• The KIPS Transactions:PartC
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• v.14C no.2
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• pp.171-178
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• 2007

In mobile ad hoc networks, an application scenario requires mostly group mobility behavior in the mix of group moving nodes and individually moving nodes. The nodes of those applications tend to belong to the movement group with similar movement behavior. Group mobility is one of the good methods to improve scalability, and reduces the protocol overhead. In this paper, we propose the multicast architecture which regards nodes that have equal group mobility in the heterogeneous group mobility network as the single entity with the multiple interfaces and composes multicast tree, The logical cooperative entity-based multicast architecture accommodates the scalability, the multicast tree simplification, and the protocol overhead reduction which arc obtained from the hierarchical multicast architecture, while it maintains the nat multicast architecture for the data transmission. It also prevents the concentration of the energy consumption dispersing data forwarding load into the several ingress/egress nodes. Results obtained through simulations show that logical cooperative entity based multicast protocol with multiple interfaces offers the protocol scalability and the efficient data transmission.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3C
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• pp.281-292
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• 2008

A main application of sensor networks are to monitor and to send information about a possibly hostile environment to a powerful base station connected to a wired network. To conserve power from each sensor, intermediate network nodes should aggregate results from individual sensors. However, it can make it that a single compromised sensor can render the network useless, or worse, mislead the operator into trusting a false reading. In this paper, we propose a protocol to give us a key aggregation mechanism that intermediate network nodes could aggregate data more safely. The proposed protocol is more helpful at multi-tier network architecture in secure sessions established between sensor nodes and gateways. From simulation study, we compare the amount of the energy consumption overhead, the time of key transmission and the ratio of of key process between the proposed method and LHA-SP. The simulation result of proposed protocol is low 3.5% a lord of energy consumption than LHA-SP, the time of key transmission and the ration of key process is get improved result of each 0.3% and 0.6% than LHA-SP.

• The KIPS Transactions:PartC
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• v.13C no.3 s.106
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• pp.303-310
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• 2006

This paper is to execute a study for characteristic analysis of synchronization clock and maximum network node number with various clock states, normal, SPT, LPT, in NG-SDH networks. Through the simulations, maximum network node numbers showed from 42 to 38 nodes in normal state. In SPT state, maximum network node numbers, when the last NE network applied to only SPT state, presented from 19 to 4 nodes, much less than normal state. Node numbers to meet specification in case of occurrence of SPT state in all NE networks decreased greatly. In LPT state, all maximum node numbers, when the last NE network applied to only LPT state, presented more than 50 nodes, and the results in case of occurrence of LPT state in all NE networks were also identified. However, node numbers to meet specification in case of LPT state in all DOTS networks were few large with difference between LPT and normal or SPT state.

• The KIPS Transactions:PartA
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• v.10A no.2
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• pp.123-130
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• 2003

This paper presents a new striped checkpointing scheme for serverless cluster computers, where the local disks are attached to the cluster nodes collectively form a distributed RAID with a single I/O space. Striping enables parallel I/O on the distributed disks and staggering avoids network bottleneck in the distributed RAID. We demonstrate how to reduce the checkpointing overhead and increase the availability by striping and staggering dynamically for communication intensive applications. Linpack HPC Benchamark and MPI programs are applied to these checkpointing schemes for performance evaluation on the 16-nodes cluster system. Benchmark results prove the benefits of the striped checkpointing scheme compare to the existing schemes, and these results are useful to design the efficient checkpointing scheme for fast rollback recovery from any single node failure in a cluster system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7B
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• pp.517-527
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• 2012

This paper considers a cooperative communication system with a single relay node, where two-layer superposition coding and successive decoding is employed to reduce the expected distortion of a Gaussian source delivered. For the system, we propose a relay scheme which forwards an appropriate relay signal at the relay node, based on the local decoding result of layers and the decoding result of layers at the destination node fed back to the relay node. In the scheme, the relay signal is designed not only by applying decode-and-forward but also by applying amplify-and-forward to reduce the outage probability in final decoding of each layer. The performance of the proposed scheme is evaluated numerically in terms of the expected distortion at various relay locations using outage probabilities derived. The results show that the proposed scheme outperforms the conventional schemes in most cases of the relay location and the gain gets larger when the relay node is closer to the source node in particular.

