• 센서학회지
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• 제19권1호
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• pp.1-7
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• 2010

Electrostatic capacitance measurement method in a fine hose was proposed, in which two ring-type electrodes were disposed on the hose in the direction of fluid flow instead of the conventional face-to-face electrodes. With the proposed electrode structure, we realized a Ringer's solution exhaustion detector for an IV(invasive vein) injection set. On a 4 mm-diameter hose of IV set, we disposed two ring-type electrodes of 10 mm width at a distance of 5 mm each other and obtained 0.72 pF and 2.51 pF for air and 10 % dextrose Ringer's solution in the hose, respectively. The capacitance between the two electrodes varied with the hose-wraparound coverage of electrode as well as the width of electrode and the distance between the electrodes. For hose-wraparound electrode coverage of 75 %, the capacitance varied from 0.62 pF to 1.98 pF with the Ringer's solution level between the two electrodes. A charge amplifier converted the capacitance. variation into electric signal and a comparator was used to detect whether Ringer's solution was exhausted or not. The result was delivered to a host using a RF transmitter with 320 MHz carrier frequency.

• Journal of Communications and Networks
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• 제14권5호
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• pp.578-587
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• 2012

One of the key elements in the emerging, packet-based long term evolution (LTE) cellular systems is the deployment of multiple femtocells for the improvement of coverage and data rate. However, arbitrary overlaps in the coverage of these femtocells make the handover operation more complex and challenging. As the existing handover strategy of LTE systems considers only carrier to interference plus noise ratio (CINR), it often suffers from resource constraints in the target femtocell, thereby leading to handover failure. In this paper, we propose a new efficient, multi-objective handover solution for LTE cellular systems. The proposed solution considers multiple parameters like signal strength and available bandwidth in the selection of the optimal target cell. This results in a significant increase in the handover success rate, thereby reducing the blocking of handover and new sessions. The overall handover process is modeled and analyzed by a three-dimensional Markov chain. The analytical results for the major performance metrics closely resemble the simulation results. The simulation results show that the proposed multi-objective handover offers considerable improvement in the session blocking rates, session queuing delay, handover latency, and goodput during handover.

• 센서학회지
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• 제19권5호
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• pp.391-397
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• 2010

This paper proposes a differential structure sensor for detecting Ringer's solution exhaustion, in which three C-type electrodes of 10 mm width are disposed on a ringer hose at a distance of 5 mm each other in the direction of Ringer's solution flow. In the center of middle electrode, two capacitances are formed at the proposed sensor. When ringer hose is filled with Ringer's solution, there is no difference between two capacitances. But capacitance difference exist under the Ringer's solution shortage, because the shortage causes the hose filled with air from the top position electrode. The capacitance difference got to maximum 1.81 pF, when air was filled between top and middle electrode and the last of hose was filled with 10 % dextrose injection Ringer's solution. The capacitance difference varied with hose-wraparound coverage of electrodes as well as the width of them. For hose-wraparound electrode coverage of 90 % and 70 %, the maximum capacitance difference was 1.81 pF and 1.56 pF, respectively. A differential charge amplifier converted the capacitance difference to electric signal, and minimized electrodes' adhering problem and external noise coupling problem.

• 방송공학회논문지
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• 제8권2호
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• pp.126-135
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• 2003

디지털 본 방송 실시 이후 디지털 방송의 수신 환경 및 수신성능을 개선하기 위해 다양한 실제 전파 수신 채널 환경에 대한 분석을 수행할 필요성이 높아지고 있다. 본 논문에서는 디지털 신호처리 기법과 고속의 하드디스크 저장 기술을 이용하여 지상파DTV의 RF신호를 실시간으로 저장 및 재생하는 시스템을 설계, 제작하고 그 성능을 분석하였다. 개발된 시스템은 DTV RF 수신신호를 하드디스크에 실시간으로 저장 및 재생하기 때문에 특정지역의 실제 전파 수신환경을 매번 측정, 분석하는 번거로운 작업을 없앨 수 있을 뿐만 아니라 기존 수신기로 수신이 곤란한 지역들의 채널 환경을 저장하거나 특정 RF신호 패턴을 저장하고 이를 실험실에서 반복적으로 재생함으로 DTV 수신기의 성능을 측정하거나 각 지역의 채널 환경을 분석하는데 효율적으로 활용될 수 있을 것이다.

• 인터넷정보학회논문지
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• 제22권5호
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• pp.1-8
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• 2021

Small-cells in heterogeneous networks are one of the important technologies to increase the coverage and capacity in 5G cellular networks. However, due to the randomly arranged small-cells, co-tier and cross-tier interference increase, deteriorating the system performance of the network. In order to manage the interference, some channel management methods use fractional frequency reuse(FFR) that divides the cell coverage into the inner region(IR) and outer region(OR) based on the distance from the macro base station(MBS). However, since it is impossible to properly measure the distance in the method with FFR, we propose a new interference aware FFR(IA-FFR) method to enhance the system performance. That is, the proposed IA-FFR method divides the MUEs and SBSs into the IR and OR groups based on the signal to interference plus noise ratio(SINR) of macro user equipments(MUEs) and received signals strength of small-cell base stations(SBSs) from the MBS, respectively, and then dynamically assigns subchannels to MUEs and small-cell user equipments. As a result, the proposed IA-FFR method outperforms other methods in terms of the system capacity and outage probability.

• 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.

