• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.5
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• pp.1354-1372
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• 2012

Route establishment in Mobile Ad Hoc Network (MANET) is the key mechanism to a successful connection between a pair of source and destination nodes. An efficient routing protocol constructs routing path with minimal time, less routing overhead and capable of utilizing all possible link connectivity. In general, most on-demand MANET routing protocols operates over symmetrical and bidirectional routing path, which is infeasible due to the inherent heterogeneous properties of wireless devices. Simulation results show that the presence of unidirectional links on a network severely affect the performance of a routing protocol. In this paper, a robust protocol independent scheme is proposed, which enable immediate rediscovery of alternative route for a path blocked by a unidirectional link. The proposed scheme is efficient; route rediscovery is locally computed, which results in significant minimization of multiple route packets flooding. Nodes may exploit route information of immediate neighbors using the local reply broadcast technique, which then redirect the control packets around the unidirectional links, therefore maintaining the end-to-end bidirectional connection. The proposed scheme along with Ad Hoc On-demand Distance Vector (AODV) and AODV-Blacklist routing protocol is investigated over three types of mobility models. Simulation results show that the proposed scheme is extremely reliable under poor network conditions and the route connectivity can be improved by as much as 75%.

• Journal of the Korea Society of Computer and Information
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• v.11 no.6 s.44
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• pp.289-298
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• 2006

Many researches are going on with regard to issues and problems related to mobile database systems, which are caused by the weak connectivity of wireless networks, the mobility and the portability of mobile clients. Mobile computing satisfies user's demands for convenience and performance to use information at any time and in any place, but it has many problems to be solved in the aspect of data management. The purpose of our study is to design Mobile Continuous Query Processing System(MCQPS) to solve problems related to database hoarding, the maintenance of shared data consistency and the optimization of logging, which are caused by the weak connectivity and disconnection of wireless networks inherent in mobile database systems under mobile client server environments. We proved the superiority of the proposed MCQPS by comparing its performance to the C I S(Client-Intercept-Slaver) model. In Addition, we experiment on proposed index structure and methodology in various methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.23-29
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• 2006

In wireless sensor networks(WSNs), it is crucial to maintain network connectivity as long as possible since nodes are battery-powered and unchange-able. We propose a new routing protocol called Energy Aware Source Routing(EASR) which can be efficient in respect of network lifetime and long-term connectivity. Our protocol is multipath source routing, only one path will be selected at the same time and each path has probability to be selected like as Energy Aware Routing(EAR) protocol. The route discovery procedure of EASR protocol is reformed from the route discovery procedure of Split Multipath Routing(SMR) protocol. However, there is the difference between SMR and EASR. In EASR, we define an overhearing ratio in order to reduce energy waste due to overhearing effect among each selected path. Thus, we can establish energy efficient multiple paths by making use of overhearing ratio. The simulation results are also demonstrated that our scheme increases in network lifetimes, and achieves reasonable packet latency time.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.335-343
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• 2014

This paper considers the crucial problem of deploying wireless relays for achieving a connected wireless sensor network in indoor environments, an important aspect related to the management of the sensor network. Several algorithms have been proposed for ensuring full sensing coverage and network connectivity. These algorithms are not applicable to indoor environments because of the complexity of indoor environments, in which a radio signal can be dramatically degraded by obstacles such as walls. We first prove theoretically that the indoor relay placement problem is NP-hard. We then predict the radio coverage of a given relay deployment in indoor environments. We consider two practical scenarios; wire-connected relays and radio-connected relays. For the network with wire-connected relays, we propose an efficient greedy algorithm to compute the deployment locations of relays for achieving the required coverage percentage. This algorithm is proved to provide a $H_n$ factor approximation to the theoretical optimum, where $H_n=1+{\frac{1}{2}}+{\cdots}+{\frac{1}{n}}={\ln}(n)+1$, and n is the number of all grid points. In the network with radio-connected relays, relays have to be connected in an ad hoc mode. We then propose an algorithm based on the previous algorithm for ensuring the connectivity of relays. Experimental results demonstrate that the proposed algorithms achieve better performance than baseline algorithms.

