• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5B
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• pp.741-752
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• 2010

The ability to seamlessly switch between the macro networks and femtocell networks is a key driver for femtocell network deployment. The handover procedures for the integrated femtocell/macrocell networks differ from the existing handovers. Some modifications of existing network and protocol architecture for the integration of femtocell networks with the existing macrocell networks are also essential. These modifications change the signal flow for handover procedures due to different 2-tier cell (macrocell and femtocell) environment. The handover between two networks should be performed with minimum signaling. A frequent and unnecessary handover is another problem for hierarchical femtocell/macrocell network environment that must be minimized. This work studies the details mobility management schemes for small and medium scale femtocell network deployment. To do that, firstly we present two different network architectures for small scale and medium scale WCDMA femtocell deployment. The details handover call flow for these two network architectures and CAC scheme to minimize the unnecessary handovers are proposed for the integrated femtocell/macrocell networks. The numerical analysis for the proposed M/M/N/N queuing scheme and the simulation results of the proposed CAC scheme demonstrate the handover call control performances for femtocell environment.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.112-120
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• 2009

Both security enhancement in wireless and fast access for mobility are required to employ wireless LAN in ITS (Intelligent Transportation Systems). However, for the case of employing IEEE 802.11i security standard, it is known that the user authentication procedure of IEEE 802.1x and 4-way handshake procedure for stronger security enforcement may not be suitable for ITS due to its large delay. In this paper, we propose fast authentication method to resolve the above authentication delay problem, and verify its performance via simulation analysis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1558-1564
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• 2006

This study addressed security requirements for ad-hoc network environments, which lies at the hour of the ubiquitous computing revolution and proposed a partially-distributed certificate management system that can ensure security in mobile ad-hoc networks. The proposed model is characterized by ie ability to handle dynamic mobility of nodes, minimize routing load and enhance expandability of network by allowing participating nodes to authenticate each other without being interrupted by joining the cluster. The security, efficiency and robustness of the proposed model were evaluated through simulation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.5
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• pp.169-175
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• 2015

In the field of health informatics converging ICT technology and medicine technology, XML-based CCR document make sure the continuity and mobility of the information of patients. When a number of clients access CCR documents, wireless data broadcast that supports any number of clients can be an alternative for the scalability. In this paper, we propose a framework for wireless data broadcast of XML-based CCR documents. We design and implement the framework that can adopt various data scheduling algorithms and indexing schemes for the optimized performances of clients. The implemented framework shows the efficiency with simulations adopting various data scheduling algorithms and indexing schemes.

• Journal of Communications and Networks
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• v.11 no.6
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• pp.626-633
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• 2009

Lawful interception (LI) involves legally accessing private communication such as telephone calls or email messages. Numerous countries have been drafting and enacting laws concerning the LI procedures. With the proliferation of portable Internet services such as the IEEE 802.16e wireless mobile networks, surveillance over illegal users is an emerging technical issue in LI. The evermigrating users and their changing IP's make it harder to provide support for seamless LI procedures on 802.16e networks. Few studies, however, on seamless LI support have been conducted on the 802.16e mobile networks environments. Proposed in this paper are a seamless LI architecture and algorithms for the 802.16e networks. The simulation results demonstrate that the proposed architecture improves recall rates in intercepting mobile user, when compared to the existing LI architectures.

• Journal of Communications and Networks
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• v.15 no.5
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• pp.527-537
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• 2013

Improving resource utilization has been a hot issue in heterogeneous wireless networks (HWNs). This paper proposes a radio resource management (RRM) method based on access proportion optimization. By considering two or more wireless networks in overlapping regions, users in these regions must select one of the networks to access when they engage in calls. Hence, the proportion of service arrival rate that accesses each network in the overlapping region can be treated as an optimized factor for the performance analysis of HWNs. Moreover, this study considers user mobility as an important factor that affects the performance of HWNs, and it is reflected by the handoff rate. The objective of this study is to maximize the total throughput of HWNs by choosing the most appropriate factors. The total throughput of HWNs can be derived on the basis of a Markov model, which is determined by the handoff rate analysis and distribution of service arrival rate in each network. The objective problem can actually be expressed as an optimization problem. Considering the convexity of the objective function, the optimization problem can be solved using the subgradient approach. Finally, an RRM optimization scheme for HWNs is proposed. The simulation results show that the proposed scheme can effectively enhance the throughput of HWNs, i.e., improve the radio resource utilization.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.5
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• pp.434-437
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• 2002

