• Title/Summary/Keyword: 부호분할 다중접속 (CDMA : Code Division Multiple Access) 시스템

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Phase-Shift-Network-Based Differential Sequential Estimation for Code Acquisition in CDMA Systems (CDMA 시스템에서 부호 획득을 위한 위상 변이 네트워크 기반의 차동 순차 추정 기법)

  • Chong, Da-Hae;Lee, Byeong-Yun;Kim, Sang-Hun;Joung, Young-Bin;Song, Iick-Ho;Yoon, Seok-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.3A
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    • pp.281-289
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    • 2007
  • In this paper, a novel pseudo noise (PN) code acquisition scheme called the phase-shift-network-based differential sequential estimation (PDSE) is proposed, in the presence of data modulation in code division multiple access (CDMA) systems. The PDSE has even less complexity compared with that of the dual correlating sequential estimation (DCSE), and the reduction in complexity becomes more significant as the period of PN code increases. Numerical results demonstrate that the PDSE performs equivalently to the DCSE with less complexity.

Code Acquisition with Receive Diversity and Constant False Alarm Rate Schemes: 2. Nonhomogeneous Fading Circumstance (수신기 다양성과 일정 오경보 확률 방법을 쓴 부호획득: 2. 벼균질 감쇄 환경)

  • Kwon Hyoung-Moon;Kang Hyun-Gu;Park Ju-Ho;Ahn Tae-Hoon;Lee Sung-Ro;Song Iick-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.7C
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    • pp.725-734
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    • 2006
  • As a sequel to Part 1, the performance characteristics of the cell averaging (CA), greatest of (GO), and smallest of (SO) constant false alarm rate (CFAR) processors in nonhomogeneous environment are obtained and compared when receiving antenna diversity is employed in the pseudonoise (PN) code acquisition of direct-sequence code division multiple access (DS/CDMA) systems. Unlike in homogeneous environment, the GO CFAR processor is observed to exhibit the best performance in nonhomogeneous environment, with the CA CFAR processor performing the second best.

Polyphase Signature Sequences for M-ary Phase Signaling (M진 위상 신호 방식에 효과적인 다상 서명 수열)

  • Park, So-Ryoung;Song, Iick-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.11C
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    • pp.1059-1065
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    • 2007
  • In this paper, we propose a class of polyphase signature sequences, whose general odd correlation properties are useful for M-ary phase signaling systems. The maximum magnitude of the general odd correlation functions of the proposed sequences are investigated and compared with those of FZC (Frank-Zadoff-Chu) sequences and those of EOE (equivalent odd and even correlation) sequences. The performance of the asynchronous M-ary phase signaling systems using the proposed sequences is simulated and compared with that using FZC sequences in direct sequence code division multiple access (DS/CDMA) systems. The performance of the system using the proposed sequence is shown to be better than that using FZC sequences when the multipath fading is in existence.

Iterative Decoding far a Satellite Broadcasting Channel (위성 통신에서의 반복 복호 기법)

  • Lee, Jae-Sun;Park, Jae-Sun;Lee, Byoung-Moo;Kim, Jin-Young
    • 한국정보통신설비학회:학술대회논문집
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    • 2009.08a
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    • pp.309-313
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    • 2009
  • In this paper, the network performance of a turbo coded optical code division multiple access (CDMA) system with cross-layer, which is between physical and network layers, concept is analyzed and simulated. We consider physical and MAC layers in a cross-layer concept. An intensity-modulated/direct-detection (IM/DD) optical system employing pulse position modulation (PPM) for satellite broadcasting communications is considered. In order to increase the system performance, turbo codes composed of parallel concatenated convolutional codes (PCCCs) is utilized. The network performance is evaluated in terms of bit error probability (BEP). From the simulation results, it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding and decoding complexity. Also, it is confirmed that the performance of such an optical CDMA network can be substantially improved by increasing the interleaver length and the number of iterations in the decoding process. The results of this paper can be applied to implement the satellite broadcasting communications.

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Performance Analysis of Maximum Likelihood Joint Detection for MIMO MC-CDMA Systems (순방향 다중 안테나 MC-CDMA 시스템에서 Maximum Likelihood 합동 검파 성능 분석)

  • Kim, Young-Ju;Song, Hyoung-Joon;Hong, Dae-Sik
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.45 no.11
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    • pp.1-8
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    • 2008
  • In this paper, we analyze the symbol error rate (SER) performance of maximum likelihood (ML) joint detection in downlink multiple-input multiple-output (MIMO) multicarrier code division multiple access (MC-CDMA) systems by deriving a tight union bound on the symbol error rate (SER). The union bound for ML joint detection is utilized to demonstrate the performance of MIMO MC-CDMA systems quantitatively in multiuser and frequency selective Rayleigh fading environments. An analysis of the diversity order of the systems shows the effects of multiple users, spread subcarriers, and multiple antennas on the ML joint detection performance. Furthermore, the analysis shows that MIMO MC-CDMA systems without full loading can achieve more diversify than MIMO orthogonal frequency division multiplexing (OFDM) systems.

