• Title/Summary/Keyword: combined systems

Search Result 2,640, Processing Time 0.027 seconds

Performance Evaluation of Bandwidth Efficient Adaptive QAM Schemes in Flat and Frquency Selective Fading Channels (균일 및 주파수 선택적 페이딩에서 대역폭 효율의 적응 QAM 성능분석)

  • 정연호
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.25 no.10A
    • /
    • pp.1473-1479
    • /
    • 2000
  • This paper presents the performance evaluation of an adaptive QAM scheme under flat and frequency selective fading channels for indoor wireless communication systems. The QAM modulation is combined with differential encoding and the demodulation process is carried out noncoherently. The adaptation is performed by varying the modulation level of QAM, depending upon received signal strength. The adaptation mechanism allows a 2- or 3-bit increase or decrease at a time, if the channel condition is considered to be significantly good or bad. Simulation results show that the average number of bits per symbol (ABPS) for each symbol block transmitted over a flat fading channel is higher than 5.0 and the BER performance is better than 10^-4 for a SNR value higher than 30 dB. For frequency selective fading channels, an oversampling technique in the receiver was employed. The BER performance obtained for frequency selective fading channels is better than 10^-4 with a SNR value of 40 dB and ABPS is found to be approximately 5.5. Therefore, this scheme is very useful in that it provides both very high bandwidth efficiency and acceptable performance with moderate SNR values over flat and frequency selective fading channels. In addition, this scheme provides reduced receiver complexity by way of noncoherent detection.

  • PDF

Fatigue Damage Model Comparison with Tri-modal Spectrum under Stationary Gaussian Random Processes (정상 정규분포 확률과정의 삼봉형 스펙트럼에 대한 피로손상 모델 비교)

  • Park, Jun-Bum;Jeong, Se-Min
    • Journal of Ocean Engineering and Technology
    • /
    • v.28 no.3
    • /
    • pp.185-192
    • /
    • 2014
  • The riser systems for floating offshore structures are known to experience tri-modal dynamic responses. These are owing to the combined loadings from the low-frequency response due to riser tension behavior, middle-range frequency response coming from winds and waves, and high-frequency response due to vortex induced-vibration. In this study, fatigue damage models were applied to predict the fatigue damages in a well-separated tri-modal spectrum, and the resultant fatigue damages of each model were compared with the most reasonable fatigue damage calculated by the inverse Fourier transform of the spectrum, rain-flow counting method, and Palmgren-Miner rule as a reference. The results show that the fatigue damage models developed for a wide-band spectrum are applicable to the tri-modal spectrum, and both the Benasciutti-Tovo and JB models could most accurately predict the fatigue damages of the tri-modal spectrum responses.

Study on the Reduced System Based on the Sub-Domain Method (영역분할 기법에 기초한 축소시스템 구축에 관한 연구)

  • Kim, Hyun-Gi;Cho, Maeng-Hyo;Kim, Hyuk;Choi, Hyoung-Gil;Choi, Jae-Rack
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.30 no.9 s.252
    • /
    • pp.1062-1069
    • /
    • 2006
  • Reduction schemes approximate the lower eigenvalues that represent the global behavior of the structures. But, they are not efficient to be applied to large-scaled problems because these schemes require considerable amount of computing time in constructing reduced one from the original large-scaled systems. In addition, the selection of the primary degrees of freedom might be localized to cause the excessive emphasis of the lower mode or lost of the important modes. In the present study, a new reduction method combined with the subdomain method is proposed. For the construction of the final reduced system the system of each domain subdivided into primary, slave and interface degrees of freedom. It is remarkably efficient and accurate comparable to full-scale system. Numerical examples demonstrate that the proposed method saves computational cost effectively and provides a reduced system which predicts accurate eigen-pairs of global system.

Structural damage detection using decentralized controller design method

  • Chen, Bilei;Nagarajaiah, Satish
    • Smart Structures and Systems
    • /
    • v.4 no.6
    • /
    • pp.779-794
    • /
    • 2008
  • Observer-based fault detection and isolation (FDI) filter design method is a model-based method. By carefully choosing the observer gain, the residual outputs can be projected onto different independent subspaces. Each subspace corresponds to the monitored structural element so that the projected residual will be nonzero when the associated structural element is damaged and zero when there is no damage. The key point of detection filter design is how to find an appropriate observer gain. This problem can be interpreted in a geometric framework and is found to be equivalent to the problem of finding a decentralized static output feedback gain. But, it is still a challenging task to find the decentralized controller by either analytical or numerical methods because its solution set is, generally, non-convex. In this paper, the concept of detection filter and iterative LMI technique for decentralized controller design are combined to develop an algorithm to compute the observer gain. It can be used to monitor structural element state: healthy or damaged. The simulation results show that the developed method can successfully identify structural damages.

Proposition of Improved Neutral Grounding Method and Analytical Evaluation on Practicality in Underground Distribution System (지중배전시스템의 개선된 중성점 접지방식 제안과 실효성에 대한 해석적 평가)

  • Jeong, Seok-San;Lee, Jong-Beom;Jang, Seong-Whan;Kim, Yong-Kap;Kwon, Shin-Nam
    • The Transactions of The Korean Institute of Electrical Engineers
    • /
    • v.60 no.3
    • /
    • pp.479-485
    • /
    • 2011
  • In 22.9kV underground distribution system, power cables are provided with multiple-point ground in which each neutral line of the distribution cable(A, B, C phases) and three-wire common grounded at every connecting section. But in such grounding methods, circulating current flows between the neutral wire and grounding wire. And power loss due to circulating current also occurs in all conductors. Therefore it is getting necessary reducing circulating current in underground distribution system. This paper presents improved grounding method to overcome such problems. The proposed grounding method eliminates circulating current in the neutral line effectively and is verified that there is no electrical problem or any ineffectiveness of operating protection systems. These analyses are carried out by EMTP/ATPDraw to compare each grounding methods in steady and transient state. This grounding method suggested in this paper can be applied on real distribution system after field tests considering elimination of circulating current was implemented.

