• 한국ITS학회:학술대회논문집
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• 2003.11a
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• pp.153-158
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• 2003

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.249-253
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• 2006

We propose a new beamforming algorithm, which is based on simplex downhill optimization method in the presence of pilot channels in cdma2000 reverse-link, for the rake structure antenna array in DS/CDMA communication system. Our approach uses the desired signal(pilot) covariance matrix and the interference covariance matrix. The beamforming weights are made according to maximum SINR criteria using simplex downhill optimization procedure. Our proposed scheme provides lower computational load, better convergence speed, better performance than existingadaptive beamforming algorithm. The simplex downhill method is well suited to finding the optimal or sub-optimal weight vector, since they require only the value of the deterministic function to be optimized. The rake beamformer performances are also evaluated under several set of practical parameter values with regard to spatial channel model. We also compare the performance between conventional rake receiver and the proposed one under same receiving power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.7A
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• pp.477-484
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• 2003

In this paper, we compared and analyzed the influence of the fading index and the number of branch of diversity in the Nakagami-m fading channel environment when the MRC diversity and the hybrid SC/MRC are applied to the DS/CDMA system. We considered that the number of branches were 2,3, and 4, respectively and applied an individual diversity type according to the number of branches, when nakagami fading index(m) were 1 and 2. We found that when the Nakagami fading index m is small, that is to say, when fading is inferior, the application of a hybrid SC/MRC diversity Rake receiver is efficient; however, when the fading environment is good, the application of the MRC diversity Rake receiver is efficient. As a result, we verified that when the actual communication environment is inferior, the hybrid SC/MRC diversity that selects a strong signal to be received on an individual number of branches could replace the MRC diversity, as a method to achieve a similar performance by reducing the complexity of the system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.932-939
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• 1998

In this paper, we analyze the performance of a multicode-CDMA system which have been proposed for the multimedia communications. The performance of a multicode-CDMA system, providing good spectrum efficiency as well as serving various bit rates, is analyzed with multipath, frequency selective, slowly fading Rayleigh channel. Also the proposed scheme adopting RAKE receiver with MRC(Maximal Ratio Combine) is advantageous to multipath channel. For a practical channel modeling, the JTC(Joint Technical Committee) recommended channel model(JTC(AIR) 23-065R6) is applied to simulation. The proposed schemehas serial-to-parallel convertor which splits input data stream of 2 Mits/s into 20 branches o 100 kbits/s. From the result of simulation, the case of RAKE receiver with 3 fingers to reduce the system complexity required the relatively large $E_{b}/N_O$ of 0 dB~1.5 dB, compared to the case of RAKE receiver with the number of path finger to keep the average error rate to be $1{\times}10^{-3}$ in channel A.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.871-879
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• 2009

The performance variations of a spatio temporal smart antenna which is equipped at the basestation of CDMA cellular communication network due to the parametric change of multipath fading environment are studied in this paper. The smart antenna of interest employs space diversity based adaptive array structure in conjunction with rake receiver that has fingers the number of which is the same as that of multipath links. The beamforming is achieved via LMS(Least Mean Square) algorithm in which a reference signal is generated using decision directed formula. It has been shown by computer simulation that the performance of our smart antenna of interest depends significantly upon not only the degree of desired signal's DOA(Direction of Arrival)spread but the number of fingers of the rake receiver. The relative insensitivity of the smart antenna's performance on desired signal's delay spread has also been observed. Computer simulation has shown that the increase of the number of fingers brings in a nonlinear enhancement of the performance of our smart antenna. The renewal of weight vector in the beamforming procedure is taken place at post PN despread stage.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.354-364
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• 2003

A general method for the evaluation of the symbol error probability (SER) of ultra wideband (UWB) systems with various kind of modulation schemes (N-PAM, M-PPM, Bi-Orthogonal), in presence of multipath channel, multiuser and strong narrowband interference, is presented. This method is shown to be able to include all the principal multiaccess techniques proposed so far for UWB, time hopping (TH), direct sequence (DS) and optical orthogonal codes (OOC). A comparison between the performance of these multiple access and modulation techniques is given, for both ideal Rake receiver and minimum mean square error (MMSE) equalizer. It is shown that for all the analyzed multiple access schemes, a Rake receiver exhibits a high error floor in presence of narrowband interference (NBI) and that the value of the error floor is in-fluenced by the spectral characteristics of the spreading code. As expected, an MMSE receiver offers better performance, representing a promising candidate for UWB systems. When the multiuser interference is dominant, all multiple access techniques exhibit similar performance under high-load conditions. If the number of users is significantly lower than the spreading factor, then DS outperforms both TH and OOC. Finally 2PPM is shown to offer better performance than the other modulation schemes in presence of multiuser interference; increasing the spreading factor is proposed as a more effective strategy for SER reduction than the use of time diversity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.12A
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• pp.958-963
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• 2003

Increasing throughput using high order data modulations in the WCDMA downlink requires the elimination of multipath interferences. For this reason, Kenichi Higuchi proposed a multipath interference canceller in WCDMA downlink. However, this paper considers the downlink signal models that only contains code channels for which code information is known to the receiver. WCDMA systems contain code channels for other active users whose code information is unknown to the receiver and these code channels degrade the performance of the multipath interference canceller. Thus, this paper proposes a multipath interference mitigation scheme which removes multipath interference induced by all the code channels within a cell. Simulation results show that the proposed scheme outperforms both the RAKE receiver and the multipath interference canceller in the WCDMA downlink.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.91-98
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• 2017

In this paper, we analyzed underwater multiple sensors acoustic communication technologies for monitoring and control of offshore plants in underwater environments. Information on underwater structure of offshore plants is transmitted and received by multiple sensors at the same time. Using multiple sensors with same frequency, we employed spread spectrum techniques to avoid interferences between these multiple sensors. Owing to the multi-path characteristic in underwater communications, the performance is degraded. In order to improve the performance of underwater multiple sensors communication, we proposed turbo equalized RAKE receiver structures. Assuming that the number of sensors is fixed to three, we conformed the effectiveness of the proposed method as compared to the conventional one.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.755-764
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• 2001

In this paper, we propose maximum likelihood (ML) decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems. The proposed DFCE uses the maximum combiner output in a RAKE receiver as decision feedback information, enabling M-ary orthogonal signals to be demodulated coherently and a RAKE receiver to use a em maximal ration combining (MRC) scheme. However, the performance of the proposed DFCE in the multiuser environment is severely degraded due to multiple access interference (MAI). To overcome this problem, a multistage parallel interference cancellation (PIC) scheme is combined with the proposed DFCE for multiuser environments. Accurate knowledge of the channel coefficient estimated by the proposed DFCE is used to regenerate the signal of each user for the multistage PIC scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed system is significantly improved in comparison with conventional noncoherent demodulation.

• Journal of information and communication convergence engineering
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• v.7 no.3
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• pp.286-291
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• 2009

In this paper, the performance of ultra-wideband (UWB) single input multiple output (SIMO) systems to achieve high data rate communications is studied in dense multipath environments. The effects of spatial and temporal diversities on the performance of multi-user time-hopping UWB systems using binary pulse position modulation (2PPM) are analyzed. The reduced-complexity Rake receivers based on the selective combining (called SRake) and partial combining (called PRake) are considered. The theoretical and simulation results show that the BER performance of the UWB system can be enhanced as the number of array elements and/or Rake fingers increases. Moreover, we observe that SRake is more effective for the IR-UWB systems to achieve a good BER performance, as compared with PRake.