• 제목/요약/키워드: long-term simulation

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Simulation of Soil Erosion due to Snow Melt at Alpine Agricultural Lands (고령지 농경지에서 융설에 의한 토양유실량 모의)

  • Heo, Sung-Gu;Lim, Kyoung-Jae;Kim, Ki-Sung;Myung, SaGong;An, Jae-Hun
    • Proceedings of the Korean Society of Agricultural Engineers Conference
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    • 2005.10a
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    • pp.241-246
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    • 2005
  • Doam watershed is located at alpine areas in the Kangwon province. The annual average precipitation, including snow accumulation during the winter, at the Doam watershed is significantly higher than other areas. Thus, pollutant laden runoff and sediment discharge from the alpine agricultural fields are causing water quality degradation at the Doam watershed. To estimate soil erosion from the agricultural fields, the Universal Soil Loss Equation (USLE) has been widely used because of its simplicity to use. The USLE rainfall erosivity (R) factor is responsible for impacts of rainfall on soil erosion. Thus, use of constant R factor for the Doam watershed cannot reflect variations in precipitation patterns, consequently soil erosion estimation. In the early spring at the Doam watershed, the stream flow increases because of snow melt, which results in erosion of loosened soil experiencing freezing and thaw during the winter. However, the USLE model cannot consider the impacts on soil erosion of freezing and thaw of the soil. Also, it cannot simulate temporal changes in USLE input parameters. Thus, the Soil and Water Assessment Tool (SWAT) model was investigated for its applicability to estimate soil erosion at the Doam watershed, instead of the widely used USLE model. The SWAT hydrology and erosion/sediment components were validated after calibration of the hydrologic component. The $R^2$ and Nash-Sutcliffe coefficient values are higher enough, thus it was found the SWAT model can be efficiently used to simulate hydrology and sediment yield at the Doam watershed. The effects of snow melt on SWAT estimated stream flow and sediment were investigated using long-term precipitation and temperature data at the Doam watershed. It was found significant amount of flow and sediment in the spring are contributed by melting snow accumulated during the winter. Thus, it is recommend that the SWAT model capable of simulating snow melt and long-term weather data needs to be used in estimating soil erosion at alpine agricultural land instead of the USLE model for successful soil erosion management at the Doam watershed.

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HeNB-Aided Virtual-Handover for Range Expansion in LTE Femtocell Networks

  • Tang, Hao;Hong, Peilin;Xue, Kaiping
    • Journal of Communications and Networks
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    • v.15 no.3
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    • pp.312-320
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    • 2013
  • Home evolved Node-B (HeNB), also called a femtocell or a femto base station, is introduced to provide high data rate to indoor users. However, two main problems arise in femtocell networks: (1) Small coverage area of HeNB, which results in limited cell-splitting gain and ping-pong handover (HO) problems and (2) high inter-femtocell interference because HeNBs may be densely deployed in a small region. In this study, an efficient cooperation mechanism called an HeNB-aided virtual-HO (HaVHO) scheme is proposed to expand the coverage area of femtocells and to reduce inter-femtocell interference. The cooperation among neighbor HeNBs is exploited in HaVHO by enabling an HeNB to relay the data of its neighbor HeNB without an HO. The HaVHO procedure is compatible with the existing long term evolution specification, and the information exchange overhead in HaVHO is relatively low. To estimate the signal to interference plus noise ratio improvement, the area average channel state metric is proposed, and the amount of user throughput enhancement by HaVHO is derived. System-level simulation shows that HaVHO has a better performance than the other four schemes, such as lesser radio link failure, lesser ping-pong handover, lesser short-stay handover, and higher user throughput.

Improvement of Soil Moisture Initialization for a Global Seasonal Forecast System (전지구 계절 예측 시스템의 토양수분 초기화 방법 개선)

  • Seo, Eunkyo;Lee, Myong-In;Jeong, Jee-Hoon;Kang, Hyun-Suk;Won, Duk-Jin
    • Atmosphere
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    • v.26 no.1
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    • pp.35-45
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    • 2016
  • Initialization of the global seasonal forecast system is as much important as the quality of the embedded climate model for the climate prediction in sub-seasonal time scale. Recent studies have emphasized the important role of soil moisture initialization, suggesting a significant increase in the prediction skill particularly in the mid-latitude land area where the influence of sea surface temperature in the tropics is less crucial and the potential predictability is supplemented by land-atmosphere interaction. This study developed a new soil moisture initialization method applicable to the KMA operational seasonal forecasting system. The method includes first the long-term integration of the offline land surface model driven by observed atmospheric forcing and precipitation. This soil moisture reanalysis is given for the initial state in the ensemble seasonal forecasts through a simple anomaly initialization technique to avoid the simulation drift caused by the systematic model bias. To evaluate the impact of the soil moisture initialization, two sets of long-term, 10-member ensemble experiment runs have been conducted for 1996~2009. As a result, the soil moisture initialization improves the prediction skill of surface air temperature significantly at the zero to one month forecast lead (up to ~60 days forecast lead), although the skill increase in precipitation is less significant. This study suggests that improvements of the prediction in the sub-seasonal timescale require the improvement in the quality of initial data as well as the adequate treatment of the model systematic bias.

