• 제목/요약/키워드: Frequency channel

검색결과 2,803건 처리시간 0.027초

Alignment of transmitters in indoor visible light communication for flat channel characteristics

  • Curuk, Selva Muratoglu
    • ETRI Journal
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    • 제44권1호
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    • pp.125-134
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    • 2022
  • Visible light communication (VLC) systems incorporate ambient lighting and wireless data transmission, and the experienced channel in indoor VLC is a major topic that should be examined for reliable communication. In this study, it is realized that multiple transmitters in classical alignment are the forceful factors for channel characteristics. In the frequency band, fluctuations with sudden drops are observed, where the fluctuation shape is related to the source layout and receiver location. These varying frequency-selective channels need solutions, especially for mobile users, because sustained channel estimation and equalization are necessary as the receiver changes its location. It is proven that using light-emitting diodes (LEDs) with highly directional beams as sources or using a detector with a narrow field of view (FOV) in the receiver may help partially alleviate the problem; the frequency selectivity of the channel reduces in some regions of the room. For flat fading channel characteristics all over the room, LEDs should be aligned in hexagonal cellular structure, and detector FOV should be arranged according to the cell dimension outcomes.

주파수 선택적 페이딩 채널에서의 다이버시티 수신 터보 등화 및 복호화 (Turbo Equalization and Decoding with Diversity Reception on the Frequency-Selective Fading Channel)

  • 임동민
    • 대한전자공학회:학술대회논문집
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    • 대한전자공학회 1999년도 추계종합학술대회 논문집
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    • pp.39-42
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    • 1999
  • In this paper, a method based on the turbo principle is presented which combines diversity reception, equalization, and channel decoding, to combat the high transmission losses over the frequency-selective fading channel. The simulation results show that with the method presented, the BER performance within 0.3 ㏈ from that on the AWGN channel can be obtained over the frequency-selective fading channel in the investigated scenarios.

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Low Pilot Ratio Channel Estimation for OFDM Systems Based on GCE-BEM

  • Wang, Lidong;Lim, Dong-Min
    • Journal of electromagnetic engineering and science
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    • 제7권4호
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    • pp.195-200
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    • 2007
  • Doubly-selective channel estimator for orthogonal frequency division multiplexing(OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model(GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of the channel destroys the orthogonality between subcarriers, and the resulting channel matrix in the frequency domain is no longer diagonal, but the main interference comes from the near subcarriers. Based on this, we propose a channel estimator with low pilot ratio. We first develop a least-square(LS) estimator under the assumption that only the maximum Doppler frequency and the channel order are known at the receiver, and then verify that the correlation matrix of inter-channel interference(ICI) is a scaled identity matrix based on which we derive an optimal pilot insertion scheme for the LS estimator in the sense of minimum mean square error. The proposed estimator has the advantages of low pilot ratio and robustness against inter-carrier interference.

OFDM 시스템을 위한 낮은 복잡도를 갖는 2-D MMSE 채널 추정 기법 (A Low-Complexity 2-D MMSE Channel Estimation for OFDM Systems)

  • 김정인;장준희;최형진
    • 한국통신학회논문지
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    • 제36권5C호
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    • pp.317-325
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    • 2011
  • OFDM (Orthogonal Frequency Division Multiplexing) 시스템에서 2-D MMSE (2-Dimensional Minimum Mean Square Error) 채널 추정 기법은 주파수/시간 선택적 특성을 가지는 채널에서 우수한 성능을 나타내는 것으로 알려져 있다. 하지만 2-D MMSE 채널 추정 방식은 주파수 축 뿐만 아니라 시간 축 까지 고려하기 때문에 행렬 크기가 커지고, 이로 인해 복잡도가 크게 증가한다는 문제점이 있다. 따라서 본 논문에서는 이러한 문제점을 해결하기 위해 l-D MMSE 채널 추정 구조를 기반으로 가중치 합을 이용하여 기존의 2-D MMSE 채널 추정 방식보다 낮은 복잡도를 갖는 방식을 제안한다. 뿐만 아니라 2-D MMSE 채널 추정을 적용하기 위해 필요한 파라미터인 RMS 지연 확산과 도플러 주파수를 추정하는 기법을 고려한다. 성능 검증 결과 제안하는 방식은 기존의 2-D MMSE 방식에 비해서 복잡도를 크게 줄일 수 있을 뿐만 아니라, 2-D MMSE 채널 추정 방법과 유사한 성능을 나타내는 것을 확인하였다.

