• 한국통신학회논문지
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• 제30권5C호
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• pp.355-363
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• 2005

이 논문은 옥내와 옥외에 걸친 무선 통신 환경에서 통신 성능을 향상시키는 기술에 관한 것이다. 옥외 무선 통신에서 신호 감쇠는 주로 채널의 페이딩 특성으로 발생되는데, 기존의 다중 안테나 방식과 배열 신호처리 알고리즘을 적용하면 이 문제를 해결할 수 있다. 그러나, 옥내 및 옥외 무선 채널을 가진 통신인 경우, 채널 특성은 페이딩과 각도 퍼짐 특성 모두에 영향을 받으므로, 일반적인 방식으로 채널의 각도 퍼짐 특성을 극복할 수 없다. 이를 해결하기 위해 이 논문에서는 옥내와 옥외에 걸친 채널 특성을 분석하고, 각각에 적합한 채널 모형을 생각한다. 또한, 옥내외 채널의 각도 퍼짐 특성을 극복하고 옥내외 통신 성능을 향상하기 위해, 새로운 평균주사 벡터 개념을 사용한 배열 안테나 처리 알고리즘을 제안하고 성능 분석을 수행한다. 컴퓨터 모의 실험을 통한 성능 분석으로 옥내 전송 신호를 옥외 환경에서 다중 안테나로 수신하는 경우, 기존 방식보다 제안된 방식이 좋은 신호대 간섭 잡음비 특성을 가짐을 보인다.

• 전기전자학회논문지
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• 제2권2호
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• pp.173-177
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• 1998

실내환경에서의 광무선 LAN은 송수신기 사이의 시정선이 성립되지 않는 경우 넓은 수광각을 얻기 위해 반구형 렌즈나 반사체를 사용해야 하며, 실내환경에서 반구형 렌즈를 사용했을 때, 교란대기를 통과하는 광신호는 진폭과 위상이 불규칙하게 변화하고, 빔을 편향시킬 수 있다. 이 페이딩은 비트오류율을 증가시켜 결국 광무선통신의 성능을 저하시키게 된다. 본 논문에서는 시정선이 성립되지 않는 광무선채널을 고려하여 수신기에 반구형 렌즈를 장착한 경우, 천정각에 따른 신호대잡음비를 고찰하고, 또한 실내온도에 기인한 교란효과가 통신성능에 미치는 영향를 살펴 본다.

• 한국통신학회논문지
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• 제33권12A호
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• pp.1251-1260
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• 2008

Diffuse wireless optical communication offers more robust optical links in terms of coverage and shadowing than line-of-sight links. However, traditional diffuse wireless infrared (IR) transceiver systems are more susceptible to multi-path distortion and great power decrease, which results in limiting high-speed performance. Multi-beam is an effective technique to compensate for multi-path distortion in a wireless infrared environment. The goal of this paper is to analyze the transmission characteristics by replacing traditional diffuse system (TDS) which contains single wide angle transmitter and single element receiver by system consisting of three-beam transmitter and non-imaging receiver (TNS) attached with compound parabolic concentrator (CPC). In the simulation, we use the recursive model developed by Barry and Kahn and build the scenario based on 10 different cases which have been listed in Table 1. Moreover, we also check the reliability of the TNS diffuse link channel by BER test on the basis of different receiver positions and room sizes. The simulation results not only show the basic transmission characteristics of TNS diffuse link, but also are references to design more efficient and reliable indoor infrared transmission systems.

• Journal of the Optical Society of Korea
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• 제20권1호
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• pp.36-41
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• 2016

Visible Light Communication (VLC) using Light Emitting Diodes (LEDs) within the existing lighting infrastructure can reduce the implementation cost and may gain higher throughput than radio frequency (RF) or Infrared (IR) based wireless systems. Current indoor VLC systems may suffer from poor downlink resource allocation problems and small system throughput. To address these two issues, we propose an algorithm called a conflict graph scheduling (CGS) algorithm, including a conflict graph and a scheme that is based on the conflict graph. The conflict graph can ensure that users are able to transmit data without interference. The scheme considers the user fairness and system throughput, so that they both can get optimum values. Simulation results show that the proposed algorithm can guarantee significant improvement of system throughput under the premise of fairness.

• 한국통신학회논문지
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• 제38C권3호
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• pp.318-326
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• 2013

본 논문에서는 선박 내 실내에서 개인 정보 전달의 효율성을 높이는 WUSB over WBAN 프로토콜 구조와 본 프로토콜에 기초한 실내 위치인식 기술을 제안한다. 이를 위해 전력 소모를 최소화 하면서 정밀한 위치 인식이 가능한 위치인식알고리즘을 제안한다. 본 논문에서 제안하는 위치인식알고리즘은 WUSB over WBAN 프로토콜 기반 센서 노드에서 GPS 없이 독립적으로 실행되어 측정된 값을 사용하여, 각 센서 노드의 위치를 추정함으로써 전력소모를 최소화한다.

