• Title/Summary/Keyword: Frequency-selective Fading Channel

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Aeronautical Telemetry Link Development for High Speed Data Transmission (고속 자료전송을 위한 비행체용 원격측정링크 개발)

  • Lee, Sangbum;Choi, Seoungduck;Kim, Whanwoo
    • Journal of the Institute of Electronics and Information Engineers
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    • v.50 no.7
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    • pp.43-51
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    • 2013
  • This paper describes the development of the telemetry link system for the high data rate transmission in high speed rocket application. In consideration of bandwidth efficiency, frequency selective fading and doppler frequency offset, we used DQPSK instead of PCM/FM which has been the primary modulation format in aeronautical telemetry. Also we used the spatial diversity with multiple receiving antennas to mitigate multipath interference which is the dominant channel impairment and the Turbo Product Code for Forward Error Correction to improve bit error rate performance.

Synchronization for Wireless LAN System Using OFDM Technique (OFDM 방식을 이용한 무선 LAN 시스템의 동기)

  • Yun, Kyung-Seok;Choi, Seung-Kuk
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.27 no.1B
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    • pp.79-89
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    • 2002
  • A synchronization method is presented for IEEE 802.11a wireless OFDM system. First the coarse symbol synchronization is achieved by measuring the moving power average of the received envelope signal. The detection probabilities and optimum thresholds for the symbol synchronization are derived. By measuring the correlation between the short training signal and received envelope signal, fine symbol synchronization can be acquired. And the frequency synchronization is achieved using long training signal. A symbol synchronization error causes a phase rotation of the constellation. After the compensation for fading channel, the rotation due to the symbol timing error can be corrected. With this method, synchronization can be well achieved over frequency selective channels.

An Efficient Power Allocation Algorithm in OFDM-based Wireless Sensor Networks using Reserve Power (OFDM 기반 무선 센서 네트워크에서의 Reserve Power를 이용한 효율적인 파워 할당 알고리즘)

  • Kim, Byung-Ho;Oh, Seoung-Youl;Kim, Chee-Ha
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.12B
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    • pp.1251-1258
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    • 2010
  • Orthogonal Frequency Division Multiplexing (OFDM) has been investigated as promising technology for future broadband communication. In this paper, we propose a power allocation algorithm for a frequency selective fading channel. However, many investigated algorithms that perform high computation overhead are not appropriate for sensor network systems due to hardware limitations. The proposed algorithm significantly reduces computational overhead and satisfies the power budget. Throughput of the algorithm is comparable to the optimum solution. Simulation results support the claim stated.

Performance evaluation of diversity reception of underwater acoustic code division multiple access using lake experiment (저수지 실험을 통한 수중 음향 코드 분할 다중 접속 방식의 다이버시티 수신 성능 검증)

  • Seo, Bo-Min;Cho, Ho-Shin
    • The Journal of the Acoustical Society of Korea
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    • v.36 no.1
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    • pp.39-48
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    • 2017
  • CDMA (Code Division Multiple Access) is promising medium access control schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design diversity schemes of underwater CDMA transceiver for the forward and reverse links. User data are multiplexed by Walsh code and a pseudo random noise code acquisition process is added for phase error correction before decoding the user data at the receiver. Then, the diversity reception using equal gain combining and maximal ratio combining is performed in order to minimize performance degradation caused by rich multipath fading of underwater acoustic channel. We evaluated the performance of diversity transceiver through lake experiment, which was performed at Lake Kyungcheon, Mungyeong city using two transmitters and two receivers placed 460 m apart at an average depth of 40 m. The lake experiment results show that user data are recovered with error-free in both of the forward and reverse links.

Performance Evaluation of Channel Shortening Time Domain Equalizer in Wireless LAN Environment (무선랜 환경에서 채널 단축 시간영역 등화기의 성능평가)

  • Yoon Seok-Hyun;Yu Hee-Jung;Lee Il-Gu;Jeon Tae-Hyun;Lee Sok-Kyu
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.3A
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    • pp.240-248
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    • 2006
  • In this paper, we consider an OFDM receiver algorithm design for IEEE 802.11a/p system, which targeting large coverage area while keeping the transmission format unchanged. Particularly, taking into account the inter-symbol interference(ISI) and inter-carrier interference(ICI) that can be induced with large RMS delay spread, we employ channel shortening time-domain equalizer(TEQ) and evaluate the receiver performance in terms of SINR and packet error rate(PER). The preamble defined in IEEE802.11a/p is used to estimated the initial equalizer tap coefficients. Primary purpose of the paper is to give an answer to the question, though partially, whether or not 16-QAM constellation can be used in none line of sight environment at the boundary of a large coverage area. To this end, we first analyze the required TEQ parameters for the target channel environment and then perform simulation for PER performance evaluation in a generic frequency selective fading channel with exponential power-delay profile.

