• Journal of Advanced Navigation Technology
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• v.1 no.1
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• pp.47-58
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• 1997

In this paper, the modified aviation TDMA protocol that can improve the aeronautical communication spectrum utilization is studied to satisfy the increasing air traffic demands. Currently European states proposed the scheme reducing the channel spacing from current 25 kHz to 8.33 kHz and U. S. FAA proposed the system using TDMA technique that divides access into four parallel circuits. The modified aviation TDMA protocol can complement the defects of these current systems. In modified aviation TDMA protocol, message channel that is used between aircraft and ground station is divided into uplink channel and downlink channel. After receiving the acknowledgement of the reservation request, aircraft sends messages at the allocated slots. Numerical analysis and simulation results show that the modified aviation TDMA scheme has high channel efficiency in the aviation environment.

• Journal of Korea Society of Industrial Information Systems
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• v.4 no.4
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• pp.1-6
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• 1999

When continuous media are transmitted over the communication networks, asynchrony which can not maintain temporal relationships among packets my occur due to a random transit delay. There exist two types of synchronization schemes ; for guaranteed or non-guaranteed resource networks. The former which applies a resource reservation technique maintains delay characteristics however, the latter supply a best-effort service. In this paper, I propose a intra-media synchronization scheme to transmit continuous media on general networks not guaranteeing a bounded delay time. The scheme controls transmission times of the packets by estimating next delay time with the delay distribution So, the arriving packets my be maintained within a limited delay boundary, and playout will be performed after buffering to smoothen small delay variations. To prevent network congestion and maintain minimum quality of service the transmitter performs media scaling-down by dropping the current packet when informed excessive delay from the receiver.

• The KIPS Transactions:PartC
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• v.11C no.2
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• pp.193-202
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• 2004

Handoff if the most Important feature for the user's mobility in a cellular communication system, which is related to resource reservation at nearby cells. For efficient resource reservation, mobility prediction has been reported as an effective means to decrease call dropping probability and to shorten handoff latency in wireless cellular environments. Several early proposed handoff schemes making use of tile user's movement history on a cell-by-cell basis work on the assumption that the user's movements are restricted to the indoor locations such as an office or a building. However, those algorithms cannot be applied to a micro-cell structure or a metropolis with complicated structure of roads. In this paper, to overcome those drawbacks we propose a new mobility prediction algorithm, which stores and uses the history of the user's positions within the current cell to predict the next cell.

• Journal of Advanced Navigation Technology
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• v.13 no.2
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• pp.208-213
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• 2009

This paper presents an adaptive call admission control(CAC) algorithm based on a target handoff call dropping probability in mobile wireless environments. This method uses a neural network for predicting and reserving the bandwidth demands for handoff calls and new calls. The amount of bandwidth to be reserved is adaptively adjusted by a target value of handoff call dropping probability(CDP). That is, if the handoff CDP exceeds the a target CDP value, the bandwidth to be reserved should be increased to reduce the handoff dropping probability below a target value. The proposed method is intended to prevent from increasing handoff call dropping probability when bandwidth to be reserved is not enough for handoff calls due to an uncertain prediction. Our simulations compare the handoff CDP in proposed CAC with that of an existing CAC. Results show that the proposed method sustains handoff call dropping probability below our target value.

• Journal of Korea Multimedia Society
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• v.12 no.3
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• pp.409-418
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• 2009

Providing Quality-of-Service (QoS) guarantee requires for each router on the path of a traffic flow not to violate the flow's delay budget allocated to itself. Since the amount of load being offered to the router is determined by the budget, some imbalance in load among routers on the path may be alleviated by means of adjusting the budget. The equal allocation applied to the resource reservation protocol (RSVP) is simple to implement, but it has the drawback of a poor resource utilization. A load balancing method in which the delay budget being allocated to a router depends on its load state was developed to improve the drawback, but it's too complex to apply to the RSVP. This paper proposes an intra-path load balancing method not only applicable to the RSVP but also more effective in improving the drawback. The proposed method first partitions the end-to-end delay bound of a flow to routers by the RSVP and then let them adjust their budgets according to both the bottleneck state of the path and their links' bandwidth availabilities. The results of the simulation applying the proposed method to an evaluation network showed that the proposed method may provide the gain of 4 ${\sim}$ 17 % compared to that in the legacy one in terms of the number of maximally admittable flows.