Design of Space Search-Optimized Polynomial Neural Networks with the Aid of Ranking Selection and L2-norm Regularization

  • Wang, Dan;Oh, Sung-Kwun;Kim, Eun-Hu
    • Journal of Electrical Engineering and Technology
    • /
    • v.13 no.4
    • /
    • pp.1724-1731
    • /
    • 2018
  • The conventional polynomial neural network (PNN) is a classical flexible neural structure and self-organizing network, however it is not free from the limitation of overfitting problem. In this study, we propose a space search-optimized polynomial neural network (ssPNN) structure to alleviate this problem. Ranking selection is realized by means of ranking selection-based performance index (RS_PI) which is combined with conventional performance index (PI) and coefficients based performance index (CPI) (viz. the sum of squared coefficient). Unlike the conventional PNN, L2-norm regularization method for estimating the polynomial coefficients is also used when designing the ssPNN. Furthermore, space search optimization (SSO) is exploited here to optimize the parameters of ssPNN (viz. the number of input variables, which variables will be selected as input variables, and the type of polynomial). Experimental results show that the proposed ranking selection-based polynomial neural network gives rise to better performance in comparison with the neuron fuzzy models reported in the literatures.

Performance Evaluation of High-performance MIMO-OFDM System using Carrier Interferometry Codes in Frequency Selective Fading Channels (주파수 선택적 페이딩 채널에서 반송파 간섭 부호를 이용한 고성능 MIMO-OFDM 시스템의 성능분석)

  • Seo Wan-woo;Chung Yeon-ho
    • Journal of the Korea Institute of Information and Communication Engineering
    • /
    • v.9 no.8
    • /
    • pp.1643-1648
    • /
    • 2005
  • MIMO system takes advantage of the spatial diversity obtained by spatially separated antennas for high- performance and high-capacity broadband wireless access. In this paper, we propose Carrier Interferometry coded MIMO-OFDM system (MIMO-CI/OFDM) which provides frequency and spatial diversity. One combined diversity gains featly improve the performance of OFDM systems. To perform a performance analysis, we have used SPW platform that provides an easy tool to analyze the performance. The results show that the performance of MIMO-CI/OFDM shows an approximately 4dB gain over the MIMO-OFDM even in highly frequency selective fading channels.

Performance Analysis of the M-PPAM DS-UWB Communication systems (M-PPAM DS-UWB 통신시스템의 성능해석)

  • Cho, Kyung-Ryong;Park, Jang-Woo
    • Journal of the Korea Institute of Information and Communication Engineering
    • /
    • v.9 no.8
    • /
    • pp.1656-1662
    • /
    • 2005
  • This paper introduces M-PPAM(M-ary Pulse Position and Amplitude Modulation) architecture, combined PPM(Pulse Position Modulation) with PAM(Pulse Amplitude Modulation). Since M-PPAM can transmit several bits using one pulse, it is mon effective than PPM or PAM. Also, to obtain the same data transmission rate with PPM or PAM, M-PPAM can use a long pulse repetition period. This method will be able to use in the multi-path fading environment such as indoor condition. To accomodate multiple users, direct sequence technique is used. This paper has provided the modeling method of the M-PPAM DS-UWB receiver covering multi-user interference(MUI) with the Standard Gaussian Approximation under Gaussian channel. The performance of the receiver is simulated.

Data-based On-line Diagnosis Using Multivariate Statistical Techniques (다변량 통계기법을 활용한 데이터기반 실시간 진단)

  • Cho, Hyun-Woo
    • Journal of the Korea Academia-Industrial cooperation Society
    • /
    • v.17 no.1
    • /
    • pp.538-543
    • /
    • 2016
  • For a good product quality and plant safety, it is necessary to implement the on-line monitoring and diagnosis schemes of industrial processes. Combined with monitoring systems, reliable diagnosis schemes seek to find assignable causes of the process variables responsible for faults or special events in processes. This study deals with the real-time diagnosis of complicated industrial processes from the intelligent use of multivariate statistical techniques. The presented diagnosis scheme consists of a classification-based diagnosis using nonlinear representation and filtering of process data. A case study based on the simulation data was conducted, and the diagnosis results were obtained using different diagnosis schemes. In addition, the choice of future estimation methods was evaluated. The results showed that the performance of the presented scheme outperformed the other schemes.

Digital Predistortion Technique for MIMO Transmitters (MIMO 송신기에서 결합한 되먹임 신호에 기반한 디지털 전치왜곡 기법)

  • Jeong, Eui-Rim
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.37C no.12
    • /
    • pp.1289-1295
    • /
    • 2012
  • An adaptive digital predistortion (PD) technique is proposed for linearization of power amplifiers (PAs) in multiple-input multiple-output (MIMO) transmitters. We consider a PD structure equipped with only one combined feedback path while conventional systems have multiple feedback paths. Hence, the proposed structure is much simpler than that of multiple feedback paths. Based on the structure, a new PD algorithm is derived. The simulation results show that linearization performance of the proposed method is almost the same as the conventional multiple feedback technique while the former is much simpler to implement than the latter.