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2009, The Journal of the Institute of Webcasting, Internet and Telecommunication
In this paper, we proposed and analyzed the performance of the adaptive switching equalization for SC-FDMA system. It is well known that SC-FDMA system have a fairly similar structure to OFDMA system. Furthermore, SC-FDMA system has great advantage of low PAPR compare to OFDM system. However, this system often suffers from wireless channel characteristics such as multipath fading and increased channel impulse response and so on. To reduce this channel influence, it strongly requires efficient adaptive equalization. Therefore, the proposed system operated upon two modes namely, ZF mode for slow speed and MMSE mode for high speed. From the simulation results, we can confirm that the proposed scheme has more efficient performance from the system complexity point of view. So we can expect that the proposed system will be applied design of 3GPP LTE uplink.
The Journal of Korean Institute of Electromagnetic Engineering and Science, 2010
Wireless communication channels with the most severe multipath fading phenomenon that appears each time a different delay is caused by the frequency selective fading. At this time, ISI due to the performance degradation of wireless communication channels and data transfer speed gives the constraints. OFDM technique can remove ISI inserting longer guard interval than channel delay spread of channel between symbol. However, the multi-path delay of the channel to be serious with the guard interval can not eliminate ISI. In this case, using the equalizer must compensate. Especially, use of equalizer is need absolutely as data rate becomes high speed. In this paper, we analyze the BER performance with pre-equalization for MIMO-OFDM over fading channel. The results of this paper can be applied to MIMO-OFDM system with equalization.
The Journal of the Institute of Webcasting, Internet and Telecommunication, 2010
In this paper, we propose the novel additional data transmission technology for DQPSK-OFDM based T-DMB system using watermarking technique. The proposed algorithms which is possible that it can transmit data in indoor or shadow region and improve transmission efficiency. We certified availability of our proposed technology by using various simulation. The results of the paper can be applied to wireless multimedia digital broadcasting systems.
The Journal of the Institute of Webcasting, Internet and Telecommunication, 2009
In this paper, we proposed spreading code slicing technique for efficient transmitter detection in AT-DMB system with single frequency network. At the transmitter, the spreading code for transmitter identification inserted using slicing technique on forehead of null symbol and then transmitted. In this point, it requires high correlation characteristic spreading code. At the receiver, peak to peak value calculated by correlation process before signal demodulation. The transmitter information by proposed technique is employed to implement the single frequency network (SFN) which is proposed for solving a frequency inefficiency problem of the MFN. The results of the paper can be applied to wireless multimedia digital broadcasting system.
The Journal of the Institute of Webcasting, Internet and Telecommunication, 2009
In this paper, we suggested new additional data transmission technology for T-DMB system using MOK-SS(Mary Orthogonal Keying-Spread Spectrum)mapping method. We applied revised watermarking method of TxID(Transmitter Identification) technology mainly had been used for conventional ATSC-DTV(Advanced Television Systems Committee-Digital TV). And proposed schemes enhanced additional data rate using MOK-SS mapping method. We certified availability of our proposed technology by using various simulation and error rate performance analysis.
The Journal of Korea Information and Communications Society, 2012
In this paper, an efficient power control based MF-TDMA resource allocation scheme is proposed for next generation military satellite communication systems. The proposed scheme has the flexibility is used to support heterogeneous terminals with differ in transmission capabilities. The method can be divided into two parts : burst size calculation and burst structure determination. At first, we estimate the link budget taken into account a dynamic satellite link state variation. Then, applicable ACM level and burst size is chosen. In burst structure determination phase, we reorganize the burst structure in time-frequency domain by controlling limited power, bandwidth, time resources. In particular, we compensate the power spectral density among different terminals to integrate them in same transponder, Furthermore, we increase the packing efficiency by controlling the ACM level of the burst in applicable power spectral density range. Simulation results show that the method increase the spectral efficiency and burst packing efficiency. In addition, slot allocation rejection ratio is successfully reduced.
The Transactions of The Korean Institute of Electrical Engineers, 2013
This paper presents a method for determining the optimal placement of distributed generation units considering voltage sags. In general, the existing methods for distributed generation placement do not consider power quality problems such as voltage sags. In this paper, a novel method based on both genetic algorithm and voltage sag assessment is proposed for determining the placement of distributed generation unit. In the proposed method, the optimal placement is determined to minimize voltage sag effects and system losses.
