Publications (13)1.34 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, a novel pseudo noise (PN) code acquisition scheme based on sequential estimation is proposed, which can not only achieve code acquisition for both inverted and non-inverted PN codes, but also demodulate the spreading data. Simulation results show that the proposed scheme has approximately half the complexity of the conventional scheme while exhibiting a similar mean acquisition time performance to that of the conventional scheme.
- [Show abstract] [Hide abstract] ABSTRACT: This paper proposes a novel distance measuring scheme based on repeated PN sequence for ultra wide-band vehicle radar systems. The proposed scheme measures the distance between a vehicle and an obstacle based on repeated use of a single short pseudo random sequence. Simulation results show that the proposed scheme provides a shorter mean distance measuring time while keeping a similar measurement error performance to that of the conventional scheme.
- [Show abstract] [Hide abstract] ABSTRACT: This paper addresses a novel Alamouti coding scheme for asynchronous cooperative communication systems over frequency selective fading channels. In the proposed scheme, the Alamouti coded form at the destination node is constructed through a simple combination of symbols at the source node, instead of the time-reversal operation at the relay nodes used in the conventional scheme. Numerical results show that the proposed scheme achieves a higher order cooperative diversity than that of the conventional scheme.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, a low complexity sequential estimation scheme for pseudo noise (PN) code acquisition is proposed, which can not only achieve code acquisition for both inverted and non-inverted PN codes, but also demodulate the spreading data. Numerical results show that the proposed scheme has approximately half the complexity of the conventional scheme while exhibiting a similar mean acquisition time performance to that of the conventional scheme.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, we propose a new periodogram-based integer frequency offset (IFO) estimation scheme robust to the fractional frequency offset (FFO) variation. We first observe the reason why the conventional IFO estimation scheme in is sensitive to the variation of the FFO, and then, propose a new IFO estimation scheme using the modified maximum-likelihood (ML) metric. The numerical results demonstrate that the proposed scheme is more robust to the variation of the FFO and has better IFO estimation performance than the conventional scheme in.
Conference Paper: Hybrid waveform inversion technique for coupled acoustic‐elastic media[Show abstract] [Hide abstract] ABSTRACT: Most full waveform inversion algorithms have been developed assuming that the governing equation of the wave-propagation phenomenon is the acoustic wave equation. However, the majority of geophysical targets are generally situated in elastic media. For this reason, waveform inversion using an acoustic wave equation has its limitations with regard to building submarine geophysical features. Accordingly, we have proposed a full waveform inversion algorithm for coupled acoustic-elastic media with irregular submarine topography that is comparable to submarine geology systems. We developed a hybrid (Laplace-Fourier domain) waveform inversion technique that uses both frequency- and Laplace-domain wavefields properly. The frequency-domain wavefield has a short-wavelength component which can describe detailed velocity models. On the other hand, the employed Laplace coefficients have a long-wavelength component which can describe macro velocity structures. In addition, we proposed a strategy for selecting frequency bands, comprising selected real frequencies and Laplace coefficients. From numerical tests, using a synthetic model (2D AA profile of the SEG/EAGE salt model) and a field dataset (North-East Atlantic), our new hybrid waveform inversion strategy provided much higher resolution images than conventional hybrid inversion schemes.
Conference Paper: Gauss‐Newton‐CG technique for acoustic‐elastic coupled media[Show abstract] [Hide abstract] ABSTRACT: We developed a frequency-domain acoustic-elastic coupled waveform inversion based on the Gauss-Newton-CG method. Despite the use of a high-performance computer system and a state-of-the-art parallel-computation algorithm, it is still computationally prohibitive to calculate the approximate Hessian explicitly for a large-scale inverse problem. Accordingly, we adopted the conjugate-gradient-least-squares (CGLS) algorithm, which is frequently used for geophysical inverse problems, to implement the Gauss-Newton method, thus calculating the approximate Hessian implicitly. To verify our algorithm, we applied it to synthetic data generated from the Marmousi-2 model. We also extended our algorithm to the North-East Atlantic to check its applicability to real data.
