Browsing by Author "Chin, Wen-Long"

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A Blind Maximum-SINR Synchronization Technique for OFDM Systems
(2008)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work presents a blind synchronizer for orthogonal frequency-division multiplexing (OFDM) systems based on signal-to-interference-and-noise-ratio (SINR) maximization. Due to the incurred losses from inter-symbol interference (ISI) and inter-carrier interference (ICI) introduced by synchronization errors, the SINR of the received data drops drastically. By taking advantage of this characteristic, both the symbol time and carrier frequency offsets are intuitively estimated by maximizing the SINR metric. For the SINR metric, we propose a blind SINR estimation, which does not need prior knowledge of the channel profiles and transmitted data. As such, the proposed maximum-SINR (MSINR) synchronization algorithm is non-data-aided (NDA) so that the transmission efficiency can be improved. Moreover, to reduce the computational complexity, the early-late gate (ELG) technique is proposed for the implementation of the synchronizer. Simulation results exhibit better performance for the MSINR algorithm than conventional techniques in multipath fading channels.
A Blind Synchronizer for OFDM Systems Based on SINR Maximization in Multipath Fading Channels
(2009-02-01)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper presents a blind synchronizer for orthogonal frequency-division multiplexing (OFDM) systems based on signal-to-interference-and-noise ratio (SINR) maximization. Due to the incurred losses from intersymbol interference (ISI) and intercarrier interference (ICI) introduced by synchronization errors, the SINR of the received data drastically drops. By taking advantage of this characteristic, both the symbol time and carrier frequency offsets are intuitively estimated by maximizing the SINR metric. For the SINR metric, two blind SINR estimations are investigated. The estimations do not need prior knowledge of the channel profiles and transmitted data. As such, the proposed maximum SINR (MSINR) synchronization algorithm is nondata aided so that the transmission efficiency can be improved. Moreover, to reduce the computational complexity, the early-late gate technique is proposed for the implementation of the synchronizer. Simulation results exhibit better performance for the MSINR algorithm than conventional techniques in multipath fading channels.
A joint synchronization algorithm for OFDM systems
(2007)
Chin, Wen-Long
;
Chen, Sau-Gee
;
Chen, Chih-Liang
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work presents a joint maximum-likelihood (ML) synchronization algorithm for symbol time (ST) offset (STO), carrier frequency offset (CFO) and sampling clock frequency offset (SCFO) for OFDM systems. Unlike most existing techniques which are time-domain approaches considering only AWGN and/or static multipath conditions, the proposed algorithm is developed in frequency-domain under time-variant multipath channels. By analyzing the received frequency-domain data, a mathematical model for the joint effects of STO, CFO and SCFO is derived. The results are used to formulate a log-likelihood function of two consecutive symbols. Based on the function, a joint ML algorithm is proposed. The joint algorithm is both efficient and robust, because the three main synchronization issues are treated altogether. Simulation results exhibit high performances in time-variant multipath fading channels.
A Low-Complexity Minimum-Interference Symbol Time Estimation for OFDM Systems
(2009-05-01)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Conventional symbol time (ST) synchronization algorithms for orthogonal frequency-division multiplexing (OFDM) systems are mostly based on the maximum correlation result of the cyclic prefix. Due to the channel effect, the estimated ST is not accurate enough. Hence, one needs to further identify the channel impulse response (CIR) so as to obtain a better ST estimation. Overall, the required computational complexity is high because it involves time-domain (TD) correlation operations, as well as the fast Fourier transform (FFF) and inverse FFT (IFFT) operations. In this work. without the FFT/IFFT operations and the knowledge of CIR, a low-complexity TD ST estimation is proposed. We first characterize the frequency-domain (FD) interference effect. Based on the derivation, the new method locates the symbol boundary at the sampling point with the minimum interference in the FD (instead of the conventional maximum TD correlation result). Moreover. to reduce the computational complexity, the proposed FD minimum-interference (MI) metric is converted to a low-complexity TD metric by utilizing Parseval's theorem and the sampling theory. Simulation results exhibit good performance for the proposed algorithm in multipath fading channels.
A low-complexity symbol time estimation for OFDM systems
(2008)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Conventional symbol time (ST) synchronization algorithms for orthogonal frequency-division multiplexing (OFDM) systems mostly are based on maximum correlation result of the cyclic prefix. Due to the channel effect, one needs to further identify the channel impulse response (CIR) so as to obtain a better ST estimation. Overall, the required computational complexity is high because it involves correlation operation, as well as the fast Fourier transform (FFT) and inverse FFT (IFFT) operations. In this work, without the FFT/IFFT operations and the knowledge of CIF, a low-complexity time-domain ST estimation is proposed. We first characterize the frequency-domain interference effect as a function of the ST by deriving some analytical equations considering the channel effect. Based on the derivation, the new method locates the symbol boundary at the sampling point with the minimum interference in the frequency-domain. Moreover, for reducing the computational complexity, the proposed frequency-domain minimum-interference metric is converted into a low-complexity time-domain metric by utilizing the Parseval's theorem and the sampling theory. Simulation results exhibit high performances for the proposed algorithm in the multipath fading channels.
A unified synchronization algorithm for OFDM systems in multipath fading channel
(2006)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In conventional OFDM synchronization algorithms, synchronization problems are considered separately. In this paper, we first derive an analytical equation combining all the synchronization errors. With the analytical results, the intercarrier-interference (ICI) due to synchronization errors can be derived. Next, we propose a unified synchronization scheme using similar operations that treats and solves all the contributing synchronization problems independently without regarding to other synchronization errors, at the same time. As a result, system performance can be improved. Besides, the delay time and the hardware complexities in the entire synchronization process can be reduced, because the mentioned advantages facilitate an efficient shared hardware realization, with small area and high hardware utilization. Performance simulations and evaluations of the proposed method are under way and will be reported in the final camera-ready paper.
