• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.8 s.350
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• pp.15-24
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• 2006

We design and implement explicit mobile multicast, named XMIP, by enhancing explicit multicast for a great number of small group multicast communications. XMIP is a straightforward multicast mechanism without maintaining multicast states due to the inheritance from the explicit multicast based on a unicast routing. This research modifies and extends the functionality of each mobility agent of IETF Mobile IP for interworking XMIP XMIP Packets captured by an extended home agent are forwarded to each extended foreign agent through nested tunnels, named X-in-X tunnels, made by the binding table of the extended home agent. X-in-X tunneling mechanism can effectively solve the serious traffic concentration problems of Mobile IP multicast specifications. Finally heterogeneous mobile networks as an XMIP testbed including CDMA2000 1X EV-DO and WLAN are actually established, and a multi-user instant messenger system for small group communications is developed for verifying the feasibility of the proposed protocols.

• Communications of Mathematical Education
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• v.22 no.3
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• pp.349-368
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• 2008

The purpose of this study was to investigate the small-group instruction of mathematics in elementary schools. For this, a sample of 742 teachers of elementary schools completed the survey. As a result, about 27.8% of the teachers reported using small group instruction while they worked with one group or they assigned to other groups worked alone. Only 2% of the teachers reported using small group in which students were encouraged to participated cooperatively. This study discusses the five issues about small group instruction in elementary school. The five issues were investigated in this survey. First, major teaching method in mathematics classroom and using of small group instruction were described. Second, frequency and period of small-group instruction were reported. Third, grouping method in small-group instruction was described. And Fourth, effect grouping practices of small-group instruction were described. Fifth, the model of small group instruction and assessment in small-group instruction were reported.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.294-306
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• 2005

Group oriented multicast applications are becoming increasingly popular in mobile ad hoc networks (MANETs). Due to dynamic topology of MANETs, stateless multicast protocols are finding increased acceptance since they do not require maintenance of state information at intermediate nodes. Recently, several multicast schemes have been proposed which scale better' with the number of multicast sessions than traditional multicast strategies. These schemes are also known as explicit multicast (Xcast; explicit list of destinations in the packet header) or small group multicast (SGM). In this paper, we propose a new scheme for small group' multicast in MANETs named extended explicit multicast (E2M), which is implemented on top of Xcast and introduces mechanisms to make it scalable with number of group members for a given multicast session. Unlike other schemes, E2M does not make any assumptions related to network topology or node location. It is based on the novel concept of dynamic selection of Xcast forwarders (XFs) between a source and its potential destinations. The XF selection is based on group membership and the processing overhead involved in supporting the Xcast protocol at a given node. If the number of members in a given session is small, E2M behaves just like the basic Xcast scheme with no intermediate XFs. As group membership increases, nodes may dynamically decide to become an XF. This scheme, which can work with few E2M aware nodes in the network, provides transparency of stateless multicast, reduces header processing overhead, minimizes Xcast control traffic, and makes Xcast scalable with the number of group members.

• Communications of the Korean Mathematical Society
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• v.14 no.1
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• pp.99-110
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• 1999

We apply sector theory to obtain some characterization on Gaois groups for subfactors. As an example of a non-irreducible inclusion of small index, a locally trivial inclusion arising from an automorphism is considered and its Galois group is completely determined by using sector theory.

• Journal of Communications and Networks
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• v.9 no.1
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• pp.75-83
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• 2007

Orthogonal frequency division multiplexing (OFDM) systems with multiple transmit antennas can exploit space-time block coding on each subchannel for reliable data transmission. Spacetime coded OFDM systems, however, are very sensitive to time variant channels because the channels need to be static over multiple OFDM symbol periods. In this paper, we propose to mitigate the channel variations in the frequency domain using a linear filter in the frequency domain that exploits the sparse structure of the system matrix in the frequency domain. Our approach has reduced complexity compared with alternative approaches based on time domain block-linear filters. Simulation results demonstrate that our proposed frequency domain block-linear filter reduces computational complexity by more than a factor of ten at the cost of small performance degradation, compared with a time domain block-linear filter.

