• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2019-2024
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• 2014

This paper presents a method to optimize the design of a planar-type antenna and reduce the number of design parameters for rapid computation. The electromagnetic characteristics of the structure are analyzed, and Taguchi method is used to identify critical design parameters. Adaptive particle swarm optimization, which has a faster convergence rate than particle swarm optimization, is used to achieve the design goal effectively. A compact dual-band USB dongle antenna is tested to verify the advantage of the proposed method. In this case, we can use only five selected geometrical parameters instead of eighteen to accelerate the optimization of the antenna design. The 10 dB bandwidth for return loss ranges from 2.3 GHz to 2.7 GHz and from 5.1 GHz to 5.9 GHz, covering all the WiBro, Bluetooth, WiMAX, and 802.11 b/g/n WLAN bands in both simulation and measurement. The optimization process enables the antenna design to achieve the required performance with fewer design parameters.

• 공학논문집
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• 제7권1호
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• pp.53-60
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• 2005

Community Wireless Networks define the next generation wireless services. Multimedia usages for financial services over community Wireless LAN (WLAN) based mesh networks require link stability. Several new services are being proposed for multimedia over WLANs. Portable Internet Services are implemented by several wireless carriers to proliferate their customer base. However, these services are still expensive and require a central telecom/wireless carrier whose monopoly and preference defines the availability of new services. Our research project identifies the usage of these critical services in public places over the financial services backbone architecture to provide efficient easy-to-use and economical services to their customers and merchants without being dependent on the central wireless carrier. The user connects to the network using his regular WLAN NIC using the Mesh Router/Bridge interconnectivity and obtains the needed multimedia and financial services from the ATM-AP Gateway, In our proposed scenario, the ATN AP-MR use AODV protocol and MR-MC is based on 802.11g/a/b IEEE standard. We use multi path routing protocols for reducing the congestion over a particular route. We demonstrate the results of our simulations and test-bed outcome to evaluate link failure rate and oversubscription factors to eliminate network congestion and non-availability of the critical financial services.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2006년도 한국컴퓨터종합학술대회 논문집 Vol.33 No.1 (D)
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• pp.97-99
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• 2006

무선 센서노드 사용한 데이터 계측 및 제어 기술은 특히 홈 네트워크 분야에 널리 적용되고 있다. 본 논문에서는 Ad-Hoc네트워크의 말단인 Base node와 인접한 노드들 사이에 조도 값을 실시간으로 전송하는 시스템을 구현하였다. 이는 OscilloscopeRF라고 하는 TinyOS에서 제공되는 프로그램이 사용하는 메시지 구조를 분석하여, 각 노드의 ID및 계측 데이터를 추출하였다. 이렇게 추출된 계측 데이터를 센서 네트워크의 Base node에서 데이터 통제 센터(DOC)로 효율적으로 전송하기 위해 TCP기반 네트워크 프로그래밍을 구현하였다. 실험 결과 센서 노드 수 및 샘플링 주기에 상관없이 안정적으로 계측 데이터 수신이 이루어짐을 확인하였다. 또한, IEEE802.11a/g 기반 무선 네트워크를 통해 계측 상황을 휴대용 단말기인 PDA에서 확인할 수 있도록 이를 구현하였다.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2006년도 춘계학술발표대회
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• pp.387-390
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• 2006

TinyOS 기반 무선 센서 노드를 사용한 실시간 계측 데이터 측정 및 제어 기술은 특히 홈 네트워크 분야에 널리 적용되고 있다. 본 논문에서는 ATMegal128L을 장착한 최소 8대 이상의 Micaz Mote 센서 노드 모듈을 사용하여 각 방의 노도 값을 실시간 측정하는 시스템을 구현하였다. 특히 TinyOS에서 제공되는 OscilloscopeRF의 메시지 구조를 분석하여, 각 노드의 ID 및 계측 데이터를 추출하였다. 또한 이렇게 추출된 계측 데이터를 센서 네트워크의 싱크 노드로부터 데이터 통제 센터(Doc)로 효율적으로 전송하기 위한 TCP 기반 네트워크 프로그래밍을 구현하였다. 실험 결과 센서 노드 수 및 샘플링 주기에 상관없이 안정적으로 계측 데이터 수신이 이루어짐을 확인하였다. 한편, IEEE802.11a/g 기반 무선 네트워크를 통해 실시간 계측 상황을 휴대용 단말기인 PDA에서 확인할 수 있도록 이를 구현하였다.

• ETRI Journal
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• 제42권2호
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• pp.163-174
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• 2020

Numerous wearable technology companies have recently developed several headmounted display (HMD) products for virtual reality (VR) services. 5G wireless networks aim at providing high-quality 3D multimedia services such as VR, augmented reality, and mixed reality. In this study, we examine the application of millimeter-wave (mmWave) technology to realize low-latency wireless communication between an HMD and its content server. However, the propagation characteristics of mmWave present several challenges such as the deafness, blockage, and beam alignment problems, and interference among content servers. In this study, we focus on an environment that provides VR services in the mmWave band and introduce existing techniques for addressing such challenges. In addition, we employ a commercialized IEEE 802.11ad VR dongle to measure the actual data rate of an mmWave VR application and identify the degree to which the performance deteriorates when the above problems occur. Finally, we verify the feasibility of the proposed solutions through a simulation of several VR scenarios in the mmWave band.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.83-88
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• 2006

