• 공학교육연구
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• 제15권5호
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• pp.93-97
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• 2012

Most of ubiquitous computing devices such as stereo camera, ultrasonic sensor based MIT cricket system and other wireless sensor network devices are widely applied to the 2 Dimensional(2D) localization system in today. Because stereo camera cannot estimate the optimal location between moving node and beacon node in Wireless Personal Area Network(WPAN) under Non Line Of Sight(NLOS) environment, it is a great weakness point to the design of the 2D localization system in indoor environment. But the conventional 2D triangulation scheme that is adapted to the MIT cricket system cannot estimate the 3 Dimensional(3D) coordinate values for estimation of the optimal location of the moving node generally. Therefore, the 3D triangulation scheme based on the space segmentation in WPAN is suggested in this paper. The measuring data in the suggested scheme by computer simulation is compared with that of the geographic measuring data in the AutoCAD software system. The average error of coordinates values(x,y,z) of the moving node is calculated to 0.008m by the suggested scheme. From the results, it can be seen that the location correctness of the suggested scheme is very excellent for using the localization system in WPAN.

• 한국IT서비스학회지
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• 제10권4호
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• pp.243-258
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• 2011

With increasing interest in ubiquitous computing technology, an infrastructure for the short-distance wireless communication has been extended socially, bringing spotlight to the security system using the image or location. In case of existing security system, there have been issues such as the occurrences of blind spots, difficulty in recognizing multiple objects and storing of the unspecified objects. In order to solve this issue, zone-based location-estimation search system for the image have been suggested as an alternative based on the real-time location determination technology combined with image. This paper intends to suggest the search service for the image zone-based location-estimation. For this, it proposed the location determination algorism using IEEE 802.15.4/ZigBee's RSSI and for real-time image service, the RTP/RTCP protocol was applied. In order to combine the location and image, at the event of the entry of the specified target, the record of the time for image and the time of occurrence of the event on a global time standard, it has devised a time stamp, applying XML based meta data formation method based on the media's feature data based in connection with the location based data for the events of the object. Using the proposed meta data, the service mode which can search for the image from the point in time when the entry of the specified target was proposed.

• 한국통신학회논문지
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• 제37권6C호
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• pp.476-482
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• 2012

본 논문은 2.4GHz 대역을 사용하는 WBAN (Wireless Body Area Network)환경에서 동일 채널을 사용하는 경우에 발생하는 간섭을 제거하기 위한 여러 간섭 제거 기술에 대해서 분석 하고 서로 비교, 평가 하였다. ML (Maximum Likelihood), OC (Optimal Combining) 그리고 MMSE (Minimum Mean Square Error) 방식이 후보 기술로 고려되었으며, 수신 성능과 구현 복잡도 사이의 trade-off 관점에서 서로 비교 하였다. IEEE 802.15.6 에서 제시 하는 채널 모델 및 간섭 시나리오를 적용하여 성능 평가를 수행한 결과, ML과 OC 알고리즘 등이 우수한 성능을 나타내는 것을 알 수 있었다. 하지만, ML과 OC의 경우 원하는 신호의 채널 정보뿐만 아니라 간섭채널의 정보를 알아야 하기 때문에 채널을 추정하기 위한 구현 복잡도 및 추정 에러에 민감한 단점을 가지고 있게 된다. 한편, 실제 채널 추정을 수행 하여 성능 비교를 한 경우에는 MMSE와의 성능 격차가 많이 감소한 것을 볼 수 있었으며, 이에 따라, 저전력 및 소형화가 필요한 WBAN 환경에 적용하기 위해서는 성능과 복잡도 사이의 trade off를 고려한 간섭 제거 기술의 선택 및 연구가 중요할 것으로 판단된다.

• 한국통신학회논문지
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• 제31권4C호
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• pp.331-340
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• 2006

이 논문에서는 다중경로 채널 환경에서 비동기식(Noncoherent) 초광대역(Ultra Wide Band) 무선통신 시스템의 고속 고신뢰 신호 동기획득을 위해, 저자들이 동기식(Coherent) 초광대역 시스템을 위해 제안하였던 TSS-LS (Two-Step Search scheme with Linear search based Second step). 기법을 비동기식 초광대역 시스템에 확장 적용하는 방안을 제안한다. 간단한 에너지 윈도우 뱅크를 사용하는 제안된 비동기식 TSS-LS 기법은 고속의 동기획득을 위해 두 단계의 서로 다른 문턱값과 탐색창을 적용하게 된다. 더욱이 다중경로 채널의 실효 지연 확산 범위에서의 시작 지점을 정확히 찾고 비동기식 초광대역 변복조와 연동했을 때 신뢰성 있는 비트오율(Bit Error Rate) 성능을 얻기 위해 두 번째 단계에서 선형 알고리즘을 적용한다. IEEE 802.15.3a의 다중경로 채널 모형을 이용한 모의실험 결과, 일반적인 탐색 기법보다 제안된 기법의 평균 동기획득 소요 시간이 큰 폭으로 단축됨을 확인할 수 있었다. 또한, 신호 동기획득 과정과 연동된 비트오율 성능 평가에서 신호대잡음비가 높을 때 이상적인 동기획득의 경우에 필적하는 매우 우수한 성능을 보임을 확인할 수 있었다.

