• 산업기술연구
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• 제21권A호
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• pp.189-198
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• 2001

In recent years, the predominant part in telecommunications is mobile communications. The next generation network is extending today's voice-only mobile networks to multi-service networks. ATM Network is possible to carry such multi-media traffic and it will be expect to use wireless ATM for the future mobile access network. One of manly important aspects for the performance of wireless ATM is the Medium Access Control (MAC) protocol. The MAC protocol must be able to satisfyingly handle the different ATM services (CBR, VBR, ABR and UBR) with their radically different performance requirements. Additionally, the MAC protocol must be able to cope with the complex radio environment where fading, multi-path propagation interference and burst-errors further complicate the situation. In this paper, a dynamic slot allocation algorithm in wireless ATM is proposed for an efficient channel sharing/media access at the MAC layer. We use equivalent capacity in the allocation of slots for VBR traffic which is variable along the time. It is simple and effective slot allocation method for VBR service. In particular, we consider the slot allocation of a session consisted of several connections for requirement of multimedia traffic. Simulation shows that the cell loss ratio is reduced by re-allocation of extra slots in Mobile Terminal (MT).

• Journal of Communications and Networks
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• 제17권3호
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• pp.247-255
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• 2015

In this paper, we propose an adaptive time division multiple access based medium access control (MAC) protocol, called bitmap-assisted shortest job first based MAC (BS-MAC), for hierarchical wireless sensor networks (WSNs). The main contribution of BS-MAC is that: (a) It uses small size time slots. (b) The number of those time slots is more than the number of member nodes. (c) Shortest job first (SJF) algorithm to schedule time slots. (d) Short node address (1 byte) to identify members nodes. First two contributions of BS-MAC handle adaptive traffic loads of all members in an efficient manner. The SJF algorithm reduces node's job completion time and to minimize the average packet delay of nodes. The short node address reduces the control overhead and makes the proposed scheme an energy efficient. The simulation results verify that the proposed BS-MAC transmits more data with less delay and energy consumption compared to the existing MAC protocols.

• Journal of Communications and Networks
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• 제17권2호
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• pp.172-183
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• 2015

To provide an efficient link maintenance approach, we propose a cross layer medium access control (LM-MAC) protocol for multichannel cognitive radio ad hoc networks. Link establishment and reliable transmission are two key problems for a perfect link maintenance mechanism. Since the cognitive user (CU) pairs have to reestablish their links each frame, in the proposed MAC protocol, three different access modes are designed to guarantee transmission efficiency in continuous frames. To enhance the transmission reliability, each CU will create a father spectrum list (FSL) after joining in the network. FSL is divided into three groups of sub-channels with different functions to compensate the packet loss caused by the primary users' appearance and the deep fading. Meanwhile, since the transmitter and the receiver will share the same FSL, periodical cooperative sensing is adopted to further optimize the former problem. Finally, compared with the existing opportunistic multichannel (OMC)-MAC protocol, the proposed LM-MAC protocol achieves better system performance in terms of saturation throughput, continuity and access delay.

• 한국정보통신학회논문지
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• 제2권3호
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• pp.379-388
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• 1998

본 논문에서는 다수의 ATM 액세스망 사용자를 위해 대역폭을 공유하면서도 등시성 트래픽과 비등시성 트래픽을 동시에 수용할 수 있도록 개발된 DMR-II (Dynamic Monitor Ring -II) 공유매체 접속 제어 프로토콜의 구조 및 동작 원리를 소개하고자 한다. DMR-II 프로토콜은 슬롯 링형 구조를 사용하며, 비등시성 트래픽에 비해 등시성 트래픽을 우선적으로 전송한다. 등시성 트래픽은 슬롯 예약 기법을 이용하여 전송되며, 통신망의 수용 한계를 초과하는 경우 블럭킹기법을 적용하여 등시성 트래픽의 지연시간 편차를 일정치 이내로 유지한다. 그리고 비등시성 트래픽은 윈도우 카운터 기법에 바탕을 둔 리셋 메커니즘을 통해 모든 노드에게 공평한 전송 기회를 제공한다.

• Journal of information and communication convergence engineering
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• 제11권3호
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• pp.153-166
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• 2013

A hierarchical time division multiple access (HTDMA) medium access control (MAC) protocol is proposed for clustered mobile underwater acoustic networks. HTDMA consists of two TDMA scheduling protocols (i.e., TDMA1 and TDMA2) in order to accommodate mobile underwater nodes (UNs). TDMA1 is executed among surface stations (e.g., buoys) using terrestrial wireless communication in order to share mobility information obtained from UNs which move cluster to cluster. TDMA2 is executed among UNs, which send data to their surface station as a cluster head in one cluster. By sharing mobility information, a surface station can instantaneously determine the number of time slots in a TDMA2 frame up to as many as the number of UNs which is currently residing in its cluster. This can enhance delay and channel utilization performance by avoiding the occurrence of idle time slots. We analytically investigate the delay of HTDMA, and compare it with that of wellknown contention-free and contention-based MAC protocols, which are TDMA and Slotted-ALOHA, respectively. It is shown that HTDMA remarkably decreases delay, compared with TDMA and Slotted-ALOHA.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권7호
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• pp.3131-3149
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• 2016

