• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.1
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• pp.308-324
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• 2018

HTTP adaptive streaming (HAS) is a promising technology for delivering video content over the Internet. HAS-based video streaming solutions rely on bandwidth estimation to select the appropriate video bitrate. Video streaming solutions that consider network conditions provide users with seamless video playback. However, when multiple clients compete for a common bottleneck link, conventional bandwidth estimation schemes that consider only one client overestimate the network bandwidth due to the ON-OFF traffic pattern. The bandwidth overestimation can cause Quality of Experience (QoE) degradation, such as unnecessary changes in video quality, and unfairness of video quality. In this paper, we propose a client-side bandwidth estimation scheme to obtain a better QoE of HAS in the multiple-client environment. The proposed scheme differentiates the client buffer status according to the buffer occupancy, and then estimates the available network bandwidth based on the buffer status and segment throughput. We evaluate the performance of HAS implemented in the ns-3 network simulator. Simulation results show that compared with the conventional schemes, the proposed scheme can enhance the QoE.

• Journal of Communications and Networks
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• v.17 no.3
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• pp.247-255
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• 2015

In this paper, we propose an adaptive time division multiple access based medium access control (MAC) protocol, called bitmap-assisted shortest job first based MAC (BS-MAC), for hierarchical wireless sensor networks (WSNs). The main contribution of BS-MAC is that: (a) It uses small size time slots. (b) The number of those time slots is more than the number of member nodes. (c) Shortest job first (SJF) algorithm to schedule time slots. (d) Short node address (1 byte) to identify members nodes. First two contributions of BS-MAC handle adaptive traffic loads of all members in an efficient manner. The SJF algorithm reduces node's job completion time and to minimize the average packet delay of nodes. The short node address reduces the control overhead and makes the proposed scheme an energy efficient. The simulation results verify that the proposed BS-MAC transmits more data with less delay and energy consumption compared to the existing MAC protocols.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.1
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• pp.105-122
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• 2011

The fundamental design goal of wireless sensor MAC protocols is to minimize unnecessary power consumption of the sensor nodes, because of its stringent resource constraints and ultra-power limitation. In existing MAC protocols in wireless sensor networks (WSNs), duty cycling, in which each node periodically cycles between the active and sleep states, has been introduced to reduce unnecessary energy consumption. Existing MAC schemes, however, use a fixed duty cycling regardless of multi-hop communication and traffic fluctuations. On the other hand, there is a tradeoff between energy efficiency and delay caused by duty cycling mechanism in multi-hop communication and existing MAC approaches only tend to improve energy efficiency with sacrificing data delivery delay. In this paper, we propose two different MAC schemes (ADS-MAC and ELA-MAC) using closed-loop control in order to achieve both energy savings and minimal delay in wireless sensor networks. The two proposed MAC schemes, which are synchronous and asynchronous approaches, respectively, utilize an adaptive timer and a successive preload frame with closed-loop control for adaptive duty cycling. As a result, the analysis and the simulation results show that our schemes outperform existing schemes in terms of energy efficiency and delivery delay.

• Journal of the Korea Society of Computer and Information
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• v.14 no.5
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• pp.77-83
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• 2009

In this parer, an improved backoff algorithm is proposed by supplementing a multiple of persistence factor for IEEE 802.11 Wireless LAN MAC. This algorithm is proposed to complement the shortcomings of the conventional BEB (Binary Exponential Backoff) algorithm which is used for retransmission to control a new contention window in DCF/EDCF MAC. In channel utilization, collision rate and Goodput viewpoint, we analysis the improved backoff algorithm and compared the result with that of the conventional algorithm In this result, we showed that the performance for PFA backoff algorithm is 10% higher than that for the conventional BEB algorithm when the number of station is 40.

• IEMEK Journal of Embedded Systems and Applications
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• v.19 no.2
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• pp.107-114
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• 2024

Mobile ad hoc networks represent self-configuring networks of mobile devices that communicate without relying on a fixed infrastructure. However, traditional routing protocols in such networks encounter challenges in selecting efficient and reliable routes due to dynamic nature of these networks caused by unpredictable mobility of nodes. This often results in a failure to meet the low-delay and low-energy consumption requirements crucial for such networks. In order to overcome such challenges, our paper introduces a novel multi-objective and adaptive routing scheme based on the Q-learning reinforcement learning algorithm. The proposed routing scheme dynamically adjusts itself based on measured network states, such as traffic congestion and mobility. The proposed approach utilizes Q-learning to select routes in a decentralized manner, considering factors like energy consumption, load balancing, and the selection of stable links. We present a formulation of the multi-objective optimization problem and discuss adaptive adjustments of the Q-learning parameters to handle the dynamic nature of the network. To speed up the learning process, our scheme incorporates informative shaped rewards, providing additional guidance to the learning agents for better solutions. Implemented on the widely-used AODV routing protocol, our proposed approaches demonstrate better performance in terms of energy efficiency and improved message delivery delay, even in highly dynamic network environments, when compared to the traditional AODV. These findings show the potential of leveraging reinforcement learning for efficient routing in ad hoc networks, making the way for future advancements in the field of mobile ad hoc networking.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.115-118
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• 2004

