• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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• pp.3862-3879
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• 2019

More and more problems for public security have occurred due to the limited solutions for drone detection especially for micro-drone in long range conditions. This paper aims at dealing with drones detection using a radar system. The radio frequency (RF) signals emitted by a controller can be acquired using the radar, which are usually too weak to extract. To detect the drone successfully, the static clutters and linear trend terms are suppressed based on the background estimation algorithm and linear trend suppression. The principal component analysis technique is used to classify the noises and effective RF signals. The automatic gain control technique is used to enhance the signal to noise ratios (SNR) of RF signals. Meanwhile, the empirical mode decomposition (EMD) based wavelet transform (WT) is developed to decrease the influences of the Gaussian white noises. Then, both the azimuth information between the drone and radar and the bandwidth of the RF signals are acquired based on the statistical analysis algorithm developed in this paper. Meanwhile, the proposed accumulation algorithm can also provide the bandwidth estimation, which can be used to make a decision accurately whether there are drones or not in the detection environments based on the probability theory. The detection performance is validated with several experiments conducted outdoors with strong interferences.

• ETRI Journal
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• v.41 no.4
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• pp.536-548
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• 2019

In this study, an electronically steerable parasitic array radiator (ESPAR) antenna via analog radio frequency (RF) switches for a single RF chain MIMO system is presented. The proposed antenna elements are spaced at ${\lambda}/64$, and the antenna size is miniaturized via a dielectric radome. The optimum reactance load value is calculated via the beamforming load search algorithm. A switch simplifies the design and implementation of the reactance loads and does not require additional complex antenna matching circuits. The measured impedance bandwidth of the proposed ESPAR antenna is 1,500 MHz (1.75 GHz-3.25 GHz). The proposed antenna exhibits a beam pattern that is reconfigurable at 2.48 GHz due to changes in the reactance value, and the measured peak antenna gain is 4.8 dBi. The reception performance is measured by using a $4{\times}4$ BPSK signal. The measured average SNR is 17 dB when using the proposed ESPAR antenna as a transmitter, and the average SNR is 16.7 dB when using a four-conventional monopole antenna.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.4
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• pp.245-250
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• 2022

As location-based services using the Global Navigation Satellite System (GNSS) are diversified, concerns about the vulnerability of GNSS to radio disturbance and deception are also growing. Accordingly, countries that own and operate GNSS, such as the United States, Russia, and Europe, are also developing additional navigation systems that can compensate for GNSS' weaknesses. Among them, an R-Mode system that transmits navigation signals using an infrastructure that transmits differential GNSS (DGNSS) information using signals from the medium frequency band currently in operation is being developed in Europe and Korea. Since 2020, Korea has improved four DGNSS transmission stations, including Chungju, Eocheongdo, Palmido, and Socheongdo, to transmit R-Mode signals and test navigation performance in some parts of the West Sea. In this paper, we intend to establish a testbed for measuring the distance of R-Mode signals currently being transmitted and analyze the results. It is confirmed that the distance measurement performance varies depending on the antenna type, diurnal variation, and propagation path of the signal.

• ETRI Journal
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• v.45 no.1
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• pp.45-59
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• 2023

In this paper, to optimize the average delay and power allocation (PA) for system users, we propose a resource scheduling scheme for wireless networks based on Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) according to the first fifth-generation standards. For delay minimization, we solve a throughput maximization problem that considers CPOFDM systems with carrier aggregation (CA). Regarding PA, we consider an approach that involves maximizing goodput using an effective signal-to-noise ratio. An algorithm for jointly solving delay minimization through computation of required user rates and optimizing the power allocated to users is proposed to compose the resource allocation approach. In wireless network simulations, we consider a scenario with the following capabilities: CA, 256-Quadrature Amplitude Modulation, millimeter waves above 6 GHz, and a radio frame structure with 120 KHz spacing between the subcarriers. The performance of the proposed resource allocation algorithm is evaluated and compared with those of other algorithms from the literature using computational simulations in terms of various Quality of Service parameters, such as the throughput, delay, fairness index, and loss rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.11
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• pp.3204-3217
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• 2023

In this paper, the downlink of the multicast based spatial modulation systems is investigated. Specifically, physical layer multicasting is introduced to increase the number of access users and to improve the communication rate of the spatial modulation system in which only single radio frequency chain is activated in each transmission. To minimize the bit error rate (BER) of the multicast based spatial modulation system, a joint optimizing algorithm of antenna selection and multicast precoding is proposed. Firstly, the joint optimization is transformed into a mixed-integer non-linear program based on single-stage reformulation. Then, a novel iterative algorithm based on the idea of branch and bound is proposed to obtain the quasioptimal solution. Furthermore, in order to balance the performance and time complexity, a low-complexity deflation algorithm based on the successive convex approximation is proposed which can obtain a sub-optimal solution. Finally, numerical results are showed that the convergence of our proposed iterative algorithm is between 10 and 15 iterations and the signal-to-noise-ratio (SNR) of the iterative algorithm is 1-2dB lower than the exhaustive search based algorithm under the same BER accuracy conditions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.5
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• pp.384-394
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• 1996

