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A Study on Discharge Characteristics by Using MF and RF Power in Remote Dielectric Barrier Discharge D.J. Kima,b,∗, Y.K. Shim, H.J. Kim and J.G. Han Geniatech Inc., Room 810, Hanlla Sigma Valley, 545 Dunchun-daero, Jungwon-gu, Seongnam-si, Gyeonggi-do, South Korea CAPST, Sungkyunkwan University, 300 ChunChun-dong, Jangan-gu, Suwon 440-746, South Korea KIST, Center for Spintronics, Hwarangno 14-gil 5, Seongbuk gu, Seoul 136-791, South Korea

The properties of AZO (98-wt% ZnO, 2-wt% Al2O3) films produced in pure Ar and Ar (98%) + H2 (2%) (H2-diluted Ar) by radio-frequency (RF) magnetron sputtering were investigated as functions of the substrate temperatures. H2-diluted Ar improved the electrical properties of the AZO films fabricated at low substrate temperatures, but this benefit gradually diminished with increasing substrate temperature. This phenomenon was explained by O-H stretching in the Zn-O bond at low temperatures and by the formation of oxygen vacancies at high temperatures. The average optical transmission was over ~85%, and the orientation of the AZO films deposited both in pure Ar and in H2-diluted Ar was in the [002] direction.

The properties of Al-doped ZnO (AZO) films were investigated as a function of gas ratio using an AZO (2 wt% ) ceramic target in a radio frequency (RF) magnetron sputtering system. The deposition process was done at and in Torr working pressure and with various ratios of gas. During the AZO film deposition process, partial gas affected the AZO film characteristics. The electron resistivity () was lowest and mobility () was highest in AZO films when the gas ratio was 2.5 %. When the gas ratio was increased above 2.5 %, the electron resistivity increased and mobility decreased with increasing gas ratio in AZO films. The carrier concentration increased with increasing gas ratio from 0 % to 7.5 %. This phenomenon was explained by reaction of hydrogen and oxygen and additional formation of oxygen vacancy. The average optical transmission in the visible light wavelength region over 90 % and an orientation of the deposition was [002] orientation for AZO films grown with all gas ratios.

This paper is devoted to the optical emission studies of Octamethylcyclotetrasiloxane (OMCTS)/O2 derived, low pressure (0.1 Torr), 13.56 MHz RF plasmas. The emission is recorded with a resolution of 0.05 nm to two RF power densities of 0.25 and 0.50 W/cm2, at wavelengths of 180–1000 nm. Emitting atomic and molecular species in plasma are identified, and spatial variation in emission intensity is recorded through the space between electrodes. The hardness, elastic modulus, infrared absorbance, refractive index, and residual stress of the resulting plasma polymer films are presented. Most of the atomic and molecular emissions have been identified, and spectra can be used as a reference for OMCTS/O2 plasmas. Optical emission spectra are dominated by molecular CO, CO+, OH, and CO2+ bands, and atomic H and O lines. The absence of emissions from the Si, SiO, SiO2, CH, CH2, and CH3, together with the infrared absorbance of films, suggests that SiOxCy:H film formation occurs by way of the dissociation of C–H and Si–C bonds, as well as the polymerization of silica rings or long chains.

The effects of isothiocyanates (ITCs) on microbiological, physicochemical, and sensory properties were investigated in tofu on days 0, 2, 4, 6, 8, and 10 of storage at 10 °C. When compared to the control (8.14 log CFU/g), the 200 ppm of ITCs (4.40 log CFU/g) effectively retarded the growth of microflora in tofu after 10 days of storage. The initial pH slightly declined after 10 days of storage, ranging between 5.81 and 6.14. The control showed significantly higher acid values over storage. Compared to the control, the preference to sensory attributes (color, taste, odor, chewiness, and over acceptance) of ITC-treated samples was highly rated after 10 days of storage. The ITCs can be used as an alternative for extending the shelf life and improving the safety of tofu.

