• Title, Summary, Keyword: frequency offset

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A Study on Efficient Frequency Offset Compensation Method for OFDM based WiBro Systems (OFDM 기반의 WiBro 시스템에서 효과적인 주파수 오프셋 보상 기법에 관한 연구)

  • Kim, Eun-Cheol;Ha, Kwang-Jun;Park, Jae-Sung;Kim, Jin-Young
    • 한국정보통신설비학회:학술대회논문집
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    • pp.437-440
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    • 2008
  • In this paper, we present and analyze a robust frequency offset estimation scheme for orthogonal frequency division multiplexing (OFDM) systems over radio communication channels. When there exists frequency offset, the loss of orthogonality occurs and the interference problem among several subcarriers in OFDM signals is introduced. The guard interval of OFDM signals is employed for estimating the frequency offset. Furthermore, in order to enhance the frequency offset estimation performance, a ternary sequence is utilized. A frequency offset is estimated based on the synchronized correlator output. The proposed frequency offset estimation scheme can be applied to track the carrier frequency offset of OFDM systems.

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A robust frequency offset estimation scheme for an OFDM system (OFDM 수신기를 위한 강인한 주파수 옵셋 보정 기법)

  • Wui, Jung-Hwa;Hwang, Hu-Mor;Song, Jin-Ho
    • Proceedings of the KIEE Conference
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    • pp.3100-3102
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    • 2000
  • In this paper, we propose to a robust frequency offset estimation method of OFDM signals. A carrier frequency offset may be decomposed into an integer multiple of the subcarrier spacing and a residual frequency offset. Fractional part of frequency offset is obtained by using the maximum likelihood estimation(MLE) method. And we use the correlation of the samples at the output of the discrete Fourier transform(DFT) to estimate integer part of frequency offset. The result shows that the estimation frequency offset is almost linear to frequency offset. We propose to an improved estimation error variance of the carrier frequency offset estimation. The proposed estimator has better performance than the conventional ones in terms of error variance and tracking range.

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Integer Frequency Offset Estimation of OFDM Systems

  • Yoon, Dae-Gung;Han, Dong-Seog
    • Proceedings of the Korea Society of Information Technology Applications Conference
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    • pp.255-258
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    • 2005
  • A blind-mode integer frequency offset estimation algorithm is proposed for an OFDM system. Imperfect integer frequency offset estimation causes ambiguity in the data sub-carrier position. Morelli's blind integer frequency offiet estimation algorithm exploits the likelihood function by comparing the power in sub-carriers. It, however, shows performance degradation when there is the fractional frequency offset. The proposed algorithm solves this by using interpolation in the frequency domain. In this algorithm, it is exploited that the effect of the frequency offset is shown as a shift of power spectrum. By calculating the covariance of over-sampled samples, most approximate samples to integer point are obtained. It enables integer frequency offset estimation less affected by fractional frequency offset.

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Joint Phase and Frequency Offset Estimator for Short Burst MPSK Transmission with Preamble

  • Kim Seung-Geun;Lim Young-Kon
    • The Journal of the Acoustical Society of Korea
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    • v.24 no.4E
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    • pp.152-157
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    • 2005
  • In this paper, a new data-aided joint phase and frequency estimator, which has very low computational complexity, is proposed and its variances of phase and frequency estimates are derived. To estimate the phase and frequency offset, first of all, the overall observation interval is divided into same length sub-intervals, and then phase estimates are independently computed based on symbols of the each sub-intervals. To be continue the sequence of computed phase estimates, proper integer multiples of $2{\pi}$ are added to (or subtracted from) the computed phase estimates, which is called linearized phase estimate. The phase offset of the proposed joint estimator is estimated by averaging the linearized phase estimates and the frequency offset by averaging the differences between consecutive linearized phase estimates. The variance of the proposed phase offset estimate is same to MCRB of phase if there is no frequency offset, but it is smaller than MCRB of phase if there is frequency offset. However, the variance of the proposed frequency offset estimate is bigger by at least 0.5 dB than MCRB of frequency with the same observation interval.

Performance Analysis of Digital M/W Transmission System adopting Frequency Offset Compensation Algorithm in Multipath Fading Channel (다중경로 페이딩 채널에서 주파수 옵셋 보상 알고리즘을 적용한 디지털 M/W 전송 시스템의 성능 분석)

  • Park, Ki-Sik
    • Journal of the Korea Society of Computer and Information
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    • v.18 no.10
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    • pp.63-70
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    • 2013
  • In this paper, we investigated frequency synchronization through computer simulation of digital M/W transmission system in multipath fading channel. we suggested frequency offset correction algorithm against frequency offset between transmitter and receiver, then evaluated the degree of constellation performance enhancement. From the performance evaluation, in case of large frequency offset, although adopting frequency offset correction scheme, residual frequency offset degraded system performance. As a result, according to frequency offset value between transmitter and receiver residual frequency offset affects system performance significantly. The results of this paper should be utilized for frequency synchronization criterion when frequency band of broadcasting system is rearranged.

