• IEMEK Journal of Embedded Systems and Applications
• /
• v.2 no.1
• /
• pp.53-59
• /
• 2007

Wimedia UWB(Ultra-Wideband) platform provides data rates up to 480Mbps in WPAN (Wireless Personal Area Network). Wimedia conformant devices access to the channels through superframe concept for communications. As the channel resource is limited, the optimal channel time required for each device needs to be estimated to share the resource efficiently among the devices. In this paper, we propose a scheme to estimate the required channel time in a super frame to satisfy the QoS of the application on a device. The channel time is estimated from the service rate which is computed from the TSPEC of the application. In the process of the estimation, we take the frame overhead for data transmission as well as the overhead due to the acknowledgement scheme, preamble, and MDSU size into consideration. We also analyze and compare the throughputs for different acknowledgement scheme, preamble, and MDSU size situations. The estimated channel time required for a given service rate is allocated in the unit of MAS(Medium Access Slot).

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.21 no.5
• /
• pp.1208-1220
• /
• 1996

In this paper, the performance of a Carrier Sense Multiple Access/Collision avoidance (CSMA/CA) protocol using stop-and-Wait automatic Repeat reQuest, which is adapted as a draft standard in IEEE 802.11, is analyzed using a mathematical method based on a renewal theory, and simulation checks are performed, which confirm the goodness of our anlysis. In order to anlayze of CSMA/CA, we model that network is composed of finite populationand channel is slotted. And, we consider the CSMA/CA protocol as a hybrid protocol of 1-persistent CSMA and p-persistent CSMA protocol. As resuls of analysis, we have found that the throughput is degraded and packet delay is increased as the number of stations, Acknowledgement (ACK) length and Distributed coordination function Inter Frame Space (DIFS) length are increased.

• Proceedings of the IEEK Conference
• /
• 2008.06a
• /
• pp.20-21
• /
• 2008

In the IEEE 802.16 Wireless MAN standard, the best effort service class is ranked on the lowest position in priority so that only scarce resource may be available for it. Also, the best effort service is usually assisted by a MAC scheme based on reservation ALOHA without explicit acknowledgement. However, the standard only specifies the skeleton of the MAC scheme. In this paper, we propose some rules to specify the indefinite part of the MAC scheme as well as to improve the throughput and delay performance of the MAC scheme. As generic rules for demanding and granting resource, we first propose non-gated exhaustive, gated exhaustive, non-gated limited, and gated limited demand rules, and deficient and full grant rules. Secondly, we propose grant regulation rules, identified as replacement and lifetime rules, to avoid excessive grant incurred by not giving acknowledgement. Noting the residual resource is inflated by adopting a grant regulation rule, we finally propose a rule for investing the residual resource to a subscriber station. Simulation results confirm that a combination of proposed rules improves the performance of the MAC scheme.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2003.05a
• /
• pp.311-315
• /
• 2003

Recently, there is asymmetrical transmission in Internet data stream. The asymmetrical transmission has much more downstream than upstream. Owing to this point, it needs to reduce the acknowledgement as element of the obsrtuction in downstream. In this paper, according to simulation's result, we know that Sack has good performance than New Reno in bottleneck environment Comparing two protocols in packet loss rate, NewReno is lower than Sack. And also comparing two protocols in throughput of ack packet, not only NewReno processes ack packet more quickly than Sack, but also NewReno processes more ack packet than Sack protocol during ten seconds in simulation. As a result, NewReno is batter than Sack in throughput of asymmetrical link.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.12B
• /
• pp.1106-1114
• /
• 2003

Several analytic models describe transmission control protocol (TCP) performance such as steady-state throughput as an averaged ratio of number of transmissions to latency. For more detailed analysis of TCP latency, the latency during packet losses are recovered should be considered. In this paper, we derive the expected duration of loss recovery latency considering the number of packet losses recovered by retransmissions. Based on the numerical results verified by simulations, TCP using selective acknowledgement (SACK) option is more effective than TCP NewReno from the aspect of loss recovery latency.

