• 정보화사회
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• s.24
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• pp.10-11
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• 1989

• TTA Journal
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• s.156
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• pp.45-50
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• 2014

• Journal of Space Technology and Applications
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• v.4 no.2
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• pp.87-104
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• 2024

CubeSats are being utilized in various fields such as Earth observation, space exploration, and verification of space science and technology due to their low cost, short development period, enhanced mission-oriented performance, and ability to perform various missions through constellation and formation flights. Recently, as the availability of CubeSats has increased and their application areas have expanded, the demand for high-speed transmission of large amounts of data obtained by CubeSats has increased unprecedentedly. Laser-based free space optical communication technology is capable of transmitting large amounts of data at high speeds compared to the existing radio communication methods, and provides various advantages such as use of unlicensed spectrum, low cost, low power, high security characteristics, and of use a small communication platform. For this reason, it is suitable as a high-performance communication technology to support CubeSat missions. In this paper, we will present the core components and characteristics of CubeSat-based space laser communication system, and recent research trends, as well as representative technology development results.

• Journal of the Korea Society of Computer and Information
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• v.25 no.10
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• pp.125-133
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• 2020

In this paper, we design 4-layer TCP/IP that utilizes minimal memory and processor resources in Internet of Things(IoT) systems. The TCP/IP designed in this paper has the following characteristics. First, memory resource is minimized by using minimal memory allocation. Second, processor resource is minimized by using minimal memory copy. Third, the execution time of the TCP/IP can be completed in a deterministic time. Fourth, there is no memory leak problem. The standard in minimal resources for memory and processor derived in this paper can be used to check whether the network subsystems of the already implemented IoT systems are efficiently implemented. As the result of measuring the amount of memory allocation and copy of the network subsystem of Zephyr, an open source IoT kernel recently released by the Linux Foundation, we found that it was bigger than the standard in minimal resources derived in this paper. The network subsystem of Zephyr was improved according to the design proposed in this paper, confirming that the amount of memory allocation and copy were decreased by about 39% and 67%, respectively, and the execution time was also reduced by about 28%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.539-546
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• 2010

In next generation wireless communication systems based on OFDM, multiple-input multiple-output (MIMO) technique is adopted in order to achieve high data throughput with limited bandwidth. As one of MIMO techniques, spatial multiplexing scheme needs high performance data detection algorithm that can be performed with low computational complexity. In this paper, we propose an algorithm that can compute QRM-MLD with reduced complexity. Also, hybrid detection technique is proposed, which can reduce the complexity by selecting between MMSE and QRM-MLD according to the channel condition. The proposed algorithm provides the trade-off between performance and complexity. The computer simulations for downlink transmission in 3GPP LTE system show that less than 0.1dB performance degradation can be achieved at 0.1% BER with 59% reduction on computational complexity compared with the conventional QRM-MLD algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.20-26
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• 2010

The downlink scheduling algorithm has a great impact on the performance of mobile telecommunication system. In proportional fairness (PF) scheduling algorithm, the resource is allocated proportionally to the quality of wireless channel. Thus, PF has difficulty in servicing the users having more downlink traffic. One can allocate the resource proportionally to the accumulated queue length. However, this leads to system throughput degradation since the users having low channel quality get more and more resource allocated due to accumulation property of queue. In this paper, we propose a new downlink scheduling algorithm, which extends PF algorithm by incorporating downlink traffic arrival rate. The proposed algorithm can effectively cope with users having more downlink traffic, and maintain high system throughput by eliminating accumulation effect in the algorithm. With computer simulations, it is verified that the proposed algorithm performs better than existing algorithms.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.113-119
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• 2018

This paper relates the AM-NM-MMA algorithm which possible to adaptive equalization performance improvement using the adaptive modulus instead of fixed modulus in the NM-MMA algorithm. The NM-MMA emerged for the tradeoff the MMA and SE-MMA algorithm characteristics, the MMA provides the less residual values in the steady state and have a slow convergence rate, the SE-MMA provides the fast convergence rate and increae the risidual values in the steady state. But the fixed modulus can not give the zero residual values in the perfect equalization state and eqaulization performance were degrade, the adaptive modulus was applied in order to reducing the residual values, and its improved performance were confirmed by simulation. For this, the equalizer output constellation, residual isi, MD, MSE, SER were used for performance index. As a result of computer simulation, the AM-NM-MMA has more good performance in equalizer output signal constellation, residual isi, MD, MSE than the NM-MMA, but not in SER performance.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.5
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• pp.3-15
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• 2003

The secure group communication enables the members, which belong to the same group, to communicate each other in a secure and secret manner. To do so, it is the most important that a group key is securely distributed among them and also group membership is efficiently managed. In detail, the generation, the distribution and the refreshment of a group key would be highly regarded in terms of low communication and computation complexity. In this paper, we show you a new protocol to generate a group key which will be safely shared within a group, utilizing the 2-party Diffie-Hellman key exchange protocol and the complete binary tree. Our protocol has less complexity of computation per group member by substituting many parts of exponentiation computations for multiplications. Consequently, each group member needs constant computations of exponentiation and multiplication regardless of the group size in the protocol and then it has less complexity of the computation than that of any other protocols.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.4
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• pp.571-578
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• 2023

In this paper, we propose a low EMI data transmitter employing a delay-locked loop for vehicles. For the low EMI characteristic, the transmitter has been designed to have low slew rate and employs the delay-locked loop to correct the amount of change in the slew rate due to process variations. According to simulation results, the proposed transmitter which the delay-locked loop has smaller slew rate change as compared to the conventional transmitter. The proposed circuit has been designed with a 65nm process technology and the data rate is 20Mbps with a supply voltage of 1.1V. As compared to a conventional transmitter, the proposed transmitter shows that variations of the slew rate become 53.6% lower in a fast condition and 13.07% lower in a slow condition.

• The Journal of the Korea Contents Association
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• v.22 no.8
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• pp.81-93
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• 2022

Recently, research on processing a large-capacity graph using GPUs has been conducting. In order to process a large-capacity graph in a GPU with limited memory, the graph must be divided into subgraphs and then processed by scheduling subgraphs. In this paper, we propose an efficient graph algorithm processing scheme in GPU environments with limited memory and performance evaluation. The proposed scheme consists of a graph differential subgraph scheduling method and a graph segmentation method. The bulk graph segmentation method determines how a large-capacity graph can be segmented into subgraphs so that it can be processed efficiently by the GPU. The differential subgraph scheduling method schedule subgraphs processed by GPUs to reduce redundant transmission of the repeatedly used data between HOST-GPUs. It shows the superiority of the proposed scheme by performing various performance evaluations.