• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.31-37
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• 2010

In this paper, a performance of a decorrelating detector for a multirate MC(multi-carrier) DS/CDMA system is analyzed and simulated in a frequency selective Rayleigh fading channel. The performance is compared with that of single rate MC-DS/CDMA system in term of bit error probability. Variable Spreading Length (VSL) is employed for MC-DS/CDMA system as multirate transmission scheme. From simulation result, it is shown that Decorrelator for multirate MC-DS/CDMA achieves high BER performance as well as that of single rate case.

• ETRI Journal
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• v.29 no.1
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• pp.79-88
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• 2007

This paper proposes a novel concept of adjusting the hardware size in a multi-carrier code division multiple access (MC-CDMA) receiver in real time as per the channel parameters such as delay spread, signal-to-noise ratio, transmission rate, and Doppler frequency. The fast Fourier transform (FFT) or inverse FFT (IFFT) size in orthogonal frequency division multiplexing (OFDM)/MC-CDMA transceivers varies from 1024 points to 16 points. Two low-power reconfigurable radix-4 256-point FFT processor architectures are proposed that can also be dynamically configured as 64-point and 16-point as per the channel parameters to prove the concept. By tailoring the clock of the higher FFT stages for longer FFTs and switching to shorter FFTs from longer FFTs, significant power saving is achieved. In addition, two 256 sub-carrier MC-CDMA receiver architectures are proposed which can also be configured for 64 sub-carriers in real time to prove the feasibility of the concept over the whole receiver.

• Journal of Korea Society of Industrial Information Systems
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• v.16 no.4
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• pp.27-35
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• 2011

Multicarrier-Direct Sequence/Code Division Multiple Access(MC-DS/ CDMA) which is a combination of Orthogonal Frequency Division Multiplexing(OFDM) and DS/CDMA has been of significant interest as a means to take such advantages as bandwidth efficiency, high bit rate and robustness against multipath fading. In this paper we study a reduced-complexity multiuser detection aided multirate MC-DS/CDMA with time(T)-domain and frequency(F)-domain spreading. The one- dimensional orthogonal variable spreading factor(1D OVSF) code extracted from 2D OVSF code are used as a spreading code in T/F-domain. The proposed system will use code grouping interference cancellation(CGIC) receiver to reduce Multiuser Interference(MUI). The CGIC receiver uses code grouping by the correlation properties of 1D OVSF code and dose not requires the code information and activity of other user. The multiuser detector with CGIC receiver will be analyzed in Time- and Frequency-domain separately(jointly). The system performance is analytically derived in Additive White Gaussian Noise(AWGN) channel and we also compare the system performance between proposed system and T/F spreaded single(multi) rate multiuser MC-DS/CDMA system. In the computer simulation results, the proposed receiver of demonstrated huge performance improvement over conventional matched filter receiver.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.959-962
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• 2009

Recently, a multi-core system is studied for single terminal's operations on various service networks for mobile systems. Therefore, it is expected that mobile systems capable of supporting WCDMA, GSM, and WiBro would be developed. Mobile systems for supporting various service networks is able to be implemented on a single chipset via SoC(System on Chip) technology, thus a noble modem design proper for SoC technology is necessary. As those systems shall be operated at different frequency band with only a single terminal, a problem that a nonlinear characteristic according to the system and its frequency band is occurred. In this paper a noble modem design for multi-core systems is proposed and the nonlinear characteristics for those systems is analysed. The proposed modem design is based on OFDM(Orthogonal Frequency Division Multiplexing) and MC-CDMA scheme. And nonlinear characteristic analysis is done by PSD measurement.

• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.61-65
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• 2009

Successive interference cancellation(SIC) for the uplink of MC-CDMA mobile communications systems is an effective method to improve performance. We propose a successive interference cancellation(SIC) technique for the uplink of MC-CDMA mobile systems with multiple receive antennas. The destination uses optimum combining(OC) to combine the signals from an OFDM Demodulator with multiple receiving antennas, and applies SIC processing to the combined signals. Achieved interference cancellation order is depends on the signal to interference-plus-noise ratio (SINR) at the output of the optimum combiner. Monte-Carlo simulations are employed to verify the proposed technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1590-1598
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• 1997

The paper first introduces the new concept of potential diversity and signal decomposability, which establish a foundaton to generalize the existing concepts of path and frequency diversities. Then it presents a new DS/CDMA system called chip-spreading OCDM system, which is an embodiment of the petential diversity concept that combines the path diversity of the DS/CDMA system and the frequency diversity of the OFDM/CDMA system. In the chip-spreading OCDM system the chip sequences in each symbol interval are first converted into aralled streams, which then simultaneously modulate different orthogonal Walsh basis functions. In the receiver, the received signal is matched to each extended basis-function which is the union of the transmitter basis-functions and their delayed replicas, and the matched-filtered chip samples are combined together after individual channel compensation. The conventional DS/CDMA system using the maximal ratio combining. In addition, it effectively resolves the high PAR and high sensitivity to frequency offset problems which are critical in multi-carrier systems.

• Journal of Advanced Navigation Technology
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• v.14 no.5
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• pp.684-690
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• 2010

Recently, the NG(Next Generation) system is studied for supporting convergence of various services and multi mode of single terminal. And a demand of user for taking the various services is getting increased, for supporting these services, many systems being able to transmit a large message have been appeared. In the NG system, it has to be supporting the CDMA and WCDMA besides the tele communication systems using OFDM method with single terminal An intergrated system can be improved with adopting of SoC technique. For adopting SoC technique on the intergrated terminal, we have to solve the non linear problem of HPA(High Power Amplifier). Nonlinear characteristic of HPA distorts both amplitude and phase of transmit signal, this distortion cause deep adjacent channel interference. We adopt a polynomial pre-distortion technique for this problem. In this paper, a noble modem design for NG mobile communication service and a method using polynomial pre-distorter with PAPR technique for counterbalancing nonlinear characteristic of the HPA are proposed.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.26-29
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• 2012

In this paper, we propose a Single Carrier Frequency Division Multiple Access(SC-FDMA) scheme with greatly enhanced tolerance of timing offset among the users. The type of the proposed scheme is similar to code spread Multiple Carrier Direct Spread Code Division Multiple Access(MC DS CDMA). The proposed scheme performs partial Discrete Fourier Transform(DFT) in order to solve high Peak to Average Power Ratio(PAPR) of the MC DS CDMA before Inverse Fast Fourier Transform(IFFT). Exploiting the property Properly Scrambled Walsh-Hadamard(PSW) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed scheme achieves Multiple Access Interference free performance with the timing offset up to ${\pm}1$ OFDM symbol duration with low PAPR. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset in multipath fading channel.

• Information and Communications Magazine
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• v.24 no.12
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• pp.65-73
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• 2007

2007년8월 v2.0을 출간하면서 표준화가 완료된 Ultra Mobile Broadband(UMB) 기술은 진보된 안테나 기술과 함께, CDMA, TDM, Layer-superposed OFDM(LS-OFDM), OFDM, OFDMA의 장점들을 하나의 Air Interface로 통합하였으며, 효율적인 자원 관리 기법을 통해 더 많은 VoIP 사용자들을 수용할 수 있게 해준다. 4x4 안테나를 사용시 20MHz의 주파수 대역에 순방향 288 Mbps, 역방향 75 Mbps의 최대 전송률을 제공하며, 양방향에 대한 평균 Network 지연시간은 약 16.8 ms을 지원하고, 10 MHz 주파수 대역에 1000명 이상의 VoIP 사용자를 지원할 수 있다. 본 고에서는 UMB의 표준화 과정 및 현황 그리고 물리 계층과 MAC 계층의 요소 기술들에 대해 고찰한다.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.66-66
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• 2004