• ETRI Journal
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• v.37 no.4
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• pp.707-716
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• 2015

The purpose of a localization system is to estimate the coordinates of the geographic location of a mobile device. The accuracy of wireless localization is influenced by nonline-of-sight (NLOS) errors in wireless sensor networks. In this paper, we present an improved time of arrival (TOA)-based localization method for wireless sensor networks. TOA-based localization estimates the geographic location of a mobile device using the distances between a mobile station (MS) and three or more base stations (BSs). However, each of the NLOS errors along a distance measured from an MS (device) to a BS (device) is different because of dissimilar obstacles in the direct signal path between the two devices. To accurately estimate the geographic location of a mobile device in TOA-based localization, we propose an optimized localization method with a BS selection scheme that selects three measured distances that contain a relatively small number of NLOS errors, in this paper. Performance evaluations are presented, and the experimental results are validated through comparisons of various localization methods with the proposed method.

• Journal of The Korean Astronomical Society
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• v.54 no.2
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• pp.49-60
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• 2021

Observations of line of sight (LOS) Doppler velocity and non-thermal line width in the off-limb solar corona are often used for investigating the Alfvén wave signatures in the corona. In this study, we compare LOS Doppler velocities and non-thermal line widths obtained simultaneously from two different instruments, Coronal Multichannel Polarimeter (CoMP) and Hinode/EUV Imaging Spectrometer (EIS), on various off-limb coronal regions: flaring and quiescent active regions, equatorial quiet region, and polar prominence and plume regions observed in 2012-2014. CoMP provides the polarization at the Fe xiii 10747 Å coronal forbidden lines which allows their spectral line intensity, LOS Doppler velocity, and line width to be measured with a low spectral resolution of 1.2 Å in 2-D off limb corona between 1.05 and 1.40 RSun, while Hinode/EIS gives us the EUV spectral information with a high spectral resolution (0.025 Å) in a limited field of view raster scan. In order to compare them, we make pseudo raster scan CoMP maps using information of each EIS scan slit time and position. We compare the CoMP and EIS spectroscopic maps by visual inspection, and examine their pixel to pixel correlations and percentages of pixel numbers satisfying the condition that the differences between CoMP and EIS spectroscopic quantities are within the EIS measurement accuracy: ±3 km s-1 for LOS Doppler velocity and ±9 km s-1 for non-thermal width. The main results are summarized as follows. By comparing CoMP and EIS Doppler velocity distributions, we find that they are consistent with each other overall in the active regions and equatorial quiet region (0.25 ≤ CC ≤ 0.7), while they are partially similar to each other in the overlying loops of prominences and near the bottom of the polar plume (0.02 ≤ CC ≤ 0.18). CoMP Doppler velocities are consistent with the EIS ones within the EIS measurement accuracy in most regions (≥ 87% of pixels) except for the polar region (45% of pixels). We find that CoMP and EIS non-thermal width distributions are similar overall in the active regions (0.06 ≤ CC ≤ 0.61), while they seem to be different in the others (-0.1 ≤ CC ≤ 0.00). CoMP non-thermal widths are similar to EIS ones within the EIS measurement accuracy in a quiescent active region (79% of pixels), while they do not match in the other regions (≤ 61% of pixels); the CoMP observations tend to underestimate the widths by about 20% to 40% compared to the EIS ones. Our results demonstrate that CoMP observations can provide reliable 2-D LOS Doppler velocity distributions on active regions and might provide their non-thermal width distributions.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.4
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• pp.105-111
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• 2010

This paper proposes the recursive algorithm for passive proximity detection system based on signal strength. The system is designed to be used in the smart medicine chest in order to provide location-based service for the senior personnel. Due to the system profile, single receiver and uni-direction communication are applied over the signal attenuation model for the determination of user existence within certain proximity. The performance of conventional methods is subjective to the sight between the transmitter and receiver unless the direction of target is known. To appreciate the temporal and spatial locality of human subjects, the authors present exponential moving average (EMA) to compensate the unexpected position error from the direction and/or environment. By using optimal parameter, the experiments with EMA algorithm demonstrates 32.26% (maximum 40.80%) reduction in average of the error probability with 50% of consecutive sight in time.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.5
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• pp.578-588
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• 1998

In this paper, we analyzed the propagation characteristics of polarization diversity in the view of diversity gain, cross correlation coefficient and average received signal strength, and compared it with those of space diversity. From the results, we could confirm that in the care of line of sight(LOS), space diversity gain is bigger than polarization diversity gain by 2 dB and the diversity gain of mobile transmitting with 90 degree is bigger than that of mobile transmitting with 45 degree by 1 dB. However, in the area of non-line of sight(NLOS), the diversity gains were all most the same in two diversity schemes and in specular cases, polarization diversity showed better performances. Also it was verified that under the NLOS conditions, diversity gain of mobile transmitting with 45 degree was at least 1 dB bigger than that of mobile transmitting with 90 degree.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.591-593
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• 2019

