• Journal of KIISE:Computer Systems and Theory
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• v.26 no.12
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• pp.1504-1515
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• 1999

무선 이동 통신망은 기존의 음성위주로 제공되던 단일 미디어 서비스의 제공으로부터 발전되어 2000년대 초까지 이동 사용자에게 고품질의 멀티미디어 데이타 서비스를 제공하고, 장소에 제한을 받지 않고 서비스를 제공받을 수 있도록 하는 IMT-2000을 실현을 목표로 발전하고 있다. 또한 다수의 서비스 사용자와 광대역의 데이타를 전송하기 위해서 셀의 반경은 점차로 축소되고 있다. 이에 따라서, 사용자의 위치등록과 핸드오버와 같은 처리에 대한 부하가 커지게 되었다. 그러므로 무선 이동통신에서 서비스 이용자에게 일정 수준 이상의 QoS를 보장해 주기 위해서 효율적인 핸드오버 알고리즘의 도입은 매우 중요한 문제가 되고 있다. 본 논문에서는 IMT-2000환경에서 보다 효율적인 QoS를 서비스 사용자에게 제공해 줄 수 있도록 하기 위해 다양한 이동체의 속도와 멀티미디어 트래픽 특성을 동시에 고려하여 신뢰성 있는 핸드오버를 제공하는 H-PS(Hybrid-Priority Scheme)알고리즘을 제안하고 시뮬레이션을 통해 성능을 분석한다.Abstract Wireless mobile communications is developed from the only single voice traffic sevice to multimedia sevices. And mobile communications will evolve IMT-2000, which is provide users with high quality multimedia services. A radius of cell is gradually reduced to accept many service users and transport the multimedia traffics. Therefore, a overhead of location tracking and handover processing are increased. Then to guarantee high QoS to service users in wireless mobile communications, efficient handover algorithm is very important issue.In this study, we propose a H-PS(Hybrid-Priority Scheme) handover scheme considering mobility and traffic characteristics in IMT-2000 networks. And performance evaluate using simulation.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.3
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• pp.322-331
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• 2013

Wireless Mesh Networks(WMNs) is generally composed of radio nodes in the mesh topology. WMNs consists of mesh client, mesh router and gateway connected to a wired network. Each client and router relay messages to the gateway for communication. WMNs is widely used recently in many areas can provide extended coverage based on multi-hop communication and ubiquitous communication at any time and any location. However the competition and collision between each node to transmit data is inevitable when the same channel is used for transmission. The transmission opportunities and the throughput of nodes located far from gateway decrease more if the communication channel is accessed based on competitive CSMA/CA scheme using DCF(Distributed Coordination Function) provided by IEEE 802.11 MAC. In this paper, we improve the performance of the TCP fairness and throughput of the nodes with more than 2 hops by applying various algorithms for controlling contention window values. Also, we evaluate the performance using ns-2 simulator, According to the results, proposed scheme can enhance the fairness characteristic of each node irrespective of data to the gateway.

• Journal of Advanced Navigation Technology
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• v.4 no.2
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• pp.171-181
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• 2000

In this paper, we propose an AVLS(Automatic Vehicle Location System) using the DSRC(Dedicated Short Range Communication) which adopts a radio communication tool between RSE(Road-Side Equipment) and OBE(On-Board Equipment) on a vehicle and uses the ISM bandwidth of 5.8GHz radio frequency. Typical AVLS uses the sensors for detecting the vehicle, but the DSRC system is developed for supporting various services such as the position of vehicle, clearance, vehicle to vehicle communication, collection and distributions of traffic and road information. Also, for fast processing, we design three-layer configuration of physical(L1), data link(L2), and application layer(L7), which simplifies the seven-layer configuration. We suggest the proposed system as a new technology for replacement of typical wireless communication system and sensors for AVLS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7B
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• pp.628-640
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• 2004

The demand for next generation networks can be condensed into always-best-connected, ubiquitous, mobile, all-lP, and converged networks. IPv6 has been introduced for all-IP ubiquitous communications, and vehicles are coming to represent an important communication platform. In this paper. we propose various resource management schemes for in-vehicle mobile networks, which are adaptive to different hardware configurations. We focus on power and wireless bandwidth since they are critical resources for mobile communications. Based on the mobility characteristics of in-vehicle networks, we propose vehicle-aware power saving schemes. The main idea behind these power saving schemes is to adjust mobile router (MR) advertisement interval and binding lifetime. In addition, according to different wireless environments, we propose adaptive bandwidth management schemes using multihoming: best-connected MR selection based on location, and high-data-rate MR selection based on priority By mathematical analysis, it is shown that our schemes save power prominently for both the dormant nodes and active nodes. In addition, simulation results show that proposed multiple mobile router architecture outperforms previous simple redundant router architecture in preserving session and providing sufficient bandwidth.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.103-113
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• 2010

