• ETRI Journal
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• v.42 no.5
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• pp.700-711
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• 2020

Because of the rapid increase of mobile traffic, flexible broadband supportive unmanned aerial vehicle (UAV)-based 6G mobile networks using free space optical (FSO) links have been recently proposed. Considering the advancements made in UAVs, big data processing, and artificial intelligence precision control technologies, the formation of an additional wireless network based on UAV aerial platforms to assist the existing fixed base stations of the mobile radio access network is considered a highly viable option in the near future. In this paper, a combined time bound optimization scheme is proposed that can adaptively satisfy the control and communication time constraints as well as the processing time constraints in FSO-based 6G UAV aerial networks. The proposed scheme controls the relation between the number of data flows, input data rate, number of worker nodes considering the time bounds, and the errors that occur during communication and data processing. The simulation results show that the proposed scheme is very effective in satisfying the time constraints for UAV control and radio access network services, even when errors in communication and data processing may occur.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1840-1846
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• 2014

An experimental outdoor optical wireless data communication system with an optical filter in the presence of sunlight or artificial light is presented. For the efficient blocking of light noise outdoors, we employ an optical filter made of microlouver film on the top of the photo diode. This filter is designed to block any light noise incident from an angle higher than $30^{\circ}$ on the assumption that light noise does not face the photo diode horizontally. Outdoor experiments daytime with the optical filtering have been conducted. The experimental results demonstrate that the optical filter effectively blocks nearly all light noise incident from the specified angle or higher and more than 90% of the transmitted data packets are successfully received. The proposed outdoor visible light data communication can thus facilitate a practical free space outdoor optical wireless data transmission.

• Current Optics and Photonics
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• v.1 no.4
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• pp.325-335
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• 2017

Hybrid radio frequency/free space optical (RF/FSO) wireless mesh networks have attracted increasing attention for they can overcome the limitations of RF and FSO communications and significantly increase the throughput of wireless mesh networks (WMNs). In this article, a resource assignment optimization scheme is proposed for hybrid RF/FSO wireless mesh networks. The optimization framework is proposed for the objective of maximizing throughput of overall hybrid networks through joint transmission slot assignment, FSO links allocation and power control with the consideration of the fading nature of RF and FSO links. The scheme is formulated as an instance of mixed integer linear program (MILP) and the optimal solutions are provided using CPLEX and Gurobi optimizers. How to choose the appropriate optimizer is discussed by comparing their performance. Numerous simulations are done to demonstrate that the performance of our optimization scheme is much better than the current case of having the same topology.

• ETRI Journal
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• v.44 no.6
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• pp.966-976
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• 2022

Optical wireless communication, or free space optics, is a promising solution for backhauls in sixth-generation mobile systems. However, the susceptibility of optical links to weather conditions has led to FSO links being furnished with radio frequency (RF) backups. These Hybrid FSO/RF systems provide enhanced link availability but lead to RF resource wastage. Cognitive radio technology, in contrast, is well known for its optimal use of RF resources and may be combined with an FSO link to create a Cognitive Hybrid FSO/RF system. This work uses such a system to analyze a configuration for a mobile backhaul in sixth-generation mobile systems. This configuration can seamlessly coexist with established large scale RF cellular networks. The performance of this configuration is analyzed with respect to outage probability and average bit error by considering the impact of optical channel turbulence, misalignment loss, RF interference, and noise. Mathematical closed-form expressions are verified by simulations.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.2
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• pp.169-174
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• 2014

This paper proposes a novel beehive-shaped reflector for application to light-emitting diode (LED) transceivers for illumination and bi-directional visible light communication (VLC). By using a diffuse propagation model extended to line-of-sight and direct signals, the distribution of illuminance and the path loss of the transceiver are investigated to evaluate the performance of the beehive-shaped reflector. To verify bi-directional communication, a VLC-based image capture system, comprising a complementary metal-oxide semiconductor (CMOS) image sensor and video processor unit, is demonstrated. Real-time images captured by the CMOS camera are successfully transmitted to the monitoring system via a free-space channel at a rate of 115.2 kbps.

• Journal of Sensor Science and Technology
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• v.22 no.6
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• pp.421-427
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• 2013

In this paper, we introduce a new synchronous visible light communication system in which the synchronizing pulse and the data bits are simultaneously transmitted using a 3-level light signal. In the transmitter, the synchronizing pulse and the data bits modulate independently two identical visible LEDs, whose output lights add in free space, make 3-level optical signal. In the receiver, a photodiode detects the light and generates a 3-level output voltage, whose positive and negative part correspond to the synchronizing pulse and the data bits, respectively. The two signals are easily separated and recovered by a simple diode circuit. This configuration provides two independent VLC channels without any multiplexing technique, simplifies the circuit design and construction of synchronous VLC systems.

• Current Optics and Photonics
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• v.1 no.4
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• pp.271-277
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• 2017

Based on the extended Huygens-Fresnel principle, the analytical propagation formulae for spectrally partially coherent Gaussian Schell-model pulsed (SPGSMP) beams propagating in turbulent atmosphere have been derived. The influences of the parameters for turbulent atmosphere and SPGSMP beams on the on-axis and off-axis spectral shift and degree of coherence for SPGSMP beams propagating in turbulent atmosphere have been analyzed, using numerical calculations. The obtained results have potential applications for SPGSMP beams in free-space optical communication and laser lidar.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.425-430
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• 2013

Robust and high speed underwater communication is severely limited when compared to communications in terrestial. In free space, RF communication operates over long distances at high data rates. However, the obstacle in seawater is the severe attenuation due to the conducting nature. Acoustic modems are capable of long range communication up to several tens of kilometers, but it has low data-rate, high power consumption and low propagation speed. An alternative means of underwater communication is based on optics, wherein high data rates are possible. In this paper, the characteristics of underwater channel in the range of visible wavelength is investigated. And the possibility of optical wireless communication in underwater is also described. The LED-based transceiver and CMOS sensor module are integrated in the system, and the performance of image transmission was demonstrated.

• Electronics and Telecommunications Trends
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• v.33 no.6
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• pp.118-128
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• 2018

With the massive increase in bandwidth for wireless communications, free space optical (FSO) communication has attracted significant interest owing to its outstanding strengths over conventional radio frequency wireless communication such as a wide bandwidth, unlicensed spectrum, low power consumption, small size, electromagnetic interference immunity, long-range propagation, and improved security. In recent years, FSO technology has been studied intensively for use in terrestrial and underwater autonomous and unmanned mobile systems, a rapidly growing application area, including robots, drones, unmanned aerial vehicles, autonomous vehicles, unmanned trains, and unmanned submarines. In this report, we review the recent trends and key technologies for the mobile FSO system, and introduce our drone-based mobile FSO system, which is currently under development.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.102-107
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• 2011

LED-based lighting motivated by significant energy savings provides an opportunistic development of widespread free-space optical communications. Their transceivers have a variety of competitive advantages over RF including high bandwidth density, reliability, lower energy consumption, and long lifetime. But, it is difficult for existing buildings and structures such as ships and vehicles to install the communication cable to the ceiling. In this paper, controller area network (CAN)-based LED lighting communication systems were proposed. Results indicate the viability of developing inexpensive CAN interface modules and transceivers might be embedded in lighting products to support the indoor wireless networking.