• Journal of Communications and Networks
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• v.18 no.3
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• pp.429-438
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• 2016

In this paper, we investigate an interference mitigation scheme by antenna selection in device-to-device (D2D) communication underlaying downlink cellular networks. We first present the closed-form expression of the system achievable rate and its asymptotic behaviors at high signal-to-noise ratio (SNR) and the large antenna number scenarios. It is shown that the high SNR approximation increases with more antennas and higher ratio between the transmit SNR at the base station (BS) and the D2D transmitter. In addition, a tight approximation is derived for the rate and we reveal two thresholds for both the distance of the D2D link and the transmit SNR at the BS above which the underlaid D2D communication will degrade the system rate. We then particularize on the small cell setting where all users are closely located. In the small cell scenario, we show that the relationship between the distance of the D2D transmitting link and that of the D2D interfering link to the cellular user determines whether the D2D communication can enhance the system achievable rate. Numerical results are provided to verify these results.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.335-344
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• 2016

Scientific CubeSat with Instruments for Global Magnetic Fields and Radiations (SIGMA) is a 3-U size CubeSat that will be operated in low earth orbit (LEO). The SIGMA communication system uses a very high frequency (VHF) band for uplink and an ultra high frequency (UHF) band for downlink. Both frequencies belong to an amateur band. The ground station that communicates with SIGMA is located at Kyung Hee Astronomical Observatory (KHAO). For reliable communication, we carried out a laboratory (LAB) test and far-field tests between the CubeSat and a ground station. In the field test, we considered test parameters such as attenuation, antenna deployment, CubeSat body attitude, and Doppler frequency shift in transmitting commands and receiving data. In this paper, we present a communication performance test of SIGMA, a link budget analysis, and a field test process. We also compare the link budget with the field test results of transmitting commands and receiving data.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.2
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• pp.105-111
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• 2009

The powers used in the motor drive system are mostly DC sources like batteries. Even AC powers in some systems are generated from DC sources by the inverter. It is can be forecasted that the DC-link communications will be widely used in various industrial fields. In this paper a novel BLDC motor drive system using DC-link communications is proposed. The characteristic of this system Is that the communication only needs 2 DC lines. There are not additional lines to translate the reference signals. And the reliability o3 the system is ensured especially under some terrible circumstances. The number of lines can be minimized when the DC-link communication method is applied in the multi motor control system and the slip ring design also can be simplified when this method is applied in rotation machines. The proposed motor system is clarified by the PSIM and MATLAB simulations and tested through the hardware prototype.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.441-450
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• 2007

In this paper, it is proposed the link performance analysis results using SNRAT(Satellite Network Resource Allocation & Analysis Tool) and verified the anticipated results by satellite communication network simulator. A communication satellite cannot be corrected or fixed for the error in orbit operation after launching unlike the ground operation equipment and has a restricted operation life. So, it is important to make possible to use satellite communications in the proper time. It is expected the link BER(Bit Error Rate), throughput and AJ(Anti-Jamming) performance using SNRAT tool before launching. And it is verified the performance of the repeaters and ground equipment specification using the satellite network simulator and is extracted the optimum operational scenarios through the tests of various network operational plans.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.1
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• pp.15-24
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• 2008

The data delivery confirmation method of MIL-STD-188-220C, which is a tactical wireless mobile Ad-Hoc communication protocol, is that a source node requires the end-to-end ack from all destination nodes and the data-link ack from 1-hop neighboring destination nodes and relaying nodes, regardless of the hop distance from a source node to destination nodes. This method has the problem to degrade the whole communication network performance because of excessive data traffic due to the duplicate use of end-to-end ack and data-link ack, and the collision among end-to-end acks on the wireless network in the case of confirming a data delivery within an 1-hop distance. In order to solve this problem, this paper has proposed the method to perform the data delivery confirmation with the improvement of communication network performance through the data traffic reduction by achieving the reliable data delivery confirmation requiring the only data-link ack within an 1-hop distance. The effects of the proposed method are analyzed in the two aspects of the data delivery confirmation delay time and the data delivery confirmation success ratio.