Conference Paper: An asynchronous cooperative transmission scheme[Show abstract] [Hide abstract] ABSTRACT: This paper proposes a novel asynchronous transmission scheme for cooperative wireless networks using Alamouti coded orthogonal frequency division multiplexing (OFDM) modulation. The proposed scheme obviates the need for the timing synchronization at the relay nodes through a renewal of the cyclic prefix (CP) of the OFDM symbol, and achieves a cooperative diversity gain through some simple complex-valued operations at the relay node. Numerical results demonstrate that the bit error rate (BER) performance of the proposed scheme, unlike that of the conventional scheme, does not degrade even when there exists a timing synchronization error at the relay nodes, and also, that the proposed scheme obtains two times higher cooperative diversity gain compared with that of the conventional scheme at the cost of the symbol transmission rate being reduced by half.
- [Show abstract] [Hide abstract] ABSTRACT: This paper proposes a novel spectrum sensing technique for the digital video broadcasting-terrestrial (DVB-T) systems, which utilizes the periodicity of pilot signals in the orthogonal frequency division multiplexing (OFDM) symbols. The proposed scheme can overcome the effect of the timing synchronization error by re-correlating the correlation values in the same sample distances. The numerical results demonstrate that the detection probability perfor-mance of the proposed scheme outperforms that of the conventional scheme when there exists a timing synchronization error.
- [Show abstract] [Hide abstract] ABSTRACT: The effectiveness of two different management schemes to dispose of heavy metal-contaminated sediments from Ulsan Bay, South Korea, soil washing and solidification/stabilization, were evaluated through a series of analyses. NaOH proved to be an effective washing reagent for As, extracting 75% of the As in sediment samples. EDTA was found to significantly enhance the extraction of Cu, Pb and Zn. However, complete removal of any metals was not achieved even after application of 100 mM concentrations of washing reagents. Therefore, a solidification/stabilization technique was applied to dredged sediment samples using ordinary Portland cement (1–40%) and fly ash (∼20%). Solidified sediments did not release meaningful amount of the metals via leaching tests. Our results suggest that solidification/stabilization is a better option for effective disposal of heavy metal-contaminated sediments than soil washing. A legal framework for the treatment of hazardous wastes and contaminated soils in Korea is discussed.
Conference Paper: A Rapid Code Acquisition Scheme for Optical CDMA Systems[Show abstract] [Hide abstract] ABSTRACT: In this paper, we propose a novel code acquisition scheme called modified multiple-shift (MMS) for optical code division multiple access (CDMA) systems. By using the modified local code whose sign is positive or negative, the proposed MMS scheme provides a shorter mean acquisition time (MAT) than the conventional multiple-shift (MS) scheme. The simulation results demonstrate that the MAT of the MMS scheme is shorter than that of the MS scheme in both single-user and multi-user environments.
Conference Paper: A Novel Two-Stage Detection Scheme for UWB Signal Acquisition[Show abstract] [Hide abstract] ABSTRACT: This paper proposes a novel detection scheme based on multiple correlator outputs to enhance the detection performance in ultra-wideband (UWB) signal acquisition. Due to the rich multipath of UWB channels, the signal energy spreads over multiple correlator outputs, which makes each correlator output have only a portion of the signal energy, and thus, degrades the detection performance of the conventional scheme where a single correlator output is used as the decision variable for detection. In the proposed two-stage detection scheme, the decision variable is formed by combining multiple correlator outputs, making it possible to collect the signal energy spread by the multipath. Simulation results show that the proposed scheme can provide a better detection performance over the conventional scheme in various UWB channel environments.
- [Show abstract] [Hide abstract] ABSTRACT: The conventional ultra-wideband (UWB) synchronization schemes could cause poor performance in receiver operations such as demodulation after the synchronization, since unreliable timing information corresponding to low-power multipath components might be transferred to the next stage. To solve this problem, in this paper, we propose novel synchronization schemes for UWB systems. We first derive an optimal scheme based on the maximum likelihood (ML) criterion and then develop a simpler suboptimal scheme. Simulation results show that both proposed schemes provide a better synchronization performance than the conventional scheme.
Sŏul, Seoul, South Korea
- College of Information and Communication Engineering (SoICE)
University of Ulsan
Urusan, Ulsan, South Korea
- Department of Civil and Environmental Engineering