• Smart Structures and Systems
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• v.30 no.5
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• pp.433-446
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• 2022

Despite efforts to reduce unexpected accidents at confined construction sites, choking accidents continue to occur. Because of the poorly ventilated atmosphere, particularly in long, confined underground spaces, workers are subject to dangerous working conditions despite the use of artificial ventilation. Moreover, the traditional monitoring methods of using portable gas detectors place safety inspectors in direct contact with hazardous conditions. In this study, a long-range (LoRa)-based wireless safety monitoring system that features the network organization, fault-tolerant, power management, and a graphical user interface (GUI) was developed for underground construction sites. The LoRa wireless data communication system was adopted to detect hazardous gases and oxygen deficiency within a confined underground space with adjustable communication range and low power consumption. Fault tolerance based on the mapping information of the entire wireless sensor network was particularly implemented to ensure the reliable operation of the monitoring system. Moreover, a sleep mode was implemented for the efficient power management. The GUI was also developed to control the entire safety-monitoring system and to manage the measured data. The developed safety-monitoring system was validated in an indoor testing and at two full-scale water pipeline construction sites.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.8 s.111
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• pp.719-724
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• 2006

In this paper, we designed the double conversion down mixer by using Half-LO frequency in 2.3 GHz band. The IF frequency is obtained by supplying two LO frequencies to HEMT in both gate type and resistive type. The proposed mixer uses Half-LO frequency the same way as conventional sub-harmonic mixers. However the proposed one uses fundamental component of Half-LO frequency in first stage instead of using second harmonic components of Half-LO frequency, and the IF frequency is obtained by resistive type mixer in second stage, thereby the proposed mixer can improve linearity in comparison with conventional active mixer. We can verify that the proposed mixer has an conversion loss of 5dBm and IIP3 of 16.25dBm by using 10 dBm Power.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.753-759
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• 2005

In this paper, we have developed a new type of single balanced mixer with the RF MEMS $180^{\circ}$ hybrid coupler using surface micromachining technology. The $180^{\circ}$ hybrid coupler in this mixer is composed of the dielectric-supported air gapped microstriplines(DAMLs) which have signal line with $10{\mu}m$ height to reduce substrate dielectric loss and dielectric posts with size of $20{\mu}m{\times}20{\mu}m$ to elevate the signal line on air with stability At LO power of 7.2 dBm, the conversion loss was 15.5 dB f3r RF frequency or 57 GHz and RF power of -15 dBm. Also, we obtained the good RF to LO isolation of -40 dB at LO frequency of 58 GHz and LO power of 7.2 dBm. The main advantage of this type of mixer is that we are able to reduce the size of the chips due to integrating the MEMS passive components.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.1
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• pp.99-104
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• 2013

In this paper, we developed a fully integrated downconverter MMIC (monolithic microwave integrated circuit) including Lange coupler and output active balun for millimeter wave applications. Concretely, ${\lambda}$/4 transmission line was added to Lange coupler for size reduction of RF/LO input, and mixed RF/LO signals were applied to gate of the FET of mixer. Active balun was used at output port for a coupling of out-of-phase IF output signals. According to measured results, the proposed downconverter MMIC showed good RF performances. For example, the downconverter MMIC showed an LO leakage power of -25 dBc at IF output port, and a RF-LO isolation of 18 dB. Therefore, off-chip components such as LO rejection filters were not required for a normal operation of the proposed downconverter MMIC. The proposed downconverter MMIC showed a conversion gain of 10.3 dB at RF frequency of 63 GHz. The size of the downconverter MMIC including all active and passive components was $2.2{\times}1.4mm^2$.

• Journal of Korea Society of Industrial Information Systems
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• v.15 no.1
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• pp.1-14
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• 2010

It is recently issued scalability, mobility and external internet connection on Wire-less sensor network. The low power wireless sensor networks based on IPv6 technology 6LoWPAN technology is being standardized in the IETF. This paper for the 6LoWPAN environment based on the routing protocol LOAD, route cost applied the packet re-transmission rate which follows in Link Qualities price which uses at course expense and packet transmission Minimum route Cost routing protocol where does on the course wherethe smallest packet re-transmission becomes accomplished proposed. The technique which proposes compared and LOAD and AODV that about 13%, about 16% energy consumption is few respectively averagely, Energy of the entire network equally, used and energy effectiveness and improvement of network life time experiment led and confirmed.