In this paper, a tradeoff between the total energy consumption-per-bit and the end-to-end rate under spatial reuse in wireless multi-hop network is developed and analyzed. The end-to-end rate of the network is the number of information bits transmitted (end-to-end) per channel use by any node in the network that is forwarding the data. In order to increase the bandwidth efficiency, spatial reuse is considered whereby simultaneous relay transmissions are allowed provided there is a minimum separation between such transmitters. The total energy consumption-per-bit includes the energy transmitted and the energy consumed by the receiver to process (demodulate and decoder) the received signal. The total energy consumption-per-bit is normalized by the distance between a source-destination pair in order to be consistent with a direct (single-hop) communication network. Lower bounds on this energy-bandwidth tradeoff are analyzed using convex optimization methods. For a given location of relays, it is shown that the total energy consumption-per-bit is minimized by optimally selecting the end-to-end rate. It is also demonstrated that spatial reuse can improve the bandwidth efficiency for a given total energy consumption-per-bit. However, at the rate that minimizes the total energy consumption-per-bit, spatial reuse does not provide lower energy consumption-per-bit compared to the case without spatial reuse. This is because spatial reuse requires more receiver energy consumption at a given end-to-end rate. Such degraded energy efficiency can be compensated by varying the minimum separation of hops between simultaneous transmitters. In the case of equi-spaced relays, analytical results for the energy-bandwidth tradeoff are provided and it is shown that the minimum energy consumption-per-bit decreases linearly with the end-to-end distance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.9
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• pp.17-26
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• 2011

Many types of services appear in a ubiquitous environment promulgated by the evolution of web service technology with the advances in wireless network technologies and mobile computing devices. These services differ according to their location environments, such as home, office, airport, and exhibition. It is required that a different set of services dynamically drops into the mobile user's device depending on their context and the distributed localized services are efficiently managed to seamlessly provide these localized services to the user. This paper proposes an Autonomic Service Composition System (ASCS) to provide useful services to the user with minimal or no effort for service selection. ASCS seamlessly installs the programs of localized services in the user's mobile device. It automatically provides localized services to users that are in the local service zone. Also ASCS can manage distributed localized services remotely and efficiently. ASCS is composed of a Remote Manager, Service Gateway, and Mobile Device. The prototype implementation uses 802.11b Wireless Network and Bundles using the OSGi Framework.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.3
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• pp.7-18
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• 2008

Radio systems decline in the system performances when one system is interfered from the other system. System parameters, which are operating frequency, transmit power, and so on, need to be determined in order that there is no interference between radio systems. We investigate the interference from the sound broadcasting service in the band 87.5-108 MHz to the ILS localizer, one of the aeronautical services, in the band of 108-112 MHz. The results are compared with the interference criteria. And then several system parameters, which are frequency, transmit power, and location, are determined in order to avoid the interference from the FM sound broadcasting service which occupies the frequency band near the band of the aeronautical services. The results of this paper can be applied to set up system parameters of the ILS localizer so that system performance can be maximized. Besides, the result of this paper can be applied for determining spectrum management policy.

• Journal of the Korea Society of Computer and Information
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• v.16 no.10
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• pp.121-129
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• 2011

In wireless sensor networks, a compromised sensor node can inject false data during data aggregation. Existing solutions of securing data aggregation require high communication cost in securing data aggregation. In this paper, we propose a monitoring-based secure data aggregation protocol that minimizes communication cost of identifying the location of false data injection attacks. The main idea is that when monitoring nodes find an injected false data, their reporting messages along with Message Authentication Codes (MACs) are summarized in a single message before sending it to the Base Station (BS). Then the BS identifies the attacking node. The simulation shows that energy consumption of the proposed protocol with short and normal concatenations of MACs are 45% and 36% lower than that of an existing protocol, respectively.

• Journal of Internet Computing and Services
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• v.11 no.2
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• pp.1-15
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• 2010

The damage of safety accidents at home can be minimized by preventing accidents in advance as well as by coping with the accidents promptly through the help of safety management system. In this paper, we identify several services to prevent and cope with the accidents that may occur at home by leveraging sensors and wireless network technology available at home network environments. In order to provide these services, we propose a context-aware system for safety management at home. The proposed system awares the dangerous situations through the information collected by the sensors in home network environment. The proposed system tries to not only prevent the accidents but also to cope with the situations using the information of rescue targets and the location where the accident occurs. We evaluate the appropriateness of sensors by implementing the proposed environments. Through OPNET simulation experiments, we also measure the amount of network traffic in order to confirm that the bandwidth of IEEE 802.15.4 is enough for the proposed system. Finally, we determine more appropriate wireless data transmission mechanism with respect to the end-to-end delay and battery consumption for the proposed system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.61-67
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• 2016

Opportunistic incremental relaying (OIR) system effectively overcomes the degradations caused by the fading of the wireless channel, and efficiently utilizes the wireless resources. Most of the OIR studies, however, assume spatially fixed relays. The user terminals which are usually served as relays move continuously, the assumption that the relays are fixed is not realistic. In this paper, the location of the spatially random user terminals are modeled by the Poisson point process, and the performance of an OIR system is derived. We noticed that the performance of the OIR system improves with the spatially random relays as well as with the fixed relays. Also the intensity of the relays and the transmitting directions toward the destination affect the performances. The performances of the maximal ratio combining (MRC) and the selection combining (SC) at the destination are compared.