To mitigate the asynchronous ICI (Inter-Cell Interference), SCM (Spatial Covariance Matrix) of the asynchronous ICI plus background noise should be accurately estimated for MIMO-OFDMA (Multiple-input Multiple-output-Orthogonal Frequency Division Multiple Access) system. Generally, it is assumed that the SCM of the asynchronous ICI plus background noise is estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and considering that training symbols are not appropriate for OFDMA system such as LTE (3GPP Long Term Evolution). Therefore, noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sinc type weighing method which can not only reduce noise effectively minimizing estimation error caused by the spectral leakage but also can be implemented using frequency-domain weighted moving average filter easily. We also consider the iterative CFR (Channel Frequency Response) and SCM estimation method which can effectively reduce the estimation error of both CFR and SCM, and improve the performance for LTE system. By using computer simulation, we show that the proposed method can provide up to 2.5dB SIR (Signal to Interference Ratio) gain compared with the conventional method, and verify that the proposed method is attractive and suitable for implementation with stable operation.

Fabry–Perot interferometry, laser induced fluorescence, and optical absorption spectroscopy were utilized to study a magnetron discharge during sputtering of the Ti and Cu targets. Doppler broadening of Ar and Ti emission lines was measured by the Fabry–Perot interferometer in a wide range of working pressure and at different power applied to the discharge. The temperatures of Ar and Ti atoms were determined by the Doppler broadening of the correspondent emission lines. Laser induced fluorescence was applied for Ti and Ti+ density determination in the same reactor. The absolute values of the Ti density in the discharge are provided based on the results done by optical absorption spectroscopy.

TiN films for metallic bipolar plates were synthesized by closed-field unbalanced magnetron sputtering (CFUBM) and the properties were controlled by adjusting the N 2 partial pressure. The corrosion behaviors of TiN films were investigated by potentiodynamic tests and electrochemical impedance spectroscopy (EIS) measurements under the condition of an aerated 1 M H 2 SO 4 + 2 ppm HF solution at 70 °C with a constant potential of 600 mV SCE . The results revealed that the variation of N 2 pressure had an influence on the corrosion resistance of TiN coating. N 2 partial pressure of 0.4 mTorr showed good corrosion resistance with the lowest corrosion current density and the highest charge transfer resistance due to the low porosity.

CrSiN coatings with different Si concentration (Si/(Cr + Si) ratio: 0, 3.7, 11.7, 20%) were deposited on stainless steel substrates using a closed field unbalanced magnetron sputtering (CFUBM) system. The variation in the microstructure of the films with the Si concentration was measured by XRD. The corrosion behavior of the CrSiN coatings in a deaerated 3.5% NaCl solution was investigated by potentiodynamic tests, electrochemical impedance spectroscopy (EIS) and surface analyses. The microstructure of the CrSiN film was found to depend on the Si concentration. The results of the potentiodynamic polarization tests showed that the corrosion current density and porosity decreased with increasing Si/(Cr + Si) ratio. The EIS measurements showed that the corrosion resistance of the Si-bearing CrN was improved by the phase transformation of the film, which led to an increase in the pore resistance and charge transfer resistance. The Si-bearing CrN possesses the best corrosion resistance at a Si/(Cr + Si) ratio of 20%, measured by the maximization of the pore resistance and charge transfer resistance.

The introduction of an electrically biased two-grid attachment inside a conventional physical vapor deposition process system produces a reactive coating deposition and increases the metal ion-to-neutral ratio in the plasma, resulting in denser and smoother films. The corrosion behavior of titanium nitride (TiN) coatings was investigated by electrochemical methods, such as potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in deaerated 3.5% NaCl solution. Electrochemical tests were used to evaluate the effect of microstructure on the corrosion behavior of TiN coatings exposed to a corrosive environment. The crystal structure of the coatings was examined by X-ray diffractometry and the microstructure of the coatings was investigated by scanning electron microscopy. In the potentiodynamic polarization test and EIS measurement, the corrosion current density of TiN deposited by the modified two-grid attachment magnetron sputtering process was lower than for TiN deposited by conventional magnetron type and also presented higher charge-transfer resistance values during 240 h total immersion time. The modified process promotes the grain refinement, which yields lower porosity.

We present experimental results of the spatial distribution of Ar and Ti optical emission and absorption lines in Ar?Ti plasma during sputtering of Ti. Measurements were performed in a dc magnetron reactor with movable planar magnetron using optical emission/absorption spectroscopy. A study was made for two different working pressures: 0.5 and 4?Pa. The results show that the intensity of emission lines decay exponentially with the increase in the distance from the target with two different decrements which correspond to the different parts of the discharge, namely the plasma region with a steep decay (up to about 1.5?cm from the target) and the 'far' region with a slow decay (more than 2?cm away from the target). Ti absorption data reveal similar behaviour. The emission decrement values which correspond to the steep decay of intensity lie in the range 1.4?3?cm?1, whereas those for slow decay group around 0.3?cm?1.

