• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1B
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• pp.11-17
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• 2003

In this paper, we presented the dynamic random access channel allocation method under the priority based scheduling policy in order to improve the system performance of HIPERLAN/2 standardized by ETSI According to the scheduling policy, AP scheduler primarily allocates the resource to the collision MT This scheduling policy bring about decreasing the transmission delay of collision MT Dynamic RCH(random access channel) allocation method decreases the collision probability by increasing the number of RCH slots in case of low traffic. While it increases the maximum throughput by increasing the number of the data transmission slots in case of high traffic Therefore dynamic allocation method of RCH slots decreases the scheduling delay and increases the throughput When we evaluate the performance of presented method based on standards, we saw that the presented method improve the performance of the MAC protocol in terms of throughput and transmission delay.

• Journal of IKEEE
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• v.20 no.3
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• pp.322-325
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• 2016

This paper proposed Enhanced Segmentized Clear Channel Assesment(ESCCA) for the IEEE 802.15.4 networks. This method divides original CCA into two groups to check precise channel status and perform additional CCA to increase throughput performance. Through the proposed method, the device can access the channel more often, so the transmission efficiency of the IEEE 802.15.4 network improves. To confirm the feasibility and usability of the proposed method, computer simulation has been performed. In the simulation, a star topology with one coordinator and a lot of devices is considered and the traffic flows are all one way, with the communication directed to the coordinator. Simulation results_ show the proposed method is improving maximum 10 kbps of throughput and decreasing maximum 15 of the average number of total CCA than IEEE 802.15.4 CCA method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.3
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• pp.469-477
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• 2015

In this paper, joint spatial division and reuse (JSDR) scheme is proposed for maximizing network throughput in densely-deployed wireless local area networks equipped with massive antenna array. The proposed JSDR scheme divides the massive spatial space into two subspaces: one is for suppressing the interference from the neighboring access points and another is for sensing the carrier sensing and transmitting the information-bearing signals to intended stations. By using computer simulation, the proposed JSDR can provide 133% higher network throughput, compared to the carrier sensing technique defined in the IEEE 802.11 standard so that the proposed JSDR is suitable for the next generation WLAN systems.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.3
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• pp.307-314
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• 2009

Large area micro pattern replication has promising application potential in many areas. Rolling imprint process has been demonstrated as one of the most competitive processes for such micro pattern replication, because it has advantages in low cost, high throughput and high efficiency. In this paper, we developed a prototype of roll-to-flat(R2F) thermal imprint system for large area micro pattern replication process, which is one of the key processes in the fabrication of flexible displays. Experimental tests were conducted to evaluate the feasibility of system and the parameters' effect on the process, such as flat mold temperature, loading pressure and rolling speed. 100mm $\times$ 100mm stainless steel flat mold and commercially available polycarbonate sheets were used for the tests. The experimental results showed that the developed R2F system is suitable for fabrication of various micro devices with micro pattern over large area.

• Journal of the Semiconductor & Display Technology
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• v.9 no.4
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• pp.19-23
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• 2010

Nanoimprint lithography (NIL) is one of the most versatile and promising technology for micro/nano-patterning due to its simplicity, high throughput and low cost. Recently, one of the major trends of NIL is large-area patterning. Especially, the research of the application of NIL to TFT-LCD field has been increasing. Technical difficulties to keep the uniformity of the residual layer, however, become severer as the imprinting area increases. In this paper we performed a numerical study for a large area NIL (the $2^nd$ generation TFT-LCD glass substrate ($370{\times}470$ mm)) by using finite element method. First, a simple model considering the surrounding wall was established in order to simulate effectively and reduce the computing time. Then, the volume of fluid (VOF) and grid deformation method were utilized to calculate the free surfaces of the resist flow based on an Eulerian grid system. From the simulation, the velocity fields and the imprinting pressure during the filling process in the NIL were analyzed, and the effect of the surrounding wall and the uniformity of residual layer were investigated.

