• Journal of the Institute of Convergence Signal Processing
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• v.8 no.4
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• pp.266-271
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• 2007

In mobile channel environments, the effect of the multi-path fading reduces the performance of the mobile communication severely. Previous studies on the effect of the multi-path fading show that, only the channel between fixed base stations and mobile terminals are considered. However, the future mobile communication service such as telematics may use the communication between moving mobile terminals, so called mobile ad-hoc communication, the studies on the channel is required for such situations. In this paper we have measured the mobile channel and analyzed the fading characteristics when using the linear array antennas. In the data measurements, we sent the QPSK modulated signal with carrier frequency of 2GHz band and received the signal using the array antennas equipped on moving vehicles. We have analyzed the fading characteristics and the effects of the fading reduction using the CDF of fading depth using data collected from two moving vehicles. The simulation results show that the beamforming technique adds 6 or 7dB to the fading margin than that of the selection diversity depending on channel environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1118-1130
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• 1999

In this paper, error performance of DS/FH CDMA system has been analyzed in a radio channel which is characterized by near-far problem and multi-path fading. The DS/FH CDMA system adopts Maximum Ratio Combining(MRC) diversity and BCH(Bose-Chau dhuri-Hocquenghem) coding techniques to enhance system performance. Using the derived error probability equation, the error performance of DS/FH CDMA system has been evaluated and shown in figures to discuss as a function of PN code length(N), hopping rate(q), number of diversity branch(M), coding rate($\gamma$) and bit energy per noise power ratio ${E_b/N_o}$. The results show that DS/FH system is more effective to restrain the affection of near-far problem and multi-path fading than DS system. And there is a substantial enhancement in performance by employing an MRC diversity or BCH coding techniques. Consequently, we expected that proposed system structure is reliable to the voice communication system in near-far problem and multi-path fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9A
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• pp.1265-1275
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• 1999

An adaptive MMSE detector can be used to cancel the MAI in CDMA system. But standard adaptive MMSE detector cannot be used in real mobile environment due to fast fading channel. Furthermore multipath reception make it more difficult to converge to optimum weight values. In this paper we discuss and model the multipath fading environment in Forward-link Synchronous CDMA channels and propose adaptive MMSE RAKE detector structure which can be applied in the mobile station. A proposed adaptive MMSE detector requires estimation of received signal delay and complex channel coefficients such as amplitude and phase variation. These burden can be solved by utilizing the common pilot channel. The pilot channel may have higher power than the traffic channel, which give more exact channel estimation. Moreover RAKE structure gives more accurate and stable result which can be used as reliable reference signal in multipath fading channel environment. With this structure, conventional adaptive algorithm such as LMS or NLMS can be applied in adaptive MMSE detector.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.4
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• pp.342-353
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• 1997

This paper presents an analytical evaluation of a hybrid direct-sequence/slow frequencyhopped code division multiple-access (DS/SFH-CDMA) system employing noncoherent M-ary frequency shift keying(MFSK) modulation in a multiple Nakagami fading (m) environment. Multipath interference (MPI) and multi-access interference (MAI) is taken into account and the spectral efficiency is calculated for uncoded as well as channel coding systems. Predetection multipath maximal ratio combining (MRC) diversity in conjunction with interleaved channel coding (Hamming(7,4) code, BCH(15, 7) code and RS (7, 4), (15, 9)) code ) is employed for improving the bit error rate (BER) performance. The BER of noncoherent hybrid system is obtained using a Gaussian interference approximation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.101-105
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• 1999

Electronic Toll Collection(ETC) System makes the telecommunication possible between the Beacon and the On Board Unit(OBU) in vehicle at the highway. In this paper, the propagation path of microwave is modelled and the induced voltage of receiving antenna is analyzed numerically according to multi-path fading effort. In this modelling, we consider the weather condition, polarization and antenna radiation pattern. Also, we suggest the diversity technique in order to re duce the fading effect. In the result, the lading effort is reduced significantly in case of the vertical polarization at the rain condition. The circular polarization is the most desirable in this application. The antenna which has the high directivity, is also desirable. Using the space diversity technique at the Beaten, the fading effect is reduced as the distance increases between the Beacon and OBU. These results are presented at the graphs whose axes are related to the magnitude of received voltage(dB) and the distance of the beacon and a vehicle.

