• Title/Summary/Keyword: Decision Feedback

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DOA(Direction of Arrival) Estimation based Beamforming technique for VBeam Reception Performance Enhancement (VBeam 수신 성능 개선을 위한 입사각 추정 기반의 빔형성 알고리즘 연구)

  • Lee, Jae-Eun;Shim, Tae-Bo
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.47 no.5
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    • pp.212-221
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    • 2010
  • The bubbles could be created from multiple source in the surface of ocean. The bubbles which are created like this affect to the intensity and the sound speed of acoustic wave which are used from the ocean. From the research, it observed Reverberation from the sea surface, using Vbeam transmission and reception equipment that was a cross-shaped Array, from 2008 July 2nd to July 3rd at 4Km from the East Sea Mookho port. It is difficult to analyze data because the received signal has ambient noise and occurrence ISI(Inter Symbol Interference) for multipath. This paper remove that ambient noise and ISI using the directions of arrival beamforming and the filter and sum beamforming. After beamforming, a following DFE(Decision Feedback Equalizer) removes the remaining multipath components. Experimental results show that the proposed technique reduce the errors caused by ISI.

Performance Improvement for Nonchoherent DS/CDMA Reverse Links using Channel Estimation and Multiuser Detection (비동기 복조 DS/CDMA 역방향 링크에서 채널 추정 및 다중 사용자 검파를 이용한 성능 개선)

  • 홍대기;윤석현;홍대식;강창언
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.12 no.5
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    • pp.755-764
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    • 2001
  • In this paper, we propose maximum likelihood (ML) decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems. The proposed DFCE uses the maximum combiner output in a RAKE receiver as decision feedback information, enabling M-ary orthogonal signals to be demodulated coherently and a RAKE receiver to use a em maximal ration combining (MRC) scheme. However, the performance of the proposed DFCE in the multiuser environment is severely degraded due to multiple access interference (MAI). To overcome this problem, a multistage parallel interference cancellation (PIC) scheme is combined with the proposed DFCE for multiuser environments. Accurate knowledge of the channel coefficient estimated by the proposed DFCE is used to regenerate the signal of each user for the multistage PIC scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed system is significantly improved in comparison with conventional noncoherent demodulation.

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Pilot Symbol Assisted Channel Estimation and Equalization for OFDM Systems in Doubly Selective Channels (주파수 선택적 시변 채널 OFDM 시스템에서의 파일럿 심볼을 이용한 채널 예측 및 등화)

  • Lim, Dong-Min
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.18 no.12
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    • pp.1408-1418
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    • 2007
  • In this paper, we analyze the performance of pilot symbol assisted channel estimation and equalization schemes for OFDM systems over frequency-selective time-varying channels and propose methods to improve the system performance. In the least square(LS) and linear minimum mean square error(MMSE) channel estimation, time domain windowing is introduced for banding the frequency domain channel matrix. The linear MMSE and decision feedback equalization schemes are employed with the pilot symbols for channel estimation taken into account in the equalization process. To reduce computational complexity, the band LU matrix factorization algorithm is introduced in solving the linear systems involved in the equalization, and the performances are compared with the known previous results by computer simulations. When time domain windowing is employed in the decision feedback equalization, the matrix related with the decision feedback process is shown to be unhanded and the resultant performance degradation is analyzed.

