• Journal of Astronomy and Space Sciences
• /
• v.21 no.2
• /
• pp.129-140
• /
• 2004

KAO(Korea Astronomy Observatory) GPS group has developed an iRTK system as a near-real time positioning system using GPS carrier phase data. We focused on improving the accuracy of positioning through the updated capability of data processing of KAO's iRTK system using low-cost L1 carrier phase receiver. The accuracy of a positioning was demonstrated by Extended Kalman filter. Experiments were accomplished using from 30m to 20km baselines. Within 10km, the positioning accuracy was improved by approximately 50-70% to the previous study using one minute observable data. However, it took two minutes to obtain 1m level positioning accuracy at 20km point. We expect that the developed iRTK system can be applied to the various fields of GPS in near-real time positioning.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• v.2
• /
• pp.15-22
• /
• 2006

This paper presents a novel signal tracking algorithm for GNSS receivers using a MLE technique. In order to perform a robust signal tracking in severe signal environments, e.g., high dynamics for navigation vehicles or weak signals for indoor positioning, the MLE based signal tracking approach is adopted in the paper. With assuming white Gaussian additive noise, the cost function of MLE is expanded to the cost function of NLSE. Efficient and practical approach for Doppler frequency tracking by the MLE is derived based on the assumption of code-free signals, i.e., the cost function of the MLE for carrier Doppler tracking is used to derive a discriminator function to create error signals from incoming and reference signals. The use of the MLE method for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited for various GNSS signals with same structure of tracking module. This paper proposes two different types of MLE based tracking method, i.e., an iterative batch processing method and a non-iterative feed-forward processing method. The first method is derived without any limitation on time consumption, while the second method is proposed for a time limited case by using a 1st derivative of cost function, which is proportional to error signal from discriminators of conventional tracking methods. The second method can be implemented by a block diagram approach for tracking carrier phase, Doppler frequency and code phase with assuming no correlation of signal parameters. Finally, a state space form of FLL/PLL/DLL is adopted to the designed MLE based tracking algorithm for reducing noise on the estimated signal parameters.

• Journal of the Institute of Convergence Signal Processing
• /
• v.7 no.4
• /
• pp.184-188
• /
• 2006

This paper presents DSP based narrow band satellite communication signal power detector for tracking control of mobile satellite antenna system. An analog filter based conventional power detector has poor performance due to frequency drift of carrier. Also, it is very difficult to change an analog filter bandwidth according to changed bandwidth of transmitted signal. To solve these difficulties, we proposed DSP based signal power detector, which is easy to change bandwidth of filter and to match shifted frequency of carrier. The proposed signal power detector consists of a FFT function to measure frequency drift of carrier, a programmable filter bank function to limit of received signal bandwidth and a power calculation function to measure power of filtered signal in 12-bit linear scale. Test results of implemented signal power detector, based on TMS320C5402 DSP, showed that it satisfied required functions and performances and properly operated.

• Journal of Ceramic Processing Research
• /
• v.19 no.5
• /
• pp.372-377
• /
• 2018

MgO or gadolinium-doped ceria (GDC, $Ce_{0.9}Gd_{0.1}O_{2-{\delta}}$) was added as a promoter to improve the oxygen transfer kinetics of $MgMnO_3$ oxygen carrier material for chemical looping combustion. Neither MgO nor GDC reacted with $MgMnO_3$, even at the high temperature of $1100^{\circ}C$. The average oxygen transfer capacities of $MgMnO_3$, 5 wt% $MgO-MgMnO_3$, and 5 wt% $GDC-MgMnO_3$ were 8.74, 8.35, and 8.13 wt%, respectively. Although the addition of MgO or GDC decreased the oxygen transfer capacity, no further degradation was observed during their use in 5 redox cycles. The addition of GDC significantly improved the conversion rate for the reduction reaction of $MgMnO_3$ compared to the use of MgO due to an increase in the surface adsorption process of $CH_4$ via oxygen vacancies formed on the surface of GDC. On the other hand, the conversion rates for the oxidation reaction followed the order 5 wt% $GDC-MgMnO_3$ > 5 wt% $MgO-MgMnO_3$ >> $MgMnO_3$ due to morphological change. MgO or GDC particles suppressed the grain growth of the reduced $MgMnO_3$ (i.e., (Mg,Mn)O) and increased the specific surface area, thereby increasing the number of active reaction sites.

• Elastomers and Composites
• /
• v.58 no.1
• /
• pp.44-56
• /
• 2023

Additive manufacturing (AM) or three-dimensional (3D) printing of metals has been drawing significant attention due to its reliability, usefulness, and low cost with rapid prototyping. Among the various AM technologies, fused deposition modeling (FDM) or fused filament fabrication is receiving much interest because of its simple manufacturing processing, low material waste, and cost-effective equipment. FDM technology uses metal-filled polymer filaments for 3D printing, followed by debinding and sintering to fabricate complex metal parts. An efficient binder is essential for producing polymer filaments and the thermal post-processing of printed objects. This study involved an in-depth investigation of and a fabrication route for a novel multi-component binder system with steel alloy powder (45 vol.%) ranging from filament fabrication and 3D printing to debinding and sintering. The binder system consisted of polyvinyl pyrrolidone (PVP) as a binder and thermoplastic polyurethane (TPU) and polylactic acid (PLA) as a carrier. The PVP binder held the metal components tightly by maintaining their stoichiometry, and the TPU and PLA in the ratio of 9:1 provided flexibility, stiffness, and strength to the filament for 3D printing. The efficacy of the binder system was examined by fabricating 3D-printed cubic structures. The results revealed that the thermal debinding and sintering processes effectively removed the binder/carrier from the cubic structures, resulting in isotropic shrinkage of approximately 15.8% in all directions. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) patterns displayed the microstructure behavior, phase transition, and elemental composition of the 3D cubic structure.

