• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.49-56
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• 2010

In this paper, a low-power frequency offset synchronization structure using CORDIC algorithm is proposed. Main blocks of frequency offset synchronization are estimation and compensation block. In the proposed frequency offset estimation block, implementation area is reduced by using sequential CORDIC, and throughput is accelerated by using 2 step CORDIC. In the proposed frequency offset compensation block, pipeline CORDIC is utilized for area reduction and high speed processing. Through MatLab simulation, function for proposed structure is verified. Proposed frequency offset synchronization structure is implemented by Verilog-HDL coding and implementation area is estimated by Synopsys logic synthesis tool.

• ETRI Journal
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• v.35 no.5
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• pp.739-747
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• 2013

This paper investigates the multifarious nature of the long-term evolution (LTE) scheme and that of the modified LTE scheme for symbol timing synchronization (STS). This investigation allows us to propose a new replica correlation-based STS scheme to overcome the inherent weaknesses of the other two schemes. The proposed STS signal combines a gold sequence and a half sine wave in the time domain, whereas conventional STS signals specify either binary sequences or complex sequences in the time domain or in the frequency domain. In the proposed scheme, a sufficient correlation property is realized by the gold sequence, and robustness against the frequency offset (FO) is achieved through the sine wave. Compared to the existing LTE-related schemes, the proposed scheme can better achieve immunity to FO and reduction in detector complexity, as well as a low peak-to-average power ratio and a low detection error rate. Performance evaluations through analysis and simulation are provided in the paper to demonstrate these attributes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.516-522
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• 2010

In this paper, the carrier frequency offset estimator is proposed for the China multimedia mobile broadcasting (CMMB). The fractional carrier frequency offset is estimated by utilizing the cyclic prefix in each CMMB symbol. In addition, the integer carrier frequency offset can be estimated with the synchronization signal in every CMMB frame. The proposed estimator is the most suitable for the frame structure of CMMB. It shows a prominent performance even in timing offset and multipath conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1795-1805
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• 1999

In an OFDM (Orthogonal Frequency-Division Multiplexing) system, the sampling frequency offset between the transmitter and receiver is known to cause the interchannel interference (ICI), resulting in performance degradation. In this paper, we propose two time-domain techniques to estimate the sampling frequency offset, especially for a high data-rate OFDM system. The first technique estimates the sampling frequency offset by using the phase difference between two received samples with a fixed amount of time interval, corresponding to the transmitted training symbol, under the assumption of perfect symbol and carrier offset synchronization. The second technique estimates the sampling frequency offset and carrier frequency offset jointly, when the two offsets exist together, by using two training symbols with different frequency components and using a sample algebraic calculation. The proposed estimation techniques for sampling frequency offset cause no time delay due to all time-domain processing, and have a good performance due to no ICI effect. The performances of the proposed techniques are demonstrated by various simulations.

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

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.7
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• pp.30-38
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• 2012

This paper presents packet detection, frequency offset estimation architecture and performance analysis for OFDM-based wireless personal area network (WPAN) systems. Packet detection structure is used to find the start point of a packet exactly in WPAN system as the correlation value passes the constant threshold value. The applied autocorrelation structure of the algorithm can be implemented simply compared to conventional packet detection algorithms. The proposed frequency offset estimation architecture is designed for phase rotation process structure, internal bit reduction to reduce hardware size and the frequency offset adjustment block to reduce look-up table size unlike the conventional structure. If the received signal can be compensated by estimated frequency offset through the correction block, it can reduce the impact on the frequency offset. Through the performance result, the proposed structure has lower hardware complexity and gate count compared to the conventional structure. Thus, the proposed structure for OFDM-based WPAN systems can be applied to the initial synchronization process and high-speed low-power WPAN chips.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.4
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• pp.424-432
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• 2016

World's leading countries are developing next generation digital broadcasting system specifications to support UHDTV (ultra-high definition television) contents and other various services. In order to maximize the transmission capacity by using the bandwidth efficiently, most broadcasting systems adopt MIMO-OFDM. In distributed-MIMO systems, multiple transmit antennas are spatially separated and therefore result in multiple timing offsets. To overcome this problem, this paper proposes a technique using a null symbol to detect each individual signal from distributed transmit antennas. By inserting null symbols before preambles, the receiver can distinguish the signals between each transmit antennas and perform frame synchronization. When the reception time difference is shorter than 500 samples, the proposed method outperforms the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.10C
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• pp.965-975
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• 2005

In this paper, we propose and evaluate joint carrier and sampling frequency offset estimation schemes based on the channel estimation sequences in PLCP (Physical Layer Convergence Procedure) preamble for the proper and effcient synchronization of the MB-OFDM WB (Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band) systems which have recently drawn explosive attention for future W-PAN (Wireless Personal Area Network) applications. In the joint estimation schemes, we first estimate the sampling frequency offset, and then estimate the carrier frequency offset using the estimated sampling frequency offset. Moreover, to improve the reliability of the estimated offset values, each process uses a combination scheme based on weighting factors. Simulation results using IEEE 802.15 Task Group 3a UWB channel models reveal that the estimation scheme using the simple weighting factors based on easily-measurable received signal power of each sub-channel shows favorably comparable performance to the ideal scheme using the weighting factors based on the perfectly-estimated frequency response of the channel.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.281-282
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• 2010

CMMB(China Multimedia Mobile Broadcasting)는 중국에서 개발된 이동 방송 시스템이다. CMMB는 시간 동기와 주파수 동기를 획득하기 위해 프레임에 포함된 두 개의 동기 신호와 OFDM 심볼을 이용한다. 이는 OFDM 심볼의 연속파일럿과 분산 파일럿을 이용하는 기존의 이동 방송시스템과 달리 CMMB를 위한 특화된 동기 알고리듬이 필요하다. 이에 본 논문은 CMMB의 프레임 구조에 적합한 시간 동기 알고리듬에 대하여 연구하였다. 제안 알고리듬은 CMMB의 동기신호를 이용하여 상관값을 구한 후 1차와 2차로 나누어 경계값을 초과 하는 값을 검색하여 프레임의 시작점으로 추정한다. 제안된 알고리듬은 컴퓨터 시뮬레이션으로 검증하였으며 다중 경로 상황에서도 우수한 성능을 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.4A
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• pp.247-255
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• 2003

In this paper, an $tan^{-1}$ circuit for the frequency synchronization of OFDM based IEEE 802.11a is presented. The proposed circuit consists of a divider, an $tan^{-1}$ ROM and a phase detector, which can detect frequency offset within 0.0491 rad. The circuit implemented with FPGA shows a pull-in range of under ${\pm}625KHz$ at 5dB AWGN. It may be useful for IEEE 802.11a WLAN standard.