• Journal of Institute of Control, Robotics and Systems
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• v.6 no.8
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• pp.638-651
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• 2000

When the bandwidth resources in a packet-switched network are shared among sessions by MAX-MIN flow control each session is required to transmit its data into the network subject to the MAX-MIN fair rate which is solely determined by network loadings. This passive behavior of sessions if fact can cause seri-ous QoS(Quality of Service) degradation particularly for real-time multimedia sessions such as video since the rate allocated by the network can mismatch with what is demanded by each session for its QoS. In order to alleviate this problem we extend the concept of MAX-MIN fair bandwidth allocations as follows: Individual bandwidth demands are guaranteed if the network can accommodate them and only the residual network band-width is shared in the MAX-MIN fair sense. On the other hand if sum of the individual bandwidth demands exceeds the network capacity the shortage of the bandwidth is shared by all the sessions by reducing each bandwidth guarantee by the MAX-MIN fair division of the shortage. we present a novel flow control algorithm to achieve this extended MAX-MIN fairness and show that this algorithm can be implemented by the existing ATM ABR service protocol with minor changes. We not only analyze the steady state asymptotic stability and convergence rate of the algorithm by appealing to control theories but also verify its practical performance through simulations in a variety of network scenarios.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.5
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• pp.553-563
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• 2015

Reportedly the fatality rate from secondary collision is six times higher than the average fatality rate from all traffic accidents. So prevention of the secondary collision is attracting significant attention from automotive industries. However, the secondary collision prevention systems that have been developed are not considering possibility of brake actuator failure that can occur by the impact during the initial collision. In this paper, a new system has been developed that could prevent secondary collision even in case of brake actuator failure by taking advantage of still operating actuators. In this system, a steering control is performed for maintaining a lane by using linear quadratic regulator. Additionally, the system attempts differential brake control with the remaining braking capability to stop the vehicle in the shortest distance. Through simulation in various collision scenarios, the system has demonstrated significant potential of preventing secondary collision that could otherwise have resulted in severe fatality.

• Journal of KIISE:Information Networking
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• v.37 no.1
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• pp.35-41
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• 2010

Since the ad-hoc network allow nodes to communicate each other without infrastructure system and predefined configuration, it comes into the spotlight that is suitable to ubiquitous society. In ad-hoc network, route recovery mechanism is considered important. Normally route recovery is needed to solve the link failure problem because there is no route maintaining system like a router in ad-hoc networks. In this paper we propose BS-AODV(Bidirectional Searching-AODV) route recovery method. The proposed method is a local repair method that can be applied in all of the network area. Unlike a limited local repair method in AODV. the proposed method adopts the bidirectional searching method where the upstream/downstream nodes can send the route maintenance messages. Restricting the flooding of route request messages, the proposed scheme attempts to minimize the costs of local repair, the performance of the proposed scheme is evaluated through the simulations. In two scenarios which variate the node numbers and node speed, the comparison among the proposed scheme, AODV and AOMDV is shown in terms of the control traffic and data delivery ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.11
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• pp.979-985
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• 2012

The design of an efficient scheduler is a key design factor in IEEE 802.16m systems, in order to support services with various QoS smoothly. Although conventional studies of schedules have been suggested, those had problems that are not able to satisfy the delay condition and make the through-put declined, because they only focused on a specific action scenario rather than reflecting practical action scenarios which have real-time and non-real-time traffics variously. In this paper, an efficient uplink scheduling algorithm is proposed for IEEE 802.16m system by introducing the concepts of Virtual Time(VT) and Virtual Finish Time(VFT) based priority determination, and separate buffers for each QoS class in the mobile terminal. Simulation results showed that the proposed scheme had satisfied the delay requirement of real-time services even with improved throughput performance compared to conventional methods.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.10a
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• pp.32-33
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• 2013

In the past, the scenario of VTS simulator was made by instructor's manual operation using waypoint definition of target ship. but in this study, we use automatic scenario creation technology with AIS data and Port-MIS data. The created VTS simaulator scenario also can be modified, added, and saved by instructor's manual operation. VTS simulator display target ship on the Electronic Navigation Chart based on S-57 format. A instructor can easily open this scenario and start, pause, stop operation wirth VTS simulator. A new modification also can be applied immediately to current scenario and can be saved new scenario file. VTS simulator using this technology can create many scenarios for a specific purpose and can be easily used for various application fields.

