• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.4
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• pp.3-9
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• 2017

Due to difficulties of continuous electric power provision to underwater communication nodes, the efficient power usage is highly required in underwater network protocol. In this paper, we studied the energy efficient MAC(Medium Access Control) protocol for underwater network supporting mobile nodes such as UUV(Unmanned Underwater Vehicle) and AUV(Autonomous Underwater Vehicle). The mobile nodes could waste the electric power in vain when the receiver moves out of the radio propagation coverage during the data exchange and thus the transmitted data fails in reaching the receiver. Expecially, such a failure is much more obvious in underwater acoustic channels since the propagation delay is about $10^5$ times slower than in terrestrial radio channels. This proposed mobility-MAC controls the data dropping stochastically in the Dropping Zone by considering the receiver's location and moving velocity. In conclusion, this selective dropping method not only improves latency and throughput by reducing invalid droppings but also boosts power efficiency by valid droppings.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.1
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• pp.41-48
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• 2015

Being a cost-efficient solution for alleviating the traffic congestion in airspace, Air Traffic Flow Management (ATFM) has drawn more attentions from not only air traffic controllers but also researchers in the field of Air Traffic Management (ATM). Among other ATFM initiatives, it is believed that Ground Delay Program (GDP) could be effectively applied to reduce the congestion particularly in the relatively small airspace with dense traffic demand. This paper introduces a novel way that suggests flights to be delayed on the departing airports together with amount of the delays (in time) for those flights to be delayed. Adopting a fast-time simulation for predicting airspace delay of each flight for a given flight plan, the method is designed to iteratively and incrementally adjust the departure times in the plan towards reducing total airspace delays. Applying the method to Jeju airport with a hypothetically high demand, the paper demonstrates the airspace delay could be significantly reduced by applying GDP at Gimpo airport where more than 60% of Juju-bound flights departure. Although the simulation model needs to be calibrated and validated for the real-world application, the results clearly shows that the approach can possibly implemented as a tool for preparing the daily plan at the pre-tactical stage defined in the ICAO ATFM manual.

• Journal of Digital Contents Society
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• v.16 no.5
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• pp.775-781
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• 2015

EBS started 2HD MMS experimental broadcasting for the first time in Korea on Feb. 11, 2015. It uses the picture compression technique based on MPEG-2 CODEC, and applies the result of the experiment about variable bit rates and changes according to the scanning types, 1080i and 720p. But when changing channels, the delay in displaying picture occurs because of the operation of the variable GOP on MMS broadcasting, which optimizes image quality by application variable bit rates. In this study, verified the relationship between the decoding time of I frames and the GOP set in the encoding step by experimenting and analyzing ON-AIR TS. By using the verification data and adjusts the Encoder GOP parameters, improved the different video display time delays according to the scanning mode 1080i and 720p.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.515-522
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• 2012

CFIT(Controlled Flight Into Terrain) is one of the major causes of aircraft accidents. In order to solve this problem, GPWS(Ground Proximity Warning System) is used to generate terrain collision warning using the distance between the aircraft and the underneath ground. Since the GPWS uses the vertical clearance only, it frequently generates false warnings. In this study, a terrain/obstacle collision avoidance warning algorithm was developed for fast flying and highly maneuvering fighters using the flight status and the geographic information. This algorithm condsiders the overall delay in the aircraft reactive motion including the pilot's reaction time. The paper presents a detailed logic and test methods.

• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1081-1089
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• 2022

This study aims to investigate and monitor the ground subsidence in Ulsan city, South Korea using time-series Small Baseline Subset (SBAS)-InSAR analysis. We used 79 Sentinel-1 SAR scenes and 385 interferograms to estimate the ground displacements at Ulsan city from May 2015 and December 2021. Two subsiding regions Buk-gu and Nam-gu Samsan-dong were found with the subsidence rate of 3.44 cm/year and 1.68 cm/year. In addition, we evaluated the possibility of removing the effect of atmospheric (tropospheric delay) phase in unwrapped phase using the Zenith Total Delay (ZTD) maps from Generic Atmospheric Correction Online Service (GACOS).We found that the difference between the SBAS-InSAR ground displacements before and after GACOS ZTD correction is less than 1 mm/year in this study.