Many applications in the area of location-based services and personal navigation require nowadays the location determination of a user not only in outdoor environment but also indoor. To locate a person or object in a building, systems that use either infrared, ultrasonic or radio signals, and visible light for optical tracking have been developed. The use of WiFi for location determination has the advantage that no transmitters or receivers have to be installed in the building like in the case of infrared and ultrasonic based location systems. WiFi positioning technology adopts IEEE802.11x standard, by observing the radio signals from access points installed inside a building. These access points can be found nowadays in our daily environment, e.g. in many office buildings, public spaces and in urban areas. The principle of operation of location determination using WiFi signals is based on the measurement of the signal strengths to the surrounding available access points at a mobile terminal (e.g. PDA, notebook PC). An estimate of the location of the terminal is then obtained on the basis of these measurements and a signal propagation model inside the building. The signal propagation model can be obtained using simulations or with prior calibration measurements at known locations in an offline phase. The most common location determination approach is based on signal propagation patterns, namely WiFi fingerprinting. In this paper the underlying technology is briefly reviewed followed by an investigation of two WiFi positioning systems. Testing of the system is performed in two localization test beds, one at the Vienna University of Technology and the second at the Hong Kong Polytechnic University. First test showed that the trajectory of a moving user could be obtained with a standard deviation of about ${\pm}$ 3 m.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.221-224
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• 2005

This paper discribes the nonlinear distortion of a pHEMT power amplifier. In the paper, we have used some commercially available power amplifiers for analyzing the relationship between the $IMD_3$ and ACPR for wireless LAN. And the $IMD_3$ results using two-tone test have been compared with ACPR to satisfy the requited 802.11g standard ACPR value. Measurement result shows that $IMD_3$ of 20MHz tone-spacing need to be more than 18.45dBc for power amplifiers. The WCDMA signal is fed into the power amplifier, for analyzing relationship between the asymmetrical $IMD_3$ and ACLR. With measurement result, the asymmetrical $IMD_3$ characteristic has increased with the increase of two-tone spacing. $IMD_3$ measurement result with maximum 20MHz of the two-tone spacing, shows that the difference between $IMD_3(lower)$ and $IMD_3(upper)$ is about 7dB. And the measured ACLR shows 5dB difference at -4MHz and +4MHz offset from center frequency.

• 대한전자공학회논문지TC
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• 제44권3호
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• pp.92-97
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• 2007

스위칭 모우드 증폭기를 마이크로파 대역에서 이용하고자 하는 많은 연구가 있으며, 이러한 증폭기 중 E급 증폭기는 이론적으로 스위칭 동작을 통해 100%의 효율을 얻을 수 있다. 본 논문에서는 2.4GHz 대역 마이크로파 E급 증폭기로 출력 전력이 17.6dBm, 66%의 전력부가효율을 갖는 설계된 증폭기를 무선 랜 송신부에서 사용하기 위해 증폭기의 비선형 왜곡을 보상하고자 테이블 참조기법(Look Up Table)을 이용한 기저대역 사전왜곡 기법을 적용하였다. 설계된 증폭기는 -3dBm의 입력 무선랜신호를 인가하였을 때 출력스펙트럼 측정 결과가 IEEE 무선랜 스펙트럼 마스크 표준규격을 만족하며, 기저대역 사전왜곡을 적용하였을 때 중심주파수에서 20MHz offset인 주파수에서 최대 5dB의 ACPR 특성이 향상되었다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1255-1261
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• 2010

An operating information and fault recode of train is very important information for safety driving and maintenance. And these information is increased and need high speed as the number of trains is increased. Wireless LAN or CDMA network is efficient to report more complicated and various information from vehicle to server in control center. Existing wireless transmission system has weakness due to transmission system is separated with TDCS and standalone. At first, standalone system needs space to be installed and cost is increased. And data transmission capacity and speed is limited by complicated structure that transmission system receive data thru serial communication like RS232 and then data transmission system send data to server in control center. This article is study to develop embedded & wireless fault code transmission device to be installed in TDCS to overcome weakness of space and to have more cost effective and simple structure. It is adapted 802.11b/g WiFi for wireless communication and OS is used embedded Linux that can easily implement wireless communication environment and ensure TCP/IP communication’s security. We also implement simple server to test wireless communication between embedded & wireless fault code transmission device and server in control center.

• 한국전자통신학회논문지
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• 제6권5호
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• pp.783-788
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• 2011

현재 센서 네트워크가 구축되어 교량의 안전 상태에 대한 감시를 수행하고 있는 대부분의 유지관리 시스템은 유선을 기반으로 하고 있다. 이러한 유선 기반의 시스템은 고가의 유선 설치비용 및 운영 중 설비에 문제가 발생할 경우 교체 및 보수작업에 고가의 비용이 소요된다. 이러한 문제를 해결하고자 기존 유선 계측시스템에 무선 센서네트워크를 적용하고자 하는 연구개발 사례들이 있지만, 전력 문제 및 동기화 문제로 인해 실제 교량의 유지관리 현장 상용화에 어려움을 격고 있다. 본 논문에서는 무선랜 기술을 적용한 WSN(Wireless Sensor Network)기반의 교량 유지관리 시스템을 제안하며, 연구수행 결과를 테스트베드 구축을 통해 시스템을 검증 하였고 기존 유선으로 수집된 데이터와 비교 하였을 때 거의 동일한 데이터를 얻을 수 있었다.