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Optimal Cell Selection Scheme for Load Balancing in Heterogeneous Radio Access Networks
HyungJune Lee(이형준) 한국통신학회 2012 韓國通信學會論文誌 Vol.37 No.12B
스마트폰의 급격한 보급에 따른 무선 접속망의 과부하 문제가 네트워크에서 중요한 문제로 부각되고 있다. 이 논문에서는 매크로 셀, 펨토 셀, 와이파이 접속망으로 다양하게 구성되어 있는 현재 이종 네트워크에서 접속망 과부하 문제를 해결하기 위한 최적의 셀 선정 기법과 리소스 할당 기법을 제안한다. 주어진 현재 서비스 부하 상태에서 네트워크가 동시에 추가 수용할 수 있는 사용자 수를 최대화할 수 있는 사용자-셀 간의 선정 기법을 제공한다. 이를 위해 이종 무선 접속망에서의 셀 선정 문제를 이진 정수계획 모형으로 최적화 문제를 수립하고, 이를 최적화 해법 도구를 이용하여 접속망 과부하를 억제할 수 있는 최적의 셀 선정 기법을 도출한다. 네트워크 레벨 시뮬레이션을 통해 이 논문에서 제안된 기법이 현재 무선 접속망에서 주로 사용되고 있는 국소적 셀 선정기법에 비해, 과부하가 걸린 무선 접속망에서 주어진 여러 셀들을 최대한 균등하게 효율적으로 활용함으로써 현저하게 네트워크 접속 장애율을 감소시킬 수 있음을 보인다. 또한 논문에서 사용된 이진 정수계획 모형의 최적화 문제를 푸는 데 소요되는 계산 복잡도에 대한 실험을 통해 제안된 알고리즘의 실용 가능성에 대해서 검증한다. We propose a cell selection and resource allocation scheme that assigns users to nearby accessible cells in heterogeneous wireless networks consisting of macrocell, femtocells, and Wi-Fi access points, under overload situation. Given the current power level of all accessible cells nearby users, the proposed scheme finds all possible cell assignment mappings of which user should connect to which cell to maximize the number of users that the network can accommodate at the same time. We formulate the cell selection problem with heterogeneous cells into an optimization problem of binary integer programming, and compute the optimal solution. We evaluate the proposed algorithm in terms of network access failure compared to a local ad-hoc based cell selection scheme used in practical systems using network level simulations. We demonstrate that our cell selection algorithm dramatically reduces network access failure in overload situation by fully leveraging network resources evenly across heterogeneous networks. We also validate the practical feasibility in terms of computational complexity of our binary integer program by measuring the computation time with respect to the number of users.
Joint Radio Selection and Relay Scheme through Optimization Model in Multi-Radio Sensor Networks
( Hyungjune Lee ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.12
We present joint radio selection and relay scheme that delivers data from a source to a sink in heterogeneous stationary sensor networks consisting of various radio interfaces. The proposed scheme finds the optimal relay nodes and their corresponding radio interfaces that minimize energy consumption throughout the network while satisfying the end-to-end packet deadline requirement. We formulate the problem of routing through radio interface selection into binary integer programs, and obtain the optimal solution by solving with an optimization solver. We examine a trade-off relationship between energy consumption and packet delay based on network level simulations. We show that given the end-to-end deadline requirement, our routing algorithm finds the most energy-efficient routing path and radio interface across mesh hops. We demonstrate that the proposed routing scheme exploits the given packet delivery time to turn into network benefit of reducing energy consumption compared to routing based on single radio interface.
Predictive Data Delivery to Mobile Users Through Mobility Learning in Wireless Sensor Networks
HyungJune Lee,Wicke, Martin,Kusy, Branislav,Gnawali, Omprakash,Guibas, Leonidas IEEE 2015 IEEE Transactions on Vehicular Technology VT Vol.64 No.12
<P>We consider applications, such as indoor navigation, evacuation, or targeted advertising, where mobile users equipped with a smartphone-class device require access to sensor network data measured in their proximity. Specifically, we focus on efficient communication protocols between static sensors and users with changing location. Our main contribution is to predict a set of possible future paths for each user and store data at sensor nodes with which the user is likely to associate. We use historical data of radio connectivity between users and static sensor nodes to predict the future user-node associations and propose a network optimization process, i.e., data stashing, which uses the predictions to minimize network and energy overheads of packet transmissions. We show that data stashing significantly decreases routing cost for delivering data from stationary sensor nodes to multiple mobile users compared with routing protocols where sensor nodes immediately deliver data to the last known association nodes of mobile users. We also show that the scheme provides better load balancing, avoiding collisions and consuming energy resources evenly throughout the network, leading to longer overall network lifetime. Finally, we demonstrate that even limited knowledge of the location of future users can lead to significant improvements in routing performance.</P>
Location-Based TDMA MAC for Reliable Aeronautical Communications
Hyungjun Jang,Eunkyung Kim,Jae-Joon Lee,Jaesung Lim IEEE 2012 IEEE transactions on aerospace and electronic syst Vol.48 No.2
<P>The growth of data traffic as air traffic increases is leading to bottlenecks. We propose a new time division multiple access (TDMA) protocol termed location-based TDMA (LBTM) to accommodate increasing data traffic and air-to-air communications. LBTM provides all three modes of communication: unicast, multicast, and broadcast. ACK needs a long guard time for reliable multicast in the aeronautical environment, because it is a long distance communication system. LBTM uses location information to overcome this problem. We can reduce the guard time of ACK and prevent collisions. In our scheme, multicast aircraft calculate ACK arrival time to ensure that ACKs arrive at the sender at different times. Therefore, LBTM reduces the amount of guard time of ACK and the total average time to complete a reliable multicast MAC request. This results in a significant increase in network utilization and throughput.</P>
Pantograph and Stagger Inspection Using Image Processing Technique
HyungJun Kim,Keehong Um 한국멀티미디어학회 2009 한국멀티미디어학회 국제학술대회 Vol.2009 No.-
We present an image processing technique for monitoring the interaction between the pantograph and the catenary system of the Korean TIX (tilting train express) train. Due to the displacement of the contact point with respect to the reference position, an image processing analysis of each frame is performed in order to detect stagger of trolley wire automatically. The proposed approach is very efficient and produces desirable output data.
A Template Matching based Hole-Filling Method for Motion-Compensated Frame Interpolation
HyungJun Lim,HyunWook Park 대한전자공학회 2010 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
This paper proposes a new motion-compensated frame interpolation method which fills hole-regions using a template matching algorithm. The proposed method constructs the partially-interpolated frame using the block-wise motion information obtained by forward motion estimation. To fill the hole-regions of the partiallyinterpolated frame, the proposed method divides the hole-regions into multiple blocks and defines their templates using neighboring pixels. By performing motion estimation for each template, the hole-regions are filled with the pixels from the previous or current frame. The experimental results show that the proposed method can interpolate the hole-regions successfully and produces visually fine images.