Blind SNR Estimation with Coherent Function for OFDM Systems
(2008-11-01)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In OFDM receivers, an accurate signal-to-noise ratio (SNR) estimation is desirable for all sorts of operations involved in high-performance baseband demodulation. In this work. conventional SNR estimation techniques are investigated. Next, a blind SNR estimation scheme for the phase-shift keying (PSK) signals based on the coherence function is proposed. The proposed method is non-data-aided (NDA) and hence bandwidth-efficient. Simulations confirm that the proposed method has the best performance from moderate to high SNRs both in AWGN and dispersive channels: however. the proposed method has worse performance when SNRs are low.
IEEE 1588 Clock Synchronization using Dual Slave Clocks in a Slave
(2009-06-01)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
IEEE 1588 is a standard used in the synchronization of independent clocks that run on separate nodes of a distributed measurement and control system. This work presents a method that employs dual slave clocks in a slave to measure the link propagation delay, clock skew and offset. By accurately deriving these parameters, the proposed approach can reduce the deviation from the master clock to several orders of magnitude better than the required specification. The proposed technique fully conforms to the IEEE 1588, and can be used in the environments of symmetric and asymmetric communication links, such as xDSL.
Joint Effects of Synchronization Errors of OFDM Systems in Doubly-Selective Fading Channels
(2008)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The majority of existing analyses on synchronization errors consider only partial synchronization error factors. In contrast, this work simultaneously analyzes joint effects of major synchronization errors, including the symbol time offset (STO), carrier frequency offset (CFO), and sampling clock frequency offset (SCFO) of orthogonal frequency-division multiplexing (OFDM) systems in doubly-selective fading channels. Those errors are generally coexisting so that the combined error will seriously degrade the performance of an OFDM receiver by introducing intercarrier interference (ICI) and intersymbol interference (ISI). To assist the design of OFDM receivers, we formulate the theoretical signal-to-interference-and-noise ratio (SINR) due to the combined error effect. As such, by knowing the required SINR of a specific application, all combinations of allowable errors can be derived, and cost-effective algorithms can be easily characterized. By doing so, it is unnecessary to run the time-consuming Monte Carlo simulations, commonly adopted by many conventional designs of synchronization algorithms, in order to know those combined error effects. Copyright (C) 2008 W.- L. Chin and S.-G. Chen.
On the Analysis of Combined Synchronization Error Effects in OFDM Systems
(2009)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work analyzes combined effects of major synchronization errors, including the symbol time offset (STO), carrier frequency offset (CFO) and sampling clock frequency offset (SCFO) of orthogonal frequency-division multiplexing (OFDM) systems. Such errors degrade the performance of an OFDM receiver by introducing inter-carrier interference (ICI) and inter-symbol interference (ISI) into the systems. Traditionally, designing an OFDM receiver needs plenty of Monte Carlo simulations because the synchronization errors are simultaneously inevitable in practical environments. Therefore, we formulate the theoretical signal-to-interference-and-noise ratio (SINR) to assist the design of OFDM receivers. By knowing the required SINR of specific application, all combinations of allowable errors can be derived. Then, cost-effective algorithms could be easily designed.
Symbol Time Synchronization Based on SINR Maximization for OFDM
(2009)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work presents a symbol time (ST) synchronization algorithm for orthogonal frequency-division multiplexing systems based on a metric of signal-to-interference-and-noise ratio (SINR) which drops drastically with the increasing ST error. The ST is intuitively estimated by maximizing the SINR metric that exploits the correlation results of the separated-by-N samples. Unlike most existing techniques considering only AWGN or time-invariant multipath channels, the proposed maximum-SINR (MSINR) technique considers the time-variant multipath channels. Compared with conventional techniques, the proposed MSINR technique is less sensitive to the carrier frequency offset and doubly-selective channel effects.
Symbol time synchronization method for OFDM systems
(2009-01-29)
Chin, Wen-Long
;
Chen, Sau-Gee
A symbol time synchronization method for OFDM systems is disclosed. The invention presents a joint maximum-likelihood (ML) synchronization method for symbol time offset (STO) for OFDM systems. The method is developed in frequency-domain under time-variant multipath channels. By analyzing the received frequency-domain data, a mathematical model for the joint effects of symbol time offset (STO), carrier frequency offset (CFO) and sampling clock frequency offset (SCFO) is derived. The results are used to formulate a log-likelihood function of two consecutive symbols. The joint estimation's method is robust, because it exhibits high performances in high mobility and time-variant multipath fading channels.
Theoretical analysis of joint synchronization error effects for OFDMA systems
(2008)
Chin, Wen-Long
;
Chen, Sau-Gee
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Few papers investigate synchronization error effects for the uplink of orthogonal frequency-division multiple access (OFDMA) systems. By contrast, this paper simultaneously analyzes the joint effects of major synchronization errors, including symbol time (ST) offset (STO), carrier frequency offset (CFO) and sampling clock frequency offset (SCFO) for the uplink of OFDMA systems in time-variant multipath fading channels. Such errors degrade the performance of an OFDMA receiver by introducing inter-carrier interference (ICI), inter-symbol interference (ISI) and multi pie-access interference (MAI) into the systems. A theoretical signal-to-interference-and-noise ratio (SINR) is formulated to characterize the losses due to synchronization errors in time-variant multipath fading channels. The results provide designers a useful reference in designing suitable synchronization algorithms for the OFDMA applications.