An abrupt increase of traffic-load in cellular CDMA systems can cause overload and degrade the quality of service (QoS) due to the insufficient radio resources. In this paper, we propose a joint coverage and resource management (JCRM) scheme which can improve the QoS degradation and spectrum utilization. The JCRM scheme hands over overloaded traffic to the neighboring cells by virtually reducing a heavily loaded cell coverage and allocates radio resources based on the necessary handover probability. The proposed scheme can be applied to the existing cellular CDMA systems as well as adaptive coverage management schemes for next generation mobile communication systems.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.343-345
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• 2012

기존의 교통제어 시스템은 고정된 녹색 신호의 길이와 주기를 갖고 있다. 그에 따라 차선 간 차량 밀집도가 불균형한 경우 교통 처리량이 저하되고 응급상황이 발생할 경우 지정체가 유발된다. 본 논문에서는 VANET을 이용하여 교통량의 실시간 정보를 수집해 적응적으로 교통 신호를 제어하는 시스템을 제안한다. 차량의 수, 평균 신호대기 시간, 차선 간 균형, 응급상황 등을 고려하여 교통 신호를 가변적으로 제어 한다. 차량이 교차로에 진입하기 전 통신모듈을 갖고 있는 신호등에게 위치, 방향, 속도 정보 등을 송신하고 traffic control system에서 교통량을 분석하여 녹색 신호를 가변적으로 할당 한다. 실험결과 제안 기법이 교통 처리량, 평균 신호대기시간에서 기존 교통신호 제어 기법보다 높은 성능을 확일 할 수 있었다.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.3
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• pp.36-46
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• 1999

본 논문에서는 DSPN(Deterministic and Stochastic Petri Net)을 이용, 교차로에서의 차량 진입과 같은 이산 사건(discrete events)적인 상황을 해석하고, 교통신호기의 동작과 차량흐름을 모델링하였다. 교차로에서의 차량 흐름을 확률적 개념으로 표현하여, 차량 변화에 따른 교차로의 상황을 토큰의 변화로 나타내었다. GreatSPN을 사용한 모의 실험을 통하여, 모델링된 교통신호기하에서의 차량의 평균 지체시간을 분석하였다. 차량 지체시간을 이용하여 단위시간연장 교통량 대응 신호기와 본 논문에서 제안한 최대시간허용 교통량 대응 신호기의 성능을 비교 분석하여, 최대시간허용 교통량 대응 신호기가 단위시간연장 교통량 신호기보다 좋은 특성을 나타냄을 보였다. 2개의 교차로로 이루어진 시스템을 본 논문에서 개발한 기본 모듈들을 서로 연결하여 분석하였고, 이러한 성능 분석을 통하여 주위 여건에 적합한 새로운 교통신호기를 구현할 수 있음을 보였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.746-748
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• 2011

MANET(Mobile Ad-hoc Network) is a self-configuration network or wireless multi-hop network based on inference topology. The proposed ATICC(Adaptive Time Interval Clustering Control) algorithm for hierarchical cluster based MANET. The proposed ATICC algorithm is time interval control technique for node management considering the attribute of node and network traffic. ATICC could be made low the network traffic. Also it could be improving the network life time by using timing control method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.12B
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• pp.1988-1995
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• 2000

ATM 망에서 제공되고 있는 음성, 영상, 데이터와 같은 다양한 서비스는 사용자의 만족도를 수용할 수 있어야 한다는 것을 전제조건으로 한다. 이러한 기본적인 요구사항을 충족시키기 위해서는 노드대 노드간의 자원관리와 오류제어 및 다양한 트래픽의 특성을 고려한 전송 순서의 결정에 해당하는 스케줄링 방법이 요구되어 진다. 본 논문에서는 이러한 기술 요소 중에서 트래픽 설정 단계에서 제공되는 트래픽 특성 및 QoS(Quality of Service) 정보를 바탕으로 교환 노드에서 발생되는 전달 지연 시간에 적응적인 스케줄링 방식을 제시하였다. 이 방식은 멀티미디어 서비스와 같이 혼합된 트래픽 특성을 갖는 구조에서 트래픽 구성비율에 따라 적용되는 지연 여유치를 매우 융통성 있고 효과적으로 조절할 수 있다. 성능분석을 위하여 기존의 스케줄링 방식인 WFQ (Weighted Fair Queueing) 방식과 제안한 스케줄링 방식의 수학적인 분석을 수행하였으며 이 두 방식의 결과식을 비교하여 교환노드에서의 평균 지연과 셀 처리에 관한 성능을 분석하였다. 그리고 수학적 분석에 대한 검증으로는 Simulation tool ARENA 3.0을 이용하여 제안한 알고리즘의 Worst case와 기존의 알고리즘의 성능을 비교하였다.