• Convergence Security Journal
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• v.10 no.1
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• pp.41-48
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• 2010

Greedy protocols show good performance in Vehicular Ad-hoc Networks (VANETs) environment in general. But they make longer routes causing by surroundings or turn out routing failures in some cases when there are many traffic signals which generate empty streets temporary, or there is no merge roads after a road divide into two roads. When a node selects the next node simply using the distance to the destination node, the longer route is made by traditional greedy protocols in some cases and sometimes the route ends up routing failure. Most of traditional greedy protocols just take into account the distance to the destination to select a next node. Each node needs to consider not only the distance to the destination node but also the direction to the destination while routing a packet because of geographical environment. The proposed routing scheme considers both of the distance and the direction for forwarding packets to make a stable route. And the protocol can configure as the surrounding environment. We evaluate the performance of the protocol using two mobility models and network simulations. Most of network performances are improved rather than in compared with traditional greedy protocols.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.6
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• pp.39-47
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• 2009

This paper presents implementation of two types of the 802.11 MAC engine for the next generation WLAN, 802.11n. The first version of MAC engine consists of hardwired logic and embedded firmware. Hardwired logic includes Tx block, Rx block, Backoff block, and ChannelManage block. Embedded firmware contains Protocol Control block, MLME block, and MSDU processing block. The first version has a time-critical fault during the atomic transmission caused by software overhead, so it can not be applied to 802.11n MAC. For that reason, the second version has additional blocks with hardwired logic modules to reduce software overhead of the first version. This enhanced version has 73Mbps throughput and it is expected to be further improved up to 129 Mbps with frame aggregation which is one of the key additional features of 802.11n. As a result, the second version of MAC engine can be applied to 802.11n MAC.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.5
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• pp.151-159
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• 2009

Network models for pedestrian flows have been studied in various ways. However, because of the simplicity and application, a number of researchers prefer the CA Model to analyze pedestrian's complicated behavior. These kinds of models based on Agent are being used as a microscopic analyzing method since it can easily adapt individuals' various characters and movement types. However, because pedestrians' movement can be (easily) effected by where they are and where they head, some models using the same rules have limit when considering pedestrians' every different movement. In this research, homogeneous section is defined as a similar movement type of individuals. With MDPM, we suggest simulation method explaining one-way walk and side-walk which could not be done in past.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6C
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• pp.581-593
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• 2002

In this paper, we proposed an Adaptive RIO scheme to solve the problem of RIO scheme that occurs when admission control is performed for QoS guarantee of Assured Service in Differentiated Services. To prevent an early random drop of the admitted In-profile packet, proposed Adaptive RIO scheme updates parameters of RIO scheme every time interval according to the estimated numbers of maximum packet arrivals of In-profile traffic and total traffic during the next time interval. The numbers of maximum packet arrivals during the next time interval are estimated based on the buffer size determined by the network topology and the ratio of bandwidth allocated to each subclass. We found from simulation results that, compared with RIO scheme, proposed Adaptive RIO scheme can improve performance of the throughput for In-profile traffic when admission control is performed or congestion occurs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1078-1087
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• 2014

In the conventional centralized mobility management schemes, it can lead to single points of failure, occurrence of a bottleneck, since all data and control are concentrated on the mobility anchor which is located in home network. In the current research of distributed mobility management, it is doing research into distributed mobility management which is supported by distributed mobility anchors. Such schemes do not consider a failure of the mobility anchor. However, it could be an issue under tactical environment since it occur non-service problem due to anchor movement, maintenance, failure, etc. In this paper, we proposed new DMM scheme named T-DMM(Tactical-Distributed Mobility Management) which can support handover even if mobility anchor breaks down. From the numerical analysis, we evaluate signaling cost and handover latency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.1
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• pp.43-56
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• 2013

