• The Journal of the Korea Contents Association
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• v.16 no.10
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• pp.299-310
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• 2016

In this paper, we perform analysis of the performance of low-power communication technology, IEEE 802.15.4 MAC (Media Access Control) protocol used in internet of things. Wide variety of devices in internet of things generate different kinds of traffic characteristics and heterogeneous traffic environment is therefore considered in contrast to existing works. With the help of the Markov chain the performance of the protocol is derived as a function of the MAC parameters and based on the results a framework to determine energy-efficient optimal MAC parameters for applications in real time is proposed. Proposed method is shown to be more efficient in terms of energy consumption through performance comparison over application scenarios compared to operation with fixing MAC parameters, and its practicability on small devices with limited computing power is verified through evaluating the accuracy and speed of the proposed framework.

• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.158-167
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• 2002

In this paper, it is analyzed that WAP packet transmission time to improve performance of WAP using SAR-QT algorithm in Bluetooth channel. The order for SAR-QT algorithm to improve the transfer capability, it is fragmented in WTP total messages that are coming down from upper layer and then the packets are sent one at time in baseband. And it is studied that transmission time for WAP over Bluetooth according to DMI, DM3 or DM5 packet type using SAR-QT algorithm in Bluetooth piconet environment. This SAR-QT algorithm decreases WAP packet transmission time of L2CAP baseband packets by sending packet that are spanning multiple slots. From the results, in WAP over Bluetooth channels, it is found out that WTP packet size ought to be increased to decrease transmission time of WAP packet. In addition, considering BER in wireless channel, optimal WTP packet size is achieved for WAP over Bluetooth in a Rician fading environment.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.4
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• pp.291-303
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• 2009

Round robin based proportional share scheduling(RRPS) defines weight which determines share for each task and allocates CPU resource to each task in proportional to its respective weight. RRPS uses fairness as the measure of performance and aims at high fairness of scheduling. However, researches for scheduling fairness problem due to synchronization among tasks have been rarely investigated. In this paper, we discuss that scheduling delay due to synchronization may result high unfairness in RRPS. We explain such a situation as weight inversion. We then propose weight inheritance protocol(WIP), a synchronization mechanism, that prevents weight inversion. We also show that WIP can reduce unfairness using fairness analysis and simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.5
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• pp.1004-1009
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• 2004

Precise time synchronization is a main technology in high-speed communications, parallel and distributed processing systems, Internet information industry and electronic commerce. Synchronized clocks are useful for many leasers. Often a distributed system is designed to realize some synchronized behavior, especially in real-time processing in factories, aircraft, space vehicles, and military applications. Nowadays, time synchronization has been compulsory thing as distributed processing and network operations are generalized. A network time server obtains, keeps accurate and precise time by synchronizing its local clock to standard reference time source and distributes time information through standard time synchronization protocol. This paper describes design issues and implementation of a network time server for time synchronization especially based on a clock model. The system uses GPS (Global Positioning System) as a standard reference time source and offers UTC (universal Time coordinated) through NTP (Network Time protocol). Implementation result and performance analysis are also presented.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.12
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• pp.2267-2273
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• 2016

In this paper, WiMedia Distributed-MAC protocol is adopted for development of an OSMU (One Source Multi Use) N-screen wireless multicast service. But, when considering wireless communication environment where channel error rate is time-variant, N-screen high-speed data is vulnerable to be lost. For this problem, a multicast relay scheme is proposed by analyzing Distributed-MAC protocol. In proposed multicast relay scheme, Multicast-free DRP Availability IE is combined and the relay node suitable for N-screen multicast transmissions is selected. Through this operation, it can avoid wireless channel with high errors and can transmit N-screen high-speed data. In simulation results, the proposed multicast relay scheme is compared with conventional Distributed-MAC multicast scheme in view points of throughput and energy consumption according to various numbers of multicast nodes and BER (Bit Error Rate) values in wireless channel. Through simulation results, it is explained that proposed multicast relay scheme should be adopted in WiMedia Distributed-MAC protocol to realize OSMU N-screen wireless multicast services.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.651-659
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• 2004

The Fast Handover protocol ［1］ provides seameless handover in wireless If networks by minimizing handover latency, which uses anticipation based on layer 2 (L2) trigger information. Therefore, it incurs higher signaling costs compared with the basic Mobile U protocol. Furthermore, since the L2 trigger is based on fluctuating wireless channel states, the handover anticipation may sometimes be incorrect. In the case of incorrect anticipation, unnecessary buffer space may be used for the purpose of providing a smooth handover. Therefore, it is essentical to analyze these overhead costs, in order to evaluate and compare the performance of Fast Handover with that of the basic Mobile U protocol. In this paper, we analyzed the overhead associated with Fast Handover including the signaling cost and the packet delivery cost. We formulated these costs based on a timing diagram and compared Fast Handover with basic Mobile Ipv6 in terms of their packet loss rates and buffer requirements. Also, we studied the impact of the L2 triggering time on the total overhead cost.

