• Journal of Satellite, Information and Communications
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• v.11 no.4
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• pp.58-62
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• 2016

In this paper, we propose a pre-processing scheme for improving indoor positioning accuracy in impulsive noise channel environments. The impulsive noise can be generated by multi-path fading effects by complicated indoor structures or interference environments, which causes an increase in demodulation error probability. The proposed pre-processing scheme is performed before a triangulation method to calculate user's position, and providing reliable input data demodulated from a received signal to the triangulation method. Therefore, we studied and proposed an adaptive threshold function for mitigation of the impulsive noise based on wavelet denoising. Through results of computer simulations for the proposed scheme, we confirmed that Bit Error Rate and Signal-to-Noise Ratio performance is improved compared to conventional schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.9
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• pp.787-794
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• 2012

The visible light communication is considered as a next generation communication technology, when utilizes LED and PD for communication. Since it is easy to provide LOS communication environment along with cheap deployment cost, the positioning system based on VLC has been actively studied. However, the existing positioning system using VLC requires a complex computation and an additional deployment cost due to sensors for example. In this paper, we propose a new positioning system based on VLC which does not require additional complexity and the cost. In addition, the procedure for operating LED panels for positioning and the recognition schemes of pilot signal are proposed. The performance of recognition schemes of pilot signal is analyzed through the computer simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.217-225
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• 2015

Recently, as the supply of smart phone is spreading and the exhibition industries are rapidly growing, future exhibitions are evolving toward active, customized, interactive, tangible services, which can give more satisfaction to visitors. To realize this services, the indoor localization in the exhibition of visitors is very important and according to the accuracy of localization the quality of services for exhibition are also different. In this paper, state-of-the art indoor localization techniques are investigated and new localization method are proposed. To achieve this goal, future exhibition service types are proposed, which are connected with IT technology. And also, BLE(Bluetooth Low Energy) technology including comparison of specifications and representative localization technologies are analysed. Furthermore we performed comparison study and simulation between RF and VLC channels. Finally based on this, we proposed converged VLC and RF(Wi-Fi and BLE) localization technique for exhibition.

• Journal of Digital Convergence
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• v.12 no.8
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• pp.249-255
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• 2014

In this paper, we proposed to reduce the interference in the visible light Communication with multi-LEDs for improving the performance of BER and satisfied the QoS. LED is not only lighting device, but also transmitting device in the VLC. Our proposed system is aim to decrease the interference in the multi-LEDs. In addition, it occurred the ISI and CCI by transmitter to receiver different distance. To solve this problem, we proposed the multi-LEDs system using walsh code to reduce ISI and CCI. In addition, our proposed system is able to improve the performance of BER and satisfied the Qos to desire users.

• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.269-273
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• 2013

Underwater acoustic channels are generally recognized as one of the most difficult communication media because of the multipath propagation, dispersion, and so on. MIMO (Multiple-input multiple-output) techniques have been actively pursued in underwater acoustic communications recently to increase the data rate over the bandwidth-limited channels. The transmit diversity techniques can be applied in this case, and one of them is Alamouti's scheme. In this paper the performances of the transmit diversity technique are evaluated via experiment. Two transmitters and two receivers were used in experiment, and the experiment was performed in indoor water tank. The error rate 5~8% was confirmed in experimental results, and these are the improved values than the error rate 14.8% for SISO(Single-input single-output) channel under same data rate condition.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.1003-1013
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• 2009

In the domestic environments, there are many tunnels since most of terrains have mountains. To ensure the quality of wireless network service in NLOS environment like tunnels which differ from indoor or outdoor wireless channels, researches on wave-propagation characteristics. through such channel are necessary. Especially, in such environment the ground repeater called Gap-Fillers are usually used for satellite mobile services. To make sure that mobile service using satellites in tunnels is available, the research about Gap Filling method is essential. This research is focus on the characterising the wave-propagation through tunnels, to find the appropriate frequency, HPBW of the Gap-Filler antennas, the number of Gap-Fillers, etc. In this paper, we present the effective Gap Filling method in tunnels for ISM band, based on analysis of ray tracing and measurement results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.1034-1041
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• 2007