• Journal of KIISE:Information Networking
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• v.30 no.4
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• pp.494-503
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• 2003

The IEEE 1394 High Speed Serial Bus is a versatile, high-performance, and low-cost method of promoting interoperability between all types of A/V and computing devices. IEEE 1394 provides two transfer modes: asynchronous mode for best effort service and isochronous mode for best effort service with bandwidth reservation. This paper shows the bus performance and compared the transfer odes first at the link level and then at the application level. For the application level performance, we analyze the bus systems with fixed and adaptive interfaces, applied between the upper layer and the 1394 layer, using polling systems. Also we verifies the analysis models with simulation studies. Based on our analysis, we conclude that the adaptive interface reduces the bus access time and so increases the bus utilization.

• Journal of KIISE:Information Networking
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• v.29 no.2
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• pp.129-140
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• 2002

In this paper, we consider the problem of packet transmission in a wavelength division multiplexed(WDM) optical network. Our network model assumes that receivers are fixed-tuned and transmitters are tunable such that optical lasers assigned to transmitters have limited access to the network bandwidth: hence each node must be equipped with multiple optical lasers and/or multiple optical filters in order to maintain a single-hop network. We first analyze scheduling all-to-all packet transmissions and present optimum scheduling for all-to-all packet transmissions. We then extend the analysis to the case of arbitrary traffic demands. We show that the scheduling with arbitrary traffic demand is NP-hard. A heuristic algorithm based on list scheduling is presented. The upper bound so obtained is compared with the lower bound and provides performance guarantees with arbitrary demands. The result are applicable to arbitrary tuning delay, arbitrary number of wavelength channels and optical lasers of arbitrary tuning ranges.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06d
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• pp.185-190
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• 2008

시간에 민감한 트래픽 서비스가 늘어감에 따라 LAN 내에서 디지털 미디어 장치들간의 저지연성을 보장해 줄 수 있는 기술의 필요성이 증대되었다. 이더넷에 기반을 둔 디지털 미디어 장치들의 시간 동기 및 저지연성을 보장해주기 위한 연구가 IEEE 802.1 AVB TG에서 진행되고 있다. IEEE 802.1 AVB TG에서 진행중인 시간동기화 방법, 대역폭 예약 방법, 트래픽 전송 방법 중에서, 본 논문은 트래픽 전송 방법에 대해 해결방안을 제시한다. 본 논문에서는 시간에 민감하지 않은 트래픽에 대해 처리하는 VQ와 시간에 민감한 또는 민감하지 않은 트래픽에 대해 처리하는 FS를 이용하여 시간에 민감한 트래픽의 저지연성을 보장함과 동시에 시간에 민감하지 않은 트래픽 전송의 공평성을 제공해 줄 수 있는 방법을 제안한다. OPNET을 이용한 시뮬레이션을 통해 제안된 방법이 다른 방법들에 비해 우수함을 확인하였다.

• Journal of the Korea Society of Computer and Information
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• v.17 no.1
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• pp.141-149
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• 2012

This paper proposes a resource management and allocation algorithm to guarantee QoS continuity of realtime multimedia services and to maximize the resource utilization in heterogeneous wireless networks simultaneously. This scheme reserves the appropriate resources to be used by real-time multimedia services and allocates those resources left unused due to decreased transmission rate of realtime services to non-realtime services. Those resources can be preempted by the need of realtime services later. Performances are analyzed by simulation.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.178-180
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• 2012

본 논문에서는 유럽의 디지털 라디오 전송 규격인 DRM(Digital Radio Mondiale)의 Band II 대역 전송 모드인 모드 E의 전송률 향상 기법을 제안한다. DRM 모드 E는 FM 방송과의 동시방송 등의 문제를 고려하여 100kHz 대역폭에서 186kbps의 전송률을 제공한다. 하지만, 이 전송률은 모바일TV 등 멀티미디어 서비스를 제공하기 위해서는 부족하기 때문에 전송률의 향상이 요구된다. 논문에 제안된 전송률 향상기법은 기존의 DRM 모드에 변조방식 및 부호방식을 추가하는 방식으로 최대 350kbps의 전송률 제공이 가능하며, FAC(Fast Access Channel)의 예약필드에 신규 방식에 대한 정보를 전송함으로써 기존 시스템과 호환성을 유지할 수 있다. 모의실험 결과에서, AWGN(Additive White Gaussian Noise) 채널의 비트오류율 le-4를 기준으로 223kbps의 전송을 위해서는 13dB의 SNR(Signal-to-Noise Ratio)이 요구되며, 351kbps의 전송률 제공을 위해서는 약 18dB의 SNR이 요구됨을 확인할 수 있다. 또한, 다중경로 페이딩 채널환경에서 부호율이 1/2인 경우에는 이동속도보다는 지연확산이 성능에 영향을 주지만, 부호율이 1/2 보다 크며 150Km/h이상 증가하면 오류마루가 발생함을 확인할 수 있다.