• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.486-490
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• 2008

본 논문에서는 Spurious NAK Suppression알고리즘을 통하여 RLP의 성능향상에 대한 기법을 제안한다. 일반적으로, Hybrid ARQ기법에서는 MAC과 Physical Layer에서의 Retransmission 및 Error Correction으로 무선환경에서의 Error를 줄이고 latency를 보장하고 있다. 그러나 Hybrid ARQ에서의 Multiple SAW나 Selective-ARQ에 의해서 인접한 Packet들 간의 out-of-sequence문제가 발생할 수 밖에 없으며, upper layer인 RLP(혹은 RLC)에서는 이를 re-sequencing하여야 하는 부담감이 생기게 된다. 본 논문에서는 RLP receiver에서의 re-sequencing방법에 있어서, 효율적으로 RLP-NAK의 전송시점을 결정하는 NAK suppression 방법을 제안하고 있으며, 실험을 통하여 높은 성능향상을 보임을 확인할 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10B
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• pp.638-643
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• 2007

Interconnecting wireless local area networks (WLANs) with third generation (3G) cellular networks has become an issue of great interest. However, a Vertical Handover (VHO) causes an abrupt change in link bandwidth. Due to such a change, TCP triggers unnecessary fast retransmission during a Downward VHO (DVHO) from a cellular network to a WLAN, causing throughput degradation. Thus, we propose a new reordering mechanism for DVHO that suppresses unnecessary retransmission due to the spurious duplicate acknowledgments. We analytically investigate the throughput of TCP in the literature and our proposed scheme. Through the numerical and simulation results, it is shown that our proposed TCP achieves better performance in terms of throughput, compared with Nodupack with SACK.

• Journal of Communications and Networks
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• v.10 no.1
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• pp.98-107
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• 2008

In mobile ad hoc networks, packet loss is unavoidable due to MAC contention, link failure or the inherent characteristics of wireless link. Since TCP relies on the timely reception of TCP ACK packets to progress the transmission of the TCP DATA packets, ACK loss obviously affects the performance due to two main problems: (a) Frequent occurrence of spurious retransmissions caused by timeout events and (b) impairment of the fast retransmit mechanism caused by the lack of a sufficient number of duplicate ACK packets. In particular, since most reactive routing protocols force the packets buffered over a path to be discarded while performing a route recovery, the performance degradation becomes more serious due to such ACK loss. In this paper, therefore, TCP with two piggybacking schemes (called TCP-pgy) is proposed in order to resolve the above-mentioned problems over reactive routing protocols. Through extensive simulations using the ns-2 simulator, we prove that our proposed schemes contribute to TCP performance improvements.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.978-981
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• 2007

TCP(Transmission Control Protocol)는 흐름제어와 오류제어 그리고 혼잡제어 등을 통해 목적지까지 효율적으로 데이터를 전송하는 프로토콜이다. 최근 라우터 성능 및 라우팅 알고리즘 등의 발달로 인해 패킷이 비순차적으로 전송되는 패킷 재배치(packet reordering)가 빈번한 발생하여 TCP 성능 저하의 주요 원인이 되고 있다. 패킷 재배치가 TCP 로 하여금 불필요한 재전송(Spurious Retransmission) 및 혼잡제어를 수행하도록 하기 때문이다. 본 논문에서는 TCP 의 신속 재전송(Fast Retransmission)의 중복 응답 임계값(dupthresh)를 동적으로 조절함으로써, 불필요한 재전송 및 혼잡제어의 발생횟수를 효율적으로 줄이는 TCP-DAD(TCP Dynamically Adjusted Dupthresh)기법을 제안한다. 본 논문은 NS-2를 이용한 시뮬레이션을 통해 TCP-DAD 가 다른 TCP 메커니즘보다 평균적으로 약 34%의 성능 향상을 보임을 증명하였다.

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.451-458
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• 2010

To detect and recover packet losses over wireless links is very important in terms of reliability in packet transmission. Most wireless communication systems adopt an automatic repeat request (ARQ) protocol operating at link layer. However, it has been constantly addressed that the interaction not harmonized sufficiently between ARQ and TCP rather degrades TCP performance. In this paper, therefore, we propose an improved scheme from the aspect of the interaction with TCP loss recovery mechanism that can be applied to selective repeat ARQ (SR-ARQ) protocol and prove that the proposed scheme improves TCP performance significantly by OPNET simulations.

• Journal of Korea Multimedia Society
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• v.13 no.10
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• pp.1525-1533
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• 2010

With the digital terrestrial television broadcasting transition, terrestrial television broadcasting have required the replacement of retransmission facilities for the analog broadcasting installed in the existing apartment, building, cable TV station, MATV system and so on. In addition, new standards have been enacted for retransmission of the digital television broadcasting in MATV system. To deal with this issue, in this paper, we propose a new 8-VSB remodulator that can retransmit signals of the terrestrial digital television broadcasting. Moreover, we present a standard and the process composition of the 8-VSB remodulator, and an experimental environment configuration for performance evaluation. To achieve this, we have implemented the 8-VSB remodulator with the sequential process components comprised of the RF signal retransmission, the TS stream modulator, the RF signal reception and demodulation. Through the simulation, we analyze the performance standard from the measured data such as spurious and phase noise. And then, we measure SNR and EVM of each attenuation step of the signal obtained by the signal processor and the 8-VSB remodulator with the same retransmission environment and conditions. Experimental results show that both the 8-VSB remodulator and the signal processor can be used as equipment for the retransmission of the terrestrial digital television broadcasting. In addition, the 8-VSB remodulator performed well to improve the transmission efficiency for the digital broadcasting signal, compare to the existing signal processor.