Affective interaction to emotion expressive VR agents (가상현실 에이전트와의 감성적 상호작용 기법)

  • Choi, Ahyoung
    • Journal of the Korea Computer Graphics Society
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    • v.22 no.5
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    • pp.37-47
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    • 2016
  • This study evaluate user feedback such as physiological response and facial expression when subjects play a social decision making game with interactive virtual agent partners. In the social decision making game, subjects will invest some of money or credit in one of projects. Their partners (virtual agents) will also invest in one of the projects. They will interact with different kinds of virtual agents which behave reciprocated or unreciprocated behavior while expressing socially affective facial expression. The total money or credit which the subject earns is contingent on partner's choice. From this study, I observed that subject's appraisal of interaction with cooperative/uncooperative (or friendly/unfriendly) virtual agents in an investment game result in increased autonomic and somatic response, and that these responses were observed by physiological signal and facial expression in real time. For assessing user feedback, Photoplethysmography (PPG) sensor, Galvanic skin response (GSR) sensor while capturing front facial image of the subject from web camera were used. After all trials, subjects asked to answer to questions associated with evaluation how much these interaction with virtual agents affect to their appraisals.

A modified FDTS/DF for considering nonlinear distortion in digital magnetic recording channels (디지탈 자기 기록 채널의 비선형 왜곡을 고려한 개선된 FDTS/DF)

  • 오대선;전원기;양원영;조용수
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.21 no.7
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    • pp.1734-1745
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    • 1996
  • In this paper, a modified fixed-delay tree search with decision feedback(FDTS/DF) for compensation of non-linear distortion in digital magnetic recording channels is discussed. Since the nonlinear distortion, which becomes significant as recording density increases, is generally well modeled by the discrete Volterra series, the proposed equlizer is composed of a nolinear feedforward filter, a linear feedback filter, and a nonlinear distorton table, the values of which are determined by considering the effect of nonlinear distortion due to future data as well as the previous and current one. At the decision stage of FDTS, a path minimizing the branch metric is chosen by using the previously detected values, current predicted value, and future predicted value. We compare the performance of the linear FDTS/DF, the previous nonlinear FDTS/DF, and the proposed nonlinear FDTS/DF by computer simulation, and confirm that the proposed one chieves the best performance at high-density recording.

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Design and Performance Analysis of a Decision-feedback Coherent Code Tracking Loop for WCDMA Systems (WCDMA 시스템을 위한 판정궤환 동기식 동기추적 회로의 설계 및 성능분석)

  • 박형래;양연실;김영선;김창주
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.4A
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    • pp.429-438
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    • 2004
  • In this paper, a decision-feedback coherent code tracking loop is designed for WCDMA systems and its performance is analyzed in terms of jitter variance considering the effect of phase and symbol estimation errors for both AWGN and fading environments. An analytical closed-form formula for jitter variance is Int derived for AWGN environments as a function of a pulse-shaping filter, timing offset, signal-to-interference ratio, and loop bandwidth while involving the phase estimation error and bit error rate, and the upper bound of jitter variance is derived for fading environments. Finally a second-order coherent code tracking loop is designed with the DPCH frame format #13 of the WCDHA forward link selected as a target system, and its performance is evaluated by the closed-form formula and compared with the simulation results for both AWGN and Rayleigh fading environments.

Noise Whitening Decision Feedback Equalizer for SC-FDMA Receivers (SC-FDMA 수신기를 위한 잡음 백색화 판정궤환 등화기)

  • Lee, Su-Kyoung;Park, Yong-Hyun;Seo, Bo-Seok
    • Journal of Broadcast Engineering
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    • v.16 no.6
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    • pp.986-995
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    • 2011
  • In this paper, we propose a noise whitening decision feedback equalizer for single carrier frequency division multiple access (SC-FDMA) receivers. SC-FDMA has the same advantage as that of orthogonal frequency division multiple access (OFDMA) in which the multipath effect can be removed easily, and also solves the problem of high peak to average power ratio (PAPR) which is the main drawback of OFDMA. Although SC-FDMA is a single carrier transmission scheme, a simple frequency domain linear equalizer (FD-LE) can be implemented as in OFDMA, which can dramatically reduce the equalizer complexity. Moreover, some residual intersymbol interference in the output of the FD-LE can be further removed by an additional nonlinear decision feedback equalizer (DFE) in time domain, because the time domain signal is a digitally modulated symbol. In the conventional DFE, however, the noise is not white at the input of the decision device and correspondingly the decision is not optimum. In this paper, we propose an improved DFE scheme for SC-FDMA systems where a linear noise whitening filter is inserted before the decision device of the conventional DFE scheme. Through computer simulations, we compare the bit error rate performance of the proposed DFE scheme with the conventional equalizers.