직교 주파수 분할 다중화 시스템의 공간 주파수 블록 코딩에서의 부호 반전 채널 스위칭 기법 (Sign Reversal Channel Switching Method for Space-Frequency Block Code in Orthogonal Frequency Division Multiplexing System)

  • 정혁구
    • 한국산업정보학회논문지
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    • 제25권5호
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    • pp.13-21
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    • 2020
  • 이 논문은 직교 주파수 분할 다중화 시스템에 사용하는 공간 주파수 블록 코딩에서의 부호 반전 채널 스위칭 알고리즘을 제안한다. 소스 데이터를 다른 안테나로 보내는 경우에는 수신기는 바뀐 그 채널에 적합하도록 결합 방법을 바꾸어야 한다. 만일 미리 정의된 채널 스위칭 시퀀스를 모르는 수신기라면, 수신한 데이터를 정확하게 복호할 수 없게 된다. 채널 스위칭을 위한 송신 데이터를 바꾸는 경우에는 데이터 심볼들을 공간 주파수 블록 코딩 형식에 맞추어서 바꾸어야 한다. 이 논문에서는 송신 안테나 간의 데이터 심볼들을 바꾸는 것이 아닌 단지 부호 반전 방법을 제안한다. 이 방법을 사용하면 다른 결합 방법을 발생시킴으로써 수신기에서 간단한 암호화로 동작함을 보였다.

Supervised learning and frequency domain averaging-based adaptive channel estimation scheme for filterbank multicarrier with offset quadrature amplitude modulation

  • Singh, Vibhutesh Kumar;Upadhyay, Nidhi;Flanagan, Mark;Cardiff, Barry
    • ETRI Journal
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    • 제43권6호
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    • pp.966-977
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    • 2021
  • Filterbank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is an attractive alternative to the orthogonal frequency division multiplexing (OFDM) modulation technique. In comparison with OFDM, the FBMC-OQAM signal has better spectral confinement and higher spectral efficiency and tolerance to synchronization errors, primarily due to per-subcarrier filtering using a frequency-time localized prototype filter. However, the filtering process introduces intrinsic interference among the symbols and complicates channel estimation (CE). An efficient way to improve the CE in FBMC-OQAM is using a technique known as windowed frequency domain averaging (FDA); however, it requires a priori knowledge of the window length parameter which is set based on the channel's frequency selectivity (FS). As the channel's FS is not fixed and not a priori known, we propose a k-nearest neighbor-based machine learning algorithm to classify the FS and decide on the FDA's window length. A comparative theoretical analysis of the mean-squared error (MSE) is performed to prove the proposed CE scheme's effectiveness, validated through extensive simulations. The adaptive CE scheme is shown to yield a reduction in CE-MSE and improved bit error rates compared with the popular preamble-based CE schemes for FBMC-OQAM, without a priori knowledge of channel's frequency selectivity.

자락요법(刺絡療法)의 문헌적(文獻的) 고찰(考察) (The Literature Study on Venesection therapy)

