• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.99-108
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• 1999

In this paper, we propose $\pi$/4 QPSK scheme with block modulation algorithm, which can reduce preamble in order to transmit ATM cell efficiently in the uplink channel of LMDS, and also designed a new carrier recovery circuit which can improve carrier synchronization performance of block demodulation algorithm. The $\pi$/4 QPSK scheme employing the proposed block modulation algorithm achieved efficient frame transmission by making use of a few preamble when carrier synchronization, symbol timing synchronization and slot timing synchronization were performed by burst data of ATM cell in LMDS environment. For performance evaluation of the proposed method, a simulation analyzing the variation of carrier synchronization, symbol timing synchronization and slot timing synchronization using LMDS environment and burst mode condition was executed. In the simulation, the proposed method showed a good performance even though the reduced preamble as a few aspossible when carrier synchronization, symbol timing synchronization and slot timing synchronization is performed.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1042-1046
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• 2011

In this paper, we analyze the STO (Symbol Timing Offset) problem in conventional ZP-OFDM (Zero Padding-Orthogonal Frequency Division Multiplexing) systems and propose a robust ZP-OFDM system with bi-directional overlap-add scheme to overcome the problem. The proposed ZP-OFDM system is able to preserve the orthogonality between subcarriers and reduce the interference from other ZP-OFDM symbols due to the BOA scheme, which exploits both ZP intervals of the previous and the current ZP-OFDM symbols, even though serious STOs result from inaccurate symbol timing synchronization. Simulation results verify that the proposed ZP-OFDM system is superior to the conventional ZP-OFDM system.

• Proceedings of the IEEK Conference
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• summer
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• pp.1-4
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• 2004

We proposed a new type of timing recovery scheme to work with a system that uses BCJR (Bahl-Cocke-Jelinek-Raviv) decoding algorithm and BPSK modulation. The unknown timing offset is estimated by the modified Mueller and $M\ddot{u}ller$ estimator with the aid of the decoder. Timing offset can be acquired as soon as the symbols are received and be updated symbol by symbol. The simulation results for turbo codes whose decoder uses BCJR algorithm show a satisfactory performance even in case of severe timing jitter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.3
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• pp.201-210
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• 1996

In this paper, we analyzed performance of a symbol timing recovery scheme for 16QAM Radio system. As a symbol timing recovery scheme, both maximum amplitude method(MAM) and wave difference method(WDM) are analyzed employing a pulse shaping filter, such as raised cosine filter(RCF) and nonlinear filter(NLF). Simulation result shows that the jitter performance of MAM or WDM using NLF is better than that using square root RCF. In order to estimate and compensate for the Rayleigh fading PSAM(Pilot Symbol Assisted Modulation) and space diversity are also employed. Consequently, BER performance of about $10^{-4}$ is obtained for $E_b/N_o$= 20 dB.

• ETRI Journal
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• v.42 no.3
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• pp.324-332
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• 2020

In this paper, a blind symbol timing offset (STO) estimation method is proposed for offset quadrature phase-shift keying (OQPSK) modulated signals, which also works for other linearly modulated signals (LMS) such as binary-PSK, QPSK, 𝜋/4-QPSK, and minimum-shift keying. There are various methods available for blind STO estimation of LMS; however, none work in the case of OQPSK modulated signals. The popular cyclic correlation method fails to estimate STO for OQPSK signals, as the offset present between the in-phase (I) and quadrature (Q) components causes the cyclic peak to disappear at the symbol rate frequency. In the proposed method, a set of close and approximate offsets is used to compensate the offset between the I and Q components of the received OQPSK signal. The STO in the time domain is represented as a phase in the cyclic frequency domain. The STO is therefore calculated by obtaining the phase of the cyclic peak at the symbol rate frequency. The method is validated through extensive theoretical study, simulation, and testbed implementation. The proposed estimation method exhibits robust performance in the presence of unknown carrier phase offset and frequency offset.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.2 s.344
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• pp.56-65
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• 2006

In this paper, we introduce modified difference type symbol timing detection method of simple structure and show the relations between S/N ratio and timing detection performance which less influenced by multipath channel delay profile and added noise level and it show very exact GI detection performance characteristics. In the computer simulations, 4 symbol time duration of short and long training of IEEE802.11a standard OFDM frame are used for symbol synchronization timing detection. The computer simulation results show the very exact symbol timing detection performance characteristic within 1 sample error of OFDM signal regardless channel delay profile from minimn phase channels of phase rotation ${\pi}/2$ to non-minimum phase channels of phase rotation ${\pi}/2$ of received OFDM signal and added noise level in channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.575-585
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• 2006

In Orthogonal Frequency Division Multiple Access (OFDMA) systems, timing synchronization in uplink is accomplished by an initial uplink synchronization called an initial ranging process. The Base Station's receiver synchronizes the symbol timing to specific user's symbol and the other user's symbols have some Symbol Timing Offset (STO). Linear phase shift is occurred by each user's STO in an OFDMA symbol. The Multiple Access Interference (MAI) caused by the summation of each user's linear phase shift degrades the performance of ranging code detection. In this paper, we propose an initial ranging symbol structure with common ranging code for phase shift estimation and compensation. We car estimate the average of phase shift that is generated by each user's STO and compensate this phase shift by using common ranging code. This scheme will suppress the MAI and provide better detection performance than conventional process.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.5
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• pp.45-53
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• 2007

To recover transmitted signal perfectly at DTV receiver, we have to acquire carrier frequency synchronization to compensate pilot signal which located in wrong position and rotated phase. Also, we need a symbol timing synchronization to compensate sampling timing error. Conventionally, to synchronize symbol timing, we use Gardner's scheme which used in multi-level signal. Gardner's scheme is well known for its sampling the timing error signal from every symbol and it makes easy to detect and keep timing sync in multi-path channel. In this paper, to discuss the problem when the received power level is out of range and we cannot get synchronization information. With this problem, we use 2 step procedures. First, we put a received signal power compensation block before Garder's timing error detector. Second, adaptive loop filter to get a fast synchronization information and averaging loop filter's output value to reduce the amount of jitter after synchronization in PLL(Phased Locked Loop) circuit which is used to get a carrier frequency synchronization and symbol timing synchronization. Using the averaging value, we can estimate offset. Based on offset changing ratio, we can adapt adaptive loop filter to carrier frequency and symbol timing synchronization circuit.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.86-89
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• 1999

In this paper, we propose a new architecture of the fast symbol timing synchronization system which has some shared hardware blocks in order to reduce the hardware complexity. The proposed system consists of received power detector, correlation power detector using shared complex moving adders, and 2-step peak detector. Our system has detected FFT starting point within three Symbols using first two reference symbols of the frame in wireless ATM system. The new architecture was designed and simulated using VHDL. Our proposed architecture also detects a correct symbol timing synchronization within three symbols under a multi-path fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.232-239
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• 2006

In this paper, we analyze the preamble model for Wireless PAN(WPAN) in proposed Ultra WideBand(UWB) Multi-Band OFDM(MB-OFDM) system of IEEE 802.15.3a standard. Besides, we propose effective Carrier Frequency Offset and Symbol Timing Offset Estimation algorithm which offers enhanced performance, and analyze its performance using Detection Probability, False Alarm Probability, Missing Probability, Mean Acquisition Time and MSE(Mean Square Error) through simulation in AWGN and UWB channel environments.