• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.380-385
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• 2006

In this paper, a program that can be utilized to measure and analyze radio propagation characteristics is developed. This program is able to control the measurement instruments including spectrum analyzer through GPIB interface and analyze the measured data to yield mean excess delay and RMS delay spread. The measured path loss can be compared with theoretical value in free space or inside a tunnel. The measured and analyzed results can also be presented in the forms of graphs. As these tasks can be conducted on the spot of the measurements, this program is very helpful in performing and verifying the measurements immediately. In this thesis radio propagation characteristics with frequency bands of 2.45 and 5.8GHz in subway tunnels are measured by using the program. Path loss and delay spread in subway tunnel is measured and compared according to the form of antenna beam and LOS(Line of Sight) and N-LOS(Non-Line of Sight).

• The Journal of the Acoustical Society of Korea
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• v.30 no.2
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• pp.63-72
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• 2011

Since the detection probability is critically dependent on the target strength (TS) in active sonar and on the radiated noise level (RNL) in passive sonar, the acoustic materials for echo reduction (ER) and transmission loss (TL) are widely used for the stealth of underwater targets. In this paper, a measurement system based on the small water tank, for the frequency range of greater than 30 kHz, is developed and verified using reference targets. In order to design the water tank and the geometry of test samples, a program is developed to calculate the arrival time of interfering signals due to the reflection from water tank walls and also due to the diffraction from the edge of the test samples. Considering all the interfering signals, an optimal experimental configuration for water tank and test samples is designed and used throughout the experiment. Next, the signal processing algorithms to estimate ER and TL are developed based on the measured propagation loss reflecting the geometric spreading characteristics of the transducer. Finally, a set of reference targets such as aluminium plate and perfectly reflecting plate are used in a small water tank to verify the developed measurement system.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1993.10b
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• pp.53-64
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• 1993

This study aims to measure the reflection loss and the material constants of the fabricated samples for electromagnectic wave absorber precisely and easily by using 20mm$\Phi$coaxial tube with the end-short-type. The authors have estabilished the extraction algorithm of material constants by one port method and proved that the results of the experiments coincided with the calculated ones. On the basis of the above results the validity of the proposed measuring method is confirmed. This measurement method could be used effectively for the design of microwave absorbe and for its evaluation.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.473-477
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• 2008

In this paper, we introduce the positioning methods using the grid sensor network. The basic operational principle of grid sensor network can be the wireless communication using the sensor node attached on the objects. Sink node receives the environmental information (e.g., temperature, humidity and so on), and transmits the information to the core database. Since the grid sensor network basically uses wireless communication, it is necessary to observe the place where grid sensor nodes to be installed. In this sense, we carried out the practical measurement on the wireless propagation in an applicable field. In addition, link budget study and SNR estimation works were done in accordance with the results from the measurement.

• Journal of Advanced Navigation Technology
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• v.17 no.5
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• pp.516-523
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• 2013

In this paper, The path loss model of Air Traffic Control(ATC) telecommunication radio channel has been studied at the Incheon International Airport(IIA) with the terminal with two antlers. We measured two frequencies among VHF/UHF channel bands. The transmitting site radiated the Continuous Wave(CW). The propagation measurement was taken using the moving vehicle equipped with receiver and antenna. The transmitting power, frequency and antenna height are the same as the current operating condition. The path loss exponent and intercept parameters were extracted by the basic path loss model and hata model. The path loss exponents at passager terminal areas were 3.32 and 3.10 respectively in 128.2 MHz and 269.1 MHz. The deviation of prediction error is 9.69 and 9.65. The new path loss equation at the terminal area was also developed using the derived path loss parameters. The new path loss was compared with other models. This result will be helpful for the ATC site selection and service quality evaluation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.770-776
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• 2013