  • 민부기;;;오민석
    • 혜화의학회지
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    • 제13권2호
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    • pp.277-287
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    • 2004
  • I have come to next conclusions in consequence of documentary study about medical books of many generations regarding venesection therapy. 1. Venesection therapy is much used for five sensory organ disease. Besides that internal disease, pain paralysis disease of muscle and joints, sugical disease, disease of woman and children, fever sunstroke CVA emergency case follow that in the order of frequency of use. 2. It is used for swollen tongue, eye pain, pharyngitis, swelling and pain in the throat, bleeding from the eye ear nose mouth or subcutaneous tissue, tonsillitis, aphthae and so on in the five sensory organ disease. Focus, sosang, jinjin yuye, taiyang, baihui are used for five sensory organ disease in the order of frequency of use. 3. It is used for malaria, headache, precordial pain, head-wind, abdominal colic, diseases characterized by acute diarrhea and vomiting, and so on in the Internal disease. Superficial venules and lymph vessesls, taiyang, quze are used for Internal disease in the order of frequency of use. 4. It is used for low back pain, hypochondriac pain, numbness, knee pain, tinea pedis, red swelling pain of hand and arm, flaccidity-syndrome, and so on in the pain paralysis disease of muscle and joints. Weizhong, superficial venules and lymph vessesls, Ashi point, zhigou are used for pain paralysis disease of muscle and joints in the order of frequency of use. 5. It is used for furuncle, tinea capitis, and so on in the sugical disease. Focus, weizhong are used for sugical disease in the order of frequency of use. 6. It is used for inflammatory disease with redness of skin, and so on in the disease of woman and children. Focus, weizhong, yanglingquan, yaoshu, sanyinjiao are used for disease of woman and children in the order of frequency of use. 7. It is used for fever, CVA, sunstroke, cadaverous coma, common cold, and so on in the fever sunstroke CVA emergency case. Sosang, weizhong, chize are used for fever sunstroke CVA emergency case in the order of frequency of use. 8. The urinary bladder channel of foot-taiyang is most used. Next there are the du channel, the stomach channel of foot-yangming, the lung channel of hand-taiyin, the gall baldder channel of foot-shaoyang, the triple-warmer channel of hand-shaoyang, the large intestine channel of hand-yangming, the spleen channel of foot-taiyin, the kidney channel of foot-shaoyin the pericardium channel of hand-jueyin the liver channel of foot-jueyin, the ren channel, the heart channel of hand-shaoyin, the small intestine channel of hand-taiyang in the order of frequency in use. 9. Superficial venules and lymph vessesls, focus, five shu points, extra-point, back point are used in the venesection therapy, those are characteristic of locating an acupuncture point.

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시스템의 손실을 고려한 AWG의 설계와 다채널 광주파수 안정화 (A Design of AWG Considerig System Loss and Multi-Channel Frequency Stabilization)

  • 이정열;김광복;안상호;엄진섭
    • 전자공학회논문지S
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    • 제35S권7호
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    • pp.6-13
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    • 1998
  • To constoruct a multi-channel system like Optical Frequency Division Multiplexing (OFDM) with the vast amount of transmission capability, a frequency stabilization is essential technique for getting narrower channel spacing and for minimizing fluctuation of oscillation frquency of each channel. This paper proposes a novel multi-channel optical frequency stabilization scheme that uses wavelength crossover properties of a Arrayed Waveguide Grating(AWG). The proposed scheme includes an effective control algorithm that carries out frequency stabilization of all channels through a simple control circuit, simulaneously. And also, a design method of AWG is included which has higher resolutio in consideration of system loss.

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주파수 선택적 페이딩을 갖는 수중 음향 채널에서 COFDM의 성능 (Performance of COFDM in Underwater Acoustic Channel with Frequency Selective Fading)

  • 서철원;박지현;박규칠;윤종락
    • 한국음향학회지
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    • 제32권5호
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    • pp.377-384
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    • 2013
  • 수중 음향 통신 채널에서 주파수 선택적 페이딩에 강한 OFDM(Orthogonal Frequency Division Multiplexing)에 전방오류정정 기법을 적용한 COFDM(Coded OFDM)의 성능을 평가하였다. OFDM은 광대역신호를 협대역 신호로 나누어 전송하는 기법으로 다중경로에 의한 성능저하를 해결하는데 효과적인 전송기법이지만, 특정 부 채널에 깊은 페이딩이 있는 경우에 오류가 증가하여 성능이 저하된다. 이러한 페이딩에 대한 오류를 감소시키기 위해 컨벌루션 코드를 적용한 COFDM을 제안한다. 다중 경로 채널에서 COFDM이 OFDM에 비해 상대적으로 우수한 전송성능을 보였다.

Sparse Channel Estimation of Single Carrier Frequency Division Multiple Access Based on Compressive Sensing

  • Zhong, Yuan-Hong;Huang, Zhi-Yong;Zhu, Bin;Wu, Hua
    • Journal of Information Processing Systems
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    • 제11권3호
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    • pp.342-353
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    • 2015
  • It is widely accepted that single carrier frequency division multiple access (SC-FDMA) is an excellent candidate for broadband wireless systems. Channel estimation is one of the key challenges in SC-FDMA, since accurate channel estimation can significantly improve equalization at the receiver and, consequently, enhance the communication performances. In this paper, we study the application of compressive sensing for sparse channel estimation in a SC-FDMA system. By skillfully designing pilots, their patterns, and taking advantages of the sparsity of the channel impulse response, the proposed system realizes channel estimation at a low cost. Simulation results show that it can achieve significantly improved performance in a frequency selective fading sparse channel with fewer pilots.