• 정보처리학회논문지C
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• 제9C권6호
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• pp.883-892
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• 2002

mobile IP는 단순히 이동성을 지원하는 것만을 목표로 제안되었기 때문에, 새로운네트워크로의 연결만을 보장할 뿐, 핸드오프 후의 QoS는 보장하지 못한다. mobile IP에서QoS는 이동 환경에서 멀티미디어 서비스나 실시간 서비스 제공시 매우 중요시되는 문제로, 핸드오프에 의한 지연과 밀접히 연관되어있다. 본 논문에서는 이러한 핸드오프 지연 문제를해결하기 위해, 액티브 네트워크에서의 정보기반 라우팅에 키워드 관리방법을 추가한 SNMP 정보기반 라우팅을 제시하고, 이를 이용하여 핸드오프 지연을 최소화하는 QoS 향상기법을 제시한다. 또한 기존 핸드오프 방법과 제시한 기법을 모델링한 후 NS-2를 사용하여시뮬레이션 한다. 시뮬레이션 결과는 제시한 기법이 핸드오프 지연을 최소화시켜 QoS를 향상시켰음을 입증한다.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2010년도 한국컴퓨터종합학술대회논문집 Vol.37 No.1(A)
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• pp.218-219
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• 2010

• Journal of information and communication convergence engineering
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• 제5권4호
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• pp.295-299
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• 2007

This paper presents the ASF(Additional Secondary Factor) modeling of DGPS beacon signal. In addition to DGPS's original purpose, the feasibility to utilize DGPS system for timing and navigation has been studied. For timing and navigation, the positioning system must know the accurate time delay of signal traveling from the transmitter to receiver. Then the delay can be used to compute the user position. The DGPS beacon signal transmits the data using medium frequency, which travels through the surface and cause the additional delay rather than the speed of light according to conductivities and elevations of the irregular terrain. We introduce the modeling of additional delay(ASF) and present the results of implementation. The similar approach is Locan-C. Loran-C has been widely used as the maritime location system and was enhanced to E-Loran(Enhanced Loran). E-Loran system uses the ASF estimation method and is able to provide the more precise location service. However there was rarely research on this area in Korea. Hence, we introduce the ASF and its estimation model. With the comparison of the same condition and data from the original Monteath model and ASF estimation data of Loran system respectively, we guarantee that the implementation is absolutely perfect. For further works, we're going to apply the ASF estimation model to Korean DGPS beacon system with the Korean terrain data.

• 한국통신학회논문지
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• 제34권5A호
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• pp.355-362
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• 2009

In real-time communication services, delay constraints are among the most important QoS (Quality of Service) factors. In particular, it is difficult to guarantee the delay requirement over wireless channels, since they exhibit dynamic time-varying behavior and even severe burst-errors during periods of deep fading. Channel throughput may be increased, but at the cost of the additional delays when ARQ (Automatic Repeat Request) schemes are used. For real-time communication services, it is very essential to predict data deliverability. This paper derives the delay distribution and the successful delivery probability within a given delay budget using a priori channel model and a posteriori information from the perspective of queueing theory. The Gilbert-Elliot burst-noise channel is employed as an a Priori channel model, where a two-state Markov-modulated Bernoulli process $(MMBP_2)$ is used. for a posteriori information, the channel parameters, the queue-length and the initial channel state are assumed to be given. The numerical derivation is verified and analyzed via Monte Carlo simulations. This numerical derivation is then applied to a rate control scheme for real-time video transmission, where an optimal encoding rate is determined based on the future channel capacity and the distortion of the reconstructed pictures.

• Journal of Communications and Networks
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• 제16권2호
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• pp.130-139
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• 2014

Due to the unpredictable nature of channel availability, carrying delay-sensitive traffic in cognitive radio networks (CRNs) is very challenging. Spectrum leasing of radio resources has been proposed in the so called coordinated CRNs to improve the quality of service (QoS) experienced by secondary users (SUs). In this paper, the performance of coordinated CRNs under fixed-rate with hard-delay-constraints traffic is analyzed. For the adequate and fair performance comparison, call admission control strategies with fractional channel reservation to prioritize ongoing secondary calls over new ones are considered. Maximum Erlang capacity is obtained by optimizing the number of reserved channels. Numerical results reveal that system performance strongly depends on the value of the mean secondary service time relative to the mean primary service time. Additionally, numerical results show that, in CRNs without spectrum leasing, there exists a critical utilization factor of the primary resources from which it is not longer possible to guarantee the required QoS of SUs and, therefore, services with hard delay constraints cannot be even supported in CRNs. Thus, spectrum leasing can be essential for CRN operators to provide the QoS demanded by fixed-rate applications with hard delay constraints. Finally, the cost per capacity Erlang as function of both the utilization factor of the primary resources and the maximum allowed number of simultaneously rented channels is evaluated.

