• Journal of Advanced Navigation Technology
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• v.18 no.3
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• pp.236-241
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• 2014

In a mobile ad hoc networks, multi-hop transmission is used to transfer data from source node to destination node and the routing protocol is the one of the important technical issues. The links between nodes can be unstable due to the changes of node location and channel conditions, and it can induce link error. To solve this problem, multipath routing was proposed. Multipath routing can reduce the data congestion and increase data throughput. In the multipath routing, however, each path can be interfered by the other path, and it can aggravate network performance. In this paper, we propose the multipath routing technique in the multi-rate MANET. The proposed multipath routing can avoid interference without the knowledge of node location. Simulation results show that the proposed multipath routing can reduce transmission delay and error.

• KIPS Transactions on Computer and Communication Systems
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• v.7 no.9
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• pp.227-234
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• 2018

Guaranteeing the end-to-end delay deadline is an important issue for quality of service (QoS) of delay sensitive systems, such as real-time system, networked control system (NCS), and cyber-physical system (CPS). Most routing algorithms typically use the mean end-to-end delay as a performance metric and select a routing path that minimizes it to improve average performance. However, minimum mean delay is an insufficient routing metric to reflect the characteristics of the unpredictable wireless channel condition because it only represents average value. In this paper, we proposes a deadline-aware routing algorithm that maximizes the probability of packet arrival within a pre-specified deadline for CPS by considering the delay distribution rather than the mean delay. The proposed routing algorithm constructs the end-to-end delay distribution in a given network topology under the assumption of the single hop delay follows an exponential distribution. The simulation results show that the proposed routing algorithm can enhance QoS and improve networked control performance in CPS by providing a routing path which maximizes the probability of meeting the deadline.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.45-51
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• 2009

We have presented a routing mechanism that selects a route by considering channel statuses in order to fast transfer delay-sensitive data in WSNs (Wireless Sensor Networks). The existing methods for real-time data transfer select a path whose latency is the shortest or the number of hops is the smallest. An algorithm to select a real-time transfer path based on link error rates according to the characteristic of wireless medium was also suggested. However, the propagation delay and retransmission timeout affected by link error rates are shorter than channel assessment time and backoff time. Therefore, the mechanism proposed in this paper estimated the time spent in using a clear channel and sending out a packet, which is based on channel backoff rates. A source node comes to select a route with the shortest end-to-end delay as a fast transfer path for real-time traffic, and sends data along the path chosen. We found that this proposed mechanism improves the speed of event-to-sink data transfer by performing experiments under different link error and channel backoff rates.

• Journal of information and communication convergence engineering
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• v.8 no.1
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• pp.6-12
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• 2010

In this paper a cross layer protocol, referred to as an underwater ad-hoc communication (UAC) protocol, is proposed for underwater acoustic networks (UANets). An underwater node (UN), which tries to transfer data to another UN or a buoy in ad-hoc manner, can access channel as well as determine routing path by employing the UAC protocol. The channel access, route determination, and reliable data transfer are designed being adaptive to underwater environments. In addition, we propose both UN and packet architectures in order to efficiently implement the UAC protocol for UANets.

• Journal of Computing Science and Engineering
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• v.2 no.4
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• pp.412-427
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• 2008

We propose ID-exchange protocol for Connectionless Location-Awareness Service (CLAS) to locate mobile nodes in indoor sensor network. When adapting location-awareness service to sensor network, the target system must be designed in accordance with various metrics which reflect the system requirement. We especially consider sustainability of the existing service which has been provided for its original purpose, such as environmental monitoring. The detailed meaning of sustainability here is that, even if location-awareness service is newly added to the existing service, the system must be assured to retain a stable network condition, and to deal with newly caused traffic properly. The CLAS ID-exchange protocol is especially designed for fixture and mobile nodes communication to achieve these properties. The protocol operates on 802.15.4 MAC layer to make mobile node work independently of the procedure to build routing table of fixture node, so a stable routing condition can be achieved even if there are many mobile nodes. Moreover, the dedicated frequency channel is assigned only for this protocol, so that traffic caused by location-awareness service can be distributed to another channel. A real system adapting the protocol was implemented to monitor fire and authorities' positions. We verified the overhead and elapsed time for location-awareness. The result shows the proposed protocol has a high performance in detecting speed, traffic distribution, and stability of overall network.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.543-549
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• 2001

