• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.257-259
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• 2010

본 논문에서는 지상파 3D HDTV 방송 서비스를 제공하기 위해 수정된 ATSC (Advanced Television Systems Committee) 전송 시스템 [2]을 위한 시변다중경로채널에 강인한 프레임 구조를 제안하고 성능을 측정하였다. 수정된 ATSC 전송 시스템 [2]은 기존 ATSC 전송 시스템[1]의 채널 부호화부를 수정하고, 변조 성상도를 증가 시키면서 적정한 수준의 TOV (Threshold of Visibility)에서의 전송 용량 증대 가능성을 확인하였다. 이를 토대로, 증가된 전송 데이터 전송률에 대한 순수 데이터 전송률을 최대한 보장하면서 시변다중경로채널에서 효율적으로 채널을 추정하고 복구하기 위해, ISI (Inter Symbol Interference)를 방지하기 위한 프레임 헤더의 보호구간에 알려진 PN (Pseudorandom Noise) 심벌을 삽입하였다. PN 심벌을 보호 구간에 이용할 경우 시간 영역에서 채널 임펄스 응답 (CIR: Channel Impulse Response)을 추정하여, 주파수 영역에서의 채널 보상을 가능케 하여 정확한 채널 추정 및 보상을 수행할 수 있다. 또한 수신기의 속도에 따른 다양한 최대 도플러 주파수가 존재하는 채널에 강인한 프레임 구조들을 제안하였다. 컴퓨터 시뮬레이션을 통해 수정된 ATSC 전송 시스템에 제안된 프레임 구조를 적용하여 TU (Typical Urban)-6 채널에서의 SER (Symbol Error Rate) 성능을 측정하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.725-728
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• 2011

멀티홉 네트워크에서 플러딩(Flooding) 기법은 토폴로지 내의 모든 노드에게 패킷을 전달하는 것이다. 대표적인 플러딩 기법인 Blind 플러딩은 패킷을 받은 모든 노드가 플러딩을 하기 때문에, 무선 네트워크의 전체적인 성능이 감소한다. 기존 연구에서는 성능 향상을 위해 중복 수신되는 패킷을 줄이는 데에만 초점이 맞춰져 있다. 하지만 실제 무선 네트워크 환경에서는 간섭에 따른 패킷 손실이 발생하고, 플러딩은 Broadcast 로 전송하기 때문에 재전송하여 손실 패킷을 복구할 수 없다. 본 논문에서는 Blind, Self-Pruning, Dominant-pruning 플러딩 기법에 재전송이 필요 없는 오류정정 기법(FEC)를 적용하여, 추가적인 잉여 데이터에 따른 전체 전송 패킷의 수와 플러딩 기법의 신뢰성을 분석 하였다.

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.485-490
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• 2010

IEEE 802.11n supports two frame aggregation schemes, aggregation for MAC service data unit (A-MSDU) and aggregation for MAC protocol data unit (A-MPDU), to improve throughput at the MAC layer. In this paper, we propose a cooperative frame aggregation (CoFA), which can recover erroneous frames in a cooperative manner based on A-MPDU. Specifically, CoFA receive multiple frames from direct and relay paths, and combined multiple frames jointly. Numerical results show that CoFA outperforms direct transmission and relay transmission over diverse channel conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.9
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• pp.700-706
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• 2013

In this paper, we propose a method for applying random linear network coding in satellite communication to improve reliability. In the proposed protocol, network-coded redundancy (NC-R) packets are transmitted in the PEP (Performance Enhancement Proxy). Therefore, if data packets is lost by wireless channel error, they can be recovered by NC-R packets. We also develop the TCP performance model of the proposed protocol and evaluate the performance of the proposed protocol. In the simulation results, It is shown that the proposed protocol can improve the TCP throughput as compared with that of the conventional TCP because the NC-R packets is sent by the sender-side PEP and the receiver-side PEP use these packets to recover the lost packets, resulting in reducing the packet loss in TCP.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.2
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• pp.186-190
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• 2008

This paper analyzes previous work on publish/subscribe in mobile ad-hoc networks with respect to collaboration methods among distributed event brokers. Our experiments suggest that approaches building event delivery structures are suitable for a scenario where there are events of various types each of which is consumed by a few subscribers. However, these approaches based on independent periodic exchange of network topology information may fail to reflect the up-to-date information when building event delivery paths. For this reason they do not correctly recover a broken path caused by node mobility, which results in lower event delivery rates. This paper proposes a scheme for building and maintaining event delivery paths based on advertisements initiated by and hence propagated from the root node. This guarantees correct recovery of event delivery paths within each period. Our experiments show that, our proposed scheme gives a better event delivery ratio with lower overhead.

