• Annual Conference of KIPS
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• 2022.05a
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• pp.82-83
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• 2022

Ad-hoc On-demand Distance Vector (AODV), is one of well-designed routing protocols in mobile ad hoc networks. It supports the functionality of node mobility modules through multiple control messages to create and maintain paths for data transfer. Even though a number of studies have been conducted to achieve rapid discovery of paths across the network, but few have focused on impact of control messages. This paper proposes a method to adjust the transmission time of messages used in path recovery according to their individual characteristics. Simulation results show the improved performance of the proposed algorithm rather than traditional AODV routing protocol.

• Journal of Information Processing Systems
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• v.20 no.2
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• pp.226-238
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• 2024

Recently, multi-access edge computing (MEC) has emerged as a promising technology to alleviate the computing burden of vehicular terminals and efficiently facilitate vehicular applications. The vehicle can improve the quality of experience of applications by offloading their tasks to MEC servers. However, channel conditions are time-varying due to channel interference among vehicles, and path loss is time-varying due to the mobility of vehicles. The task arrival of vehicles is also stochastic. Therefore, it is difficult to determine an optimal offloading with resource allocation decision in the dynamic MEC system because offloading is affected by wireless data transmission. In this paper, we study computation offloading with resource allocation in the dynamic MEC system. The objective is to minimize power consumption and maximize throughput while meeting the delay constraints of tasks. Therefore, it allocates resources for local execution and transmission power for offloading. We define the problem as a Markov decision process, and propose an offloading method using deep reinforcement learning named deep deterministic policy gradient. Simulation shows that, compared with existing methods, the proposed method outperforms in terms of throughput and satisfaction of delay constraints.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.6
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• pp.1-6
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• 2010

We present simulation results on DC characteristics of AlGaN/GaN HEMT having stair-type gate electrodes, in comparison with those of the conventional single gate AlGaN/GaN HEMTs and field-plate enhanced AlGaN/GaN HEMTs. In order to reduce the internal electric field near the gate electrode of conventional HEMT and thereby to increase their DC characteristics, we applied three-layered stacking electrode schemes to the standard AlGaN/GaN HEMT structure. As a result, we found that the internal electric field was decreased by 70% at the same drain bias condition and the transconductance (gm) was improved by 11.4% for the proposed stair-type gate AlGaN/GaN HEMT, compared with those of the conventional single gate and field-plate enhanced AlGaN/GaN HEMTs.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.2
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• pp.223-229
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• 2017

This paper analyzes the effect of a dual-metal-gate structure on the electrical characteristics of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors. These structures have two gate metals of different work function values (${\Phi}$), with the metal of higher ${\Phi}$ in the source-side gate, and the metal of lower ${\Phi}$ in the drain-side gate. As a result of the different ${\Phi}$ values of the gate metals in this structure, both the electric field and electron velocity in the channel become better distributed. For this reason, the transconductance, current collapse phenomenon, breakdown voltage, and radio frequency characteristics are improved. In this work, the devices were designed and analyzed using a 2D technology computer-aided design simulation tool.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.7
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• pp.495-499
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• 2009

An underlying assumption in geographic routing protocols, periodic position exchange among neighbors has two problems: (1) unnecessary energy consumptions of nodes in regions without data delivery and (2) position invalidation of neighbors in forwarding data. Hence, this paper proposes an on-demand geographic routing protocol in mobile wireless sensor networks. The proposed protocol make a sender acquire position information of only necessary neighbors to reduce energy consumption in data forwarding time and determine an optimal node among them as a receiver for relaying data to a destination by considering their mobility. Simulation results show that the proposed protocol is more efficient than an existing geographic routing protocol.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.4
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• pp.1001-1008
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• 2015

