• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3B
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• pp.304-310
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• 2009

In this paper, we evaluate the performance of VoIP in OFDMA-based relay systems with various capabilities of relays. We classify relays according to capability as "mid-capability (MC)" and "high-capability (HC)" relay. In system with HC relays, not only base station (BS) but also relay station (RS) performs scheduling at its ova whereas only BS performs scheduling in system with MC relays using the information reported by MS (i.e. the received signal-to-interference-plus-noise ratio (SINR) of mobile station (HS), the amount of MS traffic, etc). In system with MC relays, the controling overhead of BS is larger than that of system with HC relays. However, since BS has all MS information, efficient resource allocation and scheduling is possible. We derived the "average packet delay," "good packet ratio," and "cell goodput" in a VoIP environment. The simulation results demonstrate that the system with MC relays has better VoIP performance over that with HC relays.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.31-40
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• 2004

In this paper, we analyze mathematically the performance of the gated service scheduling in the Interleaved Polling with Adaptive Cycle Time(IPACT) was proposed to control upstream traffic for Gigabit Ethernet-PONs. In the analysis, we model EPON MAC protocol as a polling system and use mean value analysis. We divide arrival rate λ into three regions and analyze each region accordingly In the first region in which λ value is very small, there are very few ONUs' data to be transmitted. In the second region in which λ has reasonably large value, ONUs have enough data for continuous transmission. In the third region, ONUs' buffers are always saturated with data since λ value is very large. We obtain average packet delay, average Queue size, average cycle time of the gated service. We compare analysis results with simulation to verify the accuracy of the mathematical analysis. Simulation requires much time and effort to evaluate the performance of EPONs. On the other hand, mathematical analysis can be widely used in the design of EPON systems because system designers can obtain various performance results rapidly. We can design appropriate EPON systems for varioustraffic property by adjusting control parameters.

• Journal of Korea Society of Industrial Information Systems
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• v.19 no.3
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• pp.31-39
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• 2014

In KSLV-I launch mission, real-time data from the tracking stations are acquired, processed and distributed by the Mission Control System to the user group who needed to monitor processed data for safety and flight monitoring purposes. The processed trajectory data by the mission control system is sent to each tracking system for target designation in case of tracking failure. Also, the processed data are used for decision making for flight termination when anomalies occur during flight of the launch vehicle. In this paper, we propose the processing mechanism of slaving data which plays a key role of launch vehicle tracking mission. The best position data is selected by predefined logic and current status after every available position data are acquired and pre-processed. And, the slaving data is distributed to each tracking stations through time delay is compensated by extrapolation. For the accurate processing, operation timing of every procesing modules are triggered by time-tick signal(25ms period) which is driven from UTC(Universial Time Coordinates) time. To evaluate the proposed method, we compared slaving data to the position data which received by tracking radar. The experiments show the average difference value is below 0.01 degree.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.2
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• pp.201-206
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• 2016

Aircraft have a cross axis of the three each other for maintenance of aircraft position. It is called roll axis, pitch axis and yaw axis. Attitude reference system is a sensor for detecting a change of the three axis. In this paper, mobile robot platform install part of Pan-tilt and HMD attitude reference system, because of we use control camera. The acceleration sensor is very weak a lot of noise to vibration, also problem with data from process of mapping to the data problems to arise. However to solve this problem, we removed the average filter and Cosine Interpolation for Pan-tilt. Using capacity evaluation for outdoor environment for we are proposing. Mobile robot has HMD and equipped Pan-tilt. We control mobile robot camera. In this experiment result is little bit delay happening, however Pan-tilt camera is relatively stable control checking. Also, we will checking any terrain and slopes is no problem for mobile robot driving skills.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.10a
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• pp.110-113
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• 2022

Nowadays, breaking through the conventional traffic signal control method based on mathematical optimization, artificial intelligence began to be used in the area. In response to this trend, many studies are ongoing to figure out how to utilize AI technology properly for traffic signal optimization. They just simply focus on which method will work well besides lots of machine learning techniques and abandon the reward function engineering. In many cases, the reward function consists of the average delay of the vehicles in the intersection. However, this may lead to AI's misunderstanding about the traffic signal control: what AI regards as a good situation may not be realistic. Even the reward function itself may not meet the service level. Therefore, this study analyzes the problems of previous reward functions and will suggest how to reward function can be enhanced.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.821-830
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• 2001