The formation and properties of WC–Ni thin films deposited on Si were studied. A cathodic tungsten carbide arc was used at room temperature to prepare the samples. In this paper, the effect of system parameters, such as external magnetic field, etc., were investigated. Without filtering, only condensed tungsten carbide droplets were observed on the substrate, while transparent films with few droplets were produced when a filter was used to reduce the number of macroparticles. Plasma floating potential and substrate current density were determined by voltage-current analyzer. The change of plasma states during cathodic arc discharges of tungsten carbide, under various magnetic fields of straight magnetic solenoid, was analyzed by optical emission spectroscopy (OES). In addition, an intensified camera system with a fiberoptically coupled high-resolution CCD was used for the estimating distribution of plasma density around the axis of the solenoid coil. Deposition rates of about 20 nm/min of WC–Ni film were determined with α-step. Scanning electron microscopy (SEM) was employed to determine the droplet distribution of the film and surface morphology. The surface roughness remained low over the whole coil current range with values between 0.2 μm at 100 A and 0.8 μm at 200 A.

Atmospheric plasma torch has many useful characteristics such as high current, high temperature and highly intensive radiation power. The performance of non-transferred plasma torch is significantly dependent on jet flow characteristics out of nozzle. Also, the compulsory swirl is being produced to gain the shape that can concentrate the plasma to the center of gas flow. In this study, the thermal flow characteristics of non-transferred plasma torch are investigated under atmospheric conditions. Numerical analyses are carried out with various inlet angles considering the swirl strength. In order to solve the governing equations, we have used a commercial code, CFD-ACE+ with FVM and SIMPLER algorithm. Furthermore, the size of flame is also experimentally investigated with various gas species.

Multilayered WC–Ti 1− x Al x N coatings were deposited on AISI D2 steel using cathodic arc deposition method. These coatings contain structural defects such as pores or pinholes. Thus, the substrate is not completely isolated from the corrosive environment. These growth defects in the coatings are detrimental to corrosion resistance of the coatings used in severe corrosion environments. The localized corrosion of the coatings was studied in deaerated 3.5 wt.% NaCl solution using classical electrochemical technique (potentiodynamic polarization test). Coating characteristics were examined by means of glow discharge optical emission spectroscopy, scanning electron microscopy, auger electron spectroscopy and transmission electron spectroscopy. The porosity was calculated from a result of potentiodynamic polarization test of the uncoated and coated specimens. The calculated porosity is higher in the WC–Ti 0.6 Al 0.4 N than others, which is closely related to the packing factor. The positive effects of greater packing factor act on inhibiting the passage of the corrosive electrolyte to the substrate and reducing the localized corrosion kinetics. From the electrochemical tests and surface analyses, the major corrosion reaction of coatings is caused by defects (pores, pinholes and crevices), coating delamination and galvanic effect between the droplet and the coating.

In this paper, we introduce a fully synthesizable 32-bit embedded microprocessor core called the AE32000B. The AE32000B core is based on the extendable instruction set computer architecture, so it has high code density and a low memory access rate. In order to improve the performance of the core, we developed and adopted various design options, including the load extension register instruction (LERI) folding unit, a high performance multiply and accumulate (MAC) unit, various DSP units, and an efficient coprocessor interface. The instructions per cycle count of the Dhrystone 2.1 benchmark for the designed core is about 0.86. We verified the synthesizability and the area and time performances of our design using two CMOS standard cell libraries: a 0.35-μm library and a 0.18-μm library. With the 0.35-pm library, the core can be synthesized with about 47,000 gates and operate at 70 MHz or higher, while it can be synthesized with about 53,000 gates and operate at 120 MHz or higher with the 0.18-μm library.

