• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.118-127
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• 2006

The wireless transmission medium inherently broadcasts a signal to all neighbor nodes in the transmission range. Existing asynchronous MAC protocols do not provide a concrete solution for reliable broadcast in link layer. This mainly comes from that an omnidirectional broadcasting causes to reduce the network performance due to the explosive collisions and contentions. This paper proposes a directional broadcast protocol by using neighborhood information in the link layer based o,1 directional antennas, named MNDB (MAC protocol with Neighborhood for reliable Directional Broadcast). This protocol makes use of neighborhood information and DMACA (Directional Multiple Access and Collision Avoidance) scheme through 4-way handshake to support a reliable directional broadcast. To analyze its performance, MNDB protocol si compared with $RMDB^{[1]}$, the protocol 2 of reference [3], and IEEE 802.11 $protocol^{[9]}$, in terms of the number of collisions, the number of dropped packets, the number of redundant packets, and broadcast delay.

• Journal of Broadcast Engineering
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• v.11 no.3 s.32
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• pp.336-348
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• 2006

The recent advances in multimedia signal coding and transmission technologies allow lots of users to watch videos on small LCD displays. In this paper, we briefly describe an intelligent display technique to provide small-display-viewers with comfortable experiences, and study the minimum image size tolerated and utility of displaying region of interest (ROI) only when needed. The study, with 111 participants, examines minimum image size to ensure viewers pleasant viewing experiences, and evaluates the degree of satisfaction when they are viewed with region of interest (ROI) only. The experimental results show that the ROI display enhances the viewers' satisfaction when the image size becomes less than $320{\times}240$, and thus it is useful to provide the intelligent display, if necessary, which can extract and display ROI only.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.7
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• pp.774-783
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• 2007

This paper presents an integrated packaging antenna-diplexer module for wireless communication systems in the Cellular and SDMB band. The design and the realization of the proposed one are experimentally analyzed and discussed. It consists of a dual-resonance antenna and a diplexer with a multi-layer LTCC(${\varepsilon}_r=7.8,\;tan\;{\delta}=0.0043$) technology with integration capability and low loss. The dual-resonance antenna of the proposed module has the meander line structure for size reduction and has the shorting structure of an inverted F antenna to achieve good impedance matching. The diplexer of the proposed module was designed with the combination of low pass filter(LPF) and high pass filter(HPF). Decreasing the mutual interference between them provides a high isolation characteristic. The proposed antenna-diplexer module with dimensions of $27.5{\times}12.0{\times}2.2mm$ operates within a range from 813 MHz to 902 MHz for the cellular band and from 2,586 MHz to 2,655 MHz for the SDMB band. And the measured gain of the fabricated module is -1.96 dBi for Cellular band and -5.43 dBi for SDMB band. The parameters for the antenna-diplexer module are investigated and the several performances are discussed.

• Journal of KIISE:Information Networking
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• v.31 no.1
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• pp.37-52
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• 2004

Broadcast has been often used to disseminate the frequently requested data efficiently to a large volume of mobile units over a single or multiple channels. Since the mobile units have limited battery power, the minimization of the access time for the broadcast data is an important problem. There have been many research efforts that focus on the improvement if the broadcast techniques by providing indexes on the broadcast data. In this paper, we studied an efficient index allocation method for the broadcast data over multiple physical channels, which cannot be coalesced into a single high bandwidth channel. Previously proposed index allocation techniques either require the equal size of index and data or have a performance degradation problem when the number of given physical channels is not enough. These two problems will result in the increased average access time for the broadcast data. To cope with these problems, we propose an efficient tree- structured index allocation method for the broadcast data with different access frequencies over multiple physical channels. Our method minimizes the average access time for the broadcast data by broadcasting the hot data and their indexes more often than the less hot data and their indexes. We present an in-0e0th experimental and theoretical analysis of our method by comparing it with other similar techniques. Our performance analysis shows that it significantly decrease the average access time for the broadcast data over existing methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8C
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• pp.742-749
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• 2009

In this paper, we propose mitigation techniques using time-domain shortening filter (TSF) and frequency-domain shortening filter (FSF) to overcome inter-block interference (IBn and inter-carrier interference (ICn due to the time difference of arrival (TDoA) and carrier frequency offset (CFO) between downlink and uplink signals from access point (AP) and subscriber station (SS) in synchronous digital duplexing (SDD)/orthogonal frequency division multiple access (OFDMA) systems for indoor wireless communication. The proposed TSF and FSF maximize SIR for shortening in time (SIRST) and SINR for shortening in frequency (SINRSF), respectively, by using channel impulse responses and timing information among stations, obtained from mutual ranging procedure. It is verified by computer simulation that the proposed TSF and FSF reduce effectively the effects of IBI and ICI in the SDD/OFDMA systems.