• Journal of KIISE:Information Networking
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• v.30 no.4
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• pp.513-519
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• 2003

In order to deliver multicast traffic efficiently, multicast routing and reliable transmission mechanisms are required. The reliable delivery implies that lost packets must be retransmitted, which in turn requires that transmitted packets be stored in a retransmission buffer. Therefore how to manage a retransmission buffer is important and, in this paper, we try to solve the problem of how many packets should be maintained in the buffer. Our proposed scheme, the timer-based buffer management (TBM), maintains only necessary amount of buffer based on the timer value calculated from the NAKs between the replier and receivers on a multicast tree and can adjust to the dynamic network conditions. By performing simulations, we show that TBM manages the buffer efficiently regardless of the error situation, network size, and so on.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.4
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• pp.701-712
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• 2012

The concept of $k$-shortest disjoint paths is considered important because the establishment of primary and backup forwarding paths exploiting shorter distance and faster propagation time is a dominant consideration for the design of a survivable backbone network. Therefore, we need to evaluate how well the concept of $k$-shortest disjoint paths is exploited for the design of a survivable ship backbone network considering the international standard related to ship backbone networks, the IEC61162-410 standard specifying how to manage redundant message transmissions among ship devices. Performance evaluations are conducted in terms of following objective goals: link capacity, hop and distance of primary and backup paths, even distribution of traffic flows, restoration time of backup forwarding paths, and physical network topology connectivity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9B
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• pp.793-805
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• 2003

In OBS (Optical Burst Switching) networks which decouple the burst from its header, the fault of a fiber link can lead to the failure of all the light-path that traverses the fiber. Because each light-path is expected to operate at a rate of a few Gbps by using WDM (Wavelength Division Multiplexing) technology, any failure may lead to large data loss. Therefore, an efficient recovery scheme must be provided. In this paper, we analyze network utilization and BCP (Burst Control Packet) loss rate according to each link failure by applying the conventional restoration schemes in OBS networks. And through these simulation results, an ASPR scheme is proposed improve the fault management scheme in terms of recovery time and throughput. Finally, We compare the performance of our proposed scheme with that of the conventional one with respect to burst loss rate, resource utilization and throughput by OPNET simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.5
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• pp.16-24
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• 2011

The IEEE 802.11 wireless LAN (Local Area Network) is widely used for wireless access due to its easy deployment and low cost. Multicast in wireless LANs is very useful for transmitting data to multiple receivers compared to unicast to each receiver. In the IEEE 802.11 wireless LAN, multicast transmissions are unreliable since multicast data packets are transmitted without any feedback from receivers. Recently, various protocols have been proposed to enhance the reliability of multicast transmissions. They still have serious problems in reliability and efficiency due to the excessive control overhead by the use of a large number of control packets in the error recovery process, and due to a large number of retransmissions to satisfy all receivers. In this paper, we propose an effective scheme called PTRM(Proactive Transmission based Reliable Multicast). The proposed scheme uses a block erasure code to generate parity packets and to reduce the impact of independent packet error among receivers. After generating parity packets, the PTRM transmits data packets as many as receivers need to recover error, and then requests feedback from them. The simulation results show that the proposed scheme provides reliable multicast while minimizing the feedback overhead.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8B
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• pp.482-491
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• 2007

This paper proposes a k-disjoint-path routing algorithm that provides energy efficient and reliable message transmission in wireless sensor networks. The proposed algorithm sends messages through a single path without the occurrence of critical events. However, it sends through k disjoint paths(k>1) under the occurrence of critical events. The proposed algorithm detects the occurrence of critical events by monitoring changing data patterns, and calculates k from a well-defined fault model and the target-delivery ratio. Our simulations reveal that the proposed algorithm is more resilient to node failure than other routing algorithms, and it also decreases energy consumption and reduces the average delay much more than multi-path and path-repair algorithms.