• Journal of Korea Multimedia Society
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• v.20 no.4
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• pp.593-605
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• 2017

In applications which are covered wide range, it is possible that one or more number of Unmanned Aerial Vehicle(UAV) squadrons are used to perform a mission. In this case, it is most important to communicate seamlessly between the UAV squadrons. In this paper, we applied the modified OLSR(OSLR-Pds) which can prediction for state of the link for the communication in UAV squadron, and applied the modified AOMDV which can build multi-path for the communication between UAV Squadrons. The mobility of nodes are modeled using Gauss-Markov algorithm, and relative speed between nodes were calculated by derive equation of movement, and thereby we can predict link state for in a squadron and between squadrons. An experiment for comparing AODV, AOMDV and the proposed routing protocol was conducted by three factors such as packet delivery ratio, end to end delay, and routing overhead. In experiment result, we make sure that the proposed protocol performance are superior in these three factors. However, if the density of the nodes constituting FANET are too low, and if the moving speed of node is very slow, there is no difference to others protocols.

• Journal of Communications and Networks
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• v.11 no.3
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• pp.271-278
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• 2009

A new modulation scheme called multicoded-pulse position modulation (MC-PPM) is proposed for an ultrawideband (UWB) impulse radio communication system. The multicoded signal is generated by using several orthogonal codes for transmitting data simultaneously. Then, each multi-level value of the multicoded signal is converted to pulse position which results in not only an improved data rate, but also a processing gain in reception, delivering the power-efficient benefit of PPM and guaranteeing the low pulse energy for UWB systems. We notice that the modulation of multi-level values of the multicoded signal to pulse position is more efficient in terms of achievable data rate than the modulation of transmitting data based on other PPM schemes within given bandwidth and pulse energy. Therefore, as a performance measure, we focus on the achievable data rate (link capacity) of the proposed scheme and analyze it theoretically. Through simulation, we compare the link capacity of the MC-PPM scheme and other PPM schemes, such as M -ary PPM and multiple PPM. With the fixed bandwidth and same pulse energy condition, the UWB system based on the proposed MC-PPM scheme shows good link capacity and an increased data rate as L increases, which is contrary to other PPM schemes.

• Journal of the military operations research society of Korea
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• v.30 no.2
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• pp.32-49
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• 2004

The Tactical Data Link System is a standardized communication link to exchange and interface positional, situational information, command and control in real time. It has been evaluated that this Link would play an important role for tactical interoperability, situation awareness, and execution of joint operations in the future war. But considering the rapidly changing war situations, even though being admitted the necessity of the Tactical Data Link System of Army helicopter, one of superpowers in the Army, substantially we don't still have any concrete concept to build it. Therefore, this work presents how to embody the Tactical Data Link System through computer-aided system engineering on the base of Tactical Data Link System operating concept analysis of helicopters-ground units.

• 시스템엔지니어링워크숍
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• s.4
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• pp.146-150
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• 2004

The Tactical Data Link System(TDLS) is a standardized communication link to exchange and interface positional, situational information, command and control in real time. It has been evaluated that the link would play an important role for tactical interoperability, situation awareness, and execution of joint operations in the future war. This work presents how to embody the TDLS through the systems engineering approach on the base of TDLS operating concept analysis of helicopters-groud units.

• Korean Journal of Optics and Photonics
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• v.33 no.3
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• pp.113-121
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• 2022

We analyze the link availability of satellite-to-ground free-space optical (FSO) communication systems in South Korea. Using ten-year meteorological data for five major cities (Seoul, Busan, Daegu, Daejeon, and Gwangju), we theoretically predict the link availability from the power losses induced by absorption, scattering, aerosols, and scintillation in the atmospheric channel. For accurate but conservative estimation of the link availability determined by cloud cover, we propose a loss model based on the maximum value of cloud droplet concentration. The results show that the link availability ranges from 45% to 70% when a single ground station is placed in a major city in South Korea and a 20-dB link budget is allocated for atmospheric loss. However, the availabilities improve to 90% and 97% when 3- and 5-site diversities are employed, respectively.