In-band Full-duplex (IBFD) wireless communication allows improved throughput for wireless networks. The current Half-duplex (HD) medium access mechanism Request to Send/Clear to Send (RTS/CTS) has been directly applied to IBFD wireless networks. However, this is only able to support a symmetric dual link, and does not provide the full advantages of IBFD. To increase network throughput in a superior way to the HD mechanism, a novel three-way handshaking access mechanism RTS/SRTS (Second Request to Send)/CTS is proposed for point to multipoint (PMP) IBFD wireless networks, which can support both symmetric dual link and asymmetric dual link communication. In this approach, IBFD wireless communication only requires one channel access for two-way simultaneous packet transmissions. We first describe the RTS/SRTS/CTS mechanism and the symmetric/asymmetric dual link transmission procedure and then provide a theoretical analysis of network throughput and delay using a Markov model. Using simulations, we demonstrate that the RTS/SRTS/CTS access mechanism shows improved performance relative to that of the RTS/CTS HD access mechanism.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.687-708
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• 2017

The machine-to-machine (M2M) communication is featured by tremendous number of devices, small data transmission, and large uplink to downlink traffic ratio. The massive access requests generated by M2M devices would result in the current medium access control (MAC) protocol in LTE/LTE-A networks suffering from physical random access channel (PRACH) overload, high signaling overhead, and resource underutilization. As such, fairness should be carefully considered when M2M traffic coexists with human-to-human (H2H) traffic. To tackle these problems, we propose an adaptive Slotted ALOHA (S-ALOHA) and time division multiple access (TDMA) hybrid protocol. In particular, the proposed hybrid protocol divides the reserved uplink resource blocks (RBs) in a transmission cycle into the S-ALOHA part for M2M traffic with small-size packets and the TDMA part for H2H traffic with large-size packets. Adaptive resource allocation and access class barring (ACB) are exploited and optimized to maximize the channel utility with fairness constraint. Moreover, an upper performance bound for the proposed hybrid protocol is provided by performing the system equilibrium analysis. Simulation results demonstrate that, compared with pure S-ALOHA and pure TDMA protocol under a target fairness constraint of 0.9, our proposed hybrid protocol can improve the capacity by at least 9.44% when ${\lambda}_1:{\lambda}_2=1:1$and by at least 20.53% when ${\lambda}_1:{\lambda}_2=10:1$, where ${\lambda}_1,{\lambda}_2$ are traffic arrival rates of M2M and H2H traffic, respectively.

• Journal of information and communication convergence engineering
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• 제5권2호
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• pp.88-92
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• 2007

In this paper, an SS-RRA protocol that is based on Code Division Multiple Access is proposed and analyzed under the integrated voice and data traffic load. The backward logical channels consist of slotted time division frames with multiple spreading codes per slot. The protocol uses a reservation mechanism for the voice traffic, and a random access scheme for the data traffic. A discrete-time, discrete-state Markov chain is used to evaluate the performance. The numerical results show that the performance can be significantly improved by a few distinct spreading codes.

• 산경연구논집
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• 제9권9호
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• pp.15-23
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• 2018

Purpose - The purpose of this paper is to examine the determinants of non-bank depository institutions (non-bank financial corporations) lending to firms. The paper aims to contribute to the existing literature by providing empirical evidence from firm-level data and unveiling factors related to access to non-bank financial corporations by firms. Research design, data, and methodology - We used the data on borrowing by firms from CRETOP from years 2008 to 2011. Using the manufacturing industry, we examined what firm-level characteristics explained the increase in borrowing from non-bank financial corporations rather than the banks. Results - Analyzing the firm-level data from 2008 to 2011, we found that firms were more likely to borrow from non-bank financial insti­tutions as the size of the firm increases, implying that large firms have more access to non-bank financing than small and medium-sized firms. In addition, it also showed that small and medium-sized firms moved to non-bank financial corporations for loans. Conclusion - Non-bank depository institutions are not a sub­stitute for bank lending to firms. More specifically, they replace bank lending to firms mostly for large firms rather than small and medium-sized firms. Also, collateral and other firm-level characteristics do not matter in accounting for non-bank lending to firms.

• 한국정보시스템학회지:정보시스템연구
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• 제28권4호
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• pp.65-103
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• 2019

Purpose The purpose of this study is to find out in extent to which the companies in Korea and oversea, which has been subjected by different laws of their country, have guaranteed the personal information rights and have provided proper 'right to access' to the information subjects. Design/methodology/approach This study compared Korean laws with 'General Data Protection Regulation (GDPR)' of EU and 'California Consumer Privacy Act (CCPA)' to check each of the level of 'right to access' guarantee. In terms of the difference in guaranteeing the right, this study compared Korean IT leading companies with US global leading IT companies to find out how much 'right to access' are properly implemented in their policies and functions they provide. Findings The result of the study shows that 'right to access' has not been well guaranteed by Korean law, as it does not provide the right to choose method and medium by information subjects and does not clarify the types of diverse information. This was clearly opposite with the other laws providing the right to choose what method and medium that subjects want with clarifying every types of personal information possible to be more. In addition, 'right to access' has not been well guaranteed by Korean companies in comparison with by the oversea companies which proactively guarantee the right by setting the function enabling subjects to browse their information through their websites or applications.