• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.5
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• pp.400-410
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• 1988

In this paper, a fast synchronization system using SAW TDL matched filter and SAW recirculation loop not only for acquisition but also tracking in the direct sequence spread spectrum communication receiver in case of low SNR was designed and its characteristics were investigated. When signal of 16dB SNR was inputed at the receiver, the PN code of the receiver could be synchronized from the extracted signal for synchronization through SAW TDL matched filter and SAM recirculation loop for 30 recirculations. And the average synchronization time of this system was calculated. From the results, we found that this synchronization system could achieve faster synchronization of PN codes in the receiver under the circumstances of low SNR than that of using only matched filter.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.371-380
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• 2006

The performance characteristics of the cell averaging(CA), greatest of(GO), and smallest of(SO) constant false alarm rate(CFAR) processors in homogeneous environment are obtained and compared when receiving antenna diversity is employed in the pseudonoise code acquisition of direct-sequence code division multiple access (DS/CDMA) systems. From the simulation results, it is observed that the CA CFAR scheme has the best performance and the GO CFAR scheme has almost the same performance as the CA CFAR scheme in homogeneous environment. In Part 2 of this paper, the CA, GO, and SO CFAR processors for code acquisition in nonhomogeneous environment are addressed.

• Journal of Communications and Networks
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• v.6 no.1
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• pp.26-34
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• 2004

A blind interference canceller in the presence of subchipspaced multipath channels for direct-sequence code division multiple access (DS-CDMA) down-link system is considered. This technique is based on combining the existing blind interference canceller with a technique that involves assigning subchip-tap spacing to the Rake receiver. The proposed receiver minimizes the receiver’s output energy subject to a constraint in order to mitigate the multiple access interference (MAI) along each multipath component, and then suboptimally combining all the multipath components. Moreover, it is able to mitigate the mismatch problem when subchip-spaced multipath components arrive at the blind interference canceller. It is known that optimal combining techniques perform a decorrelation operation before combining, which requires both knowledge and computational complexity. In the following, we have adopted a simpler but suboptimum approach in the combining of the suppressed signals at the output of our proposed receiver. Computer simulation results verify the effectiveness of the proposed receiver to handle subchip-spaced multipath components and still suppresses MAI significantly.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.630-634
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• 2005

본 논문은 신경망을 이용한 간섭 신호 제어 복합 다층 퍼셉트론에서 DS/SS 이동 통신에서 수신된 신호를 검출하는 것에 대하여 연구한다. 수신 신호가 일정한 비트율을 갖는 채널에 전송하기 위하여 신경망을 이용한 새로운 탭 가중치 갱신 제어 방법을 제안한다. 적응 횡단선 필터는 상호 심볼간 간섭을 억압하기 위해 LMS 알고리즘 사용하고, 응답과 실제 출력간의 차인 에러를 이용하여 탭 가중치 조절 메카니즘을 통해 탭 가중치를 갱신함으로서 효과적으로 간섭을 제거한다. 본 논문은 상호 심볼간 간섭을 효율적으로 억압해온 다계층 퍼셉트론 조합을 이용하여 제안된 알고리즘을 통해 탭 가중치 갱신이 보다 효율적으로 이루어질 수 있도록 한다. 시뮬레이션을 통해 평균자승 에러의 수렴 특성이 우월하다는 것을 연구한다.

• Journal of Communications and Networks
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• v.5 no.1
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• pp.33-42
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• 2003

In this paper a two-stage maximum-likelihood (ML) detection structure for group detection in DS/CDMA systems is presented. The first stage of the receiver is a linear filter, aimed at suppressing the effect of the unwanted (i.e., out-of-grout) users' signals, while the second stage is a non-linear block, implementing a ML detection rule on the set of desired users signals. As to the linear stage, we consider both the decorrelating and the minimum mean square error approaches. Interestingly, the proposed detection structure turns out to be a generalization of Varanasi's group detector, to which it reduces when the system is synchronous, the signatures are linerly independent and the first stage of the receiver is a decorrelator. The issue of blind adaptive receiver implementation is also considered, and implementations of the proposed receiver based on the LMS algorithm, the RLS algorithm and subspace-tracking algorithms are presented. These adaptive receivers do not rely on any knowledge on the out-of group users' signals, and are thus particularly suited for rejection of out-of-cell interference in the base station. Simulation results confirm that the proposed structure achieves very satisfactory performance in comparison with previously derived receivers, as well as that the proposed blind adaptive algorithms achieve satisfactory performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4A
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• pp.352-360
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• 2008