• Journal of Communications and Networks
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• v.11 no.6
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• pp.574-588
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• 2009

Although much research has been conducted in the area of authentication in wireless networks, vehicular ad-hoc networks (VANETs) pose unique challenges, such as real-time constraints, processing limitations, memory constraints, frequently changing senders, requirements for interoperability with existing standards, extensibility and flexibility for future requirements, etc. No currently proposed technique addresses all of the requirements for message and entity authentication in VANETs. After analyzing the requirements for viable VANET message authentication, we propose a modified version of TESLA, TESLA++, which provides the same computationally efficient broadcast authentication as TESLA with reduced memory requirements. To address the range of needs within VANETs we propose a new hybrid authentication mechanism, VANET authentication using signatures and TESLA++ (VAST), that combines the advantages of ECDSA signatures and TESLA++. Elliptic curve digital signature algorithm (ECDSA) signatures provide fast authentication and non-repudiation, but are computationally expensive. TESLA++ prevents memory and computation-based denial of service attacks. We analyze the security of our mechanism and simulate VAST in realistic highway conditions under varying network and vehicular traffic scenarios. Simulation results show that VAST outperforms either signatures or TESLA on its own. Even under heavy loads VAST is able to authenticate 100% of the received messages within 107ms. VANETs use certificates to achieve entity authentication (i.e., validate senders). To reduce certificate bandwidth usage, we use Hu et al.'s strategy of broadcasting certificates at fixed intervals, independent of the arrival of new entities. We propose a new certificate verification strategy that prevents denial of service attacks while requiring zero additional sender overhead. Our analysis shows that these solutions introduce a small delay, but still allow drivers in a worst case scenario over 3 seconds to respond to a dangerous situation.

• Journal of Navigation and Port Research
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• v.33 no.6
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• pp.415-421
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• 2009

Recently, the volume of transshipment containers in Busan Port has been declining significantly and domestic ports' throughput is shown far below the projected one. Accordingly, the national port development plan made to capture the sharply increasing demand in the past seems to be subject to an amendment, and inducing port container traffic becomes a key issue. In such situation this paper aims at analysing the effect of logistics cost saving when Japanese import and export containers are transshipped in Busan port. For this we developed 3 scenarios for the movement of containers through the major container ports in western cost of Japan, analysed logistics costs together with cost savings and finally derived some implication for inducing the containers to Busan Port.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.7
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• pp.1256-1271
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• 1994

In this paper a GFC protocol based on HMR(High-speed Multimedia Ring) with a dynamic quota allocation is proposed and the performance of proposed protocol is evaluated by simulation. The HMR a medium access protocol proposed for Gbit ATM-LAN, can be applied to the GFC protocol without any modification because it uses only 4 bits for medium access of several topologies such as bus, ring and stared-bus, and priority control for satisfaction of different QoS(Quality of Service) requirements. The quota allocation method of HMR called static quota allocation has a problem of excessive access delay for the traffic with high burstness. In this paper a dynamic quota allocation method which allocates quota to the nodes according to the queue length is proposed and the performance of HMR with dynamic quota allocation is evaluated by seven simulation scenarios of CCITT. The HMR with proposed method shows better shows better access delay characteristics than the HMR with static quota allocation. Also the simulation results show that access delay performance of HMR is better than that of ATMR proposed by Japan and is similar to that of DQDB proposed by Australia.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8C
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• pp.731-741
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• 2009

Optical repeater is often installed at the isolated area. Spatial separation makes it possible to reduce the inter-code interference when secondary scrambling codes are used for traffic connected through repeater. In this paper, we propose five secondary scrambling code usage scenarios with the aids of optical repeater to maximize the user capacity. In order to evaluate the performance, dynamic system level simulation is performed. We also propose a base station-repeater switching where each active users can change access points by comparing the channel condition from base station and repeater thorough secondary common pilot channel (S-CPICH) signal to noise-interference ratio (SINR). Moreover, primary-secondary scramble code replacing scheme is proposed which replaces secondary scramble code with primary scramble code when a call using primary scramble code is ended and its corresponding OVSF code is available to users using the secondary scramble code

• Journal of Environmental Impact Assessment
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• v.7 no.2
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• pp.89-102
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• 1998

The purpose of this study is to seek AEI(Air Environmental Indices), PSI(Pollutant Standard Index) and the urban air quality control goal(the best available alternative energy program) by assessing the best ratio of energy types used in urban enterprises, based on harmful health effect and air quality standard and costs. This study is focused on an urban area(Puchun), where area sourcees are associated with heavy traffic, large population, and its industrial sources with large emissions. In the first step, air modeling, estimation of AEI and PSI, and benefit-cost analysis were carried out. In the second step, we assessed that 660 scenarios about the ratio of B-C oil, light oil and LNG used in urban enterprises with regard to air quality and cost. In the third step, the best available alternative energy program was selected for the ratio of energy species(B-C oil, light oil and LNG) by using the lexicographic method. From the emission analysis, main source of $NO_2$ is identified as industries and air quality is evaluated according to the ratio of B-C oil, light oil and LNG used in urban enterprise. The modeling data of TSP, $SO_2$, $NO_2$, CO, $O_3$, by ISC3 and PBM are respectively $118{\mu}g/m^3$, 0.027ppm, 0.025ppm, 2.0ppm, 0.55ppm in indurstrial area. That data are close to Environmental Air Quality Standard. By means of sensitivity analysis, we obtained the difference in concentration between the areas(Nae-dong, Joong-dong) according to the ratio of B-C oil, light oil and LNG used in the industries. From the result of alternatives assessment the lowest AEI value and cost, the ratio of B-C oil, light oil and LNG are 2.5%, 20%, 77.5%, respectively.