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Performance of UWB Channel Gain Estimation Algorithm Based on Frequency Response Correlation
CHOI, Jinwon,SUNG, Yu-Suk,KIM, Yong-Hwa,KIM, Seong-Cheol The Institute of Electronics, Information and Comm 2010 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.93 No.6
<P>This letter proposes an Ultra WideBand (UWB) channel gain estimation algorithm that is based on frequency response correlation. From data measured in indoor and outdoor environments, the frequency correlation statistics of the UWB channel are characterized by correlation coefficients, which are represented as functions of the frequency separation according to the propagation environments. We use empirically established correlation coefficient models to develop the proposed channel gain estimation algorithm. In this algorithm, unknown channel gains of intermediate frequencies are estimated from known channel gains of neighboring reference frequencies. The performance of the proposed algorithm is evaluated against various configurations of reference frequencies and compared with that of a conventional estimation algorithm using a linear interpolation scheme.</P>
Frequency-Dependent UWB Channel Characteristics in Office Environments
Jinwon Choi,Noh-Gyoung Kang,Yu-Suk Sung,Jun-Sung Kang,Seong-Cheol Kim IEEE 2009 IEEE Transactions on Vehicular Technology VT Vol.58 No.7
<P>This paper reports frequency-dependent ultrawideband (UWB) channel characteristics. Measurements were performed in 103 receiver locations of six different office environments. From the measured data, the effect of frequency on the path-loss properties of a UWB signal is analyzed. After analyzing the path-loss behavior to propagation environments, the path-loss exponent variation models are developed in various environments as a function of frequency. Based on these models, path-loss prediction is performed, and the accuracy of the prediction is compared with those of existing path-loss models. In addition, the frequency-dependent UWB channel correlation characteristics are investigated. For the frequency correlation statistics of the UWB channel, double-slope models representing correlation coefficients are established with and without line-of-sight (LOS) paths. Using these correlation models, a channel gain estimation algorithm is proposed. The performance of the proposed estimation algorithm is evaluated with estimation parameters, and it is confirmed that the proposed estimation algorithm has better performance than the conventional algorithm using a linear interpolation algorithm.</P>
Jinwon Choi,Yungil Lee 대한건축학회 2010 Architectural research Vol.12 No.2
Our prediction model is based on the development of “Semantic Location Model.” It embodies geometrical and topological information which can increase the efficiency in prediction and make it easy to manipulate the prediction model. Data mining is being implemented to extract the inhabitant’s location patterns generated day by day. As a result, the self-learning system will be able to semantically predict the inhabitant’s location in advance. This context-aware system brings about the key component of the ubiquitous computing environment. First, we explain the semantic location model and data mining methods. Then the location prediction model for the ubiquitous computing system is described in details. Finally, the prototype system is introduced to demonstrate and evaluate our prediction model.
Au-doped PtCo/C catalyst preventing Co leaching for proton exchange membrane fuel cells
Choi, Juhyuk,Cho, Jinwon,Roh, Chi-Woo,Kim, Beom-Sik,Choi, Min Suk,Jeong, Hojin,Ham, Hyung Chul,Lee, Hyunjoo Elsevier 2019 Applied catalysis. B, Environmental Vol.247 No.-
<P><B>Abstract</B></P> <P>Proton exchange membrane fuel cells (PEMFCs) are promising mobile power supply systems, and operate without noise or polluting emissions. Because the oxygen reduction reaction (ORR) at the cathode suffers from high overpotential and sluggish kinetics, many catalysts have been developed in efforts to enhance activity and durability for the ORR. However, most of them have complicated synthetic procedures which cannot be scaled-up easily, and have only been tested in a half-cell. High activity in a half-cell does not necessarily guarantee better performance in a single-cell. In this work, we synthesized an Au-doped PtCo/C catalyst using a simple method of gas-phase reduction and subsequent galvanic replacement, and its activity and durability were tested in a single-cell. When current densities were compared at 0.6 V after a durability test of 30,000 cycles in 0.6–1.0 V, the values were 1.40, 0.81, and 0.63 A cm<SUP>−2</SUP> for the Au-doped PtCo/C, acid-treated PtCo/C, and commercial Pt/C catalysts, respectively. Co leaching was much less in the Au-doped PtCo/C. Density functional theory (DFT) calculations confirmed that surface oxygen species bound more weakly at the catalyst surface and migration of a Co atom (Co segregation) to the surface was suppressed in the presence of Au. This facile method can provide a more realistic strategy to design better ORR catalysts for PEMFC application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Au-doped PtCo/C catalyst was prepared by gas-phase reduction and subsequent galvanic replacement in a gram-scale. </LI> <LI> The Au-doped catalyst showed enhanced activity and durability for ORR in half-cell and single-cell tests. </LI> <LI> The maximum power density after durability tests was 1.12 W cm<SUP>−2</SUP> for Au-doped catalyst and 0.69 W cm<SUP>−2</SUP> for commercial Pt/C. </LI> <LI> DFT calculations confirmed that Co leaching could be suppressed by Au doping at Pt shell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Performance Evaluation of Positioning Techniques Based on UWB Radio
Jinwon Choi,Jun-Sung Kang,Yu-Suk Sung,Seong-Cheol Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
In this paper, performances of positioning techniques based on UWB radio are evaluated. The positioning techniques for UWB systems, SS, and time based algorithms, TOA and TDOA, are the target ones to be analyzed. Using the reported CRLB of each algorithm, the location estimation error is obtained. The estimation error variation to the number of base stations is reported also.
Modeling of Localization Error in Wireless Sensor Network
CHOI, Jinwon,KANG, Jun-Sung,KIM, Yong-Hwa,KIM, Seong-Cheol The Institute of Electronics, Information and Comm 2009 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.92 No.2
<P>This letter presents the variation of localization error to network parameters, the number of range estimation results from anchor nodes (ANs) and average distance between ANs in centralized Wireless Sensor Network (WSN). In sensor network, ANs estimate the relative range to Target Node (TN) using Time-Of-Arrival (TOA) information of Ultra WideBand (UWB) radio and a fusion center determines the final localization of TN based on estimation results reported. From simulation results, the variation of localization error, which is defined as the difference between localization result of TN and its actual location, is represented as the function of number of estimation results to average distance between ANs. The distribution of localization error is matched to the Rician distribution whose K-factor value is given by the proposed formula as well. Finally, the normalized error function for the efficient localization network design is characterized.</P>
Link Selection Algorithm of UWB Communications Considering Fading Statistics
Jinwon Choi,Yu-Suk Sung,Jeong-Wook Kim,Seong-Cheol Kim 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
This paper presents the link selection algorithm of Ultra Wide Band (UWB) communications considering fading statistics. In this algorithm, UWB devices decide the wireless link considering not only received signal strength but also fading statistics. Fading statistics follows the proposed channel model to the existence of line-of-sight (LOS).