• The Journal of the Acoustical Society of Korea
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• v.24 no.8
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• pp.454-461
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• 2005

Time spread due to the multipath in underwater acoustic channel, induces ISI (Inter-Symbol Interference) which degrades the performance of the underwater acoustic communication system. The passive phase conjugation (PPC) which improves the signal to multipath interference ratio (SMR) and therefore reduces the frequency selectivity. is a diversity communication technique giving a less ISI under multipath fading channel. Its frequency selectivity depends on the number of receiver array sensors and time varying source to receiver range. In this study, frequency selectivity of the PPC and its effects on bit error of underwater acoustic communication is analyzed by numerical simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.29-37
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• 2005

One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can Provide another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.133-136
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• 2003

UWB(Ultra-Wide Band) system is transmitted using Gaussian monocycle pulse of very short pulse duration less than 1 nsec. Therefore, transmission signal has ultra-wide band spectrum to GHz band of very low power and not interfere with the existing communication system. A collision of multipath waves in UWB system with tarrier frequency very different with general wireless communication system. In this paper, the BER(Bit Error Rate) performance of UWB system applying Binary Phase Shift Keying, Quadrature Phase Shift Keying, 16-Quadrature Amplitude Modulation method under multipath channel using computer simulation is compared and analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.11
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• pp.2397-2404
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• 2012

Underwater acoustic communication has multipath error because of reflection by sea-level and sea-bottom. The multipath of underwater channel causes signal distortion and error floor. In order to improve the performance, it is necessary to employ an iterative coding scheme. Among the iterative coding scheme, turbo codes and LDPC codes are dominant channel coding schemes in recent. This paper concluded that turbo coding scheme is optimal for underwater communications system in aspect to performance, coded word length, and equalizer combining. Also, decision directed phase recovery was used for correcting phase offset induced by multipath. Based on these algorithms, we confirmed the performance in the environment of oceanic experimentation.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.290-296
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• 2006

In this paper, a generalized blind adaptive algorithm is introduced for multi-user detection of direct sequence code division multiple access (OS-COMA) wireless communication systems. The main property of the proposed algorithm is its ability to resolve the multipath fading channel resulting in inter symbol interference (ISI) as well as multiple access interference (MAI). Other remarkable properties are its low complexity and mitigation to the near-far problem as well as its insensitivity to asynchronous transmission. The proposed system is based on the minimization of the output energy and convergence to the minimum mean square error (MMSE) detector. It is blind in the sense that it needs no knowledge of the other users' signatures, only the intended user signature and timing are required. Furthermore, the convergence of the minimum output energy (MOE) detector to the MMSE detector is analytically proven in case of M-ary PSK. Depicted results show that the performance of the generalized system dominates those previously considered. Further improvements are obtained when multiple input multiple output (MIMO) technique is employed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.55-64
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• 2010

In this paper, we propose a new compensation scheme for combined channel distortions and RF impairments based on the analysis of the impacts of IQ(In-phase/Quadrature) imbalance and phase noise on the OFDM(Orthogonal Frequency Division Multiplexing) system in the direct conversion transceiver and frequency selective fading channel distortion. The proposed scheme estimates the combined distortion by the use of training symbols and the residual distortion by pilot symbols and compensates the combined distortion, including IQ imbalance, phase noise and multipath fading at the same time. The simulation results show that the proposed scheme compensates the combined distortion of IQ imbalance, phase noise and multipath fading simultaneously.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.360-367
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• 2006

In this paper, we design the complementary code keying (CCK) modulation/demodulation structure that is proposed in the IEEE 820.11b and IEEE 802.11g. And, this paper proposes the CCK Rake receiver to be fitted for the large delay spread case like the inter-vehicle communications. The channel estimation of each path in the multipath Rayleigh fading channel is done using the packet preamble and, the combining of the multipath signals in the coherent CCK Rake receiver is achieved as the symbol level combining type. In this paper, in order to validate the utilization of CCK modem for the inter-vehicle communications of the telematics communications, we suggest the CCK modem performance that is made for the multipath Rayleigh fading channel with the mobile speed of 300km/h.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.144-147
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• 2000

In this paper, we propose two receiver structures of the impulse radio (IR) system to improve its performance in multipath environments. Recently, the impulse radio system has drawn much attention for future high-speed wire-less communication services. The conventional IR receiver directly correlates received signals with the ideal reference waveform, which results in performance degradation in multipath environments. The Key idea of the proposed receiver structures is to reflect the multipath Characteristics into the IR receiver. One is to deconvolve the received waveform with estimates of the multipath gains to obtain the transmitted waveform while the other is to modify the reference waveform of the correlator according to the estimates of the multipath gains. We examine the performance of the proposed schemes for the statistical indoor wireless communication channel model using computer simulation.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.05a
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• pp.19-21
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• 2019

In this paper, we introduce VDES system and multipath channel model for maritime wireless digital communication. And we studied the influence of multipath for bit-error ratio performance by computer simulation. Next we propose time-domain adaptive equalizer to treat the influence of multipath, and review the simulation result for necessity of applying the adaptive equalizer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.618-633
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• 2000

In this paper, a Gaussian interpolation filter and cubic interpolation filter are presented to do more accurate channel estimation compared to the conventional linear interpolation filter for COFDM systems. In addition to an interpolation filter, a low pass filter using FFT and IFFT is also presented to reduce the noisy components of a channel estimate obtained by an interpolation filter. Channel estimates after low-pass filtering combined with interpolation filters can lower the error floor compared to the use of only interpolation filters. Computer simulation demonstrates that the presented channel estimation methods exhibit an improved performance compared to the conventional linear interpolation filter for COFDM systems in time-varying multipath fading channel and0.1 ~ 0.2 dB of Eb/No difference at BER=10-4 when the perfect channel estimation is compared.