In the present work, multilayered coatings with alternate layers of WC-Ti and WC-Ti 1-x Al x N were deposited for use as wear-resistant and corrosion-resistant surfaces. Ti and TiN base layers were deposited on the substrate prior to the multilayers. WC-Ti 1-x Al x N coatings with variable Al content (i.e., Al target power density) were deposited onto a steel substrate (high-speed steel; HSS) by the cathodic arc deposition method. The Al content could be controlled using an evaporation source for Al and fixing the evaporation rate of the other target sources. Four kinds of WC-Ti 1-x Al x N coatings were prepared (WC-Ti 0.6 Al 0.4 N, WC-Ti 0.53 Al 0.47 N, WC-Ti 0.5 Al 0.5 N and WC-Ti 0.43 Al 0.57 N). The corrosion behavior of WC-Ti 1-x Al x N coatings in deaerated 3.5% NaCI solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al content on the coating properties related to the corrosion behavior. The galvanic corrosion current measured between the coating and substrate showed a low value. The results of potentiodynamic polarization tests indicated that the WC-Ti 0.43 Al 0.57 N coating with lower porosity enhanced the corrosion resistance. In electrochemical impedance spectroscopy measurements, the WC-Ti 0.43 Al 0.57 N coating showed two time constants and decreased the charge transfer resistance of the coating (R et ). Multilayered coatings were analyzed by EDS and XRD techniques to evaluate the crystal structure and compound formation behavior. Surface and cross-sectional morphology of the films was observed using SEM. In addition, scratch tests were performed to measure film adhesion strength.

WC–(Ti1−xAlx)N coatings of stepwise changing Al concentration (WC–Ti0.86Al0.14N, WC–Ti0.72Al0.28N, and WC–Ti0.58Al0.42N) were deposited on AISI 1045 substrate by high-ionization sputtered PVD method. The Al concentration could be controlled by using evaporation source for Al and fixing the evaporation rate of the metals (WC alloy and Ti). The corrosion behavior of WC–(Ti1−xAlx)N coatings in deaerated 3.5% NaCl solution was investigated by electrochemical corrosion tests and surface analyses. Particular attention was paid to the effects of Al target power density on the film properties related to the corrosion behavior. The measured galvanic corrosion currents between coating and substrate indicated that WC–Ti0.72Al0.28N coating showed the best resistance of the coating tested. The results of potentiodynamic polarization tests showed that this coating had passivation and lower porosity. This indicated that this coating is effective in improving corrosion resistance. In electrochemical impedance spectroscopy, the WC–Ti0.72Al0.28N coating showed one time constant loop and the increased polarization resistance of coating relative to other samples. The better corrosion performance of WC–Ti0.72Al0.28N coating is due to the modified compactness, porosity and adhesion of the coating layer.

The corrosion behavior of Cr-N coated steels with different phases (α-Cr, CrN and Cr2N) deposited by cathodic arc deposition on AISI H13 steel was investigated in a 3.5% NaCl solution at ambient temperature. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were the techniques applied to characterize the corrosion behavior. It was found that the CrN coating had a lower current density from potentiodynamic polarization tests than others. The porosity, corresponding to the ratio of the polarization resistance of the uncoated and the coated substrate, was higher in the Cr2N coating than in the other Cr-N coated steels. EIS measurements showed, for most of the Cr-N coated steels, that the Bode plot presented two time constants. Also, the Cr2N coating represented the characteristic of Warburg behavior after 72 h of immersion. The coating morphologies were examined in planar view and cross-section by SEM analysis and the results were compared with those of the electrochemical measurement. The CrN coating had a dense, columnar grain-sized microstructure with minor intergranular porosity. From the above results, it is concluded that the CrN coating provided a better corrosion protection than the other Cr-N coated steels.

Co-WC is increasingly used for precision dies and punches in semiconductor assembly process. The enhancement of impact resistance of hard layer coatings on Co-WC dies and punches is crucial for the application of hard coatings such as TiN. In this study, Co-WC has been deposited with a TiN film after Ti bombardment at various bias voltages of 0–750 V using the cathodic arc ion plating process. The surfaces' etching morphology and the temperature increase upon pre-bombardment with Ti ion onto Co-WC were evaluated by SEM and in-situ monitoring, respectively. The increase of bias voltage over 500 V significantly induced selective etching of Co and enhanced the substrate temperature higher than 300 °C in 10 min, thereby promoting the formation of a dense TiN film onto it. The prior etching of the surface by Ti ion bombardment with a high bias voltage was very effective in improving the adhesion of the TiN film on Co-WC and therefore reduced plastic deformation and crack density around the indentation area in a Rockwell C indentation test. The impact failure of a TiN coating on Co-WC could be consequently reduced under loads up to 150 N.