• Clinical and Experimental Reproductive Medicine
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• v.42 no.2
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• pp.67-71
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• 2015

Objective: Elevated serum progesterone (P) levels on triggering day have been known to affect the pregnancy rate of in vitro fertilization (IVF). This study aimed to identify the possible factors influencing serum P levels on triggering day in stimulated IVF cycles. Methods: Three hundred and thirty consecutive fresh IVF cycles were included in the study. All cycles were first attempts and were performed in a single infertility center. The indications for IVF were male factor infertility (n=114), ovulatory infertility (n=84), endometriosis (n=61), tubal infertility (n=59), unexplained infertility (n=41), and uterine factor infertility (n=39). A luteal long protocol of a gonadotropin-releasing hormone (GnRH) agonist (n=184) or a GnRH antagonist protocol (n=146) was used for pituitary suppression. Ovarian sensitivity was defined as the serum estradiol level on triggering day per 500 IU of administered gonadotropins (OS[a]) or the retrieved oocyte number per 500 IU of administered gonadotropins (OS[b]). Results: Univariate analysis revealed that the serum P level on triggering day was associated with the serum estradiol level on triggering day (r=0.379, p<0.001), the number of follicles ${\geq}14mm$ (r=0.247, p<0.001), the number of retrieved oocytes (r=0.384, p<0.001), and ovarian sensitivity (OS[a]: r=0.245, p<0.001; OS[b]: r=0.170, p=0.002). The woman's age, body mass index, antral follicle count, and basal serum follicle stimulating hormone and estradiol levels were not associated with serum P level on triggering day. The serum P level on triggering day did not show significant variation depending on the type or cause of infertility, pituitary suppression protocol, or the type of gonadotropins used. Conclusion: The serum P level on triggering day was closely related to the response to ovarian stimulation.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.2
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• pp.80-87
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• 2013

This paper proposes a CW (Contention window) allocation scheme for real-time data transmission of emergency data on VANET (Vehicle to vehicle Ad hoc Network, V2V) protocol. The proposed scheme reduces the probability of packet collisions on V2V protocol and provides bandwidth efficiency with short delay of emergency sporadic data. In the case of high density traffic, the proposed scheme provides a decrease of recollision probability using dynamic CW adjustments. For the performance analysis, a throughput, end-to-end delays, and network loads were investigated on highway traffic. Simulation results show the performance enhancements in terms of the throughput, end-to-end delays, and network loads.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3B
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• pp.339-348
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• 2004

Packet classification is an important factor to support various services such as QoS guarantee and VPN for users in Internet. Packet classification is a searching process for best matching rule on rule tables by employing multi-field such as source address, protocol, and port number as well as destination address in If header. In this paper, we propose hardware based packet classification algorithm by employing tree bitmap of multi-bit trio. We divided prefixes of searching fields and rule into multi-bit stride, and perform a rule searching with multi-bit of fixed size. The proposed scheme can reduce the access times taking for rule search by employing indexing key in a fixed size of upper bits of rule prefixes. We also employ a marker prefixes in order to remove backtracking during searching a rule. In this paper, we generate two dimensional random rule set of source address and destination address using routing tables provided by IPMA Project, and compare its memory usages and performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.1
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• pp.77-88
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• 2010

Wireless Mesh Networks are consist of mobility mesh clients and mesh routers. WMNs can communicate with heterogeneous networks such as IEEE 802.11, IEEE 802.15, IEEE 802.16 and sensor networks. WMNs which is based on ad hoc network are on research and developing to enhance WLANs, WPANs, or WMANs. WMNs can offer environment to serve human, service to person area, campus, and metro. But WMNs has many problems to solve about enhancing performance and generalization. Among them, Existing protocol layers has many problems enhancing to optimize WMNs. This document issues problems about WMNs in protocol layer and suggest the solutions. Also, suggests the requirements and the methods of QoS supporting issue.