• 제목/요약/키워드: Capacity fade

검색결과 21건 처리시간 0.024초

A three-dimensional two-hemisphere model for unmanned aerial vehicle multiple-input multiple-output channels

  • Zixu Su;Wei Chen;Changzhen Li;Junyi Yu;Guojiao Gong;Zixin Wang
    • ETRI Journal
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    • 제45권5호
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    • pp.768-780
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    • 2023
  • The application of unmanned aerial vehicles (UAVs) has recently attracted considerable interest in various areas. A three-dimensional multiple-input multiple-output concentric two-hemisphere model is proposed to characterize the scattering environment around a vehicle in an urban UAV-to-vehicle communication scenario. Multipath components of the model consisted of lineof-sight and single-bounced components. This study focused on the key parameters that determine the scatterer distribution. A time-variant process was used to analyze the nonstationarity of the proposed model. Vital statistical properties, such as the space-time-frequency correlation function, Doppler power spectral density, level-crossing rate, average fade duration, and channel capacity, were derived and analyzed. The results indicated that with an increase in the maximum scatter radius, the time correlation and level-crossing rate decreased, the frequency correlation function had a faster downward trend, and average fade duration increased. In addition, with the increase of concentration parameter, the time correlation, space correlation, and level-crossing rate increased, average fade duration decreased, and Doppler power spectral density became flatter. The proposed model was compared with current geometry-based stochastic models (GBSMs) and showed good consistency. In addition, we verified the nonstationarity in the temporal and spatial domains of the proposed model. These conclusions can be used as references in the design of more reasonable communication systems.

하이브리드 자동차용 리튬배터리의 충전량, 용량감퇴, 저항감퇴 예측을 위한 슬라이딩 모드 관측기 설계 (The SOC, Capacity-fade, Resistance-fade Estimation Technique using Sliding Mode Observer for Hybrid Electric Vehicle Lithium Battery)

  • 김일송;이진국
    • 전기학회논문지
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    • 제57권5호
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    • pp.839-844
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    • 2008
  • A novel state of health estimation method for hybrid electric vehicle lithium battery using sliding mode observer has been presented. A simple R-C circuit method has been used for the lithium battery modeling for the reduced calculation time and system resources due to the simple matrix operations. The modeling errors of simple model are compensated by the sliding mode observer. The design methodology for state of health estimation using dual sliding mode observer has been presented in step by step. The structure of the proposed system is simple and easy to implement, but it shows robust control property against modeling errors and temperature variations. The convergence of proposed observer system has been proved by the Lyapunov inequality equation and the performance of system has been verified by the sequence of urban dynamometer driving schedule test. The test results show the proposed observer system has superior tracking performance with reduced calculation time under the real driving environments.

MIMO Capacity, Level Crossing Rates and Fades: The Impact of Spatial/Temporal Channel Correlation

  • Giorgetti, Andrea;Smith, Peter J.;Shafi, Mansoor;Chiani, Marco
    • Journal of Communications and Networks
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    • 제5권2호
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    • pp.104-115
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    • 2003
  • It is well known that Multiple Input Multiple Output (MIMO) systems offer the promise of achieving very high spectrum efficiencies (many tens of bit/s/Hz) in a mobile environment. The gains in MIMO capacity are sensitive to the presence of spatial and temporal correlation introduced by the radio environment. In this paper, we examine how MIMO capacity is influenced by a number of factors e.g., a) temporal correlation b) various combinations of low/high spatial correlations at either end, c) combined spatial and temporal correlations. In all cases, we compare the channel capacity that would be achievable under independent fading. We investigate the behaviour of "capacity fades," examine how often the capacity experiences the fades, develop a method to determine level crossing rates and average fade durations and relate these to antenna numbers. We also evaluate the influence of channel correlation on the capacity autocorrelation and assess the fit of a Gaussian random process to the temporal capacity sequence. Finally we note that the particular spatial correlation structure of the MIMO channel is influenced by a large number of factors. For simplicity, it is desirable to use a single overall correlation measure which parameterizes the effect of correlation on capacity. We verify this single parameter concept by simulating a large number of different spatially correlated channels.

A Simple If In-Phase Combiner and Its Performance for Point-to-Point Radio Relay System with Space Diversity

  • Suh Kyoung-Whoan
    • Journal of electromagnetic engineering and science
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    • 제5권1호
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    • pp.1-7
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    • 2005
  • The implementation of a simple analog in-phase combiner is presented for a high capacity radio relay system with space diversity. It provides good performance in terms of simple hardware and easy control, and measured results are in good agreement with simulated ones. To suggest practical applications, signatures with/without diversity are measured for STM-1 signal of 64-QAM radio relay system combined with a 13-tap equalizer, and they provided more than 25 dB fade depth at 10$^{-3}$ BER under the frequency selective fading condition.

