• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.3809-3822
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• 2017

Wireless Sensor Networks hold the limelight because of significant potential for distributed sensing of large geographical areas. The radio duty cycling mechanism that turns off the radio periodically is necessary for the energy conservation, but it deteriorates the network congestion when the traffic load is high, which increases the packet loss and the delay too. Although many papers for WSNs have tried to mitigate network congestion, none of them has mentioned the congestion problem caused by the radio duty cycling of MAC protocols. In this paper, we present a simple and efficient congestion control technique that operates on the radio duty cycling MAC protocol. It detects the congestion by checking the current queue size. If it detects the congestion, it extends the network capacity by adding supplementary wakeup times. Simulation results show that our proposed scheme highly reduces the packet loss and the delay.

• East Asian Economic Review
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• v.24 no.4
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• pp.417-440
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• 2020

The coronavirus pandemic of 2019-20 confronted fiscally dominant regimes around the world with the question of whether the large deficits caused by the health crisis should be monetized or financed by issuing debt. The unpleasant monetarist arithmetic of Sargent and Wallace (1981) states that in a fiscally dominant regime tighter money now can cause higher inflation in the future. In spite of the qualifier 'unpleasant,' this result is positive in nature, and, therefore, void of normative content. I analyze conditions under which it is optimal in a welfare sense for the central bank to delay inflation by issuing debt to finance part of the fiscal deficit. The analysis is conducted in the context of a model in which the aforementioned monetarist arithmetic holds, in the sense that if the government finds it optimal to delay inflation, it does so knowing that it would result in higher inflation in the future. The central result of the paper is that delaying inflation is optimal when the fiscal deficit is expected to decline over time.

• Annual Conference of KIPS
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• 2009.11a
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• pp.189-190
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• 2009

For applications involving the monitoring of large areas, dense sensor networks are not practical. For such applications, delay tolerant networks which consist of disconnected clusters of sensors that are visited periodically by a mobile robot are implemented. Because clock synchronization is critical to any data collection endeavor, and because the structure of DTNs is unique, this paper examines various clock synchronization algorithms as they apply to DTNs. A simulation tool was developed to examine and evaluate the RBS clock synchronization algorithm for DTNs.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.05a
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• pp.97-99
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• 2021

Edge caching can provide high QoE by reducing traffic in the backhaul network and reducing latency in video streaming services. But due to the limited capacity of edge cache, large amounts of content cannot be cached. In this paper, we propose an edge-fog prefix caching that reduces playback delay by caching prefixes of video content on edges and storing the rest in fog cache.

• Annual Conference of KIPS
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• 2008.05a
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• pp.999-1002
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• 2008

Many schemes to reduce the inter-MAP handoff delay in hierarchical mobile IPv6 have been proposed but the previous schemes waste relatively large network resources to decrease the path rerouting delay. In this paper, we propose the 2-layered MAP concept, where the seamless inter-MAP handoff can be supported regardless of path rerouting time. As a result, the waste of wired resources and the rate of the inter-MAP handoff can be reduced. From the performance analysis and simulation, the inter-MAP handoff rate for non-real-time traffic is only about 1/3 of the conventional result. Such advantageous features of the proposed scheme neither incur any increase of the total handoff rate nor require additional MAPs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.417-425
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• 2007

While the cyclic prefix lengths of downlink OFDMA(Orthogonal Frequency Division Multiple Access) systems are determined based on the maximum delay spreads encountered in cellular environments, the guard interval of uplink OFDMA systems should consider the timing offsets of uplink signals as well as the delay spread lengths. Especially in the cases of initial accesses, handovers, and considerable time elapsed without data transmissions between base and mobile stations in a large cell, uplink timing offsets can be large and a very long guard interval length may be required. In order to keep the small size of the cyclic prefix in uplink OFDMA systems, the systems require a method of extending the guard intervals for users with large timing offsets without affecting the cyclic prefix length of the system. This paper proposes a method extending the guard intervals of individual users in uplink OFDMA systems.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.155-162
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• 2023