This research estimated stream discharges indirectly by hydraulic channel routing. Only stage data from three stage stations and river cross section data were used to estimate Manning roughness coefficients and to compute stream discharges. When the discharges were estimated a stage-stage set of conditions was used for upstream-downstream boundary conditions. The research used the data from the upper Mississippi River. The hydraulic channel routings were performed by DWOPER (operational dynamic wave model). The global optimization program of SCE-UA was used to improve the roughness coefficient estimation module of the modified Newton-Raphson method in DWOPER. The results from SCE-US were better. For the case study of a flood, most estimated discharges except a few show errors within 10%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.147-155
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• 1993

An urban runoff model is proposed in this study, which is composed of a surface runoff model and a channel routing model. ILLUDAS is selected as the best fit model for the surface runoff computation, and the dynamic wave model using weighted four-point implicit finite difference scheme is used to perform the channel routing. The 3rd Seongbook bridge basin located in Seoul is selected as the test basin for the proposed model, and the rainfall-runoff data are collected to calibrate and verify the urban runoff model. The computed results by this model showed the fair accuracy when compared with the observed hydrographs. So the model proposed in this study could be used to compute the urban river flow as well as the outflow from the urban drainage area.

• Journal of Communications and Networks
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• v.4 no.4
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• pp.351-362
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• 2002

In this paper, we introduce a new approach to the minimum energy routing (MER) for next generation (NG) multihop wireless networks. We remove the widely used assumption of deterministic, distance-based channel model is removed, and analyze the potentials of MER within the context of the realistic channel model, accounting for shadowing and fading. Rather than adopting the conventional unrealistic assumption of perfect power control in a distributed multihop environment, we propose to exploit inherent spatial diversity of mobile terminals (MT) in NG multihop networks and to combat fading using transmit diversity. We propose the cooperation among MTs, whereby couples of MTs cooperate with each other in order to transmit the signal using two MTs as two transmit antennas. We provide the analytical framework for the performance analysis of this scheme in terms of the feasibility and achievable transmit power reduction. Our simulation result indicate that significant gains can be achieved in terms of the reduction of total transmit power and extension of network lifetime. These gains are in the range of 20-100% for the total transmit power, and 25-90% for the network lifetime, depending on the desired error probability. We show that our analytical results provide excellent match with our simulation results. The messaging load generated by our scheme is moderate, and can be further optimized. Our approach opens the way to a new family of channel-aware routing schemes for multihopNG wireless networks in fading channels. It is particularly suitable for delivering multicast/ geocast services in these networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.10
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• pp.645-653
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• 2014

Recently, the ocean field researches such as offshore plant, ocean survey and underwater monitoring systems are garnering the attention from both academy and industry. However, the communication in underwater environment is very difficult because of the unique irregular features in water. This is the reason that the application of terrestrial protocols to the water environment is not proper. This paper proposes a routing algorithm that can enhance communication reliability by utilizing channel properties in underwater environment. We address two problems that lead to the poor communication performance, signal attenuation and multi-path problem in water. Overcoming these problems, the proposed algorithm ensures high packet delivery ratio and low transmission delay. Also, this paper evaluates the performance through simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.2
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• pp.287-295
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• 2010

In this paper, we introduce a novel approach to optimization algorithm which is a distributed Mean field Genetic algorithm (MGA) implemented in MPI(Message Passing Interface) environments. Distributed MGA is a hybrid algorithm of Mean Field Annealing(MFA) and Simulated annealing-like Genetic Algorithm(SGA). The proposed distributed MGA combines the benefit of rapid convergence property of MFA and the effective genetic operations of SGA. The proposed distributed MGA is applied to the channel routing problem, which is an important issue in the automatic layout design of VLSI circuits. Our experimental results show that the composition of heuristic methods improves the performance over GA alone in terms of mean execution time. It is also proved that the proposed distributed algorithm maintains the convergence properties of sequential algorithm while it achieves almost linear speedup as the problem size increases.