상반전 기법으로 제조한 PVdF-HFP/(SiO2, TiO2) 고분자 전해질을 채용한 리튬금속 고분자 2차전지의 충방전 특성 (Charge-Discharge Characteristics of Lithium Metal Polymer Battery Adopting PVdF-HFP/(SiO2, TiO2) Polymer Electrolytes Prepared by Phase Inversion Technique)

  • 김진철;김광만
    • Korean Chemical Engineering Research
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    • 제46권1호
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    • pp.131-136
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    • 2008
  • 용매 N-methyl-2-pyrrolidone(NMP)과 dimethyl acetamide(DMAc)를 각각 사용하고 물을 비용매로 사용하는 상반전 기법에 의해, 실리카($SiO_2$)와 티타니아($TiO_2$) 나노입자가 각각 충진된 poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) 고분자 전해질을 제조하고, 이를 고용량 양극재료인 $Li[Ni_{0.15}Co_{0.10}Li_{0.20}Mn_{0.55}]O_2$를 주성분으로 하는 양전극과 리튬금속 음전극 사이에 채용하는 리튬금속 고분자 2차전지를 제작하여 그 충방전 특성을 조사하였다. 고분자 전해질 제조에 사용한 용매에 상관없이 실리카 충진재의 함량이 40~50 wt%인 상반전막을 고분자 전해질로 적용하였을 때 가장 높은 방전용량(180 mAh/g)을 나타내었으며, 이 경우 대개 80 사이클까지 초기용량의 99% 정도의 지속성을 보이다가 그 이후 급격한 용량 감소를 보였다. 이 용량 감소는 상반전막이 보장하는 용량 유지능력이 더이상 발휘될 수 없는 상태로 고분자 전해질에 리튬 dendrite가 침적되었기 때문이라 생각된다.

Control of Surface Chemistry and Electrochemical Performance of Carbon-coated Silicon Anode Using Silane-based Self-Assembly for Rechargeable Lithium Batteries

  • Choi, Hyun;Nguyen, Cao Cuong;Song, Seung-Wan
    • Bulletin of the Korean Chemical Society
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    • 제31권9호
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    • pp.2519-2526
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    • 2010
  • Silane-based self-assembly was employed for the surface modification of carbon-coated Si electrodes and their surface chemistry and electrochemical performance in battery electrolyte depending on the molecular structure of silanes was studied. IR spectroscopic analyses revealed that siloxane formed from silane-based self-assembly possessed Si-O-Si network on the electrode surface and high surface coverage siloxane induced the formation of a stable solid-electrolyte interphase (SEI) layer that was mainly composed of organic compounds with alkyl and carboxylate metal salt functionalities, and PF-containing inorganic species. Scanning electron microscopy imaging showed that particle cracking were effectively reduced on the carbon-coated Si when having high coverage siloxane and thickened SEI layer, delivering > 1480 mAh/g over 200 cycles with enhanced capacity retention 74% of the maximum discharge capacity, in contrast to a rapid capacity fade with low coverage siloxane.

Modeling of Battery for EV using EMTP/ATPDraw

  • Kim, Jun-Hyeok;Lee, Soon-Jeong;Kim, Eung-Sang;Kim, Seul-Ki;Kim, Chul-Hwan;Prikler, Laszlo
    • Journal of Electrical Engineering and Technology
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    • 제9권1호
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    • pp.98-105
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    • 2014
  • As environmentally friendly energy takes center stage, interests for Electric Vehicles/Plug in Hybrid Electric Vehicles (EVs/PHEVs) are getting increase. With this trend, there is no doubt EVs will take large portion to penetrations of total cars. Therefore, accurate EV modeling is required. Battery is one of the main components with the power system view of aspect. Hence, in this paper, reviews and discussions of some types of batteries for EV are contained by considering energy density and weight of the batteries. In addition, simulations of Li-Ion battery are accomplished with various variables such as temperature, capacity fading and charge/discharge current. It is confirmed that temperature is the main factor of capacity fading. Validation of the modeled battery is also conducted by comparing it with commercialized battery.