H.323 proposes to use Mobile IP and H.323 ad hoc conference signaling to provide Handoff function to a mobile terminal. But H.323 ad hoc conference signaling has a drawback. It requires an H.323 endpoint to do a complex conference signaling which makes inter-operability between H.323 endpoints difficult and takes the longer signaling time. In this paper, we propose an Handoff signaling using H.323 rerouting(Third party initiated Pause and Rerouting). H.323 rerouting signaling only requires an H.323 endpoint to do H.323 basic signaling in reestablishing media channel, and makes inter-operability more easier and provides the faster Handoff. To do this, our H.323 GK has derived H.245 control channel using tunneling for all H.323 calls including the fast connect calls which enable endpoints communicate each other if they don\`t have H.245 control channel. In order to evaluate the performance of the proposed signaling, we have conducted an experiment that compares a call transfer signaling using H.323 rerouting with ad hoc conference signaling in inter-operability and signaling delay. The results of our experiment shows that the call transfer signaling can inter-operate with four H.323 endpoints among five H.323 endpoints of other vendors and reduces the signaling delay average 1.4 sec.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.23-30
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• 2014

This paper proposes a dead time compensation method for an AC motor drive using phase current polarity information which is detected based on a digital programmable low-pass filter (PLPF). The polarity detection using the PLPF is an alternative solution of a conventional method which uses a general low-pass filter (LPF) and hysteresis bands in order to avoid jittering due to noises. The PLPF not only adjusts its cutoff frequency according to the synchronous frequency of AC motors but also eliminates a gain attenuation and phase delay which are main problems of the general LPF. Through the PLPF, a fundamental component signal without gain and phase distortions is extracted from the measured raw current signal with noise. By use of the fundamental component, the polarity of current is effectively detected by reducing the hysteresis band. Finally, the proposed method compensates the dead time effects by adding or subtracting average voltage value to voltage references of the controller according to the detected current polarity information. The proposed compensation method is experimentally verified by compared with the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1004-1014
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• 1999

MAC protocols in wireless ATM has to increase and maintain the system throughput performance. To achieve these purposes, this paper proposes a dynamic control algorithm called DSPA (Dynamic Signalling Period Allocation) for wireless ATM MAC protocol. The proposed DSPA algorithm consists of the following three algorithms. First, a control slot generation algorithm which generates the control slots by utilizing static and dynamic parameters from the terminals, is proposed. Second, a dynamic signalling period allocation algorithm is proposed for a base station to dynamically determine each signalling period according to current terminal states, and thus allocates the optimal signalling periods. Finally, a dynamic slot allocation algorithm is proposed to dynamically determine priorities of the terminals whenever a slot is allocated. Simulation results indicates that DSPA algorithm decreases average packet delay of the terminals by dynamic allocation of signal periods based on the system utilization, and thus increases the limitation of allowable loads that quarantee quality of services. Also the proposed algorithm is shown to maintain stable throughput even in the case of traffic variations.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.518-528
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• 2009

IEEE 802.11 wireless local area network (WLAN) has become the prevailing solution for wireless Internet access while transport control protocol (TCP) is the dominant transport-layer protocol in the Internet. It is known that, in an infrastructure-based WLAN with multiple stations carrying long-lived TCP flows, the number of TCP stations that are actively contending to access the wireless channel remains very small. Hence, the aggregate TCP throughput is basically independent of the total number of TCP stations. This phenomenon is due to the closed-loop nature of TCP flow control and the bottleneck downlink (i.e., access point-to-station) transmissions in infrastructure-based WLANs. In this paper, we develop a comprehensive analytical model to study TCP dynamics in infrastructure-based 802.11 WLANs. We calculate the average number of active TCP stations and the aggregate TCP throughput using our model for given total number of TCP stations and the maximum TCP receive window size. We find out that the default minimum contention window sizes specified in the standards (i.e., 31 and 15 for 802.11b and 802.11a, respectively) are not optimal in terms of TCP throughput maximization. Via ns-2 simulation, we verify the correctness of our analytical model and study the effects of some of the simplifying assumptions employed in the model. Simulation results show that our model is reasonably accurate, particularly when the wireline delay is small and/or the packet loss rate is low.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.1
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• pp.1-13
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• 2001

In this paper, we propose a new dynamic bandwidth allocation and call admission control for VBR video sources with QoS constraints to support an efficient resource management and at the same Lime to satisfy the user's quality or service requirements. For the dynamic bandwidth allocation, first the next amount of traffic is predicted using a modified adaptive linear prediction method that considers abrupt scene change effects. And then, we dynamically allocate the necessary bandwidth to each connection based on the currently provided quality degree by the network with respect to the user's QoS requirements in terms of average delay and loss ratio. For the admission control, we determine the acceptance or rejection or a new connection based on the quality satisfaction degrees of the existing connections. Simulation results show that our proposed dynamic schemes are able to provide a stable service, which well meets the user's quality requirements.