• 한국산업정보학회논문지
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• 제17권2호
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• pp.19-27
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• 2012

In railway tunnel environment, the reliability of a high-data-rate and real-time train-to-wayside communication should be maintained especially when high-speed train moves along the track. In China and Europe, the communication frequency around 900 MHz is widely used for railway applications. At this carrier frequency band, both of the solutions based on continuously laid leaky coaxial cable (LCX) and discretely installed base-station antennas (BSAs), are applied in tunnel radio coverage. Many available works have concentrated on the radio-wave propagation in tunnels by different kinds of prediction models. Most of them solve this problem as natural propagation in a relatively large hollow waveguide, by neglecting the transmitting/receiving (Tx/Rx) components. However, within such confined areas like railway tunnels especially loaded with train, the complex communication environment becomes an important factor that would affect the quality of the signal transmission. This paper will apply a full-wave numerical method to this case, for considering the BSA or LCX, train antennas and their interacted environments, such as the locomotive body, overhead line for power supply, locomotive pantograph, steel rails, ballastless track, tunnel walls, etc.. Involving finite-difference time-domain (FDTD) method and uni-axial anisotropic perfectly matched layer (UPML) technique, the entire wireless RF downlinks of BSA and LCX to tunnel space to train antenna are precisely modeled (so-called integrative modeling technique, IMT). When exciting the BSA and LCX separately, the field distributions of some cross-sections in a rectangular tunnel are presented. It can be found that the influence of the locomotive body and other tunnel environments is very significant. The field coverage on the locomotive roof plane where the train antennas mounted, seems more homogenous when the side-laying position of the BSA or LCX is much higher. Also, much smoother field coverage solution is achieved by choosing LCX for its characteristic of more homogenous electromagnetic wave radiation.

• 한국전자파학회논문지
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• 제19권5호
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• pp.506-514
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• 2008

WiBro 시스템과 같은 최근 통신 시스템에서 대역폭 효율을 증가시키기 위해 모든 셀에서 주파수를 재사용하는 경우, 셀 경계에 위치하는 수신기는 인접 셀로부터 오는 간섭 신호로 인해 수신 성능이 열화된다. 본 논문에서는 셀룰러 시스템에서 셀 경계에서의 하향 링크 성능 향상을 위해, 다수 개의 안테나를 가진 단말기에서 활용할 수 있는 수신 방식을 제안한다. 성능 검증을 위하여 인접 셀의 간섭 신호 세기 및 단말기의 안테나 개수의 변화에 따른 유효 신호 대 간섭 잡음비의 화률 밀도 함수와 대역폭 효율을 산출한다. 제안하는 방식은 MRC(Maximum Ratio Combining) 및 SD(Spatial Multiplexing) 방식 대비 유효 신호 대 간섭 잡음비와 대역폭 효율을 큰 폭으로 향상시킴을 분석 결과로 확인할 수 있으며, 실험을 통해 그 결과를 검증한다.

• Journal of Communications and Networks
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• 제18권3호
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• pp.476-483
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• 2016

Super Wi-Fi is a Wi-Fi-like service exploiting TV white space (WS) which is expected to achieve larger coverage than today's Wi-Fi thanks to its superior propagation characteristics. Super Wi-Fi has been materialized as an international standard, IEEE 802.11af, targeting indoor and outdoor applications, and is undergoing worldwide field tests. This paper demonstrates the true potential of indoor Super Wi-Fi, by experimentally comparing the signal propagation characteristics of Super Wi-Fi and Wi-Fi in the same indoor environment. Specifically, we measured the wall and floor attenuation factors and the path-loss distribution at 770MHz, 2.401 GHz, and 5.540 GHz, and predicted the downlink capacity of Wi-Fi and Super Wi-Fi. The experimental results have revealed that TVWS signals can penetrate up to two floors above and below, whereas Wi-Fi signals experience significant path loss even through a single floor. It has been also shown that Super Wi-Fi mitigates shaded regions of Wi-Fi by providing almost-homogeneous data rates within its coverage, performs comparable to Wi-Fi utilizing less bandwidth, and always achieves better spectral efficiency than Wi-Fi. The observed phenomena imply that Super Wi-Fi is suitable for indoor applications and has the potential of extending horizontal and vertical coverage of today's Wi-Fi.

• 한국전자파학회논문지
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• 제13권1호
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• pp.33-39
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• 2002

이동통신 시스템에서 지하 주차장, 지하상가, 터널, 빌딩 내부 등과 같이 기지국에 의한 신호의 커버리지가 충분하지 못한 지역들이 발생하게 된다. 이러한 영역의 경제적인 해결 방안으로 중계기가 널리 사용된다. 그러나, 중계기의 수가 증가할수록 역방향 링크의 기지국으로 유입되는 잡음 전력이 중계기의 숫자에 비례하여 증가하기 때문에 채널 용량이 감소하게 된다. 수십, 수백개의 중계기가 하나의 기지국에 연결되는 상황에서 이러한 채널 용량의 감소는 더 이상 무시할 수 없다. 본 논문에서는 커버리지 내에 통화 중인 사용자가 없을 때에 자동적으로 동작하지 않는 스위칭 중계기론 제안하였다. 스위칭 중계기를 사용하면 중계기의 커버리지 내에 통화중인 사용자가 없을 때 불필요한 잡음 레벨을 줄일 수 있다. 스위칭 중계기를 사용한 이동통신 시스템의 역방향 링크 채널 용량을 수학적으로 분석하여 스위칭 중계기를 사용하지 않는 상황과 비교하였다. 그 결과 스위칭 중계기를 사용할 때 충분히 채널용량이 개선되었음을 알 수 있었다.