• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.7
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• pp.728-736
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• 2014

Due to the recent development of mobile wireless telecommunication, RRHs(Remote Radio Heads) are widely being utilized to expand the cell coverage. Wire-link, an existing connection between DU(Digital Unit) and RRH through fiber cables, is considered to have limitations in relation to cost for a wide range of applications. This paper focuses on replacing the wire-link by wireless transmission using millimeter-wave, and implementing cellular network system through RRH from a remote location. After an influence element analysis on millimeter-wave wireless link transmissions, a comparative analysis between wireless link and an existing fiber link method will be made by utilizing currently commercialized LTE(Long Term Evolution), to prove the compatibility of millimeter-wave wireless link RRH method in replacing fiber link method without a significant decline in data transmission performance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.482-485
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• 2007

Recent generation of wireless computing has focus on the integrating of exisitng technologies to enhance the mobile capabilities and developing a new approaches to meet the needs of the growing pool of applications. This paper describes an integrated IEEE802.15.4 wireless CDMA based healthcare system that interacts and received the data wirelessly from wireless medical devices of patient and forward to medical center by using the cellular network. Mobile application had been developed not only as the middle ware to handle the receive and transmit of medical data between wireless sensor network and cellular network but also provides the interface for monitoring and analyzing the health condition of patients continuously at cellular phone regardless of its physical location. This system thus enables the remote healthcare monitoring and supports medical data seamlessly roams between IEEE802.15.4 wireless network and CDMA network beyond and outside the hospital environment.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.551-557
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• 2013

This research aims to conduct a study on the feasibility of the LTE communication method for developing a dedicated integrated railway wireless network. An empirical analysis was carried out by establishing a dedicated integrated railway wireless network in an approximately 12km section between Illo station and Daebul station on the Honam line. Korean wireless communication methods for railway safety are different depending on each line, which makes it difficult for railway workers to cooperate with. This causes various problems. There is the ever-present risk of accidents due to call disconnection between wireless communication systems, frequency interference from commercial networks, and crosstalk. This study verified the feasibility of the 4th generation communication system, LTE, over the dedicated integrated railway wireless network as a solution for the above mentioned problems. The result shows this communication system exceeded existing performance standards of Europe GSM-R in every test item despite the location constraint of train tracks on the base station establishment.

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.2
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• pp.48-62
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• 2006

In recent years, wireless sensor networks(WSNs) have emerged as a new fast-growing application domain for wireless distributed computing and embedded systems. Recent Progress in computer and communication technology has made it possible to organize wireless sensor networks composed tiny sensor nodes. Furthermore, ad-hoc network protocols do not consider the characteristics of wireless sensor nodes, making existing ad-hoc network protocols unsuitable for the wireless sensor networks. First, we propose power-aware routing protocols based on energy-centered routing metrics. Second, we describe power management techniques for wireless sensor nodes using the spatial locality of sensed data. Many nodes can go into a power-down mode without sacrificing the accuracy of sensed data. Finally, combining the proposed techniques, we describe an overall energy-efficient protocol for data collection. Experimental results show that the proposed routing protocol can extend the routing path lifetime more than twice. The average energy consumption per sensing period is reduced by up to 30%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.8
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• pp.942-949
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• 2016

Efficient routing protocols designed for Wireless Sensor Networks (WSN) can be extended and applied to Internet of Things (IoT) data routing, as IoT can be considered to be an extension from WSN. When the size of the data in IoT is often bigger than in conventional WSNs, existing cluster routing protocol such as LEACH may cause high data loss rate due to its incomplete load balancing. We present an enhanced LEACH-based protocol which can minimize the data loss which is an important performance measure in IoT. In our proposed protocol, the base station estimates the location of nodes by the trilateration technique to make sure optimal number of cluster heads and members in a deterministic manner. We evaluate our proposed protocol via computer simulations in terms of data loss rate and average network lifetime.

