• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.596-599
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• 2004

We propose an Alamouti-like scheme for combining space-time block coding with single-carrier frequency-domain equalization(SC-FDE) in fixed broadband wireless access environment. With two transmit antennas, the scheme is shown to achieve significant diversity gains at low complexity over frequency-selective fading channels

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.1
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• pp.50-54
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• 2016

A Wireless Sensor Network (WSN) is better than a conventional network for use in construction and Operations and Maintenance (O&M) because of its lower surveillance system cost. However, effective operation of a WSN is often difficult to obtain because the surveillance targets are usually fixed inside the building or underground. Therefore, this environmental constraint should be considered in the design of the WSN plant equipment surveillance system prior to installation. This study employs simulations of WSN-based fixed facility surveillance using the TinyOS TOSSIM simulator to investigate ideal types and setups of the WSN. Simulation target protocols included LEACH and flooding and gossiping protocols. The results show that the hierarchically-structured LEACH protocol demonstrated better load-balancing and efficiency than the flatly-structured flooding and gossiping protocol.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1279-1286
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• 2009

This paper addresses the analysis of the interference produced between the LEO(Low Earth Orbit) satellite constellation and FS(Fixed Service) system operating in the same frequency and area. At first, we calculates the interference of FS system from the LEO satellite constellation depending on the number of LEO satellite antenna beams. Simulation results show that the amount of interference that was calculated from each region. This result can be used to define the carrier level for protecting FS system from total interference by LEO satellite constellation. In the second scenario, we calculates the interference of LEO satellite system earth station by the FS link depending on radius of protection area. The presented results can be used to design FS systems minimizing interference to earth station.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10C
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• pp.929-936
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• 2009

In this paper, we consider designing a multi-input multi-output (MIMO) overlay system for fixed MIMO wireless link, where a frequency flat narrowband channel is shared by multiple transmitter and receiver pairs. Assuming the perfect knowledge of the second-order statistics of the received legacy signals and the composite channels from the overlay transmitter to the legacy receivers, the jointly optimal linear precoder and decoder matrices of the MIMO overlay system is derived to minimize the total mean squared error (MSE) of the data symbol vector, subject to total average transmission power and zero interference induced to legacy MIMO systems already existing in the frequency band of interest. Furthermore, the necessary and sufficient condition for the existence of the optimal solution is also derived.

• Electronics and Telecommunications Trends
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• v.35 no.2
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• pp.38-49
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• 2020

In recent years, the unmanned aerial vehicle (UAV) assisted mobile free space optical (FSO) communication technique has attracted considerable attention regarding its aims to provide improved communication conditions for fixed-to-fixed FSO network and promising fronthaul and backhaul solutions for 5G+ wireless networks. This can be attributed to its outstanding advantages such as fast deployment and flexible network configuration. The UAV-assisted mobile FSO system can be used to provide cost-effective internet services in rural and remote areas and in hotspot areas that are characterized by increased data traffic. Additionally, it can be used to provide secure communication services under emergency circumstances. In this report, we review recent R&D trends in wireless network technology employing the UAV-assisted mobile FSO technique and key technologies for mobile FSO wireless networks. Furthermore, we introduce drone-based mobile FSO terminals and control systems that we have developed.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.3
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• pp.180-191
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• 2022

In this paper, a single-stage alternating current (AC)-DC converter is proposed for the automated-guided vehicle wireless charging system. The proposed converter is capable of soft-switching under all input voltage (VAC: 220 Vrms ± 10%), load conditions (0-1 kW), and air gap changes (40-60 mm) by phase control at a fixed switching frequency. In addition, controlling a wide output voltage (Vo: 39~54 VDC) is possible by varying the link voltage and improving the input power factor and the total harmonic distortion factor. Experimental results were verified by making a prototype of a 1-kW wireless power charging system that operates with robustness to changes in air gaps.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.7
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• pp.4554-4561
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• 2014

In recent years, several paradigms have been identified to simplify the design of fault-tolerant distributed applications in a conventional static system. Leader Election is among the most noticeable, particularly because it is closely related to group communication, which provides a powerful basis for implementing active replications among other uses. On the other hand, despite its usefulness, to our knowledge, no study has focused on this problem in a mobile computing environment. The aim of this paper was to propose an algorithm for the leader election protocol in a fixed station based wireless networks environment. The election algorithm is much more efficient than other election algorithms in terms of the fault tolerance.

• Journal of Communications and Networks
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• v.9 no.3
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• pp.247-253
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• 2007

In this paper, downlink capacity of time duplex division (TDD) based cellular wireless networks utilizing fixed hopping stations is investigated. In the network, a number of fixed subscriber stations act as hopping transmission stations between base stations and far away subscribers, forming a cellular and ad hoc mobile network model. At the radio layer, TDD code division multiple access (CDMA) is selected as the radio interface due to high efficiency of frequency usage. In order to improve the system performance in terms of downlink capacity, we propose different time slot allocation schemes with the usage of fixed hopping stations, which can be selected by either random or distanced dependent schemes. Performance results obtained by computer simulation demonstrate the effectiveness of the proposed network to improve downlink system capacity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7A
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• pp.569-580
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• 2012

In this paper, an enhanced initial ranging algorithm for large-cell coverage fixed wireless communication system is proposed. In typical wireless communication system such as WiBro, because a round-trip delay between a transmitter and a receiver is within one OFDM (Orthogonal Frequency Division Multiplexing) symbol duration, a frequency-domain differential correlation method is generally used. However, the conventional method cannot be applied due to an increase of a maximum time delay in large-cell system. In case of an accumulative differential method, estimation errors can occur because of frequent sign transitions. In this paper, therefore, we propose an algorithm which can estimate a total timing offset in a ranging channel structure for 15 km cell. The proposed method can improve performance by sign comparison based sign error correction rule between the estimated values and using a weighting scheme based on channel correlation, the number of accumulations, and the noise reduction effect in normalization process. Also, it can estimate the integer timing offset of symbol duration by comparing peak-powers after compensating for the fractional timing offset of symbol duration.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1346-1349
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• 2002

This paper presents the design and implementation of 16-QAM modem that can be applied to fixed broadband wireless access systenm. It is implemented in the hardware prototype that consist of FPGA(Field Programmable Gate Array) for digital signal processing and analog front end module for analog signal processing. We provide 20.48Mbps data rate using implemented modem and test the modem in KOREA 26㎓ broadband wireless local loop system including IFU(Intermediate Frequency Unit) and RFU(Radio Frequency Unit) via air interface.