In nuclear power plants, the flow rate information is a major indicator of the performance of rotating equipment such as pumps, and is a very important one required for facility operation and maintenance. To measure a flow rate, various types of methods have been developed and used. Among them, the differential pressure type using orifice and the direct doppler type using ultrasonic waves are the most commonly used. However, these flow rate measurement methods have limitations in installation, conditions and status of the measuring part, etc. To solve this problem, we have studied a new technique for measuring flow rate from scratch. In this paper, we have devised a technique to estimate the flow rate using an average moving velocity of large-scale eddy in turbulence that occurs in the piping flow field. The velocity of the large-scale eddy can be measured using the pressure fluctuation signals on the inner surface of the pipe. To estimate the flow rate, at first a cross-correlation function is applied to the two pressure fluctuation signals located at different positions in the down stream for calculating the time delay between the moving eddies. In order to validate the proposed flow rate estimation method, CFD analyses for the internal turbulence flow in pipe are conducted with a fixed flow condition, where the pressure fluctuation signals on the pipe inner surface are simulated. And then the average flow velocity of the large scale eddy is to be estimated. The estimated flow velocity is turned out to be similar to the fixed (known) flow rate.

• Korean Journal of Construction Engineering and Management
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• v.16 no.3
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• pp.165-176
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• 2015

Recently many Korean large-sized construction companies as well as specialty contractors have been expanding their business in the overseas market to mitigate impacts from long-term stagnation in the domestic market. Such as a result, it has been arisen as a major issue that contractors effectively manage the delays which have been commonly faced with in international mega-projects. Therefore it can be said that the ability of the delays management leads a success of project. This paper presents a review of literature for delay analysis methods such as time impact analysis(TIA) and raises practical problems to rationally substantiate the duration of extension of time(EoT) in international mega projects which have wide scope of works as well as complicated and detailed contract baseline programs by taking theoretical approaches. We suggest the two improvement concepts to substantiate the EoT claims which are effectively applicable to practical projects. The first is to sort out dominant delays among numerous delays in advance of applying a delay analysis. The second is to set up the delay sections with the advanced concept for analysing delays' effects by TIA. This study performed a case study on an actual international mega-project. to confirm the effectiveness of improvement concepts that this practical approach is applicable for the assessment of EoT. In conclusion, this paper supposes to provide practitioner in charge for an EoT claim with an advanced substantiation methodogy when they not only analyse the construction delays by using TIA, but also negotiate with stakeholders about with the assessment of EoT.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.6 no.2
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• pp.70-80
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• 2007

Inter-vehicular communication suffers from a variety of the problem on the road, resulting in large delay in propagating emergency warning. An energy depletion as well as a transmission delay may induced by traffic accident. A transmission delay are caused by direct contention from nodes that can hear each other or indirect contention from nodes that can not hear each other, but simultaneously transmit to the same destination. A variety of works have been researched to solve the transmission delay and energy consumption problem in intelligent cars transportation systems. We consider a vehicle-to-vehicle communication protocol for disseminating an emergency information that include end-to-end and energy efficient transmission. In this paper, we propose A vehicle-to-vehicle communication protocol scheme for dissemination emergency information in intelligent cars communication based on IEEE 802.15.3 wireless personal area networks. Results from a simulation study reveal that our scheme can achieves low latency in delivering emergency warnings, and efficiency in consuming energy in stressful road scenarios.

• Journal of KIISE:Information Networking
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• v.36 no.2
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• pp.130-136
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• 2009

Delay and Disruption Tolerant Network (DTN) employs message delivery based on a store-and-forward method to conquer no guarantee of continuous end-to-end connectivity. Different from general networks, it is hard for the existing TCP/IP-based routing protocols to correctly work, due to the characteristics such as large latency and unstable link connectivity. Thus, many recent studies focus on routing protocols for DTN. In this paper, we propose a novel routing protocol for DTN with efficient message delivery utilizing mobility information such as direction or destination of mobile nodes. And this protocol is enhanced in terms of delivery ratio, decreases latency and overhead compared to the previously proposed solutions. Simulation results prove its superiority.