Trellis Defection of Tamed FM with the DLMS and Convergence

  • Kang, Min-Goo;Lee, Yang-Won;Cho, Hyung-Rae;Kang, Sung-Chul
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.1 no.2
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    • pp.199-207
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    • 1997
  • The Maximum Likelihood Sequence Estimation scheme is modified to improve the error performance of the correlative coding in the Tamed FM. To remove intersymbol interference, the Decision Feedback Equalization scheme with the delayed LMS algorithm and the Viterbi algorithm(10-symbol delay) in the delayed adaptive equalization are proposed for the performance of decision-directed adaptive equalization under the High Frequency channels, and the condition of convergence is analyzed.

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Developing a Graph Convolutional Network-based Recommender System Using Explicit and Implicit Feedback (명시적 및 암시적 피드백을 활용한 그래프 컨볼루션 네트워크 기반 추천 시스템 개발)

  • Xinzhe Li;Dongeon Kim;Qinglong Li;Jaekyeong Kim
    • Journal of Information Technology Services
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    • v.22 no.1
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    • pp.43-56
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    • 2023
  • With the development of the e-commerce market, various types of products continue to be released. However, customers face an information overload problem in purchasing decision-making. Therefore, personalized recommendations have become an essential service in providing personalized products to customers. Recently, many studies on GCN-based recommender systems have been actively conducted. Such a methodology can address the limitation in disabling to effectively reflect the interaction between customer and product in the embedding process. However, previous studies mainly use implicit feedback data to conduct experiments. Although implicit feedback data improves the data scarcity problem, it cannot represent customers' preferences for specific products. Therefore, this study proposed a novel model combining explicit and implicit feedback to address such a limitation. This study treats the average ratings of customers and products as the features of customers and products and converts them into a high-dimensional feature vector. Then, this study combines ID embedding vectors and feature vectors in the embedding layer to learn the customer-product interaction effectively. To evaluate recommendation performance, this study used the MovieLens dataset to conduct various experiments. Experimental results showed the proposed model outperforms the state-of-the-art. Therefore, the proposed model in this study can provide an enhanced recommendation service for customers to address the information overload problem.

Quadratic Sigmoid Neural Equalizer (이차 시그모이드 신경망 등화기)

  • Choi, Soo-Yong;Ong, Sung-Hwan;You, Cheol-Woo;Hong, Dae-Sik
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.36S no.1
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    • pp.123-132
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    • 1999
  • In this paper, a quadratic sigmoid neural equalizer(QSNE) is proposed to improve the performance of conventional neural equalizer in terms of bit error probability by using a quadratic sigmoid function as the activation function of neural networks. Conventional neural equalizers which have been used to compensate for nonlinear distortions adopt the sigmoid function. In the case of sigmoid neural equalizer, each neuron has one linear decision boundary. So many neurons are required when the neural equalizer has to separate complicated structure. But in case of the proposed QSNF and quadratic sigmoid neural decision feedback equalizer(QSNDFE), each neuron separates decision region with two parallel lines. Therefore, QSNE and QSNDFE have better performance and simpler structure than the conventional neural equalizers in terms of bit error probability. When the proposed QSNDFE is applied to communication systems and digital magnetic recording systems, it is an improvement of approximately 1.5dB~8.3dB in signal to moise ratio(SNR) over the conventional decision feedback equalizer(DEF) and neural decision feedback equalizer(NDFE). As intersymbol interference(ISI) and nonlinear distortions become severer, QSNDFE shows astounding SNR shows astounding SNR performance gain over the conventional equalizers in the same bit error probability.

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