Personal Rapid Transit(PRT), which is one of the next generation convergence transport technology, PRT system requires operation technology for controlling diverse vehicles and dealing with a variety of abnormal driving situations on a large scale trackway structures in expected operational area more efficiently and reliably. Before developing PRT control technology, it is essential that multiple testing procedures stepwise with building small scale test-tracks and develop real unmanned-vehicles. However, it is expected that the experiments demand huge amount of time and physical cost. Thus, simulation in virtual environment is efficient to develop wireless based control technology for multiple PRT vehicles prior to building real-test environment. In this paper, we propose a VR-based integrated simulator which physics engine is applied so that it enables simulation of front-wheel-steering PRT system rather than simple rail track system. The proposed simulator is also developed that it can reflect geographical features, infrastructures and network topology of expected driving region.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1B
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• pp.1-7
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• 2008

In group location management, when a transportation system(TS) with multiple mobile subscribers(MSs) changes location area(LA), location management is performed by group location registration by TS, instead of individual location registrations by MSs. In previous works, although it is assumed that LA in group location management is the same as that in individual location management, it is not appropriate to assume the same sized LAs since MSs in a TS have different characteristics from MSs which are not in a TS from the aspect of the speed and aggregate call arrival rates. Thus, in this paper, we propose an efficient location management scheme based on individual and group location managements with different sized LAs, and the performance of the proposed scheme is analyzed from the aspect of signaling cost at the wireless interface. Results reveal that the proposed scheme outperforms the conventional scheme by selecting an appropriate sized LA for group location management.

• The Transactions of the Korea Information Processing Society
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• v.6 no.2
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• pp.367-376
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• 1999

A variable bit-rate based video services have much limitation for bandwidth management, since its trarfic has a some variances in frame level. In particular, the bandwidth management for video which has characteristics of VBR traffic such a MPEG video could be more complicated. Also, it is difficult to manage the bandwidth effectively for proving a VCR function from VOD service, since we don't know the traffic variance exactly at that time. In this paper, we proposed the dynamic bandwidth allocation a scheme based on VBR traffic based stored video such as MPEG for interactive video service. This scheme can maximize the given total bandwidth through the prefetch based variable length bandwidth allocation scheme and dynamic bandwidth management scheme for multiple streams. Also, our scheme can be used for a MPEG-based bandwidth allocation scheme, and provides the method that can maximize the utilization of network resource for multiple stream by using a dynamic bandwidth management.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4B
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• pp.377-386
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• 2009

IPTV technology for providing multimedia content with high-speed is the network which combines existing network, multimedia and internet technology etc. But internet, broadcasting and web technologies which is now being used is not optimized to IPTV because the security problem between user who gets content service through mobile units and content server is not guaranteed. This paper proposes user certification mechanism between mobile device and content server to receive the service which the user for the content chooses by mobile device safely. The proposed mechanism uses the random number which user creates and certification token for preventing illegal user who uses other's service that already paid. Also the proposed protocol encrypts the delicate data like user's information or profile using shared-key between java card attached on user's mobile device and grant sewer and then prevents reply attack which happens often in wireless section and man-in-the-middle attack by MAC.

• Convergence Security Journal
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• v.21 no.1
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• pp.129-135
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• 2021

Greedy protocols show good performance in Vehicular Ad-hoc Networks (VANETs) environment in general. But they make longer routes causing by surroundings or turn out routing failures in some cases when there are many traffic signals which generate empty streets temporary, or there is no merge roads after a road divide into two roads. When a node selects the next node simply using the distance to the destination node, the longer route is made by traditional greedy protocols in some cases and sometimes the route ends up routing failure. Most of traditional greedy protocols just take into account the distance to the destination to select a next node. Each node needs to consider not only the distance to the destination node but also the direction to the destination while routing a packet because of geographical environment. The proposed routing scheme considers both of the distance and the direction for forwarding packets to make a stable route. And the protocol can configure as the surrounding environment. We evaluate the performance of the protocol using two mobility models and network simulations. Most of network performances are improved rather than in compared with traditional greedy protocols.