Analysis of Stream Discharge Characteristic at Control Point for Runoff Model Application (유출모의를 위한 주요제어지점 유량특성 분석)

  • Lee, Sang-Jin;Lee, Bae-Sung;Ryoo, Kyong-Sik;Hwang, Man-Ha
    • Journal of Korea Water Resources Association
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    • v.39 no.11 s.172
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    • pp.905-914
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    • 2006
  • For an accurate rainfall-runoff simulation in the river basin, not evaluation of runoff model but accurate runoff data are very important. In this study, SSARR model was applied to the Geum River basin and these results are compared with runoff data observed at the Gongju gauging station. The model results didn't good fit the discharge data determined from the rating curve at Gongju gauging station during normal and dry season, especially. For the reliability analysis for the existing rating curve, we observed new stream discharge set from 2003 to 2005. We also estimated long term runoff data from the base flow separation method and defined the hydraulic characteristics. The results show that the new observed stream discharge is similar to the rainfall-runoff model results but existing rating curve seems to be overestimated about 10-20% during normal and dry season. We found that the continuous monitoring and update for the existing rating curve at the gaging station are needed for accurate estimation of runoff data.

Resource Allocation and Power Control for Device-to-Device Communication in LTE-Advanced Based on User Area Information (LTE-Advanced에서 단말간 직접 통신을 위한 영역 정보 기반 자원할당 및 전력 제어 기법)

  • Li, Xiang;Shin, Oh-Soon;Shin, Yoan
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.1
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    • pp.32-42
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    • 2015
  • In this paper, we considered the scenario that one cellular link and muti-D2D links share the same frequency resource which can improve the spectrum efficiency during uplink communication in LTE (Long Term Evolution)-Advanced network. In order to reduce the interference caused to the D2D users, we set DME (Discovery and Management Entity) which can send the area information to eNB(evolved Node B). We proposed a resource allocation scheme by using these assistant devices to reduce the interference that CUE (Cellular User Equipment) causes to DUE Rx (D2D UE Receiver). Basing on the area information, in order to mitigate the interference among the D2D pairs which share the same frequency resource, a power control scheme has been proposed. The simulation results prove that by using the DMEs, the proposed schemes improve the stability of D2D communication and bring the highest performance of the communication system when comparing to the other different schemes.

Delay-Aware Packet Scheduling (DAPS) Algorithm in 3GPP LTE System (LTE 시스템에서 지연에 대한 QoS 보장을 위한 하향링크 패킷 스케줄링 알고리즘)

  • Choi, Bum-Gon;Chung, Min-Young;Lee, Hye-Kyung;Kim, Tai-Suk;Kang, Jee-Woong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.5B
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    • pp.498-508
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    • 2009
  • In wireless mobile environments, large bandwidth and high QoS (Quality of Service) are recently required to support the increased demands for multimedia services. LTE (Long Term Evolution) is one of the promising solutions for the next generation broadband wireless access systems. To efficiently use downlink resource and effectively support QoS, packet scheduling algorithm is one of the important features in LTE system. In this paper, we proposed DAPS (Delay-Aware Packet Scheduling) algorithm to consider QoS requirements of delays for various traffic classes as well as channel condition and fairness. To reflect delay experiences at scheduling instance, DAPS observes how queue waiting time of packet is closed to maximum allowable delay. The simulation results show that the DAPS algorithm yields better performance for delay experience by increasing the number of transmitted packets with satisfying the required delay time compared with existing scheduling algorithms.

MAC Scheduling Scheme for VoIP Traffic Service in 3G LTE (3G LTE VoIP 트래픽 서비스를 위한 MAC 스케줄링 기법)

  • Jun, Kyung-Koo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.6A
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    • pp.558-564
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    • 2007
  • 3G Long Term Evolution, which aims for various mobile multimedia service provision by enhanced wireless interface, proposes VoIP-based voice service through a Packet Switching (PS) domain. As delay and loss-sensitive VoIP traffic flows through the PS domain, more challenging technical difficulties are expected than in Circuit Switching (CS) domain based VoIP services. Moreover, since 3G LTE, which adopts the OFDM as its physical layer, introduces Physical Resource Block (PRB) as a unit for transmission resources, new types of resource management schemes are needed. This paper proposes a PRB scheduling algorithm of MAC layer for VoIP service in 3G LTE and shows the simulation results. The proposed algorithm has two key parts; dynamic activation of VoIP priority mode to satisfy VoIP QoS requirements and adaptive adjustment of the priority mode duration in order to minimize the degradation of resource utilization.