• Journal of KIISE:Information Networking
• /
• v.30 no.2
• /
• pp.233-243
• /
• 2003

With the original Transmission Control Protocol(TCP) design, which is particularly targeted at the wired networks, a packet loss is assumed to be caused by the network congestion. In the wireless environment where the chances to lose packets due to transmission bit errors are not negligible, though, this assumption may result in unnecessary TCP performance degradation. In this paper, we propose three schemes that improve the ability to conceal the packet losses in the wireless network while limiting the degree of violating TCP end-to-end semantics to a temporary incidents. If there happens a packet loss at the wireless link and there is a chance that the loss is noticed by the sending TCP, the proposed schemes send an indirect acknowledgement. Each of the proposed schemes uses different criteria to decide whether there is a chance that the packet loss occurred in the wireless part is noticed by the sender. In order to limit the buffer overhead in the base, the indirect acknowledgements are issued only when the length of buffer is less than a certain threshold. We use simulation to compare the overhead and the performance of the proposed schemes, and to show that the proposed schemes improve the TCP performance compared to Snoop with a limited amount of buffer at the base station.

• Korean Journal of Health Education and Promotion
• /
• v.12 no.1
• /
• pp.47-71
• /
• 1995

This research has been attempted to measure health acknowledgement and needs of 1158 respondents, the parents of elementary, middle, and high school students, residing in Seoul and In-chon. 1. The majority of parents had high interests in health and their children's health education. In addition, more than half of parents showed positive responses in their willingness to participate in organizational activities. 2. 41.7% of parents thought that their children were receiving health education regularly. For their recognitions of the course title, 'Physical Education' was the most highly recognized by the parents of elementary and middle school students, and 'Military Drill' for the parents of high school students. 3. A high number of parents perceived the problems of school health education. 4. There was a high number of parents, who thought that health education teachers' knowledge was deficient, and 86.3% of them agreed that additional education for 33the teachers should be desired. 5. 95.5% of parents acknowledged the necessity of health education; 78.8% of them recognized the reinforcement of health education; and 60.0% of them percepted the necessity of establishing the independent health education courses. 6. For the matter of instruction period, the majority of parents responded that health education should be taught from "kindergarten" and "elementary school". For the appropriate instruction hour per a week, the majority answered 1 hour. Most respondents answered that those, who majored in health education, should be the appropriate teachers. 7. The survey result indicated that there was a close correlation between the cognition of the importance of health education and the correspondents' health educational background, their interest and willingness to participate in health education. 8. The most desired areas of health education were Safety Education and Health-Habit. The followings were Environmental Health, Prevention of Disease, Mental Health, Growth and Nutrition, and Drug-Abuse in a sequent order. The parents of elementary school students showed a high acknowledgement on Health-Habit, Growth and Nutrition, and Prevention of disease, Safety Education. On the other hand, as the children entered into the advanced schools, the parents' recognition of the health education needs shifted into Sex education, Drug Abuse, and Mental Health. 9. Those respondents, who recognized the necessity of health education and advocated the establishment of independent health education courses, had a strong demand for the implementation of the health education.

• Proceedings of the IEEK Conference
• /
• 2008.06a
• /
• pp.699-700
• /
• 2008

In this paper, we implement Mobile AP system, which has Multihoming function providing vertical handover between WiBro and HSDPA networks. We monitor packet drop in networks during binding updates(BU) and acknowledgement(BA) and analyze handover latency. We propose methodology to reduce handover latency and describe the further development direction of Mobile AP system.

• 제어로봇시스템학회:학술대회논문집
• /
• 2002.10a
• /
• pp.56.6-56
• /
• 2002

1. Introduction 2. Process description 2.1 Process description 2.2 Assumption 3. Mathematical model 3.1 MILP model for cintinuous part 3.2 LP model for batch part 4. Exapmles and Results 5. Conclusion. Acknowledgement. Reference.

• 제어로봇시스템학회:학술대회논문집
• /
• 2002.10a
• /
• pp.57.3-57
• /
• 2002

1. Introduction 2. General flux balance model 3. MetaFluxNet 3.1 Overview of MetaFluxNet 3.2 Project file format 3.3 Construction of metabolite reaction model 3.4 Metabolic flux analysis using linear programming 3.5 Visualization of MFA results 4. Conclusion and plan 5. Acknowledgement. References.