The propagation properties of square and Gaussian pulse signals on the microstrip line are investigated by using proper conventional models to meet the frequency range of a pulse, accuracy, and geometrical requirements of the microstrip line. Numerical integration technique which has its accuracy and is easily simulated, is used to obtain the time domain response of pulse signals. The dispersion of pulse signals is analyzed regarding to the relative permittivity $\varepsilon_r$, substrate height h, strip width w of the microstrip line and pulse width $\tau$ of signal pulse. The simulation results show that small relative permittivity and small rationale of w/h are advantageous for the dispersion of the pulse signals, and that pulse signals with small bandwidth cause smaller dispersion. The results of this paper are compatible to the trade-off determination of relative permittivity, substrate height, strip width and pulse width of signal pulse when a design of MIC and MMIC is necessary.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.1
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• pp.45-49
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• 2016

The performance of underwater acoustic communication systems is sensitive to inter-symbol interference caused by delay spread developed from multipath signal propagation. The multipath nature of underwater channels causes signal distortion and error floor. In order to improve the performance, it is necessary to employ an iterative coding scheme. Of the various iterative coding schemes, turbo code and convolutional code based on the BCJR algorithm have recently dominated this application. In this study, the performance of iterative codes based on turbo equalizers with equivalent coding rates and similar code word lengths were analyzed. Underwater acoustic communication system experiments using these two coding techniques were conducted on Kyeong-chun Lake in Munkyeong City. The distance between the transmitter and receiver was 400 m, and the data transfer rate was 1 Kbps. The experimental results revealed that the performance of turbo codes is better for channeling than that of convolutional codes that use a BCJR decoding algorithm.

• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.53-58
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• 2007

The Satellite Mobile Communication System holds several advantages, such as wide coverage that guarantees the communication in a huge area. It is suitable in the ocean and forest and especially in emergency situation. However, the licensed frequency is not always occupied within all coverage and all the time. The actual utilization rate is relatively low compared to other wireless communications such as cellular systems. There are a large amount of white spaces in its coverage. Therefore, it is necessary to consider introducing additional services such as data communication, in order to increase the spectrum utilization as well as the revenue of the Satellite service provider. In this paper, we first analyze the possibility to implement new services in the licensed band of satellite mobile phone by its provider. Then we address the most significant issue for the implementation of current service, which is how to accurately detect the satellite mobile terminals. Finally, we suggest two new possible solutions namely, eigenvalue detection based methods to find out the existence of transmitted signal from the satellite mobile terminals.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.745-751
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• 2018

This paper reports on the design of a multiband multiple-input and multiple-output(MIMO) antenna for long-term evolution(LTE) vehicular communication and includes an analysis of the throughput field test results that were acquired by mounting the antenna to a vehicle. The antenna used for the field test was designed as a planar structure and included multiple stubs to obtain multiband resonant characteristics operating in the LTE(0.8~0.9 GHz, 1.7~2.2 GHz), Wi-Fi(2.4~2.48 GHz), and wireless access in vehicular environments (WAVE)(5.8~5.9 GHz) frequency bands. For the field test, antenna prototypes were mounted on the dashboard and roof of a vehicle and connected to the experimental LTE modem. The data transfer rate(throughput), signal-to-interference-plus-noise ratio(SINR), and reference signal received quality(RSRQ) were measured and analyzed in various real-world radio wave environments. Based on these results, the relationship between the SINR and throughput according to the field intensity is confirmed.

• Journal of Navigation and Port Research
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• v.29 no.1 s.97
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• pp.23-28
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• 2005

The signal in wireless multi-path channel is affected by fading and ISI because of high data rate transmission, so the signal has the high error rate. The present modulation and demodulation method of DSRC system can not expect sufficient for providing data service over 1 Mbps, so the channel equalization and advanced modulation and demodulation methods are required. OFDM is generally known as an effective technique for high data rate transmission system, since it can prevent ISI by inserting a guard interval. However, a guard interval longer than channel delay spread has to be used in each OFDM symbol period, thus resulting a considerable loss in the efficiency of channel utilization Therefore the equalizer is necessary to cancel ISI to accommodate advanced ITS service with higher bit rate and longer channel delay spread condition In this paper, the channel equalizer for the OFDM -DSRC system was designed and its performance in a multi-path fading environment was evaluated with computer simulation.