• Title/Summary/Keyword: Ofdm Signals

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Decode-and-Forward Cooperative Communication Based on IOTA-OFDM/OQAM System (IOTA-OFDM/OQAM 시스템 기반의 복호 후 전송 협력 통신)

  • Kim, Jaejin;Kim, Dong Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39A no.12
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    • pp.777-779
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    • 2014
  • In this paper, we consider IOTA-OFDM/OQAM system that improves the transmission power and rate efficiency of conventional OFDM system and propose DF relaying cooperative communication scheme based on the IOTA-OFDM/OQAM system. In the proposed scheme, the destination receives orthogonal signals from source and relay simultaneously and combines using MRC. We demonstrated that the proposed schemes get better BER performance than conventional system because of the diversity gain.

A Comparisons of TCM Schemes with OFDM in Mobile Communication Channel (이동통신 채널에서 OFDM을 적용한 TCM방식 비교분석)

  • 박성호;조범준
    • Proceedings of the Korea Multimedia Society Conference
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    • 2003.05b
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    • pp.49-52
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    • 2003
  • OFDM(Orthogonal Frequency Division Multiplexing) scheme can compensate for distortions caused by multipath delay spread and reduce the burst errors caused by the Doppler effect since OFDM signals have long symbol durations. However, OFDM is required to be improved for high speed data transmission and large capacity. Therefore, coding schemes should be combined with OFDM. In this paper, it was studied that the performance of OFDM transmission scheme was improved in mobile communication channel by applying TCM, which has advantages of error correction and bandwidth efficiency. Simulation was carried out for two TCM models with different code efficient length. By mapping two models to square 16QAM, the model with the code efficient length of 2 achieved 3dB better than the other for the BER of 10/sub -3/. In conclusion, if we want to achieve a better performance with TCNA in OFDM applications, we should select a TCM with larger code efficient length.

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Memory Reduction Method of DIT-based IFFT Bit-Reversal (DIT 기반 IFFT의 Bit-Reversal 메모리 감소 기법)

  • Kim, Jun-Ho;Piao, Zheyan;Cho, Kyung-Ju;Chung, Jin-Gyun
    • Journal of the Institute of Electronics and Information Engineers
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    • v.52 no.5
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    • pp.66-73
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    • 2015
  • IFFT is one of the key components in OFDM-based communication systems. In this paper, we propose a new memory efficient IFFT design method for OFDM-based communication systems, based on a mapping of three IFFT input signals which consist of modulated data, pilot and null signals. The proposed method focuses on reducing the memory size in the bit-reversal block which requires the largest number of memory cells in IFFT architectures. To reduce the memory size, we propose a selection mapping method based on decimation-in-time (DIT) algorithm. It is shown that the proposed method achieves a memory reduction of about 50% compared to conventional methods.

Channel Estimation Using Virtual Pilot Signal for MIMO-OFDM Systems (MIMO-OFDM 시스템을 위한 가상 기준 신호를 이용한 채널 추정 기법)

  • Seo, Heejin;Park, Sunho;Kim, Jinhong;Shim, Byonghyo
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.27 no.1
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    • pp.27-32
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    • 2016
  • In this paper, we proposed a soft decision-directed channel estimation based on MMSE estimation for MIMO-OFDM system. While the conventional method employs only pilot signals for channel estimation, the proposed algorithm performs channel estimation using pilot and reliable data signals. We also proposed selection criterion among reliable data signal for channel estimation. From numerical simulations, we show that the proposed channel estimator achieves 1 dB performance gain over conventional channel estimators.

A Novel Signaling Method using Multiple Chirps in UWB Radio (UWB 대역에서 Multiple Chirp 을 이용한 새로운 시그널링 방법)

  • Kim, Yeong-Sam;Yoon, Sang-Hun;Chong, Jong-Wha;Lee, Kyung-Kuk
    • Proceedings of the IEEK Conference
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    • 2006.06a
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    • pp.127-128
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    • 2006
  • In this paper, we propose a novel signaling method using chirp signals in UWB radio with satisfaction of FCC regulation. Chirp signals have been used in many ranging systems such as radar because of its good correlation properties. Because it is important to use broader signal bandwidth in order to get higher precision of the ranging, according to the Cramer-Rao Lower Bound, UWB radio is extremely good as the ranging systems. But, it is very difficult to apply existing chirp signals to UWB, because FCC regulates that the systems operating in UWB radio must occupy signal bandwidth more than 500MHz on the condition of stopping the frequency sweeping. So, we propose multiple chirp signals which can satisfy the regulation of FCC while maintaining chirp signal's properties. The multiple chirp signals which are composed of the sub-chirps modulated by sub-carriers can expand the signal bandwidth with the same principle of OFDM systems. The simulation results show that the BER performance of the proposed multiple chirp signals is identical to that of conventional OFDM when it is applied to data communication, and that the correlation properties of the proposed signals are almost the same with properties as those of single chirp signals whose sweeping bandwidth is the same value with the proposed one.

