• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.7
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• pp.1033-1043
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• 1999

We consider an improved multicarrier(MC) CDMA system that combines both DS-CDMA with a concatenated orthogonal/PN spreading sequence and MC modulation. This system incorporates the advantages of DS-CDMA with a concatenated sequence to achieve large user capacity and MC modulation technique to combat the effects of a multipath fading channel and intersymbol interference(ISI). Considering voice activity and imperfect sectorization, the system performance is analysed for the maximal ratio combiner(MRC) under a multicell, multiuser, and multipath Rayleigh/Rician fading channels. The performance of the system is improved much more for the single path fading channel compared to the multipath fading channel. Also the system is shown to have the more improved average bit error rate(BER) over the orthogonal MC-CDMA with the conventional PN sequence.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.47-53
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• 2007

The purpose of IEEE 802.16j is to extend coverage and to enhance throughput by using relay station additionally to conventional IEEE 802.16e . The cellular system experiences performance degradation at the cell edge due to pathloss, shadow and multipath fading. We can get advantage of spatial diversity gain by using relays more than two cooperatively in the IEEE 802.16j system. Cooperative relaying using space-time code provides better performance under multipath fading and has more robustness against the shadow fading than single relaying. In this paper, we investigate the performance of IEEE 802.16j using cooperative relaying by link level simulation. We also show that the cooperative relaying system achieves better performance than the conventional single relaying system. We apply realistic shadow model considering correlations between shadow fadings of different relaying paths. It is shown that the performance of the system depends highly on the spatial location of relay stations.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.9-18
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• 1998

In this paper, an equalization technique for OFDM(orthogonal frequency division multiplexing) in a time-variant multipath fading environment is described. A loss of subchannel orthogonality due to time-varying multipath fading channels leads to interchannel interference (ICI) which increases the error floor in proportion to Doppler frequency. A simple frequency-domain equalizer which can compensate the effect of ICI caused by time variation of multipath fading channel is proposed by modifying the previous frequency-domain equalization technique with taking into account only the ICI terms significantly affecting the error performance. The effectiveness of the proposed approach is demonstrated via computer simulation by applying it to OFDM systems when the multipath fading channel is slowly time variant.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2247-2255
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• 2015

In very shallow water acoustic communication channel, underwater acoustic (UWA) communication signal is observed as frequency selective fading signal due to time-varying multipath. This induces a time and frequency dependent inter-symbol-interference (ISI) and degrades the UWA system performance. There is no study about how the performances of the error correction codes are related to a multipath fading statistics in very shallow water. In this study, the characteristics of very shallow water multipath fading channel is analyzed and the performances of two different forward error correction (FEC) codes are compared. The convolution code (CC) and Reed-Solomon (RS) code are adopted. Sea experimental results show that RS code is better choice than CC in frequency selective channel with fading.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.10
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• pp.19-26
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• 1998

In this paper, we studied the design and implementation of fading compensation systems at aspects of narrowband mobile communication using TTIB SSB. The mobile radio channel with multipath fading places fundamental limitations on the performance of wireless communication systems. The multipath fading is compensated using pilot tone in TTIB SSB. The TTIB transceiver was implemented using the prevailing digital signal processing (DSP) techniques and compensation for the multipath fading was incorporated in the receiver in the form of DSP algorithm. In order to evaluate fading compensation performance in TTIB transceiver, we first used computer simulation. In the simulation results, we found that the TTIB transceiver could compensate for the multipath fading as expected. Second, we carried out some experiments on TTIB transceiver implementation with DSP boards and later with hardwares including RF circuits with center frequency of 145MHz. Through these experiments, we found that fading compensation performance in TTIB transceiver was almost as good as that obtained from simulation.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.424-424
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• 2004

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1996.06a
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• pp.3-7
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• 1996

In this paper, the performances of OFDM and MC-CDMA systems in a slowly-varying multipath fading environment is investigated. Time variation of the multipath channel leads to both a change of an optimal coefficient in one-tap equalizer and a loss of subchannel orthogornality, resulting in significant performance loss. A new simple one-tap equalizer which can reduce the effect of slowly time-varying multipath channel is proposed by taking into account time-variation of multipath profile and modifying the previous equalization techniques. It is demonstrated by computer simulation that the performances of OFDM and MC-CDMA systems can be improved by using the proposed one-tap equalizers when the multipath channel is slowly varying.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.353-361
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• 2000

The performance of a multi-carrier CDMA system is analyzed considering frequency selective multipath fading and Near/Far effects. The number of multicarrier, multiuser, and arms of RAKE receiver, and the decay ratio of frequency selective multipath fading are used as a parameter for the performance analysis. More over, the distribution and the strength of multiuser interference are also considered. To evaluated the Near/Far effects in a multi-carrier CDMA system, three distribution models are assumed. In the first model. interference to carrier Ratio, I/C, ranges form -4 dB to 4dB, and at each 2 dB interval 20 % of multiuser is assumed to be uniformly distributed. In the second one, I/C ranges from -2 dB to 2 dB, and 33.3% of multiuser is assumed to be equally dispersed at each 2dB interval. The third model is 0 dB of I/C, that is, with perfect power control, multiuser are assumed to be evenly located. In this paper, multi-carrier CDMA system adoption RAKE receiver is proposed to mitigate the frequency selective multipath fading. Form the results, the third model(i.e. perfect power control)shows the best performance, and the narrower range of I/C causes the less effects to the desired signal, which reads to the better performance.

• The Journal of the Acoustical Society of Korea
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• v.32 no.5
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• pp.377-384
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• 2013

In this paper, performance of COFDM (Coded Orthogonal Frequency Division Multiplexing) which is OFDM with a forward error correction code, is studied in frequency selective fading underwater acoustic communication channel. The OFDM is a multiplexing technique resistant to frequency selective multipath channel. In OFDM, a broadband information signal is transformed into several narrow band signals and transmits narrow band signals whose bandwidths are less than the channel coherence bandwidth. However, its performance is degraded in a specific narrow band signal due to its deep fading by multipath. To mitigate this degradation, COFDM which is OFDM with convolution code as a forward error correction code, is evaluated. The performance of COFDM is found to be better than that of OFDM in multipath channel.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.5-11
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• 1997

In this paper, we investigate the performance of the direct sequence/spread spectrum multiple access (DS/SSMA) system using the Trellis coded modulation (TCM) technique in both multipath fading and multi-user channel environments. For this, an expression that represents the pairwise bit error probability of the system is derived. Unlike the existing results that were performed in a more restrictive condition considering only the multi-user effect, the effects of the multipath fading as well as the multi-user environments are compositely taken into account. In order to check the validity of our analysis, although not direct, computer simulations are carried out, and they show that our expression matches exactly with the previous work for which the TCM and the multipath effects were disregarded. Moreover, it is observed that the performance of the Trellis coded DS/SSMA system can be improved dramatically comparing to the uncoded QPSK system in the multipath fading and multi-user channel environments.