Mobile Ad hoc Network(MANET) consists of a node that has mobility. In MANET, the node has routing, the node builds a network of their own, no dependent infrastructure. Topology are exchanged due to node mobility in MANET. For reducing the change of topology, hierarchical network algorithm has been investigated. In hierarchical network, cluster member node communicates through cluster head node. When the load-balancing of cluster head node is exceed, assigned cluster member node can't communicate with base station. To solve this problem, we proposed Load Tolerance algorithm. The proposed algorithm, when cluster member node can't send a message by cluster head node that exceed load-balancing, then the cluster member node sends a message by selected load tolerance node. Through a simulation, the proposed algorithm improves packet delivery ratio in cluster routing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.1
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• pp.34-45
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• 2013

Due to its self-configuring nature, the tactical mobile ad hoc network is used for communications between tactical units and the command and control center (CCC) in battlefields, where communication infrastructure is not available. However, when a tactical unit moves far away from the CCC or there are geographical constraints, the data link between two communicating nodes can be broken, which results in an invalid data route from the tactical units to CCC. In order to address this problem, in this paper we propose a hierarchical connectivity maintenance scheme, namely ADLCoM (Autonomous Data Link Connectivity Maintenance). In ADLCoM, each tactical unit has one or more GW (gateway), which checks the status of data links between tactical units. If there is a possibility of link breakage, GWs request ground or aerial unmanned vehicles to become a relay for the data link. The simulation results, based on tactical scenarios, show that the proposed scheme can significantly improve the network performance with respect to data delivery ratio.

• The KIPS Transactions:PartC
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• v.17C no.3
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• pp.281-290
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• 2010

In geographic forwarding algorithms, traditional route maintenance requires mobile nodes periodically exchange beacon messages with their neighbors. In beacon message based forwarding scheme, a longer interval reduces the number of beacons needed, but may result in significant location errors. Conversely, a shorter interval guarantees more accurate location information, but induces control overheads.Therefore, the fixed or dynamic interval scheme based forwarding schemes cannot adapt well to different mobility environments. Also, existing schemes result in the uncertainty of neighbor node's position in the forwarding table of mobile node. Therefore, this paper presents a self-adaptive location checking mechanism based proactive geo-routing algorithm for beacon-based geographic routing. Simulation results show that the proposed routing algorithm not only significantly increases the relay transmission rate but also guarantees the high end-to-end packet delivery in low and high mobility environments.

• The KIPS Transactions:PartC
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• v.16C no.4
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• pp.505-510
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• 2009

Sensor networks are composed of a great number of sensor nodes. Since all sensor nodes are energy-restricted and hard to recharge, it is very important.However, the energy consumption may significantly increase if mobile sources or sinks exist in sensor networks. The reason is that the routing information for mobile sources and sinks needs to be update frequently for efficientdata delivery. The routing algorithm supporting mobile sinks should consider not only continuous data delivery but also the energy consumption of sensor nodes. However, most of the existing research focuses on even energy consumption while the mobility of sinks and sources is rarely consider. In this paper, we propose an efficient routing protocol with multiple virtual grids to reduce energy consumption and improve packets delivery efficiency. Then this paper considers the mobility. Simulation results show that our algorithm can guarantee high data delivery ratio and lower average delivery delay, while consuming lower energy than existing routing protocols in sensor networks.

• Journal of the Korea Society of Computer and Information
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• v.12 no.6
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• pp.235-242
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• 2007

Network Mobility Basic Support protocol reduces location-update signaling by making network movements transparent to the mobile nodes (MNs) behind the mobile router (MR), but causes some problems such as sub-optimal routing and multiple encapsulations. This paper proposes an Route Optimization Employing HMIP Extension for Mobile Networks (ROHMIP) scheme for nested nubile networks support which introduces HMIP concept with relation information between MNNs behind a MR and the MR in order to localize handoff, to optimize routing and especially reduce handoff signal overhead. With ROHMIP, a mobile network node (MNN) behind a MR performs route optimization with a correspondent node (CN) as the MR sends a binding update message (BU) to mobility anchor point (MAP) via root-MR on behalf of all active MNNs when the mobile network moves. This paper describes the new mechanisms and provides simulation results which indicate that our proposal reduces transmission delay, handoff latency and signaling overhead.