Recently Task Group (TG) 4 of the Institute of Electrical and Electronics Engineers (IEEE) 802.15a has been recommended a system with ranging capability in existence of multiple Simultaneous operating piconets (SOPs) as well as low-cost, low-power. According to the ranging service, coherent and non-coherent based ranging schemes using ternary code have been adopted as a standard. However it is hard to estimate an accurate time of arrival (TOA) in case of using direct sequence based TOA estimation method because pulse repetition interval (PRI) offered by TG is more limited than the maximum excess delay (MED) of channel. To mitigate inter pulse interference (IPI) problem, this paper proposes a non-coherent TOA estimation scheme using non-periodic transmission (NPT) pattern. The proposed receiver is based on a non-coherent energy detection considering with motivation of low rate wireless personal area network (LR-WPAN). TOA information is estimated via proper comparison with a prescribed threshold after the sliding correlation and search back window (SBW) process for reducing TOA error. To verify the performance of proposed ranging scheme, two distinct channel models approved by IEEE 802.15.4a TG are considered. According to the simulation results, we could conclude that the proposed scheme have performed better performance than the conventional method on the existence of multiple SOPs.

• Journal of IKEEE
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• v.2 no.1 s.2
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• pp.1-14
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• 1998

In this paper, Antenna, LNA, Mixer, VCO, and Modulation/Demodulation in Baseband processor which are the RF main components in Wireless LAN system for ultra high-speed communications network are studied. Antenna bandwidth and selective fading due to multipath can be major obstacles in high speed digital communications. To solve this problem, wide band MSA which has loop-structure magnetic antenna characteristics is designed. Distributed mixer using dual-gate GaAs MESFET can achieve over 10dB LO/RF isolation without hybrid, and minimize circuit size. As linear mixing signal is produced, distortions can be decreased at baseband signals. Conversion gain is achieved by mixing and amplification simultaneously. Mixer is designed to have wide band characteristics using distributed amplifier. In VCO design, Oscillator design method by large signal analysis is used to produce stable signal. Modulation/Demodulation system in baseband processor, DS/SS technique which is robust against noise and interference is used to eliminate the effect of multipath propagation. DQPSK modulation technique with M-sequences for wideband PN spreading signals is adopted because of BER characteristic and high speed digital signal transmission.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.22-33
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• 2005

In this paper, an efficient signal interference control technique to improve the high convergence speed of LMS algorithms is introduced in the adaptive transversal filter of DS/SS. The convergence characteristics of the proposed algorithm, whose coefficients are multiply adapted in a symbol time period by recycling the received data, is analyzed to prove theoretically the improvement of high convergence speed. According as the step-size parameter ${\mu}$ is increased, the rate of convergence of the algorithm is controlled. Also, an increase in the stop-size parameter ${\mu}$ has the effect of reducing the variation in the experimentally computed learning curve. Increasing the eigenvalue spread has the effect of controlling which is downed the rate of convergence of the adaptive equalizer. Increasing the steady-state value of the average squared error, proposed algorithm also demonstrate the superiority of signal interference control to the filter algorithm increasing convergence speed by (B+1) times due to the data-recycling LMS technique.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.5
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• pp.152-161
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• 2017

The CBTC(Communication based Train Control) system employed on 2.4GHz ISM band adopt the IEEE802.11.x standard. Therefor communication time delay, distortion and data losses will be produced. To overcome these problems, CPSK(Continuous Phase shift keying) modulated DS/SS(Direct Sequence Spread Spectrum) transmitter with 908MHz carrier frequency is proposed. Through the eye diagram and scatter diagram the performance is analysed. And the phase noise characteristic of the local oscillator is measured about 60dBc/Hz, this means that the phase noise performance is very good compared to the signal. Reference frequency suppression of the 2nd local oscillator is 50dB below compared to the signal. Through the polarities of the complementary signal equally probable, the line spectrum of the output spectrum is eliminated. The nonlinear effects which introduce the spectral spreading or spectral regeneration is reduced remarkably.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4A
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• pp.330-335
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• 2002

In the direct sequence code division multiple access system, the problem of multiple access interference due to multiple access is generated. A interference cancelling receiver is used to solve this problem. The conventional interference cancelling receiver is structure of successive interference canceller using antenna array. In this structure, the difference of between method I and method II depends on updating weight vector. In this paper, the adaptive blind CMA array interference cancelling receiver using cost function of constant modulus algorithms is proposed to update weight vector at conventional structure. The simulation compared the proposed interference cancelling receiver with two conventional interference cancelling receivers by signal to interference ratio and bit error rate curve under additive white Gaussian noise environment. The simulation results show that the proposed receiver has about the gain of SIR of 1.5[dB] more than method I which is conventional receiver at SIR curve, and about the gain of SIR of 0.5(dB) more than method II. In BER curve, the proposed IC receiver about the gain of SNR of 2[dB] more than method I and about the gain of SNR of 0.5[dB] more than method If, Thus, the proposed interference cancelling receiver has the higher performance than conventional interference cancelling receivers.