Synthesis and Characterization of Hollow Silicon-Carbon Composites as a Lithium Battery Anode Material

  • Han, Won-Kyu;Ko, Yong-Nam;Yoon, Chong-Seung;Choa, Yong-Ho;Oh, Sung-Tag;Kang, Sung-Goon
    • 한국재료학회지
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    • 제19권10호
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    • pp.517-521
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    • 2009
  • Si-C composite with hollow spherical structure was synthesized using ultrasonic treatment of organosilica powder formed by hydrolysis of phenyltrimethoxysilane. The prepared powder was pyrolyzed at various temperatures ranging from 900 to 1300 $^{\circ}C$ under nitrogen atmosphere to obtain optimum conditions for Li-ion battery anode materials with high capacity and cyclability. The XRD and elemental analysis results show that the pyrolyzed Si/C composite at 1100 $^{\circ}C$ has low oxygen and nitrogen levels, which is desirable for increasing the electrochemical capacity and reducing the irreversible capacity of the first discharge. The solid Si-C composite electrode shows a first charge capacity of $\sim$500 mAhg$^{-1}$ and a capacity fade within 30 cycles of 0.93% per cycle. On the other hand, the electrochemical performance of the hollow Si-C composite electrode exhibits a reversible charge capacity of $\sim$540 mAhg$^{-1}$ with an excellent capacity retention of capacity loss 0.43% per cycle up to 30 cycles. The improved electrochemical properties are attributed to facile diffusion of Li ions into the hollow shell with nanoscale thickness. In addition, the empty core space provides a buffer zone to relieve the mechanical stresses incurred during Li insertion.

Microwave 채널환경에서 BL-PSF를 적용하는 OFDM/QPSK-DMR 시스템의 성능분석 (Performance A Analysis of OFDM/QPSK-DMR System Using BL-PSF over Microwave Channel Environments)

  • 안준배;양희진;오창헌;조성준
    • 한국통신학회논문지
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    • 제29권9C호
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    • pp.1279-1288
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    • 2004
  • 본 논문에서는 microwave 채널 환경에 적합한 OFDM(Orthogonal Frequency Division Multiplexing) 기반의 DMR(Digital Microwave Radio)시스템 구조를 제안하고 시스템 성능을 분석하였다. 기존의 단일 반송파 방식의 DMR 시스템은 High-level QAM변조방식을 사용하며 시스템 구성이 복잡하고, 페이딩 채널에 매우 민감한 특성을 갖기 때문에 전송용량의 한계가 발생한다. 따라서 이러한 문제점을 극복하기 위한 방안으로 페이딩 채널에 강한 OFDM 방식이 연구되어왔다. 본 논문에서는 기존 OFDM에서 사용된 windowing 방식 대신 BL-PSF(Band-Limited Pulse Shaping Filter)를 이용 하므로서 GI/GB(Guard Interval/Guard Band) 등의 잉여 데이터 사용을 지양하여 전송용량을 향상 시킬수 있도록 하였으며, IFFT/FFT 블록의 이용효율을 개선시킬 수 있도록 하였다. 본논문에서는 microwave 채널 환경에 대해 단일 반송파 방식의 DMR 시스템과 OFDM/QPSK-DMR 시스템의 성능을 시뮬레이션하여 비교분석하였다. 그 결과, 제안하는 DMR 시스템은 부 반송파의 수가 많아질수록 단일 반송파 방식의 DMR 시스템보다 우수한 fade margin을 갖는것을 알 수 있었다.

군 MicroWave 통신 환경에서의 링크 거리를 고려한 전송 성능 향상 기법 (Improving Transmission in Association with the Distance for Military Microwave Communications)

  • 윤종택;임영갑;김영호
    • 한국통신학회논문지
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    • 제39C권11호
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    • pp.1042-1049
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    • 2014
  • 군의 MicroWave 통신 환경에서 회선 설계를 위해 링크거리, 가용도, 전송용량은 중요한 요소이다. 현재 고정용 변조방식으로 운용, 미래 전송용량 증대가 가능한 변조방식으로 진화될 예정이다. 링크 거리에 따라 페이딩 발생확률의 증가로 장거리의 경우 고신뢰의 전송품질을 지속적으로 보장하기 어려울 수 있다. 대용량 전송을 위한 변조방식의 경우 장거리가 될수록 링크버짓에서 페이드 마진의 저하로 가용도가 감소되어 QoS 보장에 있어 제한사항이 발생할 수 있다. 본 논문에서는 군 MicroWave 무선 링크에서의 링크거리를 고려한 대역폭 가변 할당 및 우선순위 전송 용량 비율 설정을 이용한 우선순위 전송 기법을 통해 무선 전송 성능 향상기법을 제안하고 링크 설계를 위한 채널 전송 용량 산출방안을 제시한다.