• ETRI Journal
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• v.8 no.4
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• pp.95-102
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• 1986

본 연구에서는 이동통신 시스팀에서 채널 모델의 시뮬레이션을 수행하는데 사용 가능한 알고리즘을 개발하였으며 이동체 속도에 따라 그 특성을 분석하였다. 이동통신 채널에서는 다중 경로에 의하여 레일리 페이딩 채널이 구성되어 지는데 이의 알고리즘 개발을 위하여 실제 제작 구현이 용이한 위상 변조신호 합성 방법과 shaping 필터를 이용하는 방법을 채택하였다. 개발 알고리즘을 분석한 결과 제시한 두 모델 모두가 채널 시뮬레이션을 위하여 사용가능함을 확인하였으며 특히 레일리 분포 특성에서는 위상변조 신호 합성방식이 이론치와 더욱 유사됨을 알 수 있었다.

• The Journal of the Acoustical Society of Korea
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• v.12 no.5
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• pp.14-20
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• 1993

이 논문에서는 충격성 잡음과 비선택적 다중경로 페이딩 특성이 있는 매체에서 주파수 도약대역 확산 통신 계통의 성능을 살펴보았다. 충격성 잡음을 나타내는 데에는 ε 혼합모델을 썼고, 통신 매체와 계통의 여러 가지 매개 변수를 바꾸어 가며 이 통신 계통의 오류확률을 수치 계산 방식으로 얻었다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.644-647
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• 2002

본 논문은 레이크 수신기의 성능 개선에 관한 것으로 다중 경로 페이딩에 의한 시간 지연으로 나타나는 자기 간섭이 제거된 DS-CDMA/QPSK 신호의 성능을 분석하였다. 자기 간섭 제거를 위해 새로운 레이크 수신기를 제안하고 제안된 수신기의 시스템 성능은 차량 이동통신 환경, 실내 이동통신 환경과 실외에서 실내로 이동중인 환경으로 구분하여 레일리 페이딩 환경에서 분석하였다 제안된 레이크 수신기는 적용한 DS-CDMA 시스템의 합성 수신 SNR 증가로 오율 성능이 개선되었으며 시뮬레이션 구현으로 성능 개선을 확인할 수 있었다.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.233-236
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• 2000

본 논문에서는 다중 경로 페이딩에 의한 성능의 손실을 보상하기 위하여 간단한 equal gain combining diversity를 갖는 802.11a 무선 LAN용 OFDM 시스템의 HER 성능을 다중경로 환경 하에서 분석하였다. 모의 실험 결과에 따르면, 다중경로채널에서 전송 파워를 살펴보면, 2branch equal gain combining diversity를 사용한 무선 LAN용 OFDM시스템이 diversity를 사용하지 않는 OFDM 시스템보다 BER 10/sup -3/에서 3㏈ 정도의 이득을 줄 수 있었다. Branch 수를 3개를 사용한 경우에는 BER 10/sup -3/에서 branch 2개를 사용한 경우보다 약 2㏈정도 이득을 줄 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1C
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• pp.1-7
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• 2011

Recently, multi-hop relay transmission has drawn much attention owing to its advantage of coverage extension at low power consumption. In this paper, we derive a performance bound of multi-hop communication systems with multiple amplify-and-forward relays when the optimal path is selected. The bound is derived in generalized Nakagami fading channels with different parameters for each hop by applying the geometric mean bound to the path signal-to-noise ratio (SNR) and obtaining the moment generation function of the bound. It is shown that the bound based on the geometric mean is closer to the actual performance of optimal path selection when the fading effect is small.