• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.668-679
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• 2004

When users of mobile environments move fast or slow into a number of base stations(BS) and request the services of continuous media data such as video or audio, this study examines what the caching has the usefulness in mobile environments. Namely, to reduce packet disconnections and network overheads in mobile environments and minimize transmission delay time, we propose domain-based hierarchical caching structure and study whether application of caching has the usefulness. So we have a model based on user environments and hierarchical network structure to process continuous media services, and analyze the usefulness of caching which depends on the mobile patterns of user and the locations of caching nodes. And then, we research whether caching offers the usefulness in mobile environments. As the result, we are able to see that an adaptable application of caching is needed because the hit ratio and the number of replacement vary in large according to mobile patterns of user and locations of caching.

• Journal of Korea Multimedia Society
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• v.14 no.1
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• pp.44-53
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• 2011

H.264/SVC provides scalable video streams which consist of a base layer and one or more enhancement layers. Thus, it can efficiently adapt encoded streams to individual network conditions by dropping some layers of bit streams. However, on a dynamic environment such as the Internet, random packet losses due to network congestion can cause drastic effect on SVC quality. To avoid network congestion, the rate of video streams should be adjusted by carefully selecting a layer of each stream. In this paper, we propose three layer selection algorithms which can avoid network congestion by using the rate-distortion characteristics of streams. Simulation results show that FS(Far-Sighted) algorithm can maximize the overall PSNR value of streams by efficiently using the characteristics of video streams.

• Journal of Information Processing Systems
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• v.2 no.2
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• pp.107-113
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• 2006

It is essential to guarantee a handoff dropping probability below a predetermined threshold for wireless mobile networks. Previous studies have proposed admission control policies for integrated voice/data traffic in wireless mobile networks. However, since QoS has been considered only in terms of CDP (Call Dropping Probability), the result has been a serious CBP (Call Blocking Probability) unfairness problem between voice and data traffic. In this paper, we suggest a new admission control policy that treats integrated voice and data traffic fairly while maintaining the CDP constraint. For underprivileged data traffic, which requires more bandwidth units than voice traffic, the packet is placed in a queue when there are no available resources in the base station, instead of being immediately rejected. Furthermore, we have adapted the biased coin method concept to adjust unfairness in terms of CBP. We analyzed the system model of a cell using both a two-dimensional continuous-time Markov chain and the Gauss-Seidel method. Numerical results demonstrate that our CAC (Call Admission Control) scheme successfully achieves CBP fairness for voice and data traffic.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.286-288
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• 2005

최근 기지국(Base Station)의 도움 없이 이동 단말기 간의 다중 무선 홉을 사용하여 송,수신자 간의 데이터 전송을 가능하게 하는 Ad-hoc 통신망에 관한 연구가 활발히 진행되고 있다. 유선망과 달리 Ad-hoc 통신망은 무선 전송 매체를 사용하기 때문에 신호의 페이딩(Fading), 간섭(Interference), 잡음(Noise) 등에 의해 높은 BER(Bit Error Rate)이 발생하는 특징을 가지고 있다. 하지만, 현재 인터넷 상에서 광범위하게 사용되고 있는 전송 규약인 TCP(Transmission Control Protocol)는 유선망의 신뢰적인 전송 매체를 고려하여 개발된 프로토콜이기 때문에 TCP를 수정 없이 Ad-hoc 통신망에 적용할 경우 전송 성능이 저하되는 문제를 가지고 있다. 전송 성능이 저하되는 문제는 기존 TCP가 에러 발생의 원인을 혼잡에 의한 것으로 인식하고 불필요한 혼잡 제어를 하기 때문이다. 본 논문에서는 송신자가 에러 발생 원인을 구별하고, 그에 따라 전송률을 조절함으로써 Ad-hoc 망에서의 TCP성능 향상을 위한 방법을 제시하였다. 또한 ns-2 시뮬레이터를 이용한 실험을 통해 TCP의 성능이 제안된 알고리즘에 의해 향상되었음을 확인하였다

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3C
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• pp.408-418
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• 2004

In this paper, we propose a novel scalable video coding algorithm based on adaptively weighted multiple reference frame method. To improve the coding efficiency in the enhancement layer, the enhancement frame is predicted by the sum of adaptively weighted double motion compensated frames in the enhancement layer and the current frame in the base layer, according to the input video characteristics. By employing adaptive reference selection scheme at the decoder, the proposed method reduce the drift problem significantly. From the experimental results, the proposed algorithm shows more than 1.0 ㏈ PSNR improvement, compared with the conventional scalable H.263+ for various packet loss rate channel conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8B
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• pp.739-746
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• 2004