Fluid-borne noise produced by seawater circulating pumps propagates through the seawater connected pipes and radiates from the hull opening of a ship. This noise causes the increases of underwater radiated noise and self noise of ship. To reduce the noise propagation through the seawater connected pipes, absorptive silencer must be needed. In this paper, theoretical model to analyze the transmission loss of absorptive silencer was presented and the design parameters of absorptive silencer were verified. Theoretical calculations were performed according to a thickness, a length, an internal pressure and mechanical properties of its absorptive material in order to analyze the characteristics of absorptive silencer. From the theoretical calculation results, the absorptive silencer was manufactured and transmission loss was measured in the test facilities. The results of theory and measurement are compared and discussed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.7
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• pp.1774-1794
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• 2024

In the field of environmental sensing, it is necessary to develop radio planning techniques for the next generation Internet of Things (IoT) networks over mixed terrains. Such techniques are needed for smart remote monitoring of utility supplies, with links situated close to but out of range of cellular networks. In this paper, a three-dimension (3-D) geometric optimization algorithm is proposed, considering the positions of edge IoT devices and antenna coupling factors. Firstly, a multi-level single linkage (MLSL) iteration method, based on geometric objectives, is derived to evaluate the data rates over ISM 915 MHz channels, utilizing optimized power-distance profiles of continuous waves. Subsequently, a federated learning (FL) data selection algorithm is designed based on the 3-D geometric positions. Finally, a measurement example is taken in a meadow biome of the Mexican Colima district, which is prone to fluvial floods. The empirical path loss model has been enhanced, demonstrating the accuracy of the proposed optimization algorithm as well as the possibility of further prediction work.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.101-104
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• 1998

We report some methods for measuring a LiNbO$_3$ optical phase modulator bandwidth. Since Mach-Zehnder waveguide type, one of methods for modulation bandwidth measurement, is comparatively simple and useful, it was adapted in this work. In order to confirm this method, the waveguide of single and Mach-Zehnder type were fabricated on the same wafer. The Mach-Zehnder interferometric waveguide and the single channel waveguide were used for the measurement of the phase modulator's driving voltage and bandwidth for device fabrications, respectively. Ti-860$\AA$ in-diffusion was achieved in a wet-bubbling oxygen environment at 105$0^{\circ}C$/8hours. LINbO$_3$ internal chips were pigtailed to PMF(polarization maintaining fiber)/SMF(single mode fiber) using an epoxy curing technique. Examined were optical properties such as an insertion loss, propagation loss and mode size, and the loss mechanism of optical coupling between an optical fiber and a waveguide was considered.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.12
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• pp.5422-5441
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• 2016

Despite the abundant literature in the field, there is still the need to find a time-efficient, highly accurate, easy to deploy and robust localization algorithm for real use. The algorithm only involves minimal human intervention. We propose an enhanced Received Signal Strength Indicator (RSSI) based positioning algorithm for Wi-Fi capable devices, called the Dynamic Weighted Evolution for Location Tracking (DWELT). Due to the multiple phenomena affecting the propagation of radio signals, RSSI measurements show fluctuations that hinder the utilization of straightforward positioning mechanisms from widely known propagation loss models. Instead, DWELT uses data processing of raw RSSI values and applies a weighted posterior-probabilistic evolution for quick convergence of localization and tracking. In this paper, we present the first implementation of DWELT, intended for 1D location (applicable to tunnels or corridors), and the first step towards a more generic implementation. Simulations and experiments show an accuracy of 1m in more than 81% of the cases, and less than 2m in the 95%.

• The Journal of the Acoustical Society of Korea
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• v.33 no.5
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• pp.273-281
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• 2014

This paper analyzes the effect of a thermocline on the long-range acoustic signal propagation using the experimental data acquired in the shallow water near Jeju island. Temperature and salinity measurement data in Korea Oceanographic Data Center (KODC) show that the seasonal thermocline exists near Jeju island, and, under the thermocline, the bottom loss property strongly affects the long-range propagation of acoustic signal along the down-ward refractive paths. We estimate the bottom loss under the thermocline using experiment data obtained near Jeju island in May, 2013. The result shows that the estimated bottom losses are below 3 dB and the higher level signal is received at the deeper receiver depths. This shows that the acoustic trapping under the thermocline can be a viable long-range signal transmission channel in the shallow water with a thermocline.