A Novel OFDM frequency Offset Estimation Algorithm Using a Periodogram (주기도표를 이용한 새로운 OFDM 주파수 옵셋 추정 알고리즘)

  • Ahn, Sang-Ho;Song, Chong-Han;Lee, Myung-Soo;Lee, Seong-Ro;Jung, Min-A;Choi, Myeong-Soo;Lee, Jin-Seok;Yoon, Seok-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.2C
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    • pp.226-233
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    • 2009
  • A novel frequency offset estimation scheme using a periodogram is proposed for orthogonal frequency division multiplexing (OfDM) systems. A conventional scheme proposed by Ren has a problem that the fractional and residual frequency offset estimation steps do not compensate for the difference between the real frequency offset and estimated integer frequency offset in the noise channel. So, the frequency offset estimation performance of Ren's scheme is degraded. In this paper, a frequency offset estimation scheme is proposed, which has a larger estimation range than that of the factional and residual frequency offset estimation steps in Ren's scheme. The proposed scheme can compensate for the difference between the real frequency offset and estimated integer frequency offset, unlike Ren's scheme. From the simulation results, we can observe that the performance of the proposed scheme is better than that of Ren's scheme.

A frequency offset correction technique for coherent OFDM receiver on the frequency-selective fading channel (주파수 선택성 페이딩 채널에서 동기식 OFDM 수신기를 위한 주파수 옵셋 보정 기법)

  • 오지성;정영모;이상욱
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.21 no.4
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    • pp.972-983
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    • 1996
  • This paper proposes a new technique for frequency offset correction for OFDM systems on a frequency selective fading channel. Frequency offset in OFDM introduces interchannel interference among the multiple subcarriers of OFDM signal. To compensate the interference, this paper describes an algorithm with two stages:acquisition and tracking. At both stages, the proposed algorithm oversamples the received OFDM signal to obtain a couple of demodulated symbol sets. At acquisition stage the frequency offset is reduced to half or less of the intercarrier spacings by matching the sign pattern of each element of the sets. Next, at tracking stage the frequency offset is corrected with a frequency detector which is controlled by the correlation of the two sets. It is shown that the proposed algorithm can correct the frequency offset in the event of uncertainty in the initial offset that exceeds one half of the intercarrier spacing. In addition, the proposed algorithm is robust to transmitted symbols and channel characteristics by using oversampled symbol sets.

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Performance Analysis of Synchronous Downlink MC-CDMA with Precoding and Frequency Offset

  • Jang, Won-Mee;Lee, Moon-Woo
    • Journal of Communications and Networks
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    • v.9 no.2
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    • pp.192-197
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    • 2007
  • We analyze the performance of code division multiple access (CDMA) system with multicarrier (MC) that employs precoding in synchronous downlink channels. Even though considerable efforts are undergoing for frequency offset estimation and correction, it is inevitable for the system to bear the remaining frequency offset. Therefore it is important to predict accurately the system performance in the presence of the residual frequency offset. We obtain the bit error rate (BER) performance in terms of the number of users, the spreading factor, the number of sub-carriers, and frequency offset. We assume that the spreading factor is equal to the number of sub-carriers, although we can generalize the case. The simulation results show that the BER of MC-CDMA with precoding shows a performance that varies with frequency offset as well as system loading.

A Novel OFDM Integer Frequency Offset Estimation Scheme Using Differential Combining (차동 결합을 이용한 새로운 OFDM 정수 주차수 옵셋 추정 기법)

  • Ahn, Sang-Ho;Chong, Da-Hae;Han, Tae-Hee;Kim, Sang-Hyo;Yoon, Seok-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.8C
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    • pp.627-632
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    • 2008
  • The timing offset is one of the main error sources in estimating the frequency offset in orthogonal frequency division multiplexing (OFDM) systems. Although some works have been done to mitigate the influence of the timing offset on the frequency offset estimation, most of the investigations require the knowledge of the timing offset range, which is not generally available in practical systems. In this paper, we propose a new frequency offset estimation scheme using differential combining between two successive correlation samples, which does not require the knowledge of the timing offset range, and thus, is robust to the timing offset variation. The simulation results show that the proposed scheme is not only robust to the timing offset variation, but also generally performs better than the conventional scheme on the average, in the case of the timing offset range being not known exactly.

An OFDM Frequency Offset Estimation Scheme Robust to Timing Error (시간 오차에 강인한 OFDM 주파수 옵셋 추정 기법)

  • Kim Sang-Hun;Yoon Seok-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.6C
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    • pp.623-628
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    • 2006
  • This paper addresses the frequency offset estimation problem in the presence of the timing error for OFDM systems. When the timing error exists, the correlation value used for the frequency offset estimation could be reduced significantly due to the timing error, resulting in considerable degradation in estimation performance. In this paper, using the coherence phase bandwidth (CPB) and a threshold, a novel frequency offset estimation scheme is proposed and based on which, an efficient timing error estimation scheme is also proposed for the re-estimation of the frequency offset. The performance comparison results show that the proposed frequency offset estimation scheme is not only more robust to the timing error but also has less computational complexity, as compared with the conventional schemes. It is also demonstrated by simulation that theproposed timing error estimation scheme gives a reliable estimate of the timing error.