• KIPS Transactions on Computer and Communication Systems
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• v.11 no.12
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• pp.437-444
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• 2022

Recently, research on mobile edge services has been conducted to handle computationally intensive and latency-sensitive tasks occurring in wireless networks. However, MEC, which is fixed on the ground, cannot flexibly cope with situations where task processing requests increase sharply, such as commuting time. To solve this problem, a technology that provides edge services using UAVs (Unmanned Aerial Vehicles) has emerged. Unlike ground MEC servers, UAVs have limited battery capacity, so it is necessary to optimize energy efficiency through load balancing between UAV MEC servers. Therefore, in this paper, we propose a load balancing technique with consideration of the energy state of UAVs and the mobility of vehicles. The proposed technique is composed of task offloading scheme using genetic algorithm and task migration scheme using Q-learning. To evaluate the performance of the proposed technique, experiments were conducted with varying mobility speed and number of vehicles, and performance was analyzed in terms of load variance, energy consumption, communication overhead, and delay constraint satisfaction rate.

• 재활복지
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• v.17 no.4
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• pp.383-399
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• 2013

The purpose of this study was to comparison the effects of aqua-and-land based obstacle training on balance of chronic stroke patients. Subjects were randomly divided into an aqua group(n=15) and d land group(n=15). Both group received obstacle training for 40 minutes, 3 times a week during 12 weeks. Static balance was assessed by measuring the mean velocity of mediolateral, anteroposterior and sway area with the eyes open using Good Balance System. Dynamic balance was assessed by measuring Functional Reaching Test(FRT) and the Timed Up and Go test(TUG). Following the intervention, both groups showed significant changes static balance(the mean velocity of mediolateral, anteroposterior and sway area) and dynamic balance(FRT and TUG). There were significant difference in the mean velocity of mediolateral, anteroposterior, sway area, FRT and TUG between the two groups after the interventions. The results of this study suggest that the aqua group and land group were increase balance functions of chronic stroke patients. The aqua group was significantly higher than the land group for patients with chronic stroke patients. We hope that aquatic training can be useful for patients with chronic stroke patients to improve balance functions and the aqua training research for improve balance functions will be conducted continuously.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7A
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• pp.503-511
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• 2012

In this paper, the performance analysis of telemetering method using delayed frame time diversity (DFTD) as the outer code and Reed-Solomon (RS) code as the inner code is described. DFTD is used to transmit a real-time frame together with a time-delayed frame which was saved in the memory during a defined period. The RS code as a kind of FEC (forward error correction) is serially concatenated with DFTD. This method was applied to the design of telemetry units that have been used for flight tests in a communication environment with deep fading. The data of the flight test for four cases with no applied code, with DFTD only, with the RS code only, and with both DFTD and the RS code are used to analyze the performance. The simulation for time-delay suggests the possibility that all frame errors can be removed. And the results of 12 flight tests show the performance superiority of this new method to compare with the RS code only.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.4
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• pp.295-301
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• 2020

When a spacecraft in deep space falls into an abnormal state, an emergency communication channel between ground and the spacecraft is essential in order to perform analysis to the cause of the anomaly, and to remedy the spacecraft from the distressed state. Because the recovery actions generally comprises of long and complicated sequences of commands, the transmission of the recovery commands may require a reliable and a delay tolerant networking technology based on bundle routing. While the delay tolerant networking protocol becomes a prominent method interfacing ground and space into a internet-like Solar system network because it can address the issues of the severe communication problems in deep space, the communication system on the spacecraft which based on space packet protocol cannot use the delay tolerant networking technology directly. So a community of the consultative committee for space data systems starts a discussion of the first-hop last-hop mechanism to establish a feasible concept and standardization. This paper presents an enhanced concept of the first-hop last-hop by applying it a virtual cislunar communication environment, and we believe this contributes to make a way applicable to an interoperable relay concept of the first hop last hop between the delay tolerant networking and space packet protocol standard.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.11a
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• pp.193-196
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• 2008

지상파 DMB 동일 채널 중계기에서는 송신 안테나로부터 수신 안테나로 재입력되는 궤환 신호가 존재한다. 이 궤환 신호는 적절히 제거되지 않을 경우 수신 신호에 간섭으로 작용하게 되어 중계기 시스템의 안정성이 크게 떨어지게 된다. 과거에 진행된 연구에서는 궤환 채널을 추정하여 간섭을 제거시키는 궤환 신호 제거기(feedback canceller) 를 사용하여 이와 같은 문제를 해결하였다. 하지만 기존의 추정 알고리즘은 간단한 구현에 비해 수렴 성능과 속도 면에서 만족할만한 성능을 얻을 수 없었으며, 신호 간 상관도 제거를 위해 충분한 시간 지연을 해야 하는 단점이 있다. 본 논문은 궤환 채널 추정에 적합한 PNLMS (Proportionate Normalized Least Mean Squares) 적응형 알고리즘을 적용해 새로운 궤환 신호 제거 기법을 제안하였으며, 전산 모의 실험을 통해 이와 같은 문제를 효과적으로 해결할 수 있음을 보여준다.