Phase Tracking for Orthogonal Frequency Division Multiplexing Systems (직교 주파수 분할 다중화 시스템을 위한 위상 오차 추적)

  • Jeon, Tae-Hyun
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.43 no.12 s.354
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    • pp.61-67
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    • 2006
  • This paper proposes the algorithm for tracking of the residual phase errors incurred by carrier frequency offset and sampling frequency offset in the orthogonal frequency division multiplexing (OFDM) systems which are suitable for high data rate wireless communications. In the OFDM systems the subcarriers which are orthogonal to each other are modulated by digital data and transmitted simultaneously. The carrier frequency offset causes degradation of signal to noise ratio(SNR) performance and interference between the adjacent subcarriers. The errors in the sampling timing caused by the sampling frequency difference between the transmitter and the receiver sides also cause a major performance degradation in the OFDM systems. The residual error tracking and compensation mechanism is essential in the OFDM system since the carrier and the sampling frequency offset cause the loss of orthogonality resulting in the system performance loss. This paper proposes the scheme where the channel gain and the payload data information are reflected in the residual error tracking process which results in the reduction of the estimation error and the tracking performance improvements under the frequency selective fading wireless channels.

PAPR Reduction Method Using SLM-based WHT and DSI (SLM 기반 Walsh Hadamard 변환 및 DSI 기법을 이용한 PAPR 저감 기법)

  • Kim Sang-Woo;Kim Namil;Ryu Heung-Gyoon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.16 no.11 s.102
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    • pp.1147-1154
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    • 2005
  • In this paper, we propose some PAPR(Peak to Average Power Ratio) reduction methods using WHT(Walsh Hadamard Transform) to reduce high PAPR generated in OFDM system because of multi carrier modulation. These proposed methods are the methods which has additional PAPR reduction performance without a loss of bandwidth efficiency and a large increment of calculation complexity than common PAPR reduction methods by combining the WHT with some common methods. In this paper, we propose two PAPR reduction methods made by combining a SLM(Selective Mapping) and DSI(Dummy Sequence Insertion) with a WHT. From simulation result, we can find that the PAPR reduction methods using a WHT can get about 1 dB additional PAPR reduction performance than common PAPR reduction methods; they are SLM and DSI. And, because our proposed methods have not only PAPR reduction effect, but also frequency diversity effect, more stabile data transmission is possible in nonlinear HPA and multipath fading channel.

저압 전력선 채널 특성을 고려한 OFDM변조 전송

  • Kang Duk-Ha;Heo Yoon-Seok;Cho Ki-Hyung;Lee Dae-Young
    • The Journal of Information Technology
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    • v.6 no.2
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    • pp.1-8
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    • 2003
  • This paper is about power line communication(PLC) over the low power voltage grid. The main advantage with power line communication is the use of an existing infrastructure. The PLC channel can be modeled as having multi-path propagation with frequency-selective fading, typical power lines exhibit signal attenuation increasing with length and frequency. OFDM(Orthogonal Frequency Division Multiplexing) is a modulation technique where multiple low data rate carriers are combined by a transmitter to form a composite high data rate transmission. To implement the multiple carrier scheme using a bank of parallel modulators would not be very efficient in analog hardware. Each carrier in an OFDM is a sinusoid with a frequency that is an integer multiple of a base or fundamental sinusoid frequency. Therefore, each carrier is a like a Fourier series component of the composite signal. In fact, it will be shown later that an OFDM signal is created in the frequency domain, and then transformed into the time domain via the Discrete Fourier Transform(DFT).

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Performance analysis of OFDM and CDMA communication methods in underwater acoustic channel (수중 채널 환경에서 OFDM 및 CDMA 통신 방식별 성능 분석)

  • Kim, Kil-Yong;Kim, Min-Sang;Ko, Hak-Lim;Im, Tae-Ho
    • The Journal of the Acoustical Society of Korea
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    • v.38 no.1
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    • pp.30-38
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    • 2019
  • In recent years, researches on various communication methods have been conducted, particularly on OFDM (Orthogonal Frequency Division Multiplexing) and CDMA (Code Division Multiple Access) methods, as the use of underwater communication increases. While OFDM is, in general, advantageous in that it is resistant to Doppler in the water and it enables a high-speed communication, CDMA is resistant to frequency selective fading in the water and it can reduce energy consumption. Therefore, in this paper, we performed experiments in the shallow water in Western Sea of Korea to analyze the performance of OFDM and CDMA communication systems in the underwater channel environment. The maximum delay spread and Doppler spread were drawn by using the data obtained from the real sea area in order to analyze the underwater channel environment characteristics of the shallow water in Western Sea of Korea. The communication performances of OFDM and CDMA are shown as coded BER (Bit Error Rate) according to the variation of the maximum delay spread and the Doppler spread, respectively. The result of the analysis show that the OFDM method has more resistant performances to the underwater channel environment changes than the CDMA method.

Performance Evaluation of Underwater Code Division Multiple Access Scheme on Forward-Link through Water-Tank and Lake Experiment (수조 및 저수지 실험을 통한 수중 코드 분할 다중 접속 기법 순방향 링크 성능 분석)

  • Seo, Bo-Min;Son, Kweon;Cho, Ho-Shin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39C no.2
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    • pp.199-208
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    • 2014
  • Code division multiple access (CDMA) is one of the promising medium access control (MAC) schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. As a way of performance evaluation, sea or lake experiment has been employed along with computer simulation.. In this study, we design the underwater CDMA forward-link transceiver and evaluate the feasibility aginst harsh underwater acoustic channel in water-tank first. Then, based on the water-tank experiment results, we improved the transceiver and showed the improvements in a lake experiment. A pseudo random noise code acquisition process is added for phase error correction before decoding the user data by means of a Walsh code in the receiver. Interleaving and convolutional channel coding scheme are also used for performance improvement. Experimental results show that the multiplexed data is recovered by means of demultiplexing at receivers with error-free in case of two users while with less than 15% bit error rate in case of three and four users.