• 정보처리학회논문지D
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• 제10D권6호
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• pp.961-970
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• 2003

데이타 방송 환경에서 서버는 방송 채널을 통하여 데이타베이스 내의 데이타들을 주기적으로 방송한다. 그리고 각 클라이언트가 어떤 데이타를 액세스하기 위해서는 방송 채널을 감시하여 해당 데이타가 방송되기를 기다려야 한다. 클라이언트 데이타 캐슁은 클라이언트가 액세스하려는 데이타가 방송되기를 기다리는 시간을 줄이기 위한 매우 효과적인 기술이다. 본 논문에서는 이 대기 시간을 줄이기 위하여 LRU-CFP로 명명된 새로운 클라이언트 캐쉬 관리 기법을 제안하고, 모의 실험을 통하여 새로이 제시된 기법의 성능을 평가한다. 성능 평가 결과에 의하면 LRU-CFP 기법은 LRU, GRAY, 그리고 CF 기법보다 평균 응답시간에 있어서 더 우수한 성능을 보인다.

• 정보학연구
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• 제5권4호
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• pp.9-21
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• 2002

데이타 방송 환경에서 서버는 방송 채널을 통하여 데이타베이스내의 데이타들을 주기적으로 방송한다. 그리고 각 클라이언트가 어떤 데이타를 액세스하기 위해서는 방송 채널을 감시하여 해당 데이타가 방송되기를 기다려야 한다. 클라이언트 데이타 캐슁은 클라이언트가 액세스하려는 데이타가 방송되기를 기다리는 시간을 줄이기 위한 매우 효과적인 기술이다. 본 논문에서는 이 대기 시간을 줄이기 위하여 2Q-CF로 명명된 새로운 클라이언트 캐쉬 관리 기법을 제안하고, 모의 실험 모델을 통하여 2Q-CF 기법의 성능을 평가한다. 성능 평가 결과에 의하면 2Q-CF 기법은 LRU-CF와 CF보다 평균 응답시간에 있어서 더 우수한 성능을 보인다.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.377-385
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• 2012

The Automatic Dependent Surveillance Broadcast (ADS-B) system is a key component of CNS/ATM recommended by the International Civil Aviation Organization (ICAO) as the next generation air traffic control system. ADS-B broadcasts identification, positional data, and operation information of an aircraft to other aircraft, ground vehicles and ground stations in the nearby region. This paper explores the ADS-B based trajectory prediction and the conflict detection algorithm. The multiple-model based trajectory prediction algorithm leads accurate predicted conflict probability at a future forecast time. We propose an efficient and accurate algorithm to calculate conflict probability based on approximation of the conflict zone by a set of blocks. The performance of proposed algorithms is demonstrated by a numerical simulation of two aircraft encounter scenarios.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2010년도 하계학술대회
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• pp.9-11
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• 2010

Multiple-input multiple-output (MIMO) systems assisted by multi-relays with single antenna are considered. Signal transmission consists of two hops. In the first hop, the source node broadcasts the vector symbols to all relays, then all relays forward the received signals multiplied by each power gain to the destination simultaneously. Unlike the case of full cooperation between relays such as single relay with multiple antennas, in our case there is no closed form solution for optimal relay power gain with respect to minimum mean square error (MMSE). Thus we propose an alternative approach in which we use an approximation of the cost function based on rank-one matrix decomposition. As a cost function, we choose the trace of MSE matrix. We give several simulation results to validate that our proposed method obtains a negligible performance loss compared to optimal solution obtained by exhaustive search.

• 한국IT서비스학회지
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• 제10권2호
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• pp.247-257
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• 2011

In this paper, we propose a multiple-disseminators determining mechanism for Efficient Code Dissemination with low-delay(ECoDi) for wireless sensor networks (WSN). Code dissemination is in the spotlight as an important research issue since sensor nodes are necessary for updating new software remotely or fixing bugs dynamically. In particular, the time factor for code dissemination is the most important factor in order that the normal operation of nodes can be continuously performed as soon as finishing the dissemination. For this factor, ECoDi determines the set of disseminators through regression analysis based on the size of distributed code and the time of past unicasts and broadcasts. Then it transmits the entire code as a unicast to multiple disseminators, and the disseminators broadcast the code to the remaining neighbor nodes. Performance results on a testbed show that ECoDi reduces dissemination time significantly compared to a conventional scheme.