• Journal of Communications and Networks
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• 제16권3호
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• pp.335-343
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• 2014

This paper considers the crucial problem of deploying wireless relays for achieving a connected wireless sensor network in indoor environments, an important aspect related to the management of the sensor network. Several algorithms have been proposed for ensuring full sensing coverage and network connectivity. These algorithms are not applicable to indoor environments because of the complexity of indoor environments, in which a radio signal can be dramatically degraded by obstacles such as walls. We first prove theoretically that the indoor relay placement problem is NP-hard. We then predict the radio coverage of a given relay deployment in indoor environments. We consider two practical scenarios; wire-connected relays and radio-connected relays. For the network with wire-connected relays, we propose an efficient greedy algorithm to compute the deployment locations of relays for achieving the required coverage percentage. This algorithm is proved to provide a $H_n$ factor approximation to the theoretical optimum, where $H_n=1+{\frac{1}{2}}+{\cdots}+{\frac{1}{n}}={\ln}(n)+1$, and n is the number of all grid points. In the network with radio-connected relays, relays have to be connected in an ad hoc mode. We then propose an algorithm based on the previous algorithm for ensuring the connectivity of relays. Experimental results demonstrate that the proposed algorithms achieve better performance than baseline algorithms.

• 한국통신학회논문지
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• 제35권5C호
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• pp.472-478
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• 2010

UWB 표준인 IEEE 802.15.3a 채널의 무선 통신 시스템 환경에서 채널에 적합하고 추정 정확도가 우수한 신호 도착 방향(AOA) 매개변수 추정 기반의 실내 무선 위치인식 알고리즘을 위한 평균가중 AOA 추정기법을 제안한다. AOA 매개 변수 추정을 위한 IEEE 802.15.3a 기반의 초광대역 신호 모형을 설정하고, 종래 추정 기법보다 추정 정확도가 우수한 평균가중 기반의 다중신호 분류 기법들을 제안한다. 컴퓨터 모의실험을 통해, IEEE 802.15.3a 채널이 포함한 실내 무선 위치인식 시스템 환경을 구축하고, 제안한 AOA 추정 방식을 통해 종래 방식 보다 우수한 추정 결과를 보인다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권2호
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• pp.187-194
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• 2015

Accurate relative location estimation is a key requirement in indoor localization systems based on wireless sensor networks (WSNs). However, although these systems have applied not only various optimization algorithms but also fusion with sensors to achieve high accuracy in position determination, they are difficult to provide accurate relative azimuth and locations to users because of cumulative errors in inertial sensors with time and the influence of external magnetic fields. This paper based on ultra-wideband positioning system, which is relatively suitable for indoor localization compared to other wireless communications, presents an indoor localization system for estimating relative azimuth and location of location-unaware nodes, referred to as target nodes without applying any algorithms with complex variable and constraints to achieve high accuracy. In the proposed method, the target nodes comprising three mobile nodes estimate the relative distance and azimuth from two reference nodes that can be installed by users. In addition, in the process of estimating the relative localization information acquired from the reference nodes, positioning errors are minimized through a novel modified rounding estimation technique in which Kalman filter is applied without any time consumption algorithms. Experimental results show the feasibility and validity of the proposed system.

• Journal of Advanced Marine Engineering and Technology
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• 제38권5호
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• pp.566-572
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• 2014

Recently, indoor navigation has been applied in large convention centers by using wireless sensor networks (WSNs), which provide not only a user's path to be traveled but also orientation and shopping information to increase user's convenience. This paper presents the localization system for estimating relative coordinates without pre-deployment of the reference node based on ultra wide band (UWB) ranging system, which is relatively suitable for indoor localization compared to other wireless communications, and azimuth sensor. The proposed localization system which consists of an azimuth sensor and a mobile node composed of three nodes estimates relative coordinates of the reference node without applying any recursive and time consumption algorithms. Also, in the process of estimating relative coordinates of the reference node, ranging errors are minimized through the proposed technique and the number of nodes can be reduced. Experimental results show the feasibility and validity of the proposed system.

• Journal of Communications and Networks
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• 제8권3호
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• pp.286-289
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• 2006

Measurement results are presented for the effects of people moving near and across short-range indoor propagation links at 2.45 GHz (ISM band). Excess loss due to scattering and blockage by human bodies in the vicinity of one terminal were measured for different radio links in an office environment. Statistics on fades due to human body motion are given. Polarization coupling (depolarization) for various radio links was measured, and correlation of polarization components is discussed as a basis for using polarization diversity reception in short-range indoor systems.