateway data processing volume, handover latency, and the number of valid data sessions. The comparison results show that the proposed solutions can be an efficient way to enhance the scalability of LTE/EPC core networks.

Lifetime Maximization Considering Connectivity and Overlapped Targets in Wireless Sensor Networks

A critical issue in wireless sensor networks is an energy-efficiency since the sensor batteries have limited energy power and, in most cases, are not rechargeable. The most practical manner relate to this issue is to use a node wake-up scheduling protocol that some sensor nodes stay active to provide sensing service, while the others are inactive for conserving their energy. Especially, CTC (Connected Target Coverage) problem has been considered as a representative energy-efficiency problem considering connectivity as well as target coverage. In this paper, we propose a new energy consumption model considering overlapped targets and create a new problem, OTCC (Overlapped Target and Connected Coverage) problem of which objective is to maximize the network lifetime based on the new energy consumption model. Also, we present SPT (Shortest Path based on Targets)-Greedy algorithm to solve the problem. Our simulation results show that SPT-Greedy algorithm performs much better than the previous algorithm in terms of the network lifetime.

Distributed PDN gateway support for scalable LTE/EPC networks

Recently, due to a explosive growth in the mobile Internet traffic, the problem of excessive data traffic handling on core network and thus scalability problem have been magnified in 3GPP Long Term Evolution/System Architecture Evolution (LTE/SAE) networks. Current LTE/SAE network based on the central packet data network gateway (P-GW) used as mobility anchor cannot deal with such problems. In this paper, we propose a new LTE/SAE network architecture supporting distributed P-GWs and the corresponding distributed mobility management to solve the problems. For this, in addition to the deployment of such distributed P-GWs, we propose a dynamic and distributed mobility management by distributing MMEs (Mobility Management Entities) which dynamically manages the location information of an UEs PDN connection, and also propose a handover procedure of such PDN connections by using the proposed distributed P-GWs and MMEs. The performance of the proposed distributed LTE/SAE network system is compared with the conventional LTE/SAE network system in terms of the P-GWs data processing volume per unit time and the number of valid data sessions accommodated in the LTE/EPC core network.