LPWA has a small amount of data that can be transmitted at one time, but it can collect a very wide range of information, so it is suitable for gathering information of apartment meter or collecting data intermittently sent from industrial site. However, most of the application studies on LPWA are limited to outdoor, especially LOS environment, so it is difficult to collect information for application to apartment and industrial sites. In this paper, we have measured the communication coverage within the building, which is a NLOS environment, so that LPWA communication can be applied to apartments and industrial sites. For the experiment, LoRa module was created using sx1276, Class A was applied, and the spread factor was changed for each layer. As a result, in case of spreading factor 7 that shows increasing error and losses from the 7 floor, but the in case of spreading factor 12, the data could be seamlessly received even on the 9th floor without error and losses.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.11 s.114
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• pp.1058-1064
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• 2006

In this paper, the channel capacity of a specified wireless indoor multiple-input multiple-output(MIMO) channel is estimated by analyzing spatial characteristics of this channel using the three-dimensional ray tracing method, and a technique for deriving an optimized separation of multi-antenna elements is proposed. At first, the ray paths, the path losses, and the time-delay profile are computed using the three-dimensional ray tracing method in an indoor corridor environment, which has the line of sight(LOS) and non-line of sight(NLOS) regions. The ray tracing method is verified by a comparison between the computation results and the measurements which are obtained with dipole antennas, an amplifier and a network analyzer. Then, an MIMO system is positioned in the indoor channel environment and the ray paths and path losses are computed for four antenna-position combinations and various values of the antenna separation to obtain the channel capacity for the MIMO system. An optimum antenna-separation is derived by averaging the channel capacities of 100 receiver positions with four different antenna combinations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.2
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• pp.123-130
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• 2016

This paper describes the design and implementation scheme of HTS(Helmet Tracking System) providing coincident LOS(Line of Sight) between aircraft and HMD(Helmet Mounted Display) which displays flight and mission information on Pilot helmet. The functionality and performance of HMD system depends on the performance of helmet tracking system. The target of HTS system design is to meet real-time performance and reliability by predicting non-periodic latency and high accuracy performance. To prove an availability of a proposed approach, a robust hybrid scheme with a fusion optical and inertial tracking system are tested through a implemented test-bed. Experimental results show real-time and reliable tracking control in spite of external errors.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1643-1654
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• 2015

With standardization of IEEE 802.11n, APs with the 2.4GHz and 5GHz dual-band capability have widely been deployed over a metropolitan area by individuals and internet service providers. Moreover, due to the increasing attentions on indoor-localization technique using Wi-Fi, the need for LOS and NLOS determination scheme is increasing to enhance accuracy of the localization. In this paper, we propose a novel LOS/NLOS determination technique by using different radio attenuation characteristics in different frequency bands and different mediums. Based on this technique, we designed a LOS/NLOS-aware indoor localization scheme. The proposed LOS/NLOS determination algorithm can be used when the distance between an user device and an AP is unknown, and the proposed localization scheme provides very accurate room-level position information. We validated the proposed scheme by implementing it on Android smart phones.

• Journal of the Institute of Convergence Signal Processing
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• v.7 no.1
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• pp.17-23
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• 2006

In recent years, RFID has received much attention because of spread usage in industrial applications including factory, material flow, logistics and defense areas. However, there is only CRC-16 for error detection in ISO/IEC 18000-6 Protocols prepared for 860-960 MHz RFID, high error rates are expected in cases of high level of security and noisy envirionment. In this paper, we propose a usage of convolution code as a method for satisfying the high level of security requirement and system error performance.'1'he signal control function is implemented in a microprocessor with RF modulation and the convolutional encoding and Viterbi decoding are implemented in an FPGA chip.'The frame error rates are measured with and without convolution coding under the channel conditions of line-of- sight and non line-of-sight, respectively.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1135-1139
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• 2017

Spatial distribution of chemical species in flame is a important indicator understanding the flame structure and combustion characteristics, and optical emission spectroscopy has been widely used for the measurement because of its simple and non-intrusive methodology. In this study, we suggest the feasibility of the measurement of chemical species (OH radical) distribution in rocket plume using optical emission spectrometer which was developed for the spatially resolved measurement along the line-of-sight. In order to predict the ground state concentration of species from the measured emission intensity by optical emission spectrometer, we consider thermal and chemical excitation mechanisms in flame, and assume thermodynamic equilibrium for the thermally excited species. We also present the spatial resolution and the correction of collection characteristics of the optical emission spectrometer depending on object distance.