• 한국철도학회논문집
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• 제10권2호
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• pp.117-123
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• 2007

In this study, a ubiquitous sensor for condition monitoring of insulators and lightning arresters installed in power distribution lines and electric traction vehicles is presented. The sensor consists of two parts; a leakage current measurement and a lightning surge detection. Measured data are transmitted to a supervisory computer through ZigBee protocol based on IEEE 802.15.4. To detect leakage current, a window type Mn-ZCT is used and a low-noise amplifier with a gain of 60dB is designed, and this can measure leakage current in ranges of $100{\mu}A{\sim}5mA$. A sample-hold (S/H) and a Rogowski coil are injected to analyze the magnitude of surge current in ranges from 100A to 10kA with $8/20{\mu}s$-waveform.

• Journal of information and communication convergence engineering
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• 제13권1호
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• pp.21-26
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• 2015

A wireless sensor network (WSN) is designed and implemented for a freeze dryer. Freeze-drying technology is widely used in the fields of pharmacy and biotechnology as well as the food and agriculture industries. Taking into account the demand for high-resolution pressure and temperature measurements in a freeze dryer, the proposed WSN has a significant advantage of creating a monitoring environment in a freeze dryer. The proposed WSN uses a ZigBee/IEEE 802.15.4 network with an altimeter module that contains a high-resolution pressure and temperature sensor with a serial digital data interface. The ZigBee network is suitable for low-energy and low-data-rate applications in the field of wireless communication. The altimeter module is capable of sensing pressure in the range of 7.5-975 Torr (10-1300 mbar) and temperature in the range of $-40^{\circ}C$ to $125^{\circ}C$ with a DC power consumption of $3{\mu}W$. The implemented WSN is installed in a commercial laboratory freeze dryer in order to demonstrate its functionality and efficiency. A comparison with the temperature profile measured by a thermocouple installed in the freeze dryer reveals that the resolution of the temperature profile measured by WSN is superior to that measured by the thermocouple.

• Journal of Information Processing Systems
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• 제12권1호
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• pp.73-82
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• 2016

In cognitive radio networks (CRNs), the performance of the transmission control protocol (TCP) at the secondary user (SU) severely drops due to the mistrigger of congestion control. A long disruption is caused by the transmission of primary user, leading to the mistrigger. In this paper, we propose a cross-layer approach, called a CR-aware scheme that enhances TCP performance at the SU. The scheme is a sender side addition to the standard TCP (i.e., TCP-NewReno), and utilizes an explicit cross-layer signal delivered from a physical (or link) layer and the signal gives an indication of detecting the primary transmission (i.e., transmission of the primary user). We evaluated our scheme by implementing it onto a software radio platform, the Universal Software Radio Peripheral (USRP), where many parts of lower layer operations (i.e., operations in a link or physical layer) run as user processes. In our implementation, we ran our CR-aware scheme over IEEE 802.15.4. Furthermore, for the purpose of comparison, we implemented a selective ACK-based local recovery scheme that helps TCP isolate congestive loss from a random loss in a wireless section.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권2호
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• pp.253-270
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• 2013

To achieve accurate localization information, complex algorithms that have high computational complexity are usually implemented. In addition, many of these algorithms have been developed to overcome several limitations, e.g., obstruction interference in multi-path and non-line-of-sight (NLOS) environments. However, localization systems those have complex design experience latency when operating multiple mobile nodes occupying various channels and try to compensate for inaccurate distance values. To operate multiple mobile nodes concurrently, we propose a localization system with both low complexity and high accuracy and that is based on a chirp spread spectrum (CSS) radio. The proposed localization system is composed of accurate ranging values that are analyzed by simple linear regression that utilizes a Big-$O(n^2)$ of only a few data points and an algorithm with a self-calibration feature. The performance of the proposed localization system is verified by means of actual experiments. The results show a mean error of about 1 m and multiple mobile node operation in a $100{\times}35m^2$ environment under NLOS condition.

• ETRI Journal
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• 제35권6호
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• pp.1084-1093
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• 2013

problem of pedestrian localization using mobile nodes containing impulse radio ultra wideband (IR-UWB) is considered. IEEE 802.15.4a-based IR-UWB can achieve accurate ranging. However, the coverage is as short as 30 m, owing to the restricted transmit power. This factor may cause a poor geometric relationship among the mobile nodes and anchor nodes in certain environments. To localize a group of pedestrians accurately, an enhanced cooperative localization method is proposed. We describe a sequential algorithm and define problems that may occur in the implementation of the algorithm. To solve these problems, a batch algorithm is proposed. The batch algorithm can be carried out after performing the sequential algorithm to linearize the nonlinear range equation. When a sequential algorithm cannot be performed due to a poor geometric relationship among nodes, a batch algorithm can be carried out directly. Herein, Monte Carlo simulations are presented to illustrate the proposed method and verify its performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권9호
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• pp.1528-1543
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• 2011

With increasing the using of wireless technologies in essential fields such as the medical application, this paper proposes different scenarios for the transmission of images over wireless networks. The paper uses the IEEE ZigBee 802.15.4 for applying the proposed schemes. It is a Wireless Personal Area Network (WPAN). This paper presents a novel chaotic interleaving scheme against error bursts. Also, the paper studies the proposed interleaver with the convolutional code with different constraint lengths (K). A comparison study between the standard scheme and proposed schemes for image transmission over a correlated fading channel is presented. The simulation results show the superiority of the proposed chaotic interleaving scheme over the traditional schemes. Also, the chaotic interleaver packet-by-packet basis gives a high quality image with (K=3) and reduces the need for the complex encoder with K=7.