An ATM/AAL2 is standardized to transmit delay sensitive application services, which has small size packet, efficiently. An AAL2 transmission scheme is used to deliver voice and data traffic on the lob interface between base station (Node-B) and Radio Network Controller (RNC) in UMTS network. To predict AAL2 performance, a detailed end-to-end UMTS network performance simulator was developed. We performed detailed simulation(cell packing density and bandwidth gain) for voice and data services in UTRAN. The results indicate that the maximum bandwidth gain in Node-B is about 17% and the bandwidth gain of AAL2 multiplexing in $I_{ub}$ for data services is less than that for voice service. Futhermore, the more offered load increase the more the bandwidth gain decreases in a concentrator.

• Journal of Internet Computing and Services
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• v.2 no.3
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• pp.9-17
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• 2001

Ad-Hoc networks consist of a set of mobile hosts that communicate using wireless links, without the use of other communicate support facilities (such as base stations). The topology of an Ad-Hoc network changes due to the movement of mobile host. which may lead to sudden packet loss. Recently, a large amount of research has focused on the routing protocols needed in such an environment. but researches about Internet traffic performance analysis were unexhausted. Accordingly, we have simulated Ad-Hoc mobile network that using AODV routing protocol and Ad-Hoc mobile network topology size and node speed as simulation estimation-factor to analysis traffic performance. As the result of the simulation, we identify that TCP /Reno was more sensitive than TCP/Sack about node speed and a number of the node.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.2936-2951
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• 2016

An emerging satellite technology, Operationally Responsive Space (ORS) is expected to provide a fast and flexible solution for emergency response, such as target tracking, dense earth observation, communicate relaying and so on. To realize large distance transmission, we propose the use of available relay satellites as relay nodes. Accordingly, we apply software defined network (SDN) technology to ORS networks. We additionally propose a satellite network architecture refered to as the SDN-based ORS-Satellite (Sat) networking scheme (SDOS). To overcome the issures of node failures and dynamic topology changes of satellite networks, we combine centralized and distributed routing mechanisms and propose a fast recovery routing algorithm (FRA) for SDOS. In this routing method, we use centralized routing as the base mode.The distributed opportunistic routing starts when node failures or congestion occur. The performance of the proposed routing method was validated through extensive computer simulations.The results demonstrate that the method is effective in terms of resoving low end-to-end delay, jitter and packet drops.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.8
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• pp.3040-3053
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• 2015

Wideband code division multiple access (WCDMA), high speed packet access (HSPA) and HSPA+ are third generation partnership project (3GPP) standards. These systems are the major wireless communication standards. In order to test the performance of WCDMA/HSPA/HSPA+ signal in a base station, the measurement hardware is required to the evaluation of the transmitted signals. In this paper, the algorithm for the performance measurement of the WCDMA/HSPA/HSPA+ is proposed. Also, the performance of the measurement algorithm is used to evaluate the generated signal by the WCDMA/HSPA/HSPA+ signal generator. Generally, the algorithm of normal modems cannot be applied to the measurement system because the signal measurement equipment needs to guarantee the high accuracy. So, the WCDMA/HSPA/HSPA+ signal measurement algorithm for the accurate measurement is proposed. By the simulation, it is confirmed that the proposed measurement algorithm has good performance compared with the specification. Therefore, the proposed algorithm can be usefully applied to verify the performance of the measurement using the simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.12
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• pp.5442-5463
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• 2016

Designing efficient routing protocols for a wireless sensor network with mobile sinks (mWSN) is a challenging task since the network topology and data paths change frequently as sink nodes move. In this paper, we design a novel lightweight reactive ring based routing protocol called R3, which removes the need of proactively maintaining data paths to mobile sinks as they move in the network. To achieve high packet delivery ratio and low transmission cost, R3 combines ring based forwarding and trail based forwarding together. To support efficient ring based forwarding, we build a ring based structure for a network in a way such that each node in the network can easily obtain its ring ID and virtual angle information. For this purpose, we artificially create a virtual hole in the central area of the network and accordingly find a shortest cycled path enclosing the hole, which serves as base ring and is used for generating the remaining ring based structure. We accordingly present the detailed design description for R3, which only requires each node to keep very limited routing information. We derive the communication overhead by ring based forwarding. Extensive simulation results show that R3 can achieve high routing performance as compared with existing work.