• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1B
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• pp.9-18
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• 2006

Advances in wireless network are enabling the development of ubiquitous multimedia services. These multimedia services need efficient platforms to comply with the requirements of mobile computing. We introduce an adaptive service platform based on mobile agent and grid systems while specifying the challenges of ubiquitous multimedia services and focusing on frequent disconnections and scarce resources. We applied our platform to framework RtoA (Ready-to-Attend) which supports mobile users to access compute-intensive multimedia service, specifically, mobile education and video conferencing. RtoA includes hand-off, speaker and listener service which enable people to attend a conference or a class with satisfying quality of multimedia service. ns-2 based simulation verifies that our scheme is an efficient way to reduce energy consumption of mobile devices and to improve the response time of mobile applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7B
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• pp.502-509
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• 2008

Wireless sensor networks consist of sensor nodes which are expected to be battery-powered and hard to replace or recharge. Thus, reducing the energy consumption of sensor nodes is an important design consideration in wireless sensor networks. For the implementation of energy-efficient MAC protocol, Sensor-MAC based on IEEE 802.11 protocol. In this paper, which has energy efficient scheduling, was proposed. In this paper, we propose Dynamic S-MAC that is dynamically operated by network-traffic states. Dynamic S-MAC protocol improves energy consumption of S-MAC due to change the frame length according to network-traffic states. Using NS-2 Simulation, we compare the performance of Dynamic S-MAC with S-MAC protocol.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.12
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• pp.69-77
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• 2010

This paper presents a fast IP mobility management scheme in heterogeneous networks using the multiple wireless network interlaces. More specifically, in order to minimize the packet loss and handover latency due to handover, the E-HMIPv6, IETF HMIPv6 has been extended, is presented where the multiple tunnels between E-MAP and mobile node are dynamically constructed. E-HMIPv6 is composed of the extension of IETF HMIPv6 MAP, handover procedure, and simultaneous multiple tunnels. In order to demonstrate superior to the proposed method, the NS-2 simulation has done for performance evaluation of TCP and UDP-based application comparison with the existing mobility management method.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.4
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• pp.239-243
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• 2011

In wireless ad-hoc network, the detection of link breakage and re-establishing the route path causes lots of network overhead and results in communication delay. In the LBN method, the node causing a link breakage actively sends a message to neighbors so that they can instantly start re-establishing process of new path. In this paper we describe the result of network simulation we performed using NS2 to show the effectiveness of LBN method.

• The KIPS Transactions:PartC
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• v.12C no.3 s.99
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• pp.437-442
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• 2005

The measurement of RTT (Round Trip Time) can be used for the analysis of Internet congestion. However, simple measuring of RTT which measures only hun around time of a packet can not infer a packet forward/backward delay variation. In this thesis, we present a new algorithm which can be used for the estimation of forward/backward delay variation of packets. These delay variations are implication of network congestion state. In this algorithm, the reference forward/backward delay can be determined based on the minimum RTT value. The delay variation of each packet can be calculated by comparing reference delay with the packet delay. We verified our proposed algorithm by NS-2 simulation and delay measuring in a real network.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.9
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• pp.690-694
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• 2009

In this paper, we propose a hybrid MAC architecture for reducing energy consumption and maximizing network lifetime in wireless sensor networks. For this purpose, the hybrid MAC architecture is proposed for energy efficient by combining inter-cell TDMA and intra-cell CSMA scheme. Based on the ns-2 simulation result, we prove that the proposed architecture improves energy efficiency as compared with CSMA and TDMA.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.4
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• pp.758-765
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• 2008

Wide-spread deployment of infrastructure WLANs has made Wi-Fi an integral part of today's Internet access technology. WLANs suffer from degraded system throughput and each node's throughput fluctuates significantly in the saturation regime. In this paper, we propose a link layer traffic control mechanism which controls the offered load of DCF system. It is shown that the link layer traffic controller can improve DCF system throughput and reduce nodes' throughput fluctuation with properly controlled offered load. We propose a dynamic traffic control algorithm which can find an optimal offered load and show its performance improvement with ns-2 simulation.

• Journal of the Korea Society for Simulation
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• v.16 no.2
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• pp.17-26
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• 2007

In this paper, we propose a basic virtual grid-based routing algorithm in order to devise an efficient routing method in ad hoc networks using the location information of nodes, energy level, etc. A packet is forwarded to the X-axis direction at first based on the location information of a destination node, and then it is forwarded to the Y-axis direction as its location becomes close to the destination from the viewpoint of the X-axis. Due to the selection of next hop nodes to deliver a packet from a certain node to a destination node, we can regard the whole network as a virtual grid network. The proposed routing algorithm determines routing paths using the local information such as the location information of a destination and its neighbor nodes. Thus, the routing path setup is achieved locally, by which we can expect reduction in network traffics and routing delays to a destination. To evaluate the performance of the proposed routing algorithm, we used the network simulator ns2 and compared its network throughput with that of an existing routing algorithm.

• Journal of Digital Contents Society
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• v.16 no.3
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• pp.365-371
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• 2015

In wireless network, the amount of video streaming packet information in receiver replay buffer can be varied according tothe wireless network condition. By the effect, unforeseeable delay and jitter are generated and then busty video traffics can be made. If the amount of buffer information coming in receiver replay buffer is larger than the amount of a specific buffer information, buffer overflow is generated. Such a problem makes the image skip effect and packet loss, and then causes the quality degradation and replay discontinuity of the video streaming service in destination receiver. To solve the buffer overflow problem, this paper applies the token bucket for the busty traffic to the receiver terminal and analyzes the effect of the token bucket. The simulation result using NS-2 and JSVM shows that the proposed scheme with the token bucket has significantly better performance than the conventional scheme without the token bucket in terms of overflow generation number, packet loss rate and PSNR.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.4
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• pp.80-85
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• 2011

A time-pickoff circuit used for time measurement suffers from a timing error due to the dependence of the generation time of a timing pulse on the size of the input signal, i.e., time walk. In this study, a time-pickoff method, which employs an automatic gain control (AGC) circuit, is proposed for reducing the timing error. The AGC circuit is added to the input of the comparator, and it renders the sizes of input signals of the comparator relatively uniform. The performance of the proposed time-pickoff method is analyzed using the SPICE simulation, and experiments are performed to confirm the analytical results. The measured time walk is reduced to 2.000 ns by 65% for input signals with a dynamic range of 20 dB as compared to a typical leading-edge discriminator.