• The KIPS Transactions:PartC
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• v.13C no.4 s.107
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• pp.427-434
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• 2006

Broadband Convergence Network(BcN) is a critical infrastructure to provide wired-and-wireless high-quality multimedia services by converging communication and broadcasting systems, However, there exist possible danger to spread the damage of an intrusion incident within an individual network to the whole network due to the convergence and newly generated threats according to the advent of various services roaming vertically and horizontally. In order to cope with these new threats, we need to analyze the vulnerabilities of BcN in a system architecture aspect and classify them in a systematic way and to make the results to be utilized in preparing proper countermeasures, In this paper, we propose a new classification of vulnerabilities which has been extended from the ITU-T recommendation X.805, which defines the security related architectural elements. This new classification includes system elements to be protected for each service, possible attack strategies, resulting damage and its criticalness, and effective countermeasures. The new classification method is compared with the existing methods of CVE(Common Vulnerabilities and Exposures) and CERT/CC(Computer Emergency Response Team/Coordination Center), and the result of an application to one of typical services, VoIP(Voice over IP) and the development of vulnerability database and its management software tool are presented in the paper. The consequence of the research presented in the paper is expected to contribute to the integration of security knowledge and to the identification of newly required security techniques.

• Journal of Korea Multimedia Society
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• v.10 no.2
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• pp.269-277
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• 2007

Network clustering has been proposed to provide that sensor nodes minimize energy and maximize a network lifetime by configuring clusters, Although dynamic clustering brings extra overhead like as head changing, head advertisement, it may diminish the gain in energy consumption to report attribute tasks by using cluster heads. Therefore, this paper proposes a new routing algorithm which configures cluster to reduce the number of messages when establishing paths and reports to the sink by way of cluster heads when responding sens ing tasks. All sensor nodes only broadcast bitmap once and maintain a bitmap table expressed by bits, allowing them to reduce node energy and to prolong the network lifetime. After broadcasting, each node only updates the bitmap without propagation when the adjacent nodes broad cast same query messages, This mechanism makes nodes to have abundant paths. By modifying the query which requests sensing tasks, the size of cluster is designed dynamically, We try to divide cluster by considering the number of nodes. Then, all nodes in a certain cluster must report to the sub- sink node, The proposed routing protocol finds easily an appropriate path to report tasks and reduces the number of required messages for the routing establishment, which sensor nodes minimize energy and maximize a network lifetime.

• Journal of KIISE:Information Networking
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• v.33 no.1
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• pp.38-48
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• 2006

For extending of hot-spot of WLAN, (2) proposes internetworking scheme between wireless LAN (WLAN) and mobile ad-hoc network (MANET), which employ the same layer-2 protocol with different mode. Compared to internetworking schemes between UMTS (Universal Mobile Telecommunications Systems) and WLAN (3-4), the scheme from (2) has relatively low overhead and latencies because WLAN and MANET are physically and logically similar to each other. However, the mode switching algorithm proposed in r2] for internetworking between WLAN and MANET only considers signal strength and determines handoff, and mobile nodes following a zigzag course in pollution area may perform handoff at short intervals. Furthermore, (2) employs mobile IPv6 (MIPv6) at base, which brings still high delay on handoff and overhead due to signal message exchange. In this paper, we present optimized internetworking scheme between WLAN and MANET, modified from (2). To settle ping-pong handoff from (2), we propose adaptive mode switching algorithm. HMIPv6 is employed for IP connectivity and mobility service in WLAN, which solves some shortcomings, such as high handoff overhead and vulnerable security. For routing in MANET, OLSR is employed, which is a proactive Protocol and has optimally reduced signal broadcasting overhead. OLSR operates with current P protocol compatibly with no change or modification. The proposed internetworking scheme based on adaptive mode switching algorithm shows better performance than scheme from (2).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.469-476
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• 2021

An electronic attack (EA) system is an essential weapon system for performing electronic warfare missions that contain signal tracking and jamming against multiple threats using electromagnetic waves, such as air defense radars, wireless command and communication networks, and guided missiles. The combat effectiveness can be maximized, and the survivability of militarily protecting combat power can be enhanced through EA mission operations, such as disabling the functions of multiple threats. The EA system can be used as a radio frequency jamming system to respond to drone attacks on the core infrastructure, such as airports, power plants, and communication broadcasting systems, in the civilian field. This study examined the criteria for classification according to the electronic attack missions of foreign EA systems based on an aviation platform. The foreign R&D trends by those criteria were investigated. Moreover, by analyzing the R&D trends of domestic EA systems and future battlefields in the domestic security environments, this paper proposes technological development plans of EA systems suitable for the future battlefield environments compared to the foreign R&D trends.