In this paper, we propose a FD USE (frequency domain minimum mean square error) equalizer algorithm for MBOK DS-UWB (M-ary bi-orthogonal keying direct sequence UWB) systems considered as a PHY proposal for high-speed wireless communication in IEEE 802.15.TG3a. The conventional FD MMSE equalization scheme has a structural limit due to insertion of the cyclic prefix (CP) in all transmit packets, but the proposed scheme is able to equalize the channel effect without CP. In order to overcome channel estimation error by multipath delay, we introduce a moving FFT and a moving average scheme. Compared with conventional FD MMSE equalizer and the traditional TD (time domain) MMSE-RAKE receiver, the proposed FD MMSE equalizer has better BER performance and we demonstrate this result by computer simulation.

• The Journal of the Acoustical Society of Korea
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• v.32 no.6
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• pp.494-501
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• 2013

The convolution code(CC) of code rate 1/2 as a forward error correction (FEC) in Quadrature Phase Shift Keying (QPSK) is applied to decrease bit error rate (BER) by background noise and multipath in shallow water acoustic channel. Ratio of transmitting signal bandwidth to channel coherence bandwidth is defined as frequency selectivity index. BER and bit energy-to-noise ratio gain of transmitted signal according to frequency selectivity index are evaluated. In the results of indoor water tank experiment, BER is well matched theoretical results at frequency selectivity index less than about 1.0. And bit energy-to-noise ratio gain is also matched theoretical value of 5 dB. BER is effectively decreased at frequency selective multipath channel with frequency selectivity index higher than 1.0. But bit energy-to-noise ratio greater than a certain size in terms of CC weaving is effective in reducing bit errors. In the results, the defined frequency selectivity index in this study could be applied to evaluate a performance of CC in multipath channel. Also it could effectively reduced BER in a low speed underwater acoustic communication system without an equalizer.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.07a
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• pp.26-27
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• 2015

본 논문에서는 대역폭 효율을 향상시키는 공간 변조(spatial modulation) 다중 안테나 시스템을 제안한다. 기존의 공간 변조 다중 안테나 시스템은 다중 송신 안테나 중 하나의 안테나를 사용하여 채널 간에 간섭을 피할 수 있어서 다중 경로가 많은 실내 환경에서 적합하다. 그러나 심벌 전송 구간마다 한 개의 안테나만을 선택하여 전송하므로 다중 안테나의 최대 부호 이득을 얻을 수 없다. 이를 극복하기 위하여 시공간블록부호화 방식을 적용한 공간 변조 다중 안테나 시스템은 두 개의 안테나를 사용하여 수신 성능을 향상시키지만 대역폭 효율이 향상되지 않는 단점이 있다. 본 논문에서는 Hybrid STBC 시스템을 적용한 공간 변조를 제안하여 공간 변조 다중 안테나 시스템의 대역폭 효율을 개선한다.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.2069-2070
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• 2006

본 논문은 UWB(Ultra Wideband) 펄스 기반의 단일 송수신을 통한 UWB 레인징 시스템에서 거리산출의 모호성을 제거하고 그 성능을 향상시키기 위한 듀얼윈도우처리기법을 새롭게 제안한다. 일반적으로 UWB 레인징시스템은 UWB 전송펄스의 높은 시간분해능을 이용하여 거리를 산출하는데, 비가역성(Non-coherent) UWB 송수신기 구조에서는 신호가 언제 수신 될지 모르는 정보 표본값들로부터 최초도착 성분을 추출하게 되고 이로 인해 거리산출오차가 크게 발생되어 진다. 실내무선채널환경(CMI)의 UWB 레인징 시뮬레이션 결과 본 논문에서 제안된 듀얼윈도우처리기술을 적용 시 1m 거리산출 확률오차기준으로 대략 98% 정확도를 보인 반면에 그렇지 않은 경우는 75%이하의 레인징 정확도 성능을 나타낸다