Journal of High Speed Networks, 2020
In the wireless sensor network (WSN), wireless communication is said to be the dominant power-consuming operation and it is a challenging one. Virtual Multiple-Input–Multiple-Output (V-MIMO) technology is considered to be the energy-saving method in the WSN. In this paper, a novel multihop virtual MIMO communication protocol is designed in the WSN via cross-layer design to enhance the energy efficiency, reliability, and end-to-end (ETE) and Quality of Service (QoS) provisioning. On the basis of the proposed protocol, the optimal set of parameters concerning the transmission and the overall consumed energy by each of the packets is found. Furthermore, the modeling of ETE latency and throughput of the protocol takes place with respect to the bit-error-rate (BER). A novel hybrid optimization algorithm referred as Flight Straight Moth Updated Particle Swarm Optimization (FS-MUP) is introduced to find the optimal BER that meets the QoS, ETE requirements of each link with lower power cons...
2019
최근 대용량 전력 전송 시스템에서 모듈형 다단 컨버터(Modular Multilevel Converter; MMC)를 이용한 고압 직류(high voltage DC; HVDC) 송전 시스템이 각광받고 있다. 일반적으로, 전압형 컨버터는 AC 단 출력전압 합성 방법에 따라 AC 단 전압 사용률이 달라지며, MMC 시스템에 있어서도 마찬가지이다. 따라서, HVDC 송전시스템의 DC 단의 용량이 정해져 있는 경우에도 출력 전압 합성 방법에 따라 AC 단으로 공급 가능한 최대 무효 전력의 크기를 변화시킬 수 있다. 본 논문에서는 대표적인 전압 변조 방식에 따른 암 에너지 맥동을 수학적으로 분석하였으며, 이를 MMC의 실제 스케일의 시뮬레이션으로 검증하였다.
Korea Society of Coastal Disaster Prevention, 2016
The Runge-Kutta DGFEM (Discontinuous Galerkin Finite Element Method) is applied to the discretization of 1D high-order Boussinesq equation of Madsen et al. (2002). Discontinuous Galerkin method is used, which allows discontinuities at the element interfaces, for the spatial discretization and explicit high-order Runge-Kutta method is adopted in time integration. The connection between interfaces is set as an approximate Riemann problem and Lax-Friedrichs numerical fluxes are employed. To remove the unnecessary oscillations, Savitzky-Golay filter is applied to the solution at each time step. When necessary, a numerical sponge layer is set to mimic the open boundary condition and relaxation zone is set for the internal wave generation. As benchmark case studies, the propagation of sine (linear) wave and nonlinear wave over a submerged breakwater are simulated with the developed numerical model. For the latter case study, the results are compared with experimental data and good agreement is observed.
Journal of manufacturing engineering & technology, 2013
In this paper, in order to overcome shortcomings of manual inspection for the automotive PWM Shaft, we developed an automated inline inspection system. The automated inline inspection system consists of the work feeder unit, conveying unit, outer diameter check unit, run-out and roundness check unit, machine vision, defective separation unit and status alarm unit. We used the machine vision system for automatic inspection process and designed the inline systems for automatic feeding and selecting process. Also the repeated operation test was performed in order to verify the precision and reliability of the proposed automated inline inspection system.
Journal of the Korean Society of Marine Engineering, 2010
In this paper, we propose a method for swing-up and stabilization of a SESIP(Self-Erecting Single Inverted Pendulum) system which is one of the typical nonlinear systems. We use PV(Proportional velocity) controller for swinging up the pendulum and employ a PI-type state-feedback controller for stabilizing the pendulum. Control is switched to a stabilizing controller, which is designed to balance the inverted position of pendulum and the cart position to the near vertical position. Computer simulations are performed to illustrate the control performance of the proposed scheme.
The Transactions of the Korean Institute of Electrical Engineers, 2017
Electric energy is consumed or regenerated according to an operation of electric rail cars in urban railway power substations. A thyristor dual converter system is used to deal with the electric energy. Since the AC input voltage of power substations is 22.9kV ± 10%, the magnitude of the AC voltage fluctuates according to load conditions, so the secondary side voltage of the DDY transformer also fluctuates. In the thyristor dual converter, the response characteristics of the DC output voltage and the DC output current are changed based on an initial firing angle in the cross mode conversion between the forward mode and the reverse mode. Therefore, this paper proposes the initial firing angle tracking algorithm considering fluctuation of the AC input voltage. The effectiveness of the proposed algorithm is verified by a simulation compared with the conventional algorithm.