• Journal of the Korea Society of Computer and Information
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• v.25 no.12
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• pp.135-144
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• 2020

In graph theory, the least-cost path is discovered by searching the shortest path between a start node and destination node. The least cost is calculated as a one-dimensional value that represents the difference in distance or price between two nodes, and the nodes and edges that comprise the lowest sum of costs between the linked nodes is the shortest path. However, it is difficult to determine the shortest path if each node has multiple attributes because the number of cost types that can appear is equal to the number of attributes. In this paper, a shortest path search scheme is proposed that considers multiple attributes using the Euclidean distance to satisfy various user requirements. In simulation, we discovered that the shortest path calculated using one-dimensional values differs from that calculated using the Euclidean distance for two-dimensional attributes. The user's preferences are reflected in multi attributes and it was different from one-dimensional attribute. Consequently, user requirements could be satisfied simultaneously by considering multiple attributes.

• The KIPS Transactions:PartC
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• v.16C no.6
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• pp.737-746
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• 2009

Given the increased interest in ubiquitous computing, wireless sensor network has been researched widely. The localization service which provides the location information of mobile user, is one of important service provided by sensor network. Many methods to obtain the location information of mobile user have been proposed. However, these methods were developed for only one mobile user so that it is hard to extend for multiple mobile users. If multiple mobile users start the localization process concurrently, there could be interference of beacon or ultrasound that each mobile user transmits. In the paper, we propose APL(Adaptive Power Control based Resource Allocation Technique for Efficient Localization Technique), the localization technique for multiple mobile nodes based on adaptive power control in mobile wireless sensor networks. In APL, collision of localization between sensor nodes is prevented by forcing the mobile node to get the permission of localization from anchor nodes. For this, we use RTS(Ready To Send) packet type for localization initiation by mobile node and CTS(Clear To Send) packet type for localization grant by anchor node. NTS(Not To Send) packet type is used to reject localization by anchor node for interference avoidance and STS(Start To Send) for synchronization between 모anchor nodes. At last, the power level of sensor node is controled adaptively to minimize the affected area. The experimental result shows that the number of interference between nodes are increased in proportion to the number of mobile nodes and APL provides efficient localization.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.4
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• pp.31-37
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• 2008

Conventional cooperative communications can attain gain of spatial diversity and path loss reduction because destination node independently received same signal from source node and relay node located between source node and destination node. However, these techniques bring about decreased spectral efficiency with relay node and increased complexity of receiver by using maximal ratio combining (MRC). This paper has proposed cooperative ARQ protocol that can improve the above problems and can get the better performance. This method can increase the spectral efficiency than conventional cooperative communication because if the received signal from source node is satisfied by the destination preferentially, the destination transmits ACK message to both relay node and source node and then recovers the received signal. In addition, if ARQ message indicates NACK relay node operates selective retransmission and we can increase reliability of system compared with that of general ARQ protocol in which source node retransmits data. In the proposed protocol, the selective retransmission and ARQ message are to be determined by comparing log-likelihood ratio (LLR) computation of received signal from source node with predetermined threshold values. Therefore, this protocol don't waste redundant bandwidth with CRC code and can reduce complexity of receiver without MRC. We verified spectral efficiency and BER performance for the proposed protocol through Monte-Carlo simulation over Rayleigh fading plus AWGN.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1053-1058
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• 2011

In this paper, we propose a concatenated single antenna diversity system to assure the data transmission reliability between flight type air nodes which move according to their atypical orbit, then analyze its performance. The proposed system achieve a diversity gain using single antenna and a coding gain from convolutional code simultaneously. Simulation result about the bit error rate(BER) of the proposed system shows that its BER performance is about 9.5dB greater than convolutional code at $10^{-4}$ and about 14dB greater than space time block code at $10^{-3}$ which has a full diversity gain. In addition, compared with space time trellis code with diversity gain and coding gain, the proposed system shows the better 4dB at a BER of $10^{-5}$. Therefore, it is necessary that concatenated single antenna diversity should be adopted to the reliable data transmission of flight type air nodes.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.24 no.1
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• pp.165-170
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• 2014

In this paper, a hierarchical authentication protocol is proposed to minimize authentication delay in proxy mobile IPv6 networks. The authentication function of the AAA server is distributed to the LMAs and the MAGs. If the LMAs or the MAGs have authentication information of the MNs, they authenticate the MN on behalf of the AAA servers. Therefore, the authentication delay is reduced. The AAA server is vulnerable to denial-of-service attack. If the AAA server is down, MNs cannot access the proxy mobile IPv6 network until they are authenticated. The proposed scheme reduces the load on the AAA server by distributing the authentication function to the LMAs and the MAGs.