• 한국통신학회논문지
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• 제40권4호
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• pp.653-658
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• 2015

다양한 강점을 지닌 클라우드 서비스는 현대 IT 사업에 주요 이슈 중 하나이다. 클라우드 환경에서 서비스 제공자는 사용자의 동적인 자원 요구량을 예측하여 사용자의 QoS를 만족시켜야 한다. 사용자의 자원 요구량을 예측하는 기존 모델들은 사용자의 QoS는 만족시키지만 서비스 제공자의 이득은 보장하지 않는다. 본 논문에서는 Q-learning 기반의 자원 예측 모델을 제안하여 사용자의 QoS 뿐만 아니라 서비스 제공자의 이득을 최대화하였다. 또한 제안 기법의 성능 분석을 위해 실측 데이터를 이용하여 다른 예측 모델들과 비교함으로써 제안 기법의 우수함을 증명하였다.

• Journal of the Optical Society of Korea
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• 제20권6호
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• pp.704-715
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• 2016

In this paper, we explore a low-complex bandwidth allocation (BA) scheme with multi-level service guarantees in VLC-OFDM systems. Effective capacity theory, which evaluates wireless channel capacity from a novel view, is utilized to model the system capacity under delay QoS constraints of the link layer. Since intensity modulation of light is used in the system, problems caused by frequency selectivity can be neglected. Then, the BA problem can be formulated as an integer programming problem and it is further relaxed and transformed into a concave one. Lagrangian formulation is used to reformulate the concave problem. Considering the inefficiency of traditional gradient-based schemes and the demand for distributed implementation in local area networks, we localize the global parameters and propose a quasi-distributed quadratic allocation algorithm to provide two-level service guarantees, the first level is QoS oriented, and the second level is QoE oriented. Simulations have shown the efficient performance of the proposed algorithm. The users with more stringent QoS requirements require more subcarriers to guarantee their statistical delay QoS requirements. We also analyze the effect of subcarrier granularity on the aggregate effective capacity via simulations.

• 전기학회논문지
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• 제63권4호
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• pp.502-508
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• 2014

In this paper, a delay-dependent $H_{\infty}$ filtering problem is investigated for discrete-time delayed nonlinear systems which include a more general sector nonlinear function instead of employing the commonly used Lipschitz-type function. By using the Lyapunov-Krasovskii functional approach, a less conservative sufficient condition is established for the existence of the desired filter, and then, the corresponding solvability condition guarantee the stability of the filter with a prescribed $H_{\infty}$ performance level. Finally, two simulation examples are given to show the effectiveness of the proposed filtering scheme.

• 대한전기학회논문지:전력기술부문A
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• 제48권10호
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• pp.1287-1292
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• 1999

In large-scale systems, we frequently encounter the time-delay and the uncertainty, and these should be considered in the design of controller because these are the source of the degradation of the system performance and instability of system. In this paper, we consider the robust stability of the linear large scale systems with the uncertainties and the time-delays. The considered uncertainties are both structured uncertainty and the unstructured uncertainty. Also, the considered time-delays are time-varying having finite time derivative limits. Based on the Lyapunov theorem and the linear matrix inequality(LMI) technique, we present two sufficient conditions that guarantee the robust stability of the system. The conditions are expressed as the LMI forms which can be easily checked their feasibility by using the well-known LMI control toolbox. Finally, we show by two examples that our results are less conservative than the previous results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(2)
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• pp.321-324
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• 2002

Nowadays variable delay arithmetic units have been used for implementing a datapath of\ulcorner target system in pursuit of performance improvement. However. adoption of variable delay arithmetic units requires modification of a typical synchronous control units design methodology. There is a representative approach, which is called a monolithic approach. Although its results are good, its proposed methodology may cause critical problems in the aspects of area and performance with the size increase of initial system specifications. In order to solve this problems, a distributed approach is suggested. Experimental results show that the Proposed method can guarantee original performance of an initial system specification with minimized additional area increase.