• Proceedings of the Korean Society of Computer Information Conference
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• 2019.07a
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• pp.103-104
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• 2019

최근 스마트시티 구축 사업에서 사물인터넷 기반 서비스 개발이 활발히 진행 중이다. 그 서비스들을 제공하기 위해 사용되어야 할 디바이스 수가 수백만 개까지 증가할 것으로 예상하고 있으며 수백만 개의 디바이스들을 수용하기 위해서는 Massive IoT 네트워크의 환경 구축을 필요로 하고 있다. 따라서 본 논문에서는 Massive IoT 네트워크 환경을 구축하기 위해 저전력 광역 네트워크(LPWAN) 기술 중 LoRa(Long Range) 네트워크가 적용이 가능한지를 LoRaSim을 이용하여 시뮬레이션한다. 시뮬레이션한 결과 중 충돌 횟수를 통해 충동률을 구하고 그래프를 이용하여 신뢰성을 나타내며, Massive IoT 네트워크에 적합성에 대해 분석한다.

• Smart Media Journal
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• v.13 no.1
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• pp.45-51
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• 2024

Long Range Wide Area Network (LoRaWAN) is a widely adopted Internet of Things (IoT) protocol due to its high range and lower energy consumption. LoRaWAN utilizes Adaptive Data Rate (ADR) for efficient resource (e.g., spreading factor and transmission power) management. The ADR manages these two resource parameters on the network server side and end device side. This paper focuses on analyzing the ADR and Gaussian ADR performance of LoRaWAN. We have performed NS3 simulation under a static scenario by varying the antenna height. The simulation results showed that antenna height has a significant impact on the packet delivery ratio. Higher antenna height (e.g., 50 m) has shown an improved packet success ratio when compared with lower antenna height (e.g., 10 m) in static and mobility scenarios. Based on the results, it is suggested to use the antenna at higher allevation for successful packet delivery.

• KIISE Transactions on Computing Practices
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• v.24 no.1
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• pp.1-9
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• 2018

Low-power long-range networks (LoRa) has a comprehensive coverage of up to 30 km, so that long-range positioning is possible. However, the position error in the current LoRa environment is over 500 m. This makes it difficult to use practical location services in the LoRa environment. In this paper, we propose a method to improve the position accuracy by correcting an inaccurate visual error when sending a signal from a mobile node to a gateway through the reference node of each zone in the LoRa environment. Experiments were carried out using MATLAB, and a radio propagation algorithm, the Hata model, was used to cancel out the stationary noise and to evaluate the environmental noise. Experimental results showed that the error range decreased as the number of reference nodes increased and a mobile node approach the reference node.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.3
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• pp.15-23
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• 2020

As the IoT industry expands, various application services based on location information of devices are released. In order to transmit the location information, various wireless communication technologies such as Bluetooth and Wi-Fi are used. However, these technologies have limited coverage, and cellular networks with relatively wide coverage have the disadvantage of paying for use. In this paper, we implemented our own location information system using LoRa, a low power long distance wireless communication technology. As a result, no cost is incurred and it has relatively wider coverage than other wireless communication technologies using LoRa technology. The implementation system enables LoRa communication based on IPv6 using CoAP and 6LoWPAN, and enables multiple devices to interwork with the existing Internet environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.2
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• pp.113-119
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• 2017

In this paper, we have shown the performance analysis results of the LoRa low power wide area network under duty cycle local regulation in Korean RFID/USN frequency band. Especially, we analyzed uplink throughput and data transmission time of a single LoRa end device. From the analysis results, duty cycle regulation, in which a data transmission should be ended within 0.4 second, limits the performance of LoRa network. Therefore, it is necessary to revise Korea's duty cycle regulation referencing EU regulation in order to assess LoRa network in Korea.