• Journal of Korean Society for Quality Management
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• v.45 no.1
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• pp.65-92
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• 2017

Purpose: The performance of global major airports is evaluated and several research questions are examined relative to the measures characterizing airport performance. Methods: The two-stage internal structure of airport performance is considered by decomposing it into physical operations and revenue generation. In the physical operations stage, operating costs, number of runways, terminal area and number of employees are used as inputs, while passenger throughput, cargo throughput and aircraft movements are taken as outputs. Subsequently, in the revenue generation stage, the outputs from the preceding stage are taken as inputs, while revenue is used as output. Results: Based upon this two-stage modeling of airport performance, a multiplicative two-stage network data envelopment analysis model is employed to calculate the overall and stage efficiencies of 59 airports using the recent data in the 2014 Airport Benchmarking Report published by the Air Transport Research Society. Several internal and external factors are also considered such as airport size, airport geographical location, proportion of international passengers, ownership (listed or not) and management style, and statistical analysis is performed to examine their impacts on airport performance. Conclusion: It is shown that the airports exhibit statistically significant difference across regions, and also some statistically significant factors affecting airport performance are identified.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.7
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• pp.67-72
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• 2005

If the PNC is shutting down or wants to leave the WPAN, it uses the handover process to give control to another device in the piconet. However when the PNC is selected, only the device capability information is checked in the WPAN standard specification and no detail criteria is described. In this paper, the PNC selection method with considering the number and density of device to maximize the piconet data throughput in the WPAN is studied. From the numerical analysis results, the considering with the devices concentration has higher data throughput compared with the uniform distribution. For the efficient performance, the device distribution within the piconet should be considered in the PNC selection.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.160-162
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• 2001

Cyclic-Reservation Multiple-Access(CRMA) is an access scheme for high-speed local and metropolitan area networks based on folded-bus or dual-bus configurations. CRMA provides high throughput and fairness independent of the network speed or distance. This paper describes a simulation-based quantitative analysis of the performance gains obtained by introducing slot reuse in CRMA. Generally, a longer cycle length means a longer access delay and a lower throughput. There-fore, it is desirable to develop a scheme such that the cycle length is the shortest. In this paper, we will study the problem of reducing the total number of empty slots generated within every cycle. However, it has been shown that the problem is NP-complete under the constraint that all empty slots used by a station in a cycle are required to be consecutive. We present the algorithm that improves previous novel approach by using previous node information. We compare our slots reuse scheme with several slot reuse algorithms such as region scheme (FMR), address schemes, novel approach in terms of the following two important performance criteria: average cycle length and average slot utilization ratio. As compared with the one proposed in novel algorithm, the new scheme makes the cycle length much shorter. Besides, the resulting slot utilization and the access delay are better than those of the other two schemes.

• Journal of Advanced Navigation Technology
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• v.16 no.3
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• pp.471-479
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• 2012

In cellular femto systems, femto Base stations(f-BSs) can be installed unnecessarily and overcrowded in small areas. This will cause an interference problem and it can impact on the capacity, blocking probability, and coverage of femtocells in the shared channel systems. In this paper, we propose a load distribution scheme by using forced handover and probabilistic subchannel scheduling policy to resolve the problem. The proposed scheme operates in distributed manner though communication with neighboring f-BSs, and includes self-detection of overcrowded area and radio resource management based on measurements. We evaluate the performance of the proposed scheme in terms of average cell throughput and average throughput per users.

• Journal of KIISE:Information Networking
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• v.37 no.3
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• pp.234-242
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• 2010

The demand on various broadcasting services has been greatly increasing in the area of mobile communication. In IEEE802.16e standard and mobile WiMAX, the multicast broadcast service (MBS) uses shared downlink channel for efficiently supporting a number of users. In this paper we propose a dynamic modulation and coding scheme with relay network to enhance the performance of MBS. The proposed approach employs the adaptive modulation and coding scheme for both the base station and relay station to achieve consistently high throughput. The result of computer simulation with NS-2 shows that the throughput and transmission time are significantly improved by using the proposed approach compared to the existing schemes having a fixed modulation level for the RSs.