• The KIPS Transactions:PartD
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• v.12D no.4 s.100
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• pp.521-530
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• 2005

Many researches are going on with regard to issues and problems related to mobile database systems, which are caused by the weak connectivity of wireless networks, the mobility and the Portability of mobile clients. Mobile computing satisfies user's demands for convenience and Performance to use information at any time and in any Place, but it has many Problems to be solved in the aspect of data management. The purpose of our study is to design Mobile Query Processing System(MQPS) to solve problems related to database hoarding, the maintenance of shared data consistency and the optimization of logging, which are caused by the weak connectivity and disconnection of wireless networks inherent in mobile database systems under mobile client-server environments. In addition, we proved the superiority of the proposed MQPS by comparing its performance to the C-I-S(Client-Intercept- Server) model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3A
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• pp.269-278
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• 2010

There are tendency that wireless sensor network is one of the important techniques for the future IT industry and thereby application areas in it are getting growing. Researches based on the hierarchical network topology are evaluated in good at energy efficiency in related protocols for wireless sensor network. LEACH is the best well known routing protocol for the hierarchical topology. However, there are problems in the range of message broadcasting, which should be expand into the overall network coverage, in LEACH related protocols. This dissertation proposes a new routing protocol to solve the co-shared problems in the previous protocols. The basic idea of our scheme is using the table for nodes connectivity and node energy information. The results show that the proposed protocol could support the load balancing by distributing the clusters with a reasonable number of member nodes and thereby the network life time would be extended in about 1.8 times longer than LEACH.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.2
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• pp.1250-1264
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• 2017

This paper presents the architecture design, implement, experimental validation of a bistatic backscatter wireless communication system in Wi-Fi network. The operating principle is to communicate a tag's data by detecting the power level of the power modulated Wi-Fi packets to be reflected or absorbed by backscatter tag, in interconnecting with Wi-Fi device and Wi-Fi AP. This system is able to provide the identification and sensor data of tag on the internet connectivity without requiring extra device for reading data, because this uses an existing Wi-Fi AP infrastructure. The backscatter tag consists of Wi-Fi energy harvesting part and a backscatter transmitter/a power-detecting receiver part. This tag can operate by harvesting and generating energy from Wi-Fi signal power. Wi-Fi device decodes information of the tag data by recognizing the power level of the backscattered Wi-Fi packets. Wi-Fi device receives the backscattered Wi-Fi packets and generates the tag's data pattern in the time-series of channel state information (CSI) values. We believe that this system can be achieved wireless connectivity for ultra- low-power IoT and wearable device.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.3
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• pp.585-594
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• 2017

Wireless Docking system can provide enhanced convenience to user experience of handheld device such as smart phone by using previously deployed peripheral devises such as monitor and keyboard. In this environment, user can easily use the handheld device with variable peripheral devices at any docking system place. This system would be composed of peripherals except host computing device contrarily to previous desktop and laptop environment. For this system, Wi-Fi Alliance has been developing standard technology based on Wi-Fi Direct(Wi-Fi Peer-to-Peer Technical Specifications v1.2, 2010) technology. However, this system can make a problem which may lead to complex connectivity on handheld device due to non-compatible communication interface. To address given problem, we designed a new method of Bluetooth tunneling technology via previous Wi-Fi Direct communication, and evaluated it with experiment results.

• Journal of Korea Multimedia Society
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• v.10 no.12
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• pp.1632-1644
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• 2007

Wireless Mesh Networks aim to attain large connectivity with minimum performance degradation, as network size is increase. As such, scalability is one of the main characteristics of Wireless Mesh Networks that differentiates it from other wireless networks. This characteristic creates the need for bandwidth efficiency strategies to ensure that network performance does not degrade as the size of the network increase. Several researches have been done to realize mesh networks. However, the researches conducted were mostly focused on a per TCP/IP layer basis. Also, the studies on bandwidth efficiency and bandwidth improvement are usually dealt with as separate issues. This paper aims to simultaneously study bandwidth efficiency and improvement. Aside from optimizing the bandwidth given a fixed capacity, the capacity is also increased using results of physical layer studies. In this paper, the capacity is improved by using the concept of non-overlapping channels for wireless communication. A channel allocation scheme is conceptualized to choose the transmission channel that would optimize the network performance parameters with consideration of chosen Quality of Service (QoS) parameters. Network utility maximization is used to optimize the bandwidth after channel selection. Furthermore, a routing scheme is proposed using the results of the network utilization method and the channel allocation scheme to find the optimal path that would maximize the network gain.

• Journal of the Semiconductor & Display Technology
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• v.14 no.2
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• pp.17-22
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• 2015

In recent years, wireless sensor networks have become an important part of data communications. Sensors provide information about the required measurements or control states over wireless networks. The energy efficient routing protocol of wireless sensor networks is the key issue for network lifetimes. The routing protocol must ensure that connectivity in a network is remained for a long period of time and the energy status of the sensor in the entire network must be in the same level in order not to leave the network with a wide difference in the energy consumptions of the sensors. In this paper we propose a new routing protocol based on AODV protocol that considers the energy efficiency when the protocol determines the routing paths, which is called AODV-EE. The proposed method prevents an imbalance of power consumption in sensors of wireless networks. From the simulation results it is shown that the proposed algorithm can be effectively used in collecting and monitoring data without concerning about the disconnection of the networks.