• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.10C
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• pp.1017-1026
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• 2005

In burst OFDM system, the frame synchronization should be performed first for the acquisition of received frame and the estimation of the correct FFT-window position. The conventional frame synchronization algorithms using design features of the preamble symbol, the repetition pattern of the OFDM symbol by pilot sub-carrier allocation rule and Cyclic Prefix(CP), has difficulty in the detection of precise frame timing because its correlation characteristics would increase and decrease gradually. Also, the algorithm based on the correlation between the reference signal and the received signal has performance degradation due to frequency offset. Therefore, we adopt a differential correlation method that is robust to frequency offset and has the clear peak value at the correct frame timing for frame synchronization. However, performance improvement is essential for differential correlation methods, since it usually shows multiple peak values due to the repetition pattern. In this paper, we propose an enhanced frame synchronization algorithm based on the differential correlation method that shows a clear single peak value by using differential correlation between samples of identical repeating pattern. We also introduce a normalization scheme which normalizes the result of differential correlation with signal power to reduce the frame timing error in the high speed mobile channel environments.

• 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.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.57-61
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• 2006

As high speed internet users are tremendously increasing, three are keenly in need of development of high speed portable internet technology which can provide high quality wireless internet service cheaply even in the mobile. Unlike the FDD-CDMA, TDD-OFDMA has relatively poor wave environment with inducing interference, fading and delay because it agrees to multi-carrier modulation method and time-division radio telecommunication system. To solve this problem, it is necessary to develop repeater operating by digital signal processing method which have more strict wireless channel control and wave signal processing technology over TDD telecommunication equipments. This thesis is dealing with design and implementation of Digital RF Repeater which implemented 'Synchronization Acquisition Unit', 'TDD signal switching Unit', 'Feedback Signal Cancellation Unit'. Over this argument, we will develop digital RF repeater with more cheap, more adaptive in wave environment like oscillation control, adaptive wave monitoring and output increasing and having control function as a result it will be helpful for success in high speed portable internet service business.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.10
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• pp.34-41
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• 1998

In this paper, we evaluate synchronization techniques suitable for high-speed ATM satellite communications with a transmission rate of 155Mbit/s, and propose optimal algorithms that improve the tracking performance, where QPSK is selected for a modulation scheme, and the receiver is operated in burst mode. Based on these asumptions, we proposed modified algorithms and architectures for automatic frequency control(AFC), carrier recovery(CR), and symbol timing recovery(STR) for burst acquisition. Analysis is performed under AWGN environments with respect to the number of required symbol, steady-state stability, and hardware implementation for the proposed algorithms.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.307-310
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• 2001

In this paper we describe the design and implementation of uplink receiver for BWLL base station modem. The demodulator consists of digital down converter, matched filter and synchronization circuits. For symbol timing recovery we use Gardner algorithm. And we use forth power method and decision directed method for carrier frequency recovery and phase recovery, respectively. For the sake of performance analysis, we compare simulation results with the board implemented by FPGA which is APEX20KE series chip for Alter. The performance results show it works quite well up to the condition that a frequency offset equal to 4.7% of symbol rate.1

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.725-733
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• 2006

In this paper, we propose an algorithm which makes the frequency of output signal synchronize with frequency of input signal in Equalization Digital On-channel Repeater (EDOCR) system which was proposed to overcome the disadvantage of conventional Digital On-Channel Repeater (DOCR). Also, we verify the algorithm by using the mathematical equivalent model and analysis the performance by implying the algorithm to EDOCR. The main idea is to use the frequency offset information, which comes from carrier recovery in the receiving part of EDOCR, when the demodulated symbol is re-modulated in transmitting part. Based on the proposed algorithm, EDOCR not only makes the output signal synchronized with input signal in frequency but also emit the output signal which satisfies the ATSC transmission standard without additional equipments such as Global Positioning System (GSP).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.630-643
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• 2001

In this paper, the performance of a Multi-Carrier DS-CDMA system with Hybrid $SC/MRC- L_{c}/L$ diversity in the multipath Rayleigh fading environment is analyzed and compared with that of a Wideband DS-CDMA system. Each carriers of the number of the input diversity branches in the Multi-Carrier DS-CDMA system is L and among L, the branches of $L_c$ are chosen to be maximum-ratio-combined. And the diversity outputs are coherent-detected and despread by the correlator of each carrier. As the result, we have known that the structure of the Wideband DS-CDMA system with Hybrid $SC/MRC-L_{c}/L$ diversity reception becomes simple due to no synchronization of bit or phase and in terms of the error performance, the performance of Hybrid $SC/MRC- L_{c}/L$ diversity is better than that of selection diversity, but worse than that of MRC diversity. Moreover, the performance of a Multi-Carrier DS-CDMA system is better than that of a Wideband DS-CDMA system in multipath Rayleigh fading channel since Hybrid $SC/MRC- L_c/L$ diversity can obtain gain from each diversity branch. In case four carriers are used and required BER is $10^{-6}$ in wireless data communication, Hybrid SC/MRC-2/4 diversity can increase more 17 users than Hybrid SC/MRC-2/3 diversity because the better input branches can be selected through increase of input branches.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.468-475
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• 2009

In OFDM-based Full Duplex Relays (FDR) with Decode and Forward (DF) scheme, an interference cancellation technique in the frequency domain is more efficient than the one in the time domain. However, an Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) may occur due to the timing mismatch between the feedback interference signal and the desired signal from Base Station (BS) when the feedback interference cancellation and demodulation are performed in the frequency domain. In this paper, the effects of timing mismatch on the synchronous type and asynchronous type of OFDM-based FDR are analyzed for uplink and downlink cases. Then, synchronization procedure and methods for reducing ISI and ICI in OFDM-based FDR with frequency-domain feedback interference canceller are proposed and verified by computer simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1734-1741
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• 2007

In this paper, the Hybrid SC/MRC-2/4 method in which bit synchronization and phase synchronization were not required was applied to the orthogonal MC DS-CDMA system in which each normalized subcarrier interval and processing gain had the same value, respectively, and the direct sequence spread code of each subcarrier was orthogonal. In the broadband wireless system in which multi-carrier transmission was used, a Doppler frequency shift occurred, which was caused by the difference between the highest subcarrier frequency md the lowest subcarrier frequency. In order to complement phase error caused by the shift, the orthogonal MC DS-CDMA system was analyzed so that the receiving signal could be perfectly synchronized by adjusting the PLL gain suitable for the entire system. As a result of simulations, as the PLL gain was increased, the change in the intervals was close to the case of perfect synchronization however, it became less when the PLL gain reached more than a certain value. Therefore, by selecting a proper PLL gain suitable for the system the orthogonal MC DS-CDMA can be designed in which the Hybrid SC/MRC method is applied.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.109-114
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• 2009

An orthogonal frequency division multiplexing(OFDM) system is effective to bandwidth because of orthogonality of subcarriers and robust to multipath fading. However, if there is a frequency offset, we lose the orthogonality of subcarriers and that results in inter-carrier interference(ICI) which increases errors in the system. In this paper, we propose an algorithm that estimates the fine frequency offset using a correlation method in OFDM systems. This scheme compares two correlation values in different frequency offsets with opposite directions. From the difference between two correlation values we can derive a fine frequency offset estimation algorithm. Its performance is verified by computer simulations.