• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.2C
• /
• pp.226-233
• /
• 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.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.6C
• /
• pp.656-663
• /
• 2009

Recently, frequency offset estimation method for orthogonal frequency division multiplexing has been proposed by Ren et al. (REA). The method can estimate an frequency offset independently from training symbol structure. In REA method, however, the detection probability of integer frequency offset is varying according to fractional frequency offset. In this paper, we first analysis REA frequency offset estimation method, and define new detection criteria suitable for the method. Then, we propose efficient integer frequency offset estimation method based on the new detection criteria and maximum likelihood method. The proposed method still has the advantages of REA method, while overcome the drawback. The numerical results demonstrate that the proposed methods outperform the REA method, in terms of integer frequency offset detection probability.

• Proceedings of the IEEK Conference
• /
• 2006.06a
• /
• pp.125-126
• /
• 2006

본 논문에서는 주파수 오차가 큰 IEEE 802.15.4 시스템에서의 프레임 동기 및 주파수 추정기법을 제안한다. 주파수 오차의 영향을 제거하기 위해 coherent 방식이 아닌 non-coherent 방식의 프레임 동기가 요구된다. 차등 신호와 절대값을 이용하여 주파수 옵셋의 영향을 완벽히 제거한 프레임 동기를 제안하였다. 그리고 주파수 옵셋 추정의 분산을 줄이기 위한 over-sampling 주기의 주파수 옵셋 검출 기법을 제안하였다.

• Proceedings of the KIPE Conference
• /
• 2011.11a
• /
• pp.211-212
• /
• 2011

본 논문은 전기자동차용 배터리 충전기를 위한 전류옵셋 보상기법을 제안한다. 인버터 내부의 스위치의 성능차이 또는 내부 회로의 문제로 인해 입력전류에 옵셋이 발생하게 되면 배터리 충전기와 연결된 직류단 전압에 선 주파수에 해당하는 리플성분이 발생할 수 있다. 이러한 직류단 리플은 배터리 충전 시출력전압의 리플이 되어 배터리의 수명과 성능에 악영향을 끼친다. 제안하는 전류옵셋 보상기법은 추가적인 수동소자나 센서의 추가 없이 입력전류 옵셋을 효과적으로 제어한다. 50kW 급의 전기자동차용 배터리 충전기모델을 이용한 시뮬레이션 결과는 제안하는 보상기법의 타당성과 안정성을 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.6C
• /
• pp.623-628
• /
• 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.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.10A
• /
• pp.992-1003
• /
• 2007

In this paper, a channel estimation technique based on pilot tones, which does not degrade channel estimation performance even with the existence of symbol timing offset (STO) in OFDM systems, is proposed. The proposed technique performs channel estimation by interpolating channels with respect to amplitude and phase with a minimum computational complexity, differently from the conventional interpolation techniques. The proposed technique requires neither the estimation of fine STO in advance nor trigonometric operation for phase interpolation, signifying a significant reduction in computational complexity. Since the performance of the proposed technique does not depend on the STO present in OFDM systems. It can be directly applied to the following areas in OFDM-based communication system: elimination of fine STO estimation step in the synchronization procedure, elimination of STO estimation step in multiuser uplink, and channel estimation in multi-hop relay system. It is verified by computer simulation that the proposed technique can improve the performance of channel estimation significantly in the presence of STOs, compared with previous channel estimation techniques based on pilot tones.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.6C
• /
• pp.554-561
• /
• 2010

This paper proposes an integer frequency offset estimation scheme robust to timing offset for the orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems. The proposed scheme exploits a feature that a sample distance between a continual pilot and a scattered pilot nearest to it in an OFDM symbol belongs to one of predetermined distances. First after calculating a correlation value of every continual pilot and its nearest scattered pilot. Then, it is divided into several groups according to the sample distances. Since correlation values with the same sample distance undergo the same effect of the timing offset, the effect of the timing offset can be removed by re-correlating these correlation values. From the simulation results we can confirm that the proposed algorithm estimates the integer frequency offset with the robustness to the timing offset when compared to a conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.5C
• /
• pp.548-554
• /
• 2009

OFDM systems are very sensitive to the frequency offset. Therefore, frequency offset estimation is one of the most important procedures in OFDM systems. Ren's periodogram-based frequency offset estimation scheme consists of three steps which estimates the frequency offset accurately. However, there are the drawbacks of the limited frequency offset estimation ranges in the second and third estimation steps of the Ren's scheme. This ranges are insufficient compared with the overall signal bandwidth, making the high complexity of the first estimation step. In this paper, we propose a novel lower complexity frequency offset estimation scheme for OFDM systems which extends the frequency offset estimation range. The simulation results show that the proposed scheme has a wider frequency offset estimation range and lower complexity than those of the Ren's scheme.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.6A
• /
• pp.592-598
• /
• 2008

In this paper, a novel pilot-aided integer frequency offset estimation scheme is proposed for orthogonal Sequency division multiplexing (OFDM)-based digital video broadcasting (DVB) systems. The conventional pilot-aided integer frequency offset estimation scheme proposed for OFDM-based DVB systems exploits the partial information of combinations provided by pilots. Thus, in this paper, we propose a novel integer frequency offset estimation scheme exploiting all information of pilot combinations. To compare the performance of the proposed scheme with that of the conventional scheme, we conduct a simulation in additive white Gaussian noise (AWGN) and multipath Rayleigh channels, which shows that the proposed scheme outperforms the conventional scheme in terms of the probability of integer frequency offset estimation failure.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.11A
• /
• pp.1004-1011
• /
• 2005

In OFDM (Orthogonal Frequency Division Multiplexing) system, sampling frequency offset causes performance degradation due to increase of ICI. Sampling frequency offset can be generally estimated by correlation of the pilot signal or the known pattern within two contiguous OFDM symbol however, this method has the throughput degradation and the difficulty in applying to various OFDM systems. In this paper, we propose a new algorithm for sampling frequency offset estimation which can solve aforementioned issues. The proposed algorithm uses a single OFDM symbol to prevent throughput degradation and to apply to various OFDM-based communication systems flexibly Also, the proposed algorithm can enhance reliability by observing more number of correlations compared to the established algorithm in frequency domain. Extensive computer simulation shows that the proposed algorithm can improve the system performance in various channel conditions.