Clean Technology, 2012
The performance of the ammonia injection gun (AIG) used for maximizing the utilization of reducing agent in the selective catalytic reduction (SCR) system is decided by several parameters such as the pattern of flow distribution, geometry of the air distribution manifold (ADM) and the array and geometry of nozzles. In the study, the uniformity of jet flows from the nozzles in AIG was analyzed statistically by using the computational fluid dynamics (CFD) method to evaluate the role of design parameters on the performance of the SCR system. The uniformity of jet flows from the nozzles is being deteriorated with increasing the supplying flow rate to the AIG. Distribution rates to each branch pipe become lower with decreasing distance to the header, and flow rates from nozzle are also reduced with decreasing distance to the header. The uniformity of jet flows from nozzles becomes stable significantly when the ratio of summative area of nozzles to each sectional area of the branch pipe is below 0.5.
The Journal of the Acoustical Society of Korea, 2013
We present a parametric array signal generating system using 3×16 transducer array which is composed of multi-resonant frequency transducers of 20kHz and 32.5kHz. To drive transducer array, sixteen channel amplifier using LM1875 chips is designed and implemented, and the PXI system based on the LabView 8.6 for arbitrary signal generation and analysis is used. Using the proposed system, we measure sound pressure level and beam pattern of difference frequency and verify the nonlinear effect of difference frequency. The theoretical absorption range and the Rayleigh distance are 15.51m and 1.933m, respectively and we verify that sound pressure of difference frequency is accumulated and increased at the near-field shorter than the Rayleigh distance. We verify that the beam pattern of the measured difference frequency and the beam pattern obtained by the superposition of two primary frequencies are similar, and high directional parametric signal was generated.
Transactions of the Korean Society of Mechanical Engineers A, 2010
Journal of the Korean Society of Marine Engineering, 2008
Journal of Institute of Control, Robotics and Systems, 2019
Constrained devices such as wireless sensor network (WSN) nodes, which have limited capabilities, are widespread in Internet of Things (IoT) applications. To connect devices with low computing power and limited memory to the Internet, the Internet Engineering Task Force (IETF) proposed the Constrained Application Protocol (CoAP), a light-weighted standard communication protocol. CoAP has a worst-case communication delay greater than 10 times the average delay time depending on the wireless network environment. In this paper, we propose an algorithm that dynamically assigns a re-transmission timeout (RTO) parameter value specified in the CoAP to reduce the communication delay and delay variance. In our proposed algorithm, delay times were measured, for either a pre-defined period or number of transmissions, to calculate an average delay time and set the average delay time equal to the RTO value for the next communication period. To evaluate the stability of the algorithm, Round Trip Time (RTT) was adopted as a performance index in several experiments. Every 1,000 RTT values were measured to calculate average time delay, and this average value was set to the RTO value for the subsequent round. The experimental results show that the performance of our proposed algorithm was improved around 10 times better than that of the basic algorithm in the CoAP in terms of the delay variance, which was calculated by dividing the worst-case RTT value by the average RTT value. The average RTT of the proposed algorithm was also improved 14% comparing with that of the basic one.
Journal of Fluid Machinery, 2010
Axial fan (축류홴), Multi-sectioning design method (멀티섹션 설계기법), Camber angle (캠버각), Stagger angle (설치각),
Journal of the Korean Society of Precision Engineering, 2013
In Projection Stereolithography Apparatus (PSLA), Digital Micromirror Device (DMD) and Liquid Crystal Display (LCD) are used as a beam pattern generator. The DMD shows high resolution, but it is mostly applied in micro stereolithography due to high cost and fabricable area. In LCD, the size of pattern beam is freely controlled due to various panel sizes. The LCD, however, has some limitations such as short life time by the high power light source, non-uniform light intensity of pattern beam and low transmittance of UV-light. To solve these problems in LCD-based PSLA, a Scanbeam-SLA with LCD of 19 inches and visible LED-array is developed. In this system, the light module works like a scanner for uniform illumination. The system configuration, working principle and fabrication examples are addressed in this study.
Journal of Sensor Science and Technology, 2010
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