A duplex surface treatment technique based on calorizing and plasma nitriding was developed to improve the wear and oxidation resistance of H13 steel at high temperatures. The effects of the relative thickness of the calorized layer to the depth of plasma nitriding on the wear and oxidation properties at temperatures up to 900 °C were investigated in this work. High-temperature wear tests were performed at 500 °C with dry conditions in open air using a ball-on-disk type tribotest machine. Isothermal oxidation tests were performed at 900 °C for up to 100 h under controlled atmosphere. The results indicated that the specimens with a calorized layer as an intermediate phase between the surface duplex layer and the base metal showed higher wear and oxidation resistance than the specimens with a nitrided layer alone. During exposure to elevated temperatures, the aluminum in the calorized layer diffused to the surface and formed an aluminum oxide layer. This oxide layer protected the specimens from further oxidation and prevented the nitrogen from diffusing out of the surface, thus resulting in the retention of surface hardness even after exposure to high temperatures.

Duplex plasma surface treatment by calorizing and plasma nitriding was carried out on mild steel and high alloyed tool steel to improve their elevated temperature wear properties. Effects of calorizing on the plasma nitriding behavior of the steels and the characteristics of the duplex-treated specimens were analyzed using SEM, EDS, XRD, and a microhardness tester. Calorizing on mild steel created a FeAl compound layer of approximately 120 μm thickness, resulting in the improvement of the surface hardness by a factor of 2. Subsequent plasma nitriding increased the surface microhardness above 1200 Hv (0.1 kgf) and the nitriding depth was of the order of 80 μm. The high alloyed tool steels showed a decrease in microhardness in the Al-diffused layer upon calorizing. The subsequent plasma nitriding, however increased the hardness up to 1280 Hv and the nitriding depth of over 80 μm was obtained. The room temperature wear resistance of the duplex-treated steels was slightly better than that of the nitrided one, but there was considerable improvement in the high temperature wear resistance at 500°C in the duplex-treated steels when both the wear volume and the weight change due to oxidation were considered.

The photo-induced reaction of the functionalized cyclopentadienyl complexes (η 5 -C 5 H 4 CMe 2 R)W(CO) 3 Me (R  indenyl, C 9 H 7 ; fluorenyl, C 13 H 9 ) with alkynes C 2 R′ 2 (R′ = H, Ph) in solution yields the products (η 5 -C 5 H 4 CMe 2 R)W(CO)(C 2 R′ 2 )Me and (η 5 : η 1 -C 5 H 4 CMe 2 C 13 H 8 )-W(CO)(C 2 R′ 2 ). In these complexes the alkyne acts as a four electron ligand. A comparison of the molecular structures of (η 5 -C 5 H 4 CMe 2 C 13 H 9 )W(CO)(HC 2 Ph)Me and (η 5 : η 1 -C 5 H 4 CMe 2 C 13 H 8 )W(CO)(C 2 Ph 2 ) with (η 5 -C 5 H 5 Cr(CO)(C 2 H 2 )(NO) indicates that the different metal-alkyne bond distances are good criterea whether the alkyne ligand acts as four or two electron ligand.

Upon photolysis the indenyl and fluorenyl functionalized cyclopentadienyl complexes (η 5 -C 5 H 4 CMe 2 R)M(CO) 3 Me (R  C 9 H 7 (indenyl), C 13 H 9 (fluorenyl); M  Mo, W) and (η 5 -C 5 H 4 (CH 2 ) 3 C 13 H 9 ) W(CO) 3 Me are dealkylated to give methane, the monomeric tricarbonyl complexes (η 5 : η 1 -C 5 H 4 CMe 2 C 9 H 6 ) M(CO) 3 and (η 5 : η 1 -C 5 H 4 CMe 2 C 13 H 8 )W(CO) 3 , and the dinuclear complex [(η 5 -C 5 H 4 (CH 2 ) 3 C 3 H 9 )W(CO) 3 ] 2 ( 6 ). The molecular structures of (η 5 : η 1 -C 5 H 4 CMe 2 C 9 H 6 )Mo(CO) 3 and (η 5 : η 1 -C 5 H 4 CMe 2 C 13 H 8 )W(CO) 3 indicate that the C 9 H 6 unit is σ-bonded to the metal via the five-membered ring and the C 13 H 8 moiety via a six-membered ring. The dimeric complex 6 is held together by a comparatively long WW bond (3.2257(6) A).

