• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.1
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• pp.71-76
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• 2022

Since brightness is proportional to the operating current, a method of connecting several LEDs in series and driving with a constant current source is widely used for driving circuits of LED lights. Because several LEDs are connected in series, if some LEDs open due to a fault, the current path is broken and all other LEDs connected in series are turned off. In this paper, we designed a circuit to solve this problem by connecting a Zener diode having a breakdown voltage of about 0.4V higher than the LED operating voltage in parallel with each LED to create a current bypass in case of LED failure. Through simulations and experiments, it was confirmed that the current of the Zener diode hardly flows when the LED is operating normally, and that the Zener diode stably operates as a current bypass when the LED fails.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.2
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• pp.71-76
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• 2022

Round-robin is widely used for the scheduling of large-scale parallel workloads in the computing units of GPGPU. Round-robin is easy to implement by sequentially allocating tasks to each computing unit, but the load balance between computing units is not well achieved in multi-workload environments like cloud. In this paper, we propose a new thread block scheduling policy to resolve this situation. The proposed policy manages thread blocks generated by various GPGPU workloads with multiple queues based on their computation loads and tries to maximize the resource utilization of each computing unit by selecting a thread block from the queue that can maximally utilize the remaining resources, thereby inducing load balance between computing units. Through simulation experiments under various load environments, we show that the proposed policy improves the GPGPU performance by 24.8% on average compared to Round-robin.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.315-333
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• 2021

Due to the Global Navigation Satellite System (GNSS) modernization, recently launched GNSS satellites transmit signals at various frequency bands such as L1, L2 and L5. Considering the Korean Positioning System (KPS) signal and other GNSS augmentation signals in the future, there is a high probability of applying more complex communication techniques to the new GNSS signals. For the reason, GNSS receivers based on flexible Software Defined Radio (SDR) concept needs to be developed to evaluate various experimental communication techniques by accessing each signal processing module in detail. This paper proposes a novel SDR-based A-GNSS receiver capable of processing multi-GNSS/RNSS signals at multi-frequency bands. Due to the modular structure, the proposed receiver has high flexibility and expandability. For real-time implementation, A-GNSS server software is designed to provide immediate delivery of satellite ephemeris data on demand. Due to the sampling bandwidth limitation of RF front-ends, multiple SDRs are considered to process the multi-GNSS/RNSS multi-frequency signals simultaneously. To avoid the overflow problem of sampled RF data, an efficient memory buffer management strategy was considered. To collect and process the multi-GNSS/RNSS multi-frequency signals in real-time, the proposed SDR A-GNSS receiver utilizes multiple threads implemented on a CPU and multiple NVIDIA CUDA GPGPUs for parallel processing. To evaluate the performance of the proposed SDR A-GNSS receiver, several experiments were performed with field collected data. By the experiments, it was shown that A-GNSS requirements can be satisfied sufficiently utilizing only milliseconds samples. The continuous signal tracking performance was also confirmed with the hundreds of milliseconds data for multi-GNSS/RNSS multi-frequency signals and with the ten-seconds data for multi-GNSS/RNSS single-frequency signals.

• International Journal of Internet, Broadcasting and Communication
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• v.14 no.3
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• pp.182-192
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• 2022

This study analyzed the effects of the all-in-one automatic fire shutter (hereinafter referred to as "all-in-one shutter") installed along the fire compartment in a five-story high school building on the evacuation time by using the Pathfinder simulation program. When the all-in-one shutter was added as a new variable, the evacuation time was delayed, indicating insufficient evacuation safety. The evacuation time exceeded the appropriate standard when the evacuation exit was designated to the students in the present state of being placed on the 2nd, 3rd, and 4th floors and the all-in-one shutter was activated. When students were placed on the 1st, 2nd and 3rd floors under the same conditions, the evacuation time was also greatly exceeded. However, when the width of the entrance was set to 130cm, the evacuation time was almost the same as when the all-in-one shutter was not installed. In high-rise school buildings, the bottleneck caused by all-in-one shutters is becoming a major factor in evacuation barriers. To ensure the evacuation safety of school buildings, it has been judged that evacuation education and training to predict the evacuation time required through the all-in-one shutter entrance and induce an evacuation procedure suitable for the standard evacuation time should be carried out in parallel. The implications of this study and suggestions for effective fire compartments and follow-up studies were discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.5
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• pp.442-453
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• 2023

Tandem or multijunction solar cells (MJSCs) can convert sunlight into electricity with higher efficiency (η) than single junction solar cells (SJSCs) by dividing the solar irradiance over sub-cells having distinct bandgaps. The efficiencies of various common SJSC materials are close to the edge of their theoretical efficiency and hence there is a tremendous growing interest in utilizing the tandem/multijunction technique. Recently, III-V materials integration on a silicon substrate has been broadly investigated in the development of III-V on Si tandem solar cells. Numerous growth techniques such as heteroepitaxial growth, wafer bonding, and mechanical stacking are crucial for better understanding of high-quality III-V epitaxial layers on Si. As the choice of growth method and substrate selection can significantly impact the quality and performance of the resulting tandem cell and the terminal configuration exhibit a vital role in the overall proficiency. Parallel and Series-connected configurations have been studied, each with its advantage and disadvantages depending on the application and cell configuration. The optimization of both growth mechanisms and terminal configurations is necessary to further improve efficiency and lessen the cost of III-V on Si tandem solar cells. In this review article, we present an overview of the growth mechanisms and terminal configurations with the areas of research that are crucial for the commercialization of III-V on Si tandem solar cells.

