• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.23 no.5
• /
• pp.1270-1281
• /
• 1998

Frequency offset in an orthogonal frequency division multiplexing (OFDM) system is known to cause the inter-channel interference (ICI), amplitude and phase distortion of a received signal, resulting in a severe performance degradation of the total system. In this paper, we propose an improved pilot-based masimum likelihood frequency offset estimation technique, which uses the predefined sync-subchannels, and derive the error performance of the proposed frequency offset estimator analytically. The proposed technique improves the performance of the frequency offset estimator by adding up the frequency offset caused by coherent phase changes and averaging out the effect caused by random phase error. It is confirmed by computer simulations that the upper bound of error variance for the proposed frequency offset estimator analytically derived in this paper is correct, and that the proposed estimator has better performance than the previous ones in terms of error variance, tracking range, and time-varying characteristics of a channel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.9A
• /
• pp.781-787
• /
• 2005

In this paper, an estimation method of intercell carrier frequency-offset(CFO) in orthogonal frequency division multiplexing(OFDM)-based cellular systems is proposed for a user's equipment(UE), especially at the cell boundary, in downlink channels. Also, after deriving an estimation method of intercell CFO from the signals received by adjacent base stations(BSs), we propose a cell-searching method using the estimated CFOs. It is shown by computer simulation that the proposed methods can uniquely estimate the intercell CFOs and identify the target BS with a high detection probability.

• Trans-
• /
• v.6
• /
• pp.35-42
• /
• 2019

Un jour, à la fin d'un symposium autour du célèbre film « La Bataille d'Alger » de Pontecorvo, quelqu'un a dit que l'histoire véridique était trop difficile à retrouver (à savoir ce qu'il s'était vraiment passé), il fallait donc la créer (dans le sens d'inventer). J'étais si surpris par cette conclusion anti-historique que je n'ai pu répondre. Nous pouvons faire l'histoire au présent par nos actions, mais ce qui a été fait est fait, et restera historique autant que possible dans la mesure où des historiens sérieux et libres pourront faire leur travail. Max Stirner a dit « Nous ne pouvons être libre de tout, mais nous pouvons tenter de faire nos écrits aussi libres que nous sommes ». Si nous rapportons cette idée à l'Histoire, cela veut dire que ce n'est pas parce que l'histoire est le résultat des recherches faites par des humains qu'elle doit être faussée. L'homme est faillible mais il est aussi perfectible. En tant qu'historien du cinéma, les questions importantes sont de savoir ce qui constitue une archive, (le Mal d'archive de Derrida, qui développe la pensée sur la constitution de la connaissance selon Foucault, intervient très à propos, ici) et comment les utiliser, dans les films en particulier, fiction ou documentaire.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.7A
• /
• pp.623-631
• /
• 2010

In this paper, various of pilot-assisted channel estimation techniques for 3GPP LTE downlink are tested under multipath Rayleigh fading channel. At first, the conventional channel estimation techniques are applied with linear zero-forcing (ZF) equalizer, such as one dimensional least square (1-D LS) linear interpolation, two dimensional (2-D) wiener filter, the time and frequency dimension separate wiener filter and maximum likelihood estimator (MLE). Considering the practical implementation, we proposed two channel estimation techniques by combining time-dimension wiener filter and MLE in two manners, which showed a good tradeoff between system performance and complexity when comparing with conventional techniques. The nonlinear decision feedback equalizer (DFE) which can show a better performance than linear ZF equalizer is also implemented for mitigating inter-carrier interference (ICI) in our system. The complexity of these algorithms are calculated in terms of the number of complex multiplications (CMs) and the performances are evaluated by showing the bit error rate (BER).

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

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.1
• /
• pp.29-37
• /
• 2005

One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can Provide another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.

• Proceedings of the Korean Society of Applied Pharmacology
• /
• 2003.11a
• /
• pp.114-114
• /
• 2003

Ginseng is a medicinal herb widely used in Asian countries, and its pharmacological effects has been demonstrated in various systems such as cardiovascular, central nervous, and endocrine systems. Its effects are mainly attributed to the ginsenosides. We hypothesize that a component of Panax ginseng, ginsenoside-Rbl, acts by binding to estrogen receptor. We have investigated the estrogenic activity of ginsenoside-Rbl in a transient transfection system using estrogen receptors ${\alpha}$ or ${\beta}$ with estrogen -responsive luciferase plasmids in COS monkey kidney cells. Ginsenoside-Rbl activated both estrogen receptors ${\alpha}$ and ${\beta}$ in a dose-dependent manner (0.5 -100 M ). Activation was inhibited by the specific estrogen receptor antagonist ICI 182,780, indicating that the estrogenic effect of ginsenoside-Rbl is estrogen receptor dependent. Next, we evaluated the ability of ginsenoside-Rbl to induce estrogen-responsive progesterone receptor gene by semi-quantitative RT-PCR assays. MCF-7 cells treated with l7${\beta}$-estradiol or ginsenoside- Rb1 exhibited an increased expression of progesterone receptor mRNA. However, ginsenoside-Rbl failed to displace the specific binding of ［3H］17${\beta}$-estradiol to estrogen receptor in MCF-7 cells as examined by whole cell ligand binding assays, suggesting that there is no direct interaction of ginsenoside-Rbl with estrogen receptor. Our results indicate that estrogen-like activity of ginsenoside-Rbl is independent of direct estrogen receptor association.

• Carbon letters
• /
• v.9 no.4
• /
• pp.303-307
• /
• 2008

The studies on integrated operation of fuel cell with fuel processor are very essential prior to its commercialization. In this study, Polymer Electrolyte Membrane Fuel Cell (PEMFC) was operated with a fuel processor, which is mainly composed of two parts, methanol steam reforming reaction and preferential oxidation (PROX). In fuel processor, ICI 33-5 (CuO 50%, ZnO 33%, $Al_2O_3$ 8%, BET surface area: $66\;m^2g^{-1}$) catalyst and CuO-$CeO_2$ catalyst were used for methanol steam reforming, preferential oxidation (PROX) respectively. PEMFC was operated by hydrogen fuel generated from fuel processor. The resulting gas from PROX reactor is used to operate PEMFC equipped with our prepared anode and cathode catalyst. PtRu/C catalyst gives more tolerance to CO.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37B no.10
• /
• pp.921-928
• /
• 2012

In this paper, we propose a novel interference alignment transceiver for multi-cell MIMO downlink channels with arbitrary number of cells and users per cell. We design the receive beamformer to align the interference from undesired base stations to the effective inter-cell interference (ICI) channels. Subsequently, we design the transmit precoder which can nulllify the interference from the corresponding base station. The proposed transceiver design can attain the degrees of freedom (DOF) equal to the number of streams per user. Accordingly, we investigate conditions for the antenna configuration. From numerical results, we confirm that the proposed transceiver design can achieve higher DOF than the conventional scheme under equal antenna configuration.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.6C
• /
• pp.594-601
• /
• 2003

High-speed WLAN(Wireless Local Area Network) systems operating in 5GHz band use OFDM transmission technique. OFDM technique transmits data in parallel and has many advantage compared with the serial transmission system-for example, robustness to time variance of channel. OFDM technique use the orthogonal multicarriers. The ICI(InterChannel Interference) caused by the orthogonality destruction between subcarriers. hamper the BER performance. In this paper, we propose the synchronization techniques for high-speed WLAN system designed to support user data rates up to 54Mbps at 5GHz. The proposed synchronization techniques are the reduced complexity structure having the similar performance compared with the conventional synchronization techniques.