• Communications for Statistical Applications and Methods
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• v.4 no.1
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• pp.317-325
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• 1997

Group testing is an efficient method to classify units from a population as infected or non-infected and useful in estimating the infection rate when the population infection rate is small. Upper bounds are the focus of interest in group testing, but has not been studied extensively. In this paper, the upper bound derived from the uniformly most powerful test is proposed and compared with the classical approachers, Thompson's and Bhattacharyya et al.'s methods.

• Journal of the Korean earth science society
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• v.41 no.3
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• pp.307-319
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• 2020

The purpose of this study was to determine whether there are differences in the verbal interactions of earth science gifted depending on their communications structures and group status in small group activities. To this end, a small group activity was conducted to measure the density of the earth, and 8 small groups were selected, including 4 co-ownership type and 4 monopolistics type groups with different communication structures. And then, the framework was developed for analyzing verbal interactions to compare the differences in characteristics between small groups. The results are as follows. First, regardless of the communication structures, there were showing a simple pingpong-type communication structures for all small groups. Second, negative interactions such as 'restraint', 'command', 'complaint', and 'lack of confidence' predominantly appeared in all small groups. Third, the students in the status of out-lookers in small groups were mainly verbal interactions, such as instructing the other person, acting against the other person's actions, and expressing dissatisfaction with the attitudes and abilities of members. Therefore, teachers should guide students to use higher-level verbal interactions in their group activities in small group activities, and engage in students communication to prevent negative interactions from occurring. The teachers also need to check the level of achievement for students in the status of out-lookers in advance and guide them to participate more actively in small group activities. This study is meaningful in that it can be sued to design teaching and learning to improve students' problem solving and communication skills.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.2
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• pp.498-514
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• 2012

Machine to machine (M2M) communications is the hottest issue in the standardization and industry area, it is also defined as machine-type communication (MTC) in release 10 of the 3rd Generation Partnership Project (3GPP). Recently, most research have focused on congestion control, sensing, computing, and controlling technologies and resource management etc., but there are few studies on security aspects. In this paper, we first introduce the threats that exist in M2M system and corresponding solutions according to 3GPP. In addition, we present several new security issues including group access authentication, multiparty authentication and data authentication, and propose corresponding solutions through modifying existing authentication protocols and cryptographic algorithms, such as group authentication and key agreement protocol used to solve group access authentication of M2M, proxy signature for M2M system to tackle authentication issue among multiple entities and aggregate signature used to resolve security of small data transmission in M2M communications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.1-19
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• 2015

With the recent popularity of smart terminals, the demand for high-data-rate transmission is growing rapidly, which brings a new challenge for the traditional cellular networks. Both device-to-device (D2D) communication and small cells are effective to improve the transmission efficiency of local communication. In this paper, we apply D2D communication into a small cell network system (SNets) and study about the optimization problem of resource allocation for D2D communication. The optimization problem includes system scheduling and resource allocation, which is exponentially complex and the optimal solution is infeasible to achieve. Therefore, in this paper, the optimization problem is decomposed into several smaller problems and a hierarchical scheme is proposed to obtain the solution. The proposed hierarchical scheme consists of three steps: D2D communication groups formation, the estimation of sub-channels needed by each D2D communication group and specific resource allocation. From numerical simulation results, we find that the proposed resource allocation scheme is effective in improving the spectral efficiency and reducing the outage probability of D2D communication.

• Communications for Statistical Applications and Methods
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• v.6 no.1
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• pp.293-303
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• 1999

When test outcomes of units are dichotomous and he infection rate is small group testing is more efficient that noe-to-one testing in estimating the true p and classifying units as infected or not. In this paper two-sided hypothesis testing and confidence intervals are derived based on the UMP(uniformly most powerful) unbiased test. The UMP unbiased approach is compared with Thompson's and Bhattacharyya et al.'s approaches by computing the length of confidence intervals and capture probabilities and shown to have a number of desirable properties. Unequal allocation one of advantages of the proposed approach is also mentioned.