• Journal of the Institute of Convergence Signal Processing
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• v.23 no.4
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• pp.234-240
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• 2022

This paper proposes a customized AI exercise recommendation service for balancing the relative amount of exercise according to the working environment by each occupation. WISDM database is collected by using acceleration and gyro sensors, and is a dataset that classifies physical activities into 18 categories. Our system recommends a adaptive exercise using the analyzed activity type after classifying 18 physical activities into 3 physical activities types such as whole body, upper body and lower body. 1 Dimensional convolutional neural network is used for classifying a physical activity in this paper. Proposed model is composed of a convolution blocks in which 1D convolution layers with a various sized kernel are connected in parallel. Convolution blocks can extract a detailed local features of input pattern effectively that can be extracted from deep neural network models, as applying multi 1D convolution layers to input pattern. To evaluate performance of the proposed neural network model, as a result of comparing the previous recurrent neural network, our method showed a remarkable 98.4% accuracy.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.2
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• pp.361-366
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• 2023

Apache Hadoop, a representative framework for distributed processing of big data, has the advantage of increasing cluster size up to thousands of nodes to improve parallel distributed processing performance. However, reducing the size of the cluster is limited to the extent of permanently decommissioning nodes with defects or degraded performance, so there are limitations to operate multiple nodes flexibly in small clusters. In this paper, we discuss the problems that occur when removing nodes from the Hadoop cluster and propose a dynamic down-scaling technique to manage the distributed cluster more flexibly. To do this, we design and implement a modified Hadoop system and interfaces to support dynamic down-scaling of the cluster which supports temporary pause of a node and reconnection of it when necessary, rather than decommissioning the node when removing a node from the Hadoop cluster. We have verified that effective downsizing can be performed without performance degradation based on experimental results.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.2
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• pp.291-298
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• 2023

SRAM-based in-memory computing is one of the technologies to solve the bottleneck of von Neumann architecture. In order to achieve SRAM-based in-memory computing, it is essential to design efficient SRAM bit-cell. In this paper, we propose a low-power differential sensing 8+T SRAM bit-cell which reduces power consumption and improves circuit performance. The proposed 8+T SRAM bit-cell is applied to ripple carry adder which performs SRAM read and bitwise operations simultaneously and executes each logic operation in parallel. Compared to the previous work, the designed 8+T SRAM-based ripple carry adder is reduced power consumption by 11.53%, but increased propagation delay time by 6.36%. Also, this adder is reduced power-delay-product (PDP) by 5.90% and increased energy-delay- product (EDP) by 0.08%. The proposed circuit was designed using TSMC 65nm CMOS process, and its feasibility was verified through SPECTRE simulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.4
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• pp.381-389
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• 2009

Orthogonal frequency division multiplexing(OFDM) that is very useful for the high-speed communication system has serious problem of high peak-to-average power ratio(PAPR) in time domain. Because of this, the non-linear distortion can be produced and system performance gets worse. CI-OFDM system can get the peak power lowered. In this CI-OFDM system, each parallel data is distributed into N all sub-carriers and conveyed by the orthogonal phase factor. Also, CI-OFDM shows frequency diversity effect. Therefore, CI-OFDM system is better than ordinary OFDM system in terms of BER performance and the PAPR reduction. When it is implemented, however, there is a serious problem whether it can separate and compensate the phase factor in order in the receiver. Because all bits are transmitted simultaneously over all subcarriers and each other phase factors in transmitter. In this paper, we propose and evaluate a FD-CI-OFDM system that is a version of improved CI-OFDM. This is designed by use of the Walsh Hadamard sequence. The FD-CI-OFDM shows better performance than ordinary OFDM and CI-OFDM system.

• Journal of the Korea Convergence Society
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• v.2 no.4
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• pp.29-37
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• 2011

Dispersed generation (DG) such as wind power (WP) and Photovoltaic systems (PV) that has been promoted at the national level recently is mainly being introduced into distribution systems adjacent to consumers because it is generation on a small scale when compared to current generation. Due to its characteristics, DG can be operated by interconnection with distribution systems to present security of more stable power and efficient use of power facilities and resources. Problems on protection coordination of distribution systems by reverse flow of DG can roughly be divided into three possibilities: excess in rated breaking capacity (12.5KA) of protective devices by a fault in DG current supply, failure to operate protective devices by an apparent effect that can occur by reduction in impedance parallel circuit fault current due to interconnection of DG, and malfunction of protective devices by interconnection transformer connection type. The purpose of this study is to analyze problems in protection coordination that can occur when DG is operated by interconnection with distribution systems by conducting modeling and simulations by using theoretical symmetrical components and MATLAB/SIMULINK to present methods to improve such problems.