Hybrid Beamformer of CDMA Reverse Link in the Correlated SIMO Channel (CDMA 역방향 링크의 상관된 SIMO 채널을 위한 복합형 빔 성형 방식)

  • 최영관;김동구
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.11
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    • pp.81-86
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    • 2004
  • Hybrid beamformer composed of Direction-of-Arrival (DOA) based scheme followed by Maximal Ratio Combining (MRC) is proposed to overcome the degradation due to inaccurate channel estimation caused by insufficient pilot power, which happens in conventional Single-Input Multiple-Output (SIMO) Code Division Multiple Access (CDMA) reverse link. The proposed scheme could provide more accurate channel estimation and interference reduction at the expense of diversity gam in the spatially correlated SIMO channel. As a result, hybrid scheme outperforms conventional MRC beamformer for six or more antennas in the channel environment, in which Angle-of-Spread (AOS) is within 30$^{\circ}$.

Collision Performance Improvement in Orthogonal Code Hopping Multiplexing Systems Using Multiple Antennas (다중 안테나를 이용한 직교 부호 도약 다중화 시스템의 성능향상)

  • Jung, Bang-Chul;Lee, Woo-Jae;Park, Yeoun-Sik;Jeon, Seong-Keun
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.15 no.10
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    • pp.2100-2112
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    • 2011
  • An orthogonal code hopping multiplexing (OCHM) technique has been proposed for accommodating a large number of users with low channel activities than the number of orthogonal codewords through statistical multiplexing in downlink cellular systems. In this paper, a multiple input multiple output (MIMO) antenna based OCHM system is proposed to improve the performance. Each modulated symbol is repeated N times and the N repeated symbols are transmitted simultaneously using N transmit antennas. Through repetitions, the effect of perforations that the OCHM system experiences is decentralized among the repeated symbols and the full perforation probability is significantly reduced. Each receiver detect the transmitted signal using its pre-assigned code hopping pattern. Simulation results show that the proposed scheme saves the required energy for a given frame error rate (FER).

Optimal Chip Rate of Power and Rate Adapted DS/CDMA Communication Systems in Nakagami Fading Channels (나카가미 페이딩 채널에서 전력 및 전송률 적응화 직접 대역확산 부호분할 다중접속 통신시스템을 위한 최적 칩률에 관한 연구)

  • Lee, Ye-Hoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.2A
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    • pp.128-133
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    • 2010
  • We investigate the optimal chip rate of power or rate adapted direct-sequence code division multiple access (DS/CDMA) communication systems in Nakagami fading channels. We find that the optimal chip rate that maximizes the spectral efficiency depends upon both the channel parameters, such as multipath intensity profile (MIP) and line-of-sight (LOS) component, and the adaptation scheme itself. With the rate adaptation, the optimal chip rate is less than $1/T_m$, irrespective of the channel parameters, where $1/T_m$ is multipath delay spread. This indicates that with the rate adaptation, correlation receiver achieves higher spectral efficiency than RAKE receiver. With the power adaptation, however, the optimal chip rate and the corresponding number of tabs in RAKE receiver are sensitive to MIP and LOS component.

Multirate Multicarrier DS/CDMA with 2-Domain Spreading (2차원 확산을 사용하는 다중전송률 MC-DS/CDMA 시스템)

  • Kim, Nam-Sun
    • 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.

On optimal design of soft-decision multistage detectors for asynchronous DS/CDMA systems (비동기 DS/CDMA 시스템을 위한 연판정 다단 검출기의 최적 설계)

  • 고정훈;주정석;이용훈
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.22 no.9
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    • pp.2035-2042
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    • 1997
  • We consider the design of soft decision functions for each stage of multistage detection for coherent demodulation in an asynchronous code-division multiple-access(CDMA) system. In particular, the sigmoid function, which is shown to be optimal under the mean square error(MSE) criterion, andmultilevel quantizers that best approximate the sigmoid function are derived. At each stage of multistage detection, the parameters of these decision functions are adjusted depending on estimated input statistics. Computer simulation results demonstrate that multistage detectors employing these soft decision functions perform considerably better than those with hard decision.

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