The mono-substituted cyclopentadiene compounds AH (AH  C 5 H 5 CMe 2 C 9 H 7 , C 5 H 5 CMe 2 C 13 H 9 , C 5 H 5 (CH 2 ) 3 C 13 H 9 ) react with one equivalent of MeLi to give the corresponding cyclopentadienyl anions A − . The reactions of the anions A − and the complexes (CH 3 CN) 3 M(CO) 3 (M  MO, W) afford AM(CO) 3 − and the consequent reactions with MeI lead to the neutral complexes AM(CO) 3 Me. Photolysis of the indenyl-substituted complexes (η 5 -C 5 H 4 CMe 2 C 9 H 7 )M(CO) 3 Me in solution gives the novel π-complexes (η 5 : η 2 -C 5 H 4 CMe 2 C 9 H 7 )M(CO) 2 Me. The products are characterized by IR and NMR spectroscope, and X-ray crystallography.

A precise estimation and compensation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system, because sampling frequency mismatch between the transmitter and the receiver dramatically degrades the system performance due to the loss of orthogonality between the subcarriers. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose two SFO estimation methods which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation / compensation are mainly specialized on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has good performance and stable operation through extensive simulation.

To mitigate the asynchronous ICI (Inter-Cell Interference), the CFR (Channel Frequency Response) and SCM (Spatial Covariance Matrix) should be accurately estimated. Therefore, the enhanced asynchronous ICI mitigation scheme which can effectively reduce the estimation error of both CFR and SCM, and improve performance for MIMO (Multiple-Input Multiple-Output)-OFDMA (Orthogonal Frequency Division Multiple Access) system is derived. In particular, the lower-bound performance is approached to within 1 dB, by using the proposed method for both MMSE (Minimum Mean Square Error) and ML (Maximum Likelihood) receiver in the presence of asynchronous ICI.

In 3GPP Long Term Evolution (LTE) system, initial cell search procedure comprises two steps using primary synchronization signal (PSS) and secondary synchronization signal (SSS). This paper presents SSS detection method for second step of initial cell search. In general, coherent detection using estimated channel frequency response (CFR) at PSS is used for SSS detection, but performance degradation is occurred by difference of channel between PSS and SSS in time division duplex (TDD) mode. Thus we propose non-coherent detection using partial correlation and differential correlation. Moreover, we consider cyclic-prefix (CP) detection algorithm that uses CP and its repetition part of data symbol, and we investigate influence of CP detection in SSS detection process.

In this paper, we propose a coarse and fine frequency synchronization method which is suitable for the 3rd Generation Partnership Project (3GPP) long term evolution (LTE) orthogonal frequency division multiple access (OFDMA) system in time division duplexing (TDD) mode. In general, primary synchronization signal (PSS) correlation based estimation method and cyclic prefix (CP) correlation based tracking loop are applied for coarse and fine frequency synchronization in 3GPP LTE OFDMA system, respectively. However, the conventional coarse frequency synchronization method has performance degradation caused by fading channel and signal to noise ratio (SNR) loss. Also, the conventional fine frequency synchronization method cannot guarantee stable operation in TDD mode because there is no signal in uplink subframe. Therefore, in this paper, we propose enhanced coarse and fine frequency synchronization methods which can estimate more accurately in low SNR and high speed channel environments and has stable operation for TDD frame structure, respectively. By computer simulation, we show that the proposed methods outperform the conventional methods, and verify that the proposed frequency synchronization method can guarantee stable operation in 3GPP LTE OFDMA system in TDD mode.

To mitigate the asynchronous ICI (inter-cell interference), SCM (spatial covariance matrix) of the asynchronous ICI plus background noise should be accurately estimated for MIMO-OFDMA (multiple-input multiple-output-orthogonal frequency division multiple access) system. Generally, it is assumed that the SCM of the asynchronous ICI plus background noise is estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and training symbol is also not appropriate for MIMO-OFDMA system such as LTE (3GPP long term evolution). Therefore, a noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sine type weighing method which can not only reduce the noise effectively minimizing estimation error caused by the spectral leakage but also implement frequency-domain moving average filter easily. By using computer simulation, we show that the proposed method can provide up to 3 dB SIR (signal to interference ratio) gain compared with the conventional method, and verify that the proposed method is attractive and suitable for implementation with stable operation.

A precise estimation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose a SFO estimation method which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation /compensation are mainly based on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has a good performance and stable operation through extensive simulation.