• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.5
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• pp.3-9
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• 2015

The wireless communication system adopts an appropriate retransmission scheme on each system protocol layer to improve reliability of data transmission. In each system protocol layer, the retransmission scheme operates in independently other layers and operates based on the parameters without reference to end-to-end performance of wireless communication system. For this reason, it is difficult to design the optimal system parameters that satisfy the QoS requirements for each service class. Thus, the performance analysis of wireless communication system is needed to design the optimal system parameters according to the end-to-end QoS requirements for each service class. In this paper, we derive the mathematical model to formulate the end-to-end performance of wireless communication system. We also evaluate the performance at the MAC and transport layers in terms of average spectral efficiency and average transmission delay. Based on the results of performance evaluations, we design the optimal system parameters according to the QoS requirements of service classes. From the results, the HARQ combined with AMC is appropriate for the delay-sensitive service and the ARQ combined with AMC is appropriate for a service that is insensitive to transmission delay. Also, the TCP can be applied for the delay-insensitive service only.

• Journal of Korea Multimedia Society
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• v.12 no.11
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• pp.1593-1608
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• 2009

If a certain relay node in multi-hop wireless networks might become a malicious node that does not cooperate with other nodes or a selfish node, network throughput will be dramatically decreased. Most of existing ad hoc routing protocols assuming that the nodes will fully cooperate with other nodes do not resolve the problem of network performance degradation due to malicious and selfish nodes. This paper presents the CARE (Cooperative Ad hoc routing protocol based REputation) scheme incorporating the reputation management that can achieve a multi-hop wireless network with high throughput performance. The proposed scheme provides the horizontal cross-layer approach which can identify misbehaving malicious, selfish nodes dropped out of the hop-by-hop based packet processing in the network and then set up an optimal packet routing path that will detour misbehaving nodes. And the vertical cross-layer approach contained in the CARE scheme attempts to improve the quality of routing paths by exploiting the quality of link information received from the MAC layer. Besides, it provides high TCP throughput by exploiting the reputation values of nodes acquired from the network layer into the transport layer. A case study on experiments and simulations shows that the CARE scheme incorporating vertical and horizontal cross-layer approaches yields better performance in terms of the low rate of packet loss, fast average packet delivery time, and high TCP throughput between end-to-end nodes.

• Journal of information and communication convergence engineering
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• v.2 no.1
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• pp.9-14
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• 2004

In this paper the modeling of the RLP layer in CDMA2000 is presented, which uses the NAK based ARQ scheme for Random Error Channels. The RLP performs a partial link recovery through limited number of RLP frame transmission in case of frame error. In case when the RLP fails due to excessive frame error, the control is passed on to the higher (TCP) layer. The TCP layer provides the complete end-to-end recovery. Thus the reliable performance at the TCP/RLP is essential to maintain the required Quality of Service in the DS-CDMA wireless links. The modeling is done for the performance analysis of the system in terms of the throughput and the mean extra delays, which are calculated analytically and are compared with the results generated by the simulations. This paper studies the effect of the random errors over different types of RLP frame formats and also the performance of the NAK based ARQ mechanism used under these conditions. The simulation provides with the over all characteristics of the throughput and the mean extra delay in terms of realistic environment parameters like Eb/No and probability of packet error (PE), based on the channel conditions.

• Journal of Sensor Science and Technology
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• v.20 no.3
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• pp.162-167
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• 2011

In this paper, we propose a vision system using a field programmable gate array(FPGA) and a smart vision chip. The output of the vision chip is varied by illumination conditions. This chip is suitable as a surveillance system in a dynamic environment. However, because the output swing of a smart vision chip is too small to definitely confirm the warning signal with the FPGA, a modification was needed for a reliable signal. The proposed system is based on a transmission control protocol/internet protocol(TCP/IP) that enables monitoring from a remote place. The warning signal indicates that some objects are too near.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.283-285
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• 2003

슈퍼컴퓨터 사용자들은 FTP(File Transfer Protocol)을 이용해서 대용량의 파일을 전송한다. 전송되는 데이터들은 승용차나 비행기 설계, 의약품 개발. 기상 예보 그리고 복잡한 수학적 계산 등과 같이 다양한 분야에 걸친 연구관련 데이터로서 고성능 슈퍼컴퓨터에 의한 연산 처리가 요구된다 기존의 FTP 는 네트워크 상태에 따라 전송 지연이나 데이터 손실 등의 문제로 사용자의 불편을 초래하였다. 이에 전송 성능을 효율적으로 높이고 데이터 손실을 최소화를 제공하는 연구가 필요하다. 근래의 TCP (Transmission Control Protocol) 성능 향상 연구에 관한 연구들의 관심은 크게 두 가지이다. 하나는 윈도우 사이즈 조절(auto-tuning)이고, 다른 하나는 Multi-stream 이다. 본 연구에서는 파일 전송 성능 향상을 위한 방법으로 윈도우 사이즈 조절 방법을 사용하였고, 네트워크 상태에 따라 QoS(quality of Service)를 제공한다. 이런 성능 향상 결과로 신뢰성 있는 네트워크를 제공하여 사용자들은 신속하게 데이터를 전송하며 연산처리 결과가 더욱 정확하다고 신뢰할 수 있다. 본 고에서는 대용량 파일을 전송 할 때 성능을 향상시키는 관련 연구를 알아보고 대용량 파일 전송 중 네트워크 상태에 따라 005를 능동적으로 작용하여 테스트하고 성능을 분석하였다.

