• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.671-674
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• 2001

본 논문에서는 직접확산방식 무선 LAN의 이기종간 간섭특성에 관하여 검토를 하였다. 그 결과 일대일의 통신을 하는 2종의 무선 LAN에 있어서 변조 파라미터의 다른 두 종류의 무선LAN을 D/U비가 15dB이상이 되도록 조합함으로써 전송효율 특성은 동일 시스템의 두조를 사용하는 것보다도 개선되는 것을 알았다. 또한, 이기종간 간섭모델을 상정하여 디지털 신호처리해석을 사용하여 무선 LAN의 이기종간 간섭특성에 대한 비트 에러율(BER) 및 전송효율 특성을 구했다. 계산결과는 측정 결과와 거의 일치하고 이기종간 간섭 환경에서의 일대일 통신에 있어서 전송효율 특성을 보다 명확히 하였다. 이상의 결과는 이기종간 간섭파에 있어서 무선 LAN의 통신 특성의 추정에 유효하다고 생각된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.2004-2010
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• 1999

This paper presents the blind multiuser detector using the constant modulus algorithm(CMA) to solve the near-far problem in DS-CDMA systems. The convergence property of the detector is compared with the conventional MOE(minimum output energy) detector by means of SIR(signal-to-interference ratio). The MOE detector needs both the spreading code of the users and the timing information, while proposed methods needs only information about the spreading code of users Simulation results show that the CMA-based detector is superior to the conventional blind MOE multiuser detector. For this, the BER performance was tested using different values of SNR and near-far ratio. The SIR is also investigated for different number of users in AWGN and Rayleigh fading channels. We have observed that the proposed blind multiuser detector performs better than conventional MOE multiuser detector.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.417-425
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• 2013

Digital communication technology have been focused on the higher data efficiency and the effective coding of information. Also, it is very important to improve security and minimize the interference of the external sources, Chaos communications system is studied to improve security and minimize the interference by effective encoding of information in the nonlinear systems such as DCSK(Differential Chaos Shift Keying) and CDSK(Correlation Delay Shift Keying). In this paper, we evaluate anti