• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.4
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• pp.830-837
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• 2009

In this thesis, Multi-code/Multi-carrier CDMA(MC/MC CDMA) system which is combination of Multi-code CDMA and Multi-carrier CDMA is analyzed. This system is suitable fur multi-rate services that use multi-codes and high data rate transmission that employ multi-carriers. In addition, the MC/MC CDMA system is robust against frequency selective fading, is good for narrowband interference rejection, and has higher spectral efficiency. In this paper, The users are assigned OVSF codes as a spreading code according to their data rates and divides the active users having different representative code split into a number of groups for effective cancellation. At the receiver, The code grouping interference canceller performs cancellation between the groups. The proposed receiver does not require any information about interference users, such as code, data and amplitude, and has relatively low complexity. The results show the large improvement in performance that can be attained by cancellation scheme.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.1
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• pp.110-118
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• 2009

The PB/MC-CDMA(Partial Block Multi Carrier Code Division Multilple Access) system can improve the performance by reducing the ICI(Inter-Code Interference) between users. Also, this system can achieve the frequency diversity gain by avoiding ISI(Inter Symbol Interference). Therefore, the performance of PB/MC-CDMA system is better than that of conventional MC-CDMA(Multi Carrier Code Division Multiple Access) system. However, similarly to other multi-carrier systems, it still has a PAPR(Peak to Average Power Ratio) issue. In this paper, we propose a peak power reduction technique involving optimized spreading code selection without side information for the PB/MC-CDMA. The PB/MC-CDMA system in each block of units reuses the code so the extra code will be remained. This extra code is divided into several groups to calculate the PAPR and solving the PAPR problem by transferring the selected code which has minimum peak power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.855-863
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• 1999

Recently a number of multi-rate CDMA systems have been proposed for the third generation mobile communication system. Multi-Code CDMA (MC-CDMA) offers the system construction advantage of being able to use a single-rate receiver. But MC-CDMA suffers from the distortion due to the nonlinearity of the power amplifier. In this paper, we analyze the effect of the nonlinearity on the bit error rate performance of MC-CDMA systems. A polynomial model is used to represent the amplifier amplitude nonlinearities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1494-1500
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• 1999

In order to provide high speed multimedia data rate service, Multi-Code CDMA has been proposed which converts high speed serial data stream into N parallel low speed data streams with orthogonal PN codes for spreading. However this signal has multi level and causes interferences to be increased at the neighboring cell boundary in the reverse link. Therefore in order to solve the above mentioned problem, M/B-MC/CDMA, in which multi level signal is converted to binary level signal using M/B conversion, is proposed and the performance is compared with MC-CDMA.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.17-20
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• 1999

In this Paper, we discuss reducing the number of orthogonal code in Multi-Code CDMA (MC-CDMA) system. MC-CDMA system is highlighted for multi-media communication services, but conventional MC-CDMA(CMC-CDMA) system are needed many more orthogonal codes compared to traditional direct sequence CDMA(DS-CDMA) systems. in this paper, we propose the system which can reduce the number of orthogonal codes using sub-orthogonal code(SOC) technique. We certificate that the performance of the proposed system shows the almost same result under gaussian noise environment as compared to CMC-CDMA system through Monte-Curio computer simulation method.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.5
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• pp.131-138
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• 2008

The channel parameters such as RMS delay spread and Doppler frequency have an effect on performance of system. This paper investigates the effect between the Inter-Code Interference (ICI) and the frequency diversity gain in the multi-rate MC-CDMA system. The multi-rate MC-CDMA system has achieved the more variable data rate than the MC-CDMA and moreover it has the better performance than the OFDMA system, because it has achieved the frquency diversity gain. However, the frequency diversity gain and ICI have a trade-off relationship by using the spreading code. Therefore, we have improved the system performance by efficient choice of system parameters. In order to evaluate the effectiveness of the frequency diversify gain and the ICI effect, we perform simulations by altering the Doppler frequency and RMS delay spread.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.3
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• pp.309-315
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• 1998

This paper is analyzed the performance of coded MC-CDMA system using the multi-carrier with narrow band that is suggested to solve ISI and ICI of DS-CDMA system. In this paper, considered channel model is indoor mobile radio communication environment with Rician fading distribution and fading of multi-carrier have mutual independent characteristics. For the performance analysis of MC-CDMA system, first, bit error probability of uncoded system is simulated in the reverse and forward Rician channels. And then, it is simulated that bit error probability of coded MC-CDMA system for users, multicarriers and SNR, using (7,4) Hamming code, (15,7) BCH code and 1/2-convolutional code with 7 constraint length.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1637-1647
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• 2001

Multi-Code CDMA (MC-CDMA) can not only be integrated easily with a conventional system, but also achieve good spectral efficiency and high processing gain. However, it suffers from high value of peak-to-average power ratio (PAPR). In this paper, we propose the Multi-Phase CDMA (MP-CDMA) system that can provide variable rate service and is not susceptible to the non-linear characteristics of amplifier. The clipping is introduced between at the output of multi-code modulator and at the input of MPSK modulator in order to improve the performance of MPSK chip demodulator and reduce the system complexity, The system performances are compared for the different Number of codes and different clipping levels, respectively. The optimum clipping level is also evaluated for the different number of codes in both, AWGN and frequency flat fading channel.

• Journal of electromagnetic engineering and science
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• v.7 no.1
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• pp.1-6
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• 2007

Recently, Mc(Multi-code) modulation/demodulation(modem) technique has been explored for high speed data transmission in wireless environment. The conventional Mc modem generates some side effects such as allocating Walsh codes, which motivates to propose a novel Mc modem method with sub-code. Our proposed system should expanded the size of sub-code to provide high-rate data transmission, which also affect adversely to the performance of the system with high PAPR(Peak to Average Power Ratio). Thus, in this paper, we propose a novel pre-coded Multi-Dimensional HCOC(High Capacity Orthogonal Code) Mc modem technique to reduce the high PAPR, which enables the performance improvement. This proposed system can be easily designed by concatenating HCOC Mc modem with the generic Mc modem. The pre-coding technique that is used in this paper is CAC(Constant Amplitude Coding), that helps the system maintain the constant transmission power and reduce the maximum transmission power.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.20-27
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• 2002

The demand for multimedia transmission in wireless networking is rapidly increasing. Performance evaluation in the CDMA system has been carried out on the voice-oriented system without re-transmission or buffering. We propose a multimedia access protocol with buffering and ARQ which can meet a variety of QoS requirements. We study the effect of buffering in MC-CDMA(Multi-Code CDMA) and design a dynamic rate control algorithms, whose simulation shows the efficiency of MC-CDMA.