A small size and light-weight DSP board is newly designed for a real time multi-distributed control system that overcomes constraints on time and space. There are a variety of protocols for a real-time distributed control system. In this research, we selected CAN for the multi distributed control, which was developed by the BOSCH in the early 1980's. If CAN and Internet are connected together, the system attains the characteristics of a distributed control system and a remote control system simultaneously. To build such a system. The TCP/IP-CAN Gateway which converts a CAN protocol to TCP/IP protocol and vice verse, was designed. Moreover, the system is required to be small and light-weighted for the high mobility and cost effectiveness. The equipment in remote place has a TCP/IP-CAN Gateway on itself to be able to communicate with another systems. The received commands in the remote site are converted from TCP/IP protocol to CAN protocol by the TCP/IP-CAN Gateway in real time. A simulation system consists of a TCP/IP-CAN Gateway in remote place and a command PC to be connected to Ethernet.

• ETRI Journal
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• v.38 no.3
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• pp.551-559
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• 2016

In this paper, we propose a hybrid sensor calibration scheme for mobile crowdsensing applications. As the number of newly produced mobile devices containing embedded sensors continues to rise, the potential to use mobile devices as a sensor data source increases. However, because mobile device sensors are generally of a lower performance and cost than dedicated sensors, sensor calibration is crucial. To enable more accurate measurements of natural phenomena through the use of mobile device sensors, we propose a hybrid sensor calibration scheme for such sensors; the scheme makes use of mobile device sensors and existing sensing infrastructure, such as weather stations, to obtain dense data. Simulation results show that the proposed scheme supports low mean square errors. As a practical application of our proposed scheme, we built a temperature map of a city using six mobile phone sensors and six reference sensors. Thanks to the mobility of the sensors and the proposed scheme, our map presents more detailed information than infrastructure-based measurements.

• ETRI Journal
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• v.39 no.3
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• pp.353-363
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• 2017

Recently, sink mobility has been shown to be highly beneficial in improving network lifetime in wireless sensor networks (WSNs). Numerous studies have exploited mobile sinks (MSs) to collect sensed data in order to improve energy efficiency and reduce WSN operational costs. However, there have been few studies on the effectiveness of MS operation on WSN closed operating cycles. Therefore, it is important to investigate how data is collected and how to plan the trajectory of the MS in order to gather data in time, reduce energy consumption, and improve WSN network lifetime. In this study, we combine two methods, the cluster-head election algorithm and the MS trajectory optimization algorithm, to propose the optimal MS movement strategy. This study aims to provide a closed operating cycle for WSNs, by which the energy consumption and running time of a WSN is minimized during the cluster election and data gathering periods. Furthermore, our flexible MS movement scenarios achieve both a long network lifetime and an optimal MS schedule. The simulation results demonstrate that our proposed algorithm achieves better performance than other well-known algorithms.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.3
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• pp.29-36
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• 2005

With the rapid growth of the Internet, the Internet-based robot has been realized by connecting off-line robot to the Internet. However, because the Internet is often irregular and unreliable, the varying time delay in data transmission is a significant problem for the construction of the Internet-based robot system. Thus, this paper is concerned with the development of an Internet-based robot system, which is insensitive to the Internet time delay. For this purpose, the PPS (Position Prediction Simulator) is suggested and implemented on the system. The PPS consists of two parts : the robot position prediction part and the projective virtual scene part. In the robot position prediction part, the robot position is predicted for more accurate operation of the mobile robot, based on the time at which the user's command reaches the robot system. The projective virtual scene part shows the 3D visual information of a remote site, which is obtained through image processing and position prediction. For the verification of this proposed PPS, the robot was moved to follow the planned path under the various network traffic conditions. The simulation and experimental results showed that the path error of the robot motion could be reduced using the developed PPS.