• Journal of information and communication convergence engineering
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• v.8 no.1
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• pp.1-5
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• 2010

In this paper, we propose for improving QoS in wireless micro cellular network using Cellular-IP/PRC(Paging Route Cache) with Paging Cache and Route Cache in Cellular-IP and propose for performance of realtime and non-real time handoff service using Handoff state machine Paging Route Cache. Although the Cellular-IP/PRC technology is devised for mobile internet communication, it bas its vulnerability in frequent handoff environment. On the other hand, Cellular IP combines the capability of cellular networks to provide high performance handoff and efficient location management of active and idle mobile users with the inherent flexibility, robustness and scalability found in IP networks. Also Cellular-IP/PRC use semi-soft handoff. During semi-soft hand off a mobile host may be in contact with either of the old and new base stations and receive packets from them. Packets intended to the mobile node are sent to both base stations and buffered, so when the mobile host eventually moves to the new location it can continue to receive packets without interruption. It should be suitable for realtime service such as multimedia traffic. But, much waste of resource will occur in this method, especially for non-real time services such as FTP and E-mail. Therefore, a new algorithm that performs different handoff according to characteristic of each traffic by use of reserved field in IP packet is proposed in this thesis. This hand off state machine using differentiated handoff improves quality of services in Cellular-IP/PRC. Suggested algorithm shows better performance than existing technology in wireless mobile internet communication environment. Matlab simulation results are improving QoS, show call drop and call blocking provided to Paging Router Cache during handoff state machine in Cellular-IP/PRC.

• The KIPS Transactions:PartC
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• v.11C no.5
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• pp.659-670
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• 2004

Handoff is one of the most important features for the user's mobility in a wireless cellular communication system. It is related to resource reservation at nearby cells. Resource reservation to the new connection point should occur prior to handoff to enable the user to receive the data or services at the new location, at the same level of service as at the previous location. For the efficient resource reservation, mobility prediction has been reported as an effective means to decrease the call dropping probability and to shorten the handoff latency in a wireless cellular environment. A recently proposed algorithm, ZMHB, makes use of the history of the user's positions within the current cell to predict the next cell. But, the prediction of the ZMHB algorithm is found to be 80∼85% accurate for regular and random movements. In this paper, we propose a new improved ZMHB mobility prediction algorithm, which is called Detailed-ZMHB that uses detailed-zone-based tracking of mo-bile users to predict user movements. The effectiveness of the proposed algorithm is then demonstrated through a simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.643-650
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• 2014

Recently, the wireless communication applications are studied in various environment by the development of short range communication system like wireless sensor networks. This paper presents the analysis of localization schemes for ship application using received signal strength. The localization schemes using received signal strength from wireless networks are classified under two methods, which are Range based method and Range free method. Range based methods estimate the location with least square estimation based on estimated distance using path-loss model. Range free methods estimated the location with the information of anchor nodes linked to target. Simulation results show the appropriate localization scheme for each cabin environments based on the empirical path-loss model in warship's internal space.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.6
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• pp.207-214
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• 2011

In this paper, using Zigbee-based wireless sensor networks and Lego MindStorms NXT robot, a remote monitoring and navigation system for mobile robot has been developed. Mobile robot can estimate its position using encoder values of its motor, but due to the existing friction and shortage of motor power etc., error occurs. To fix this problem and obtain more accurate position of mobile robot, a ultrasound module on wireless sensor networks has been used in this paper. To overcome disadvantages of ultrasound which include straightforwardness and narrow detection coverage, we rotate moving node attached to mobile robot by $360^{\circ}$ to measure each distance from four fixed nodes. Then location of mobile robot is estimated by triangulation using measured distance values. In addition, images are sent via a network using a USB Web camera to smart phone. On smart phones we can see location of robot, and images around places where robot navigates. And remote monitoring and navigation is possible by just clicking points at the map on smart phones.

• Journal of Advanced Navigation Technology
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• v.10 no.4
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• pp.291-298
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• 2006

A new intelligent paging algorithm is proposed in this paper to maximize the paging capacity in wireless link of mobile communication systems. Intelligent paging algorithms have been studied to utilize limited wireless resource efficiently, in which a location area is divided to several paging areas which are searched sequentially. Previous intelligent paging methods mainly use location probability distribution of the paging target terminal to determine paging areas. However, these methods make the paging traffic of each cell non-uniformly distributed. Therefore, in relatively low paging load conditions, there exist cells congested with paging traffic in which paging traffic queues are overflowed and paging messages are lost. The proposed method determines paging areas to make the paging traffic distributed uniformly among cells by considering current paging traffic distribution in each cell. Performance evaluation shows that the proposed method outperforms the previous paging schemes much with respect to paging processing capacity.