• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.5
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• pp.910-920
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• 2006

We consider the problem of estimating a code-timing of DS-CDMA signal in antenna array systems in the presence of flat fading channels and near-far environments. We derive an approximate maximum likelihood algorithm of estimating the code-timing of a desired user for DS-CDMA systems to better utilize the time-varying characteristics of the fading process. In the development of code timing estimator, the given observation bits are divided into many sets of sub-windows with each sufficiently large. The proposed method uses sub-windows with equal size associated with the coherence time of channel fading. The alternative approach is that without the estimation of the fading rate, the sufficiently given observation bits are simply separated into two consecutive sets of sub-windows. The derivation of the proposed algorithms is based on multiple antennas partially correlated in space. The impacts of spatial fading correlation on acquisition and men acquisition time performance of the proposed algorithms are also examined.

• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.126-133
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• 2004

Photogrammetry, as its name implies, is a 3-dimensional coordinate measuring technique that uses photographs as the fundamental medium for metrology. In the last few years the accuracy of photogrammetry has increased dramatically thanks to the rapid advance of digital camera manufacturing technique. This paper discusses photogrammetric measurement of the interface surface of MSC(Multi-Spectral Camera), which is a main payload of KOMPSAT-2. Total 24 paper targets on the objective surfaces and two scale bars calibrated with high accuracy were used for measurement, and multiple images were taken from 11 different camera angles by using a spacecraft rotation dolly. As a result of analysis, 3D coordinates of each targeted point were obtained and the flatness value based on the selected reference plane was calculated and compared with the pre-determined requirement. The technique acquired by this study is expected to be used for the 3D precise measurement of ultra-light weight and inflatable space structures such as a satellite antenna and a solar array.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1307-1312
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• 2015

The recent adoption of Bluetooth LE technology in smart phones triggered commercial interest in RSSI-based positioning technology. Estimation error in RSSI measurement due to the antenna pattern, multipath fading, environmental noise has to be considered for designing beacon systems. The paper proposes an analysis method and beacon planning rules for a small and isolated indoor service area, based on probabilistic model of RSSI estimation error. As an practically important guide, the beacons have to be installed at the boundary of the service area to minimize the maximum position error, whereas the beacons have to be evenly distributed in the service space to minimize the average estimation error.

• Journal of Korean Society for Geospatial Information Science
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• v.22 no.1
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• pp.47-54
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• 2014

Precise Point Positioning (PPP) algorithms using GPS code pseudo-range measurements were developed and their accuracy was validated for the purpose of implementing them on a portable device. The group delay, relativistic effect, and satellite-antenna phase center offset models were applied as fundamental corrections for PPP. GPS satellite orbit and clock offsets were taken from the International GNSS Service official products which were interpolated using the best available algorithms. Tropospheric and ionospheric delays were obtained by applying mapping functions to the outputs from scientific GPS data processing software and Global Ionosphere Maps, respectively. When the developed algorithms were tested for four days of data, the horizontal and vertical positioning accuracies were 0.8-1.6 and 1.6-2.2 meters, respectively. This level of performance is comparable to that of Differential GPS, and further improvements and fine-tuning of this suite of PPP algorithms and its implementation at a portable device should be utilized in a variety of surveying and Location-Based Service applications.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.464-466
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• 2018

In this paper, a dense cellular network is considered in which each base station equipped with multiple antennas simultaneously communicates with multiple single-antenna users. Based on limited feedback, each user feeds back its quantized channel state information (CSI) to its associated transmitter, and the transmitter broadcasts multiple data streams prepared for the scheduled users using a space-division multiple access scheme. As the amount of CSI is limited at the transmitter, the downlink throughput increases with the number feedback bits. However, the increased number of feedback bits requires the correspondingly increased amount of uplink resources. Thus, an appropriate balance between the downlink throughput and the uplink resource usage should be considered in realistic systems. A net spectral efficiency defined in this context is used in this paper, and the optimal number of feedback bits that maximizes the net spectral efficiency is analyzed. This paper particularly focuses on the case when the received signal power is much smaller than the noise power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.50-58
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• 2008

The use of space-division multiple access(SDMA) in the downlink of multiuser multi-input/multi-output(MIMO) wireless transmission systems can provide substantial gains in system throughput. When the channel state information(CSI) is available at the transmitter, a considerable performance improvement can be attained by adapting the transmission rates to the reported CSI. In addition, to combat frequency selective fadings in wideband wireless channels, bit-interleaved coded OFDM(BIC-OFDM) modulation schemes are employed to provide reliable packet delivery by utilizing frequency diversity through channel coding. In this paper, we propose an adaptive modulation and coding(AMC) scheme combined with an opportunistic scheduling technique for the MIMO BIC-OFDM with bandwidth-limited feedback channels. The proposed scheme enhances the link performance by exploiting both the frequency diversity and the multiuser diversity. To reduce the feedback information, the proposed AMC scheme employs rate adaptation methods based on an OFDM symbol rather than on the whole subchannels. Simulation results show that the proposed scheme exhibits a substantial performance gain with a reasonable complexity over single antenna systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.3
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• pp.362-370
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• 2011

This paper presents a K-band radar system installed on the ground moving vehicle to detect and track a high-speed target. The presented radar is separated into three search regions to satisfy a wide area detection and a limitation of the installing space of the radar, and each region performs detecting the target independently and tracking the detected target automatically. The presented radar radiating K-band FMCW waveform acquires range and velocity information of the target at the every dwell and receiving antenna of the radar is applied the multiple baseline interferometer to extract the precise angle information of the target. 3-dimensional tracking accuracy of the radar is 0.25 m RMSE measured actually through a fire experiment of an imitation target.

• 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 Korean Institute of Communications and Information Sciences
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• v.40 no.3
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• pp.469-477
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• 2015

In this paper, joint spatial division and reuse (JSDR) scheme is proposed for maximizing network throughput in densely-deployed wireless local area networks equipped with massive antenna array. The proposed JSDR scheme divides the massive spatial space into two subspaces: one is for suppressing the interference from the neighboring access points and another is for sensing the carrier sensing and transmitting the information-bearing signals to intended stations. By using computer simulation, the proposed JSDR can provide 133% higher network throughput, compared to the carrier sensing technique defined in the IEEE 802.11 standard so that the proposed JSDR is suitable for the next generation WLAN systems.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.23 no.1
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• pp.97-106
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• 2020

Urban parks provide a variety of ecosystem services and are an important means of providing positive functions to urban ecosystems. Recently, various studies on wildlifes in urban parks have been conducted. However, there is a lack of research on habitat use in urban parks at important times such as before and after fledging in bird ecology. This study analyzed habitat use and home-range before and after fledging on Cheongsa park, a neighborhood park located in Cheonan city. An artificial nest was set up to check and capture great tit in fledging time. One female was captured and attached to the NTQB-2 (0.4g) radio transmitter, the location was tracked using SIKA Radio Tracking Receiver, hand-held three element Yagi antenna and GPS. Location information was recorded for 10 minutes for 3 hours each morning and afternoon for 12 days from May 17 to May 31, 2019. As a result, the home-range of the target species was 1.776 ha (MCP) and the core area was 499 ㎡ (KD 50%). The average daily home-range was 0.513 ha for the entire period, 0.688 ha before fledging, 0.339 ha after fledging based on MCP. The bird moved about 29.9 m on average and moved up to 131.7 m. For the most of the time, the great tit stayed inside the park, but the bird also used small green spaces such as street trees, tree flower beds, and green areas of unused lands. The results of this study could be applied to the study of habitat use and the greenery management policy of the urban park considering wild birds.