• Journal of the Institute of Convergence Signal Processing
• /
• v.2 no.3
• /
• pp.32-38
• /
• 2001

Multi-carrier data transmission system performance is mostly limited by Inter- symbol-interference that is caused by a dispersive characteristic of the transmission channel. In order to enhance the system performance to meet the service requirements of local access, the channel impulse response shortening method incorporated with a channel frequency response compensation method is proposed. For a fast and efficient implementation of the equalizer proposed, Kalman and LMS algorithms are successively used. To verify the channel equalization performance, a set of computer simulation is performed on a filter bank based multitone system operating in a typical high-speed local area data transmission environment. The results showed us a comparable signal-to-interference improvement over the conventional multitone equalization scheme.

• Korean Journal of Materials Research
• /
• v.16 no.5
• /
• pp.292-296
• /
• 2006

Effects of rapid thermal annealing of bismuth telluride thin films on their thermoelectric properties were investigated. Films with four different compositions were elaborated by co-sputtering of Bi and Te targets. Rapid thermal treatments in range of $300{\sim}400^{\circ}C$ were carried out during 10 minutes under the reducing atmosphere (Ar with 10% $H_2$). As the temperature of thermal treatment increased, carrier concentrations of films decreased while their mobilities increased. These changes were clearly observed for the films close to the stoichiometric composition. Rapid thermal treatment was found to be effective in improving the thermoelectric properties of $Bi_2Te_3$ films. Recrystallization of $Bi_2Te_3$ phase has caused the enhancement of thermoelectric properties, along with the decrease of the carrier concentration. Maximum values of Seebeck coefficient and power factor were obtained for the films treated at $400^{\circ}C$ (about $-128{\mu}V/K$ and $9{\times}10^{-4}\;W/K^2m$, respectively). With further higher temperature ($500^{\circ}C$), thermoelectric properties deteriorated due to the evaporation of Te element and subsequent disruption of film's structure.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.4 no.5
• /
• pp.691-708
• /
• 2010

An important issue of supporting multi-users with diverse quality-of-service (QoS) requirements over wireless networks is how to optimize the systematic scheduling by intelligently utilizing the available network resource while, at the same time, to meet each communication service QoS requirement. In this work, we study the problem of a variety of communication services over multi-media heterogeneous cognitive OFDM system. We first divide the communication services into two parts. Multimedia applications such as broadband voice transmission and real-time video streaming are very delay-sensitive (DS) and need guaranteed throughput. On the other side, services like file transmission and email service are relatively delay tolerant (DT) so varying-rate transmission is acceptable. Then, we formulate the scheduling as a convex optimization problem, and propose low complexity distributed solutions by jointly considering channel assignment, bit allocation, and power allocation. Unlike prior works that do not care computational complexity. Furthermore, we propose the FAASA (Fairness Assured Adaptive Sub-carrier Allocation) algorithm for both DS and DT users, which is a dynamic sub-carrier allocation algorithm in order to maximize throughput while taking into account fairness. We provide extensive simulation results which demonstrate the effectiveness of our proposed schemes.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.21 no.2
• /
• pp.173-180
• /
• 2003

As the utility value of GPS in surveying field is on the increase after the conversion into the world geodetic system, most of the baseline processing programs seeking the relative baseline vector for the roving point based on the base point are dependent on the foreign software, and such dependence remains a stumbling block to its wide application. In this study an algorithm was established settling ambiguity through LAMBDA techniques and the baseline processing program was developed for Ll carrier phase using visual c＋＋ 6.0, which is an object-oriented language. And the developed program proved that it maintained a difference of less than 4.9 cm over the short baseline of 4.9 km or shorter when compared with other commercialized programs.

• Journal of Communications and Networks
• /
• v.7 no.3
• /
• pp.248-257
• /
• 2005

In this paper, we develop design procedures for carrier tracking loop for orthogonal frequency division multiplexing (OFDM) systems or other systems of blocked data. In such communication systems, phase error measurements are made infrequent enough to invalidate the traditional loop design methodology which is based on analog loop design. We analyze the degradation in the OFDM schemes caused by the tracking loop and show how the performance is dependent on the rms phase error, where we distinguished between the effect of the variance in the average phase over the symbol and the effect of the phase change over the symbol. We derive the optimal tracking loop including optional delay in the loop caused by processing time. Our solution is general and includes arbitrary phase noise apd additive noise spectrums. In order to guarantee a well behaved solution, we have to check the design against margin constraints subject to uncertainties. In case the optimal loop does not meet the required margin constraints subjected to uncertainties, it is shown how to apply a method taken from control theory to find a controller. Alternatively, if we restrict the solution to first or second order loops, we give a simple loop design procedure which may be sufficient in many cases. Extensions of the method are shown for using both pilot symbols and data symbols in the OFDM receiver for phase tracking. We compare our results to other methods commonly used in OFDM receivers and we show that a large improvement can be gained.