• Title, Summary, Keyword: Random media

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Estimation of Incoherent Scattered Field by Multiple Scatterers in Random Media

  • Seo, Dong-Wook;Lee, Jae-Ho;Lee, Hyung Soo
    • ETRI Journal
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    • v.38 no.1
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    • pp.141-148
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    • 2016
  • This paper proposes a method to estimate directly the incoherent scattered intensity and radar cross section (RCS) from the effective permittivity of a random media. The proposed method is derived from the original concept of incoherent scattering. The incoherent scattered field is expressed as a simple formula. Therefore, to reduce computation time, the proposed method can estimate the incoherent scattered intensity and RCS of a random media. To verify the potential of the proposed method for the desired applications, we conducted a Monte-Carlo analysis using the method of moments; we characterized the accuracy of the proposed method using the normalized mean square error (NMSE). In addition, several medium parameters, such as the density of scatterers and analysis volume, were studied to understand their effect on the scattering characteristics of a random media. The results of the Monte-Carlo analysis show good agreement with those of the proposed method, and the NMSE values of the proposed method and Monte-Carlo analysis are relatively small at less than 0.05.

An SSD-Based Storage System for an Interactive Media Server Using Video Frame Grouping

  • Jeong, Yo-Won;Park, Youngwoo;Seo, Kwang-Deok;Yoo, Jeong Ju;Park, Kyu Ho
    • ETRI Journal
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    • v.35 no.1
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    • pp.69-79
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    • 2013
  • For real-time interactive multimedia operations, such as video uploading, video play, fast-forward, and fast-rewind, solid state disk (SSD)-based storage systems for video streaming servers are becoming more important. Random access rates in storage systems increase significantly with the number of users; it is thus difficult to simultaneously serve many users with HDD-based storage systems, which have low random access performance. Because there is no mechanical operation in NAND flash-based SSDs, they outperform HDDs in terms of flexible random access operation. In addition, due to the multichannel architecture of SSDs, they perform similarly to HDDs in terms of sequential access. In this paper, we propose a new SSD-based storage system for interactive media servers. Based on the proposed method, it is possible to maximize the channel utilization of the SSD's multichannel architecture. Accordingly, we can improve the performance of SSD-based storage systems for interactive media operations.

The Probability Based Ordered Media Access (IEEE 802-15.4에서 우선순위 IFS를 이용한 확률기반 매체 접근 방법)

  • Jean, Young-Ho;Kim, Jeong-Ah;Park, Hong-Seong
    • Proceedings of the KIEE Conference
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    • pp.321-323
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    • 2006
  • The IEEE 802.15.4 uses a CSMA/CA algorithm on access of media. The CSMA/CA algorithm does Random Backoff before the data is transmitted to avoid collisions. The random backoff is a kind of unavoidable delays and introduces the side effect of energy consumptions. To cope with those problems we propose a new media access algorithm, the Priority Based Ordered Media Access (PBOMA) algorithm, which uses different IFSs. The PBOMA algorithm uses Sampling Rate and Beacon Interval to get a different access probability(or IFS). The access probability is higher, the IFS is shorter. Note that The transfer of urgent data uses tone signal to transmit it immediately. The proposed algorithm is expected to reduce the energy consumptions and the delay.

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Practical Implementation and Performance Evaluation of Random Linear Network Coding (랜덤 선형 네트워크 코딩의 실용적 설계 및 성능 분석)

  • Lee, Gyujin;Shin, Yeonchul;Koo, Jonghoe;Choi, Sunghyun
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.9
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    • pp.1786-1792
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    • 2015
  • Random linear network coding (RLNC) is widely employed to enhance the reliability of wireless multicast. In RLNC encoding/decoding, Galois Filed (GF) arithmetic is typically used since all the operations can be performed with symbols of finite bits. Considering the architecture of commercial computers, the complexity of arithmetic operations is constant regardless of the dimension of GF m, if m is smaller than 32 and pre-calculated tables are used for multiplication/division. Based on this, we show that the complexity of RLNC inversely proportional to m. Considering additional overheads, i.e., the increase of header length and memory usage, we determine the practical value of m. We implement RLNC in a commercial computer and evaluate the codec throughput with respect to the type of the tables for multiplication/division and the number of original packets to encode with each other.

A study on random access protocol based on reservation access for WDM passive star coupler network (WDM passive star coupler 망에서 예약 방식에 기반한 임의 접근 프로토콜에 관한 연구)

  • 백선욱;최양희;김종상
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.21 no.4
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    • pp.893-910
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    • 1996
  • Recently, there ary many researches on local area multichannel network as WDM technology developes. An ideal media access protocol in a multichannel network is one that shows short access delay under low load and high throughput under heavy load. This paper proposed a new media access protocol for WDM passive star coupler network. The proposed one is a random access rpotocol based on reservation. Access delay is short under low load by using random access method, and high throughput is achieved under heavy load by usin greservation access. Analytic model for the performance analysis of the proposed protocol is developed and performance of the proposed protocol is compared with the previous ones. The effect on the performance of the number of the nodes and channels, and the number of transceivers in each node are analyzed.