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An Efficient Scheme to Achieve Differential Unitary Space-Time Modulation on MIMO-OFDM Systems

  • Liu, Shou-Yin;Chong, Jong-Wha
    • ETRI Journal
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    • v.26 no.6
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    • pp.565-574
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    • 2004
  • Differential unitary space-time modulation (DUSTM) has emerged as a promising technique to obtain spatial diversity without intractable channel estimation. This paper presents a study of the application of DUSTM on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with frequency-selective fading channels. From the view of a correlation analysis between subcarriers of OFDM, we obtain the maximum achievable diversity of DUSTM on MIMO-OFDM systems. Moreover, an efficient implementation strategy based on subcarrier reconstruction is proposed, which transmits all the signals of one signal matrix in one OFDM transmission and performs differential processing between two adjacent OFDM blocks. The proposed method is capable of obtaining both spatial and multipath diversity while reducing the effect of time variation of channels to a minimum. The performance improvement is confirmed by simulation results.

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Performance Analysis of PAR Reduction Method using Combined Method in OFDM (OFDM에서 혼합방법을 이용한 PAR 경감법의 성능 해석)

  • 변건식;장은영;김성곤;전제훈
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.7 no.1
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    • pp.42-49
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    • 2003
  • OFDM should be used for the fourth generation communication for high speed communication. Because of high spectral efficiency and high tolerance to fading channel, OFDM is applied to many high speed wire and wireless communication such as DAB (Digital Audio Broadcast), DVB(Digital Video Broadcast), IMT 2000 etc. Inter-modulation, however, is derived from PAR(Peak to Average Power Ratio) of OFDM signals. The paper describes PTS(Partial Transmit Sequence) and SLM(Select Mapping) of an existing methods which can reduce PAR. And then this papers proposed the new method that is called "Combine method". The method proposed in this paper is to combine PTS and SLM. As a result of the simulation, Combine PAR method is better than the existing methods.

Analysis of Nonlinear Distortions OFDM Systems (OFDM 시스템의 비선형 왜곡 분석)

  • 전원기;조용수
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • 1998.06a
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    • pp.165-170
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    • 1998
  • In this paper, the effect of nonlinear distortion, caused by a high-power amplifier (HPA) in an orthogonal frequency division multiplexing (OFDM) system, on the receiver part is analyzed. Since the HPA, which can be modeled by a memoryless Volterra system, distorts OFDM signals in a nonlinear fashion, the received signal at each subchannel includes the multiplicative distortion of 1-st order as well as additive nonlinear distortion of higher-order. The nonlinear distortion can be viewed as a nonlinear interchannel interference (NICI) since it consists of harmonic distortions and intermodulation distortions, produced by other subchannels affecting the subchannel of interest. In this paper, were analytically derive the variance of NICI in terms of average input power using the Volterra model for HPA, and then calculate the bit-error rate (BER) performance of an OFDM system. Also, we propose a simple method to compensate for the phase distortion in OFDM system amplified by HPA, and calculate its BER performance. Validity of the proposed approach is verified by computer simulations for an OFDM system employing 16-QAM constellation input.

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Analysis of Channel Modeling and High Speed Data Transmission Channels for Broadband Power-Line Communication (광대역 전력선통신을 위한 채널모델링과 고속데이터 전송특성분석)

  • Rhee, Young-Chul
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.11 no.10
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    • pp.1821-1827
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    • 2007
  • In this paper, an analytic transfer channel modeling function by impulse signal propagation effects in indoor power-line network are analysed. The modeled channel parameters of power line channel including background noise is applied to the OFDM system and we analysis BER for QPSK and 16-QAM modulation signals with simulation. By the representation of gain for OFDM modulation, we can estimate the characteristic parameters of OFDM in Broadband power line communication.

Improved time and frequency synchronization for dual-polarization OFDM systems

  • Ninahuanca, Jose Luis Hinostroza;Tormena Jr., Osmar;Meloni, Luis Geraldo Pedroso
    • ETRI Journal
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    • v.43 no.6
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    • pp.978-990
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    • 2021
  • This article presents techniques for improved estimation of symbol timing offset (STO) and carrier frequency offset (CFO) for dual-polarization (DP) orthogonal frequency division multiplex (DP-OFDM) systems. Recently, quaternion multiple-input multiple-output OFDM has been proposed for high spectral efficiency communication systems, which can flexibly explore different types of diversities such as space, time, frequency, and polarization. This article focuses on synchronization techniques for DP-OFDM systems using a cyclic prefix, where the application of quaternion algebra leads to new improved estimators. Simulations performed for DP system methods show faster reduction of STO estimator variance with a double-slope line in the logvariance line versus signal-to-noise ratio (SNR) plot compared with singlepolarization (SP) counterparts, and simulations for CFO estimates show a 3-dB gain of DP over SP estimates for same SNR values defined, respectively, for quaternion-valued or complex-valued signals. Cramer-Rao bounds for STO and CFO are derived for the synchronization methods, correlating with the observed gains of DP over SP OFDM systems.