Adaptive Partitioning based Downlink Call Admission Control in 3G LTE (3G LTE의 Adaptive Partitioning 기반 다운링크 호 수락제어 방식)

  • Jun, Kyung-Koo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.6A
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    • pp.565-572
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    • 2007
  • 3G Long Term Evolution (3G LTE) is a next generation cellular networks system capable or providing various mobile multimedia services by using OFDMA and MIMO based radio access technology. Among many differences from existing WCDMA based systems, the facts that 3G LTE uses Physical Resource Block (PRB) as its radio resources and provides all services through the PS domain make the development of new resource management schemes necessary. This paper proposes an adaptive partitioning based downlink call admission control scheme. It separates realtime call requests from non-realtime ones, specifies maximum allowable resource amounts for each type, but if the maximum is exceeded, call requests are accepted with probability proportional to remaining resource amounts. Despite the fact that such adaptive concept has been already adopted by other call admission schemes, the contributions of our paper, which are that we are able to find an efficient way to apply the proposed scheme exploiting PRB characteristics and measure the resource usage of base stations by PRB utilization and payload ratio, are still valid. When judging from simulation results in comparison with others, our scheme is able to prioritize realtime call requests over non-realtime ones, and at the same time, overall system performance is superior.

Performance Analysis of Cyclostationary Signal Detection Scheme for LTE System (LTE 시스템을 위한 Cyclostationary 신호 검출 기법의 성능 분석)

  • Kim, Seung Jong;Kim, Kyung Ho;Hwang, Yu Min;Kim, Jin Young
    • Journal of Satellite, Information and Communications
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    • v.9 no.2
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    • pp.28-32
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    • 2014
  • In this paper, we analyzed the performance of cyclostationary signal detection scheme for LTE system. We applied the cyclostationary signal detection scheme to the cognitive radio(CR) technology, which improves the usage efficiency of spectrums and shares frequencies, and we detected the signal in the long term evolution(LTE) band. LTE system has been designated as the standard to improve the maximum data rate and provide the low latency in the 3rd generation partnership project(3GPP). In this paper, we generated the LTE signals based on the orthogonal frequency division multiple access(OFDMA) and analyzed the performance of signal detection in accordance with the segment and threshold of the generated signals. Gaussian channel was used in the simulation and we discussed the future studies to apply the CR to the LTE system.

Surface Cover Effect for Reducing Nitrogen Load in Organic Farming Fields using APEX Model (APEX 모형을 이용한 유기농경지에서의 질소 부하량 저감을 위한 지표피복 효과)

  • So, Hyunchul;Jang, Taeil;Kim, Dong-Hyeon;Seol, Dong-Mun;Yoon, Kwangsik
    • Journal of The Korean Society of Agricultural Engineers
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    • v.60 no.5
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    • pp.55-67
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    • 2018
  • The objectives of this study were to monitor organic farming upland compared with conventional upland field and to evaluate nutrient loads reduction of surface cover effect with long-term historical climate data. APEX(Agricultural Policy Environmental eXtender) model was validated with experimental data and used for assessing surface cover scenarios for 30-year simulation periods. The validated values of RMSE(Root Mean Square Error), RMAE(Root Mean Absolute Error), $R^2$ and E(Nash-Sutcliffe efficiency) for runoff were 1.17-1.37 mm/day, 0.28-0.45 mm/day, 0.88-0.90 and 0.82-0.94 in two treatments, respectively. Those for water quality (nitrogen) were 0.05-0.16 kg/ha, 0.52-0.75 kg/ha, 0.67-0.72 and 0.32-0.70 in two treatments, respectively, and therefore the validated model showed good agreement with the observed runoff and nitrogen load for the study period. When decreasing the surface cover rate of organic farming field to 75%, 50%, 25%, and 0% (conventional field), average annual runoff increased by 7%, 15%, 23% and 31%, respectively. Under same condition of decreasing the surface cover rate, average annual nitrogen loads increased by 1.4 times, 1.7 times, 2.0 times, and 2.3 times compared with organic farming field, respectively. This study showed that it is possible to present an appropriate surface cover ratio to maintain conventional production and minimize nonpoint sources pollution for organic farming system, although long-term monitoring is needed to determine its effects on environmental concerns, crop competition, and other uncertainty.