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Comparison of Detection Probability for Conventional and Time-Reversal (TR) Radar Systems

  • Yoo, Hyung-Ha;Koh, Il-Suek
    • Journal of electromagnetic engineering and science
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    • v.12 no.1
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    • pp.70-76
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    • 2012
  • We compare the detection probabilities of the time-reversal(TR) detection system and the conventional radar system. The target is assumed to be hidden inside a random medium such as a forest. We propose a TR detection system based on the SAR(Synthetic Aperture Radar) algorithm. Unlike the conventional SAR images, the proposed TR-SAR system has an interesting property. Specifically, the target-related signal components due to the time-reversal refocusing characteristics, as well as some of clutter-related signal components are concentrated at the time-reversal reference point. The remaining clutter-related signal components are scattered around that reference point. In this paper, we model the random media as a collection of point scatterers to avoid unnecessary complexities. We calculate the detection probability of the TR radar system based on the proposed simple random media model.

Fluctuation of Transport Properties of Random Heterogeneous Media (비정형 혼합재 이동성질의 변동)

  • Kim, In-Chan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.9
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    • pp.3015-3029
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    • 1996
  • The notion of effective transport property of a heterogeneous medium implies that the medium is large enough that the ergodic theorem holds and local fluctuation of the property can be neglected. In case that the medium is not large enough compared to its characteristic microstructure length scale, the effective property fluctuates and differs from the value of the medium being large enough. As a representative transport phenomenon, diffusion was considered and the fluctuation of varying effective diffusion property, diffusion coarseness $C_k$, was defined as a quantifying parameter. Scaled effective diffusion property, $^*$>/k$_1$ and $C_k$ were computed for the two phase random media consisting of matrix of diffusion coefficient k$_1$ and spheres of diffusion coefficient k$_2$. Numerical simulations were performed by use of the so-called first passage time technique and data were collected for existing microstructure models of hard spheres(HS), overlapping spheres(OS) and penetrable concentric shells(PCS).

Design and Implementation of Real-Time Video Transport System using Variable Size Random Linear Coding (가변 크기 Random Linear Coding 기반의 실시간 무선 비디오 전송 시스템의 실험적인 설계 및 구현)

  • Kim, Jong-Ryool;Park, Joon-Sang;Kim, Jong-Won
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • pp.187-190
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    • 2009
  • 네트워크 코딩 중 RLC (random linear coding)은 다양한 연구들에서 이미 그 효용성이 입증되었으며 실제 유/무선 네트워크 환경에서 RLC를 적용하는 연구들이 최근 활발하게 진행되고 있다. RLC는 간단한 방법론적인 특성과 그 효용성으로 인해 많은 관심을 받고 있지만, 실제 환경에서 RLC 디코딩 과정이 요구하는 높은 성능 복잡도로 인하여 실용성에 한계를 가진다. 이러한 상황에서 최근 병행 방법 (Parallelized method)을 이용해 RLC 디코딩 과정의 복잡도를 개선하고 이를 실제적인 비디오 전송에 적용하는 연구들이 진행되고 있다. 본 논문에서는 이러한 연구들과 더불어 무선 환경에서의 실시간 비디오 전송을 위한 비디오의 특성을 고려하는 RLC 기반의 실시간 비디오 전송 시스템을 제안한다. 또한 제안한 시스템 실험적으로 구현하고, 이를 실제 무선 네트워크 환경에서 검증하였다.

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Comparison of synthetic seismograms referred to inhomogeneous medium (불균질 매질에 따른 인공 합성 탄성파 자료 비교)

  • Kim, Young-Wan;Jang, Seung-Hyung;Yoon, Wang-Joong;Suh, Sang-Yong
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.197-202
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    • 2007
  • Most of seismic reflection prospecting assumes subsurface formation to be homogeneous media. These models are not capable of estimating small scale heterogeneity which is verified by well log data or drilling core. And those synthetic seismograms by homogeneous media are limited to explain various changes at field data. So we developed a inhomogeneous velocity model which can estimate inhomogeneity of background medium to implement numerical modeling from homogeneous medium and inhomogeneous medium on the model. Background medium using three autocorrelation functions in order to generate inhomogeneous velocity media was according to dominant wavelength of background medium and correlation length of random medium. And then we compared shot gathers. The results show that numerical modeling implemented at inhomogeneous medium depicts complex wave propagation of field data.

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Numerical Simulation of Irradiance Scintillation through a Gaussian Random Medium (가우시안 랜덤매질을 통과한 광도변동의 시뮬레이션)

  • Jeong Ki Pack
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.29A no.11
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    • pp.40-48
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    • 1992
  • The wave-kinetic numerical method is used in simulating the irradiance scintillations of optical wave through a two-dimensional random medium containing weak Gaussian fluctuations of the refractive index. The results are compared to existing analytical or numerical results. The wave-kinetic method is a phase-space ray-tracing method for certain key ray trajectories, and the irradiance is calculated by reconstructing the entire beam from these trajectories. The strength of the wave-kinetic method lies in the fact that it can be applied to any type of random media.

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