• Journal of Communications and Networks
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• 제7권4호
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• pp.478-488
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• 2005

To conserve the usage of energy, indexing techniques have been developed in a wireless mobile environment. However, the use of interleaved index segments in a broadcast cycle increases the average access latency for the clients. In this paper, we present the broadcast-based location dependent data delivery scheme (BBS) for dynamic range queries. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. Then, we present a data prefetching and caching scheme, designed to reduce the query response time. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients, and the size of the service area.

• Journal of information and communication convergence engineering
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• 제9권1호
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• pp.38-43
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• 2011

This paper proposes a centralized backoff control scheme for guaranteeing fair packet transmissions in S-ALOHA CDMA system. In S-ALOHA CDMA system, simultaneously transmitted packets act as multiple access interferences, so that unsuccessful packet transmissions are caused entirely by multiple access interferences. Therefore, in order to maximize the system performance, the levels of MAI should be kept at an optimal level. In the proposed scheme, the base station broadcasts the packet transmission probability, which is calculated based on the level of MAI. Mobile stations attempt to transmit their packet with the received probability. Simulation results show that the proposed scheme can guarantee a good fairness among all the mobile stations.

• ETRI Journal
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• 제43권4호
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• pp.758-768
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• 2021

In this work, the secrecy of a typical wireless cooperative dual-hop non-orthogonal multiple access (NOMA)-enabled decode-and-forward (DF) relay network is investigated with the impact of collaborative and non-collaborative eavesdropping. The system model consists of a source that broadcasts the multiplexed signal to two NOMA users via a DF relay, and information security against the eavesdropper nodes is provided by a helpful jammer. The performance metric is secrecy rate and ergodic secrecy capacity is approximated analytically. In addition, a differential evolution algorithm-based power allocation scheme is proposed to find the optimal power allocation factors for relay, jammer, and NOMA users by employing different jamming schemes. Furthermore, the secrecy rate analysis is validated at the NOMA users by adopting different jamming schemes such as without jamming (WJ) or conventional relaying, jamming (J), and with control jamming (CJ). Simulation results demonstrate the superiority of CJ over the J and WJ schemes. Finally, the proposed power allocation outperforms the fixed power allocation under all conditions considered in this work.

• 한국정보과학회논문지:시스템및이론
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• 제29권1호
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• pp.10-15
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• 2002

이논문은 nckdnjs 하리퍼큐브에서 O(m+n-1) 이내에서 크기 m인 메세지를 브로드캐스트 하는 파 이프라인 브로드캐스트(pipelined broadcast)를 제안한다. 이것은 도달가능집합(reachable set)으로 부터 유도된 복제 나무(replication tree)를 이용한다. 이 브로드캐스트방식은 O(m[n/log(n+1)])의 수행시간을 갖는 Ho-Kao 의 알고리즘에 비해 성능이 크게 개선된 결과이다. 브로드개스트 통신은 메시지 복제 기능을 갖는 all-port 휨홀 라우터를 이용한다. 이 논문은 알고리즘 기술 및 실제 구현시 이전 방식들과의 성능비 교도 제시한다.

• Journal of Positioning, Navigation, and Timing
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• 제9권3호
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• pp.237-248
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• 2020

GNSS has been evolving dramatically in recent years. There are currently 6 GNSS (4 GNSS, AND 2 RNSS) constellations, which are GPS (USA), GLONASS (Russia), BeiDou (China), Galileo (EU), QZSS (Japan), and IRNSS (India). The Number of navigation satellites is expected to be over 150 by 2020. As the number of both constellations and satellites used for the improvement of positioning performance, high accuracy, and robustness of precise positioning is more promising. However, a large amount of the correction messages is required to support the augmentation system for the available satellites of all the constellations. Since bandwidth for the correction messages is generally limited, sending or scheduling the correction messages might be a critical issue in the near future. In this study, we analyze the relationship between the size of the bandwidth and Real-Time Kinematics (RTK) performance. Multiple Signal Messages (MSM), the only Radio Technical Commission for Maritimes (RTCM) message that supports multi-constellation GNSS, has been used for this assessment. Instead of the conventional method that broadcasts all the messages at the same time, we assign the MSM broadcasting interval for each constellation in 5 seconds. An open sky static and dynamic test for this study was conducted on the roof of Sejong University. Our results show that the RTK fixed position accuracy is not affected by the 5-second interval corrections, but the ambiguity fixing rate is degraded for poor DOP cases when RTK correction are transmitted intermittently.