• Journal of KIISE:Information Networking
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• v.32 no.1
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• pp.20-28
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• 2005

TCP(Transmission Control Protocol) is one of the most important Internet protocols, which is widely used in wireless networks as well as wired networks. However, when TCP is deployed for wireless networks, it takes severe performance degradation because TCP was designed for wired network. To overcome this drawback, a number of TCP variants have been proposed in the literature. However, most previous schemes did not consider TCP enhancement over heterogeneous networks. In heterogeneous networks, an mobile node (MN) may move from one access network to another(i.e., vertical handover). In the case of vertical handover, an MN experiences a TCP performance degradation caused by the packet loss and the sudden change of link characteristics between two different access networks. In this work, we investigate the TCP performance degradation occurred in vortical handover across heterogeneous networks. First, we have conducted the measurement study over GPRS-WLAN testbed. In the measurement study. we observed the TCP performance degradation in the case of handover from WLAN to GPRS. In order to study more different TCP behaviors during vertical handover, we performed comprehensive simulations using a network simulator 2(ns-2). Based on measurement and simulation results, we investigated how to improve TCP performance in vertical handover and we concluded that the existing mechanisms cannot be perfect solutions and new mechanisms are strongly required.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.668-672
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• 2009

In wireless ad-hoc network, knowing the available bandwidth of the time varying channel is imperative for live video streaming applications. This is because the available bandwidth is varying all the time and strictly limited against the large data size of video streaming. Additionally, adapting the encoding rate to the suitable bit-rate for the network, where an overlarge encoding rate induces congestion loss and playback delay, decreases the loss and delay. While some effective rate controlling methods have been proposed and simulated well like VTP (Video Transport Protocol) [1], implementing to cooperate with the encoder and tuning the parameters are still challenging works. In this paper, we show our result of the implementation experiment of VTP based encoding rate controlling method and then introduce some techniques of our parameter tuning for a video streaming application over wireless environment.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.340-342
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• 2005

최근 기지국(Base Station)의 도움 없이 이동 단말기(Mobile Device) 간의 다중 무선 홉을 사용하여 송수신자 간의 데이터 전송을 가능하게 하는 Ad-hoc 통신망에 관한 연구가 활발히 진행되고 있다. Ad-hoc 통신망을 구성하는 이동 단말은 이동성을 고려하여 한정된 배터리로 동작을 하게 된다. Ad-hoc 통신망에서 이동 단말은 종단(End Host)으로만 동작하는 것이 아닌 중계 노드(Intermediate Node)로도 동작을 하기 때문에 통신상에 경로를 제공하는 중요한 역할도 한다. 하지만, 현재 인터넷 상에서 광범위하게 사용되고 있는 전송 규약인 TCP(Transmission Control Protocol)는 수동적인(Reactive)혼잡 제어(Congestion Control)방식으로 망의 혼잡으로 인한 패킷 손실 발생 이전까지 전송 윈도우의 크기를 증가 때문에 반복적인 혼잡과 그로 인한 패킷 손실로 인해 불필요한 재전송을 반복하게 된다. 이와 같이 기존 TCP는 무선 통신망에서 동작하는 이동 단말의 한정된 배터리 전원을 고려하지 않고 동작하기 때문에 이동 단말의 에너지를 불필요하게 낭비하는 문제를 가지게 된다. 본 논문은 Ad-hoc 망에서 이동 단말의 에너지 효율을 개선하기 위해 불필요한 재전송 방지 및 망 상태에 따라 전송률을 적절하게 조절하는 TCP의 새로운 혼잡 제어 기법을 제시하였다. 또한 ns-2 시뮬레이터를 이용한 실험을 통해 이동 단말의 에너지 효율이 제안된 혼잡 제어 기법에 의해 향상되었음을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1406-1424
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• 2017

Recent advancements in network infrastructures provide increased opportunities to support data delivery over multiple paths. Compared with multi-homing scenario, overlay network is regarded as an effective way to construct multiple paths between end devices without any change on the underlying network. Exploiting multipath characteristics has been explored for TCP with multi-homing device, but the corresponding exploration with overlay network has not been studied in detail yet. Motivated by improving quality of experience (QoE) for reliable data delivery, we propose a multipath message transport protocol based on application level relay (MPMTP-AR). MPMTP-AR proposes mechanisms and algorithms to support basic operations of multipath transmission. Dynamic feedback provides a foundation to distribute reasonable load to each path. Common source decrease (CSD) takes the load weight of the path with congestion into consideration to adjust congestion window. MPMTP-AR uses two-level sending buffer to ensure independence between paths and utilizes two-level receiving buffer to improve queuing performance. Finally, the MPMTP-AR is implemented on the Linux platform and evaluated by comprehensive experiments.

• Annual Conference of KIPS
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• 2014.11a
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• pp.409-411
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• 2014

WAVE 기술은 차량이 고속 이동환경에서 차량간 또는 차량과 인프라간 패킷을 짧은 시간 내에 주고 받을 수 있는 무선통신 기술이다. 본 논문의 목적은 차량이 WAVE 시스템에 통신 할 때 상대방의 인증서가 폐기 되었는지 확인하기 위한 CRL(Certificate Revocation List) 다운로드 프로토콜을 설계하는 것이다. CRL 다운로드 프로토콜은 WAVE 시스템 환경에 맞추기 위해 TCP(Transmission Control Protocol)가 아닌 UDP(User Datagram Protocol) 상에서 동작한다. 그리고 보안기능을 지원하기 위해 ECDSA 를 사용하여 상호 인증을 하고 ECIES 를 사용하여 인증서의 기밀성을 보장한다. 또한 이 프로토콜은 MAC 을 CRL 데이터에 붙여 데이터의 무결성을 보장하고, UDP 상에서 동작할 때 발생할 수 있는 데이터의 손실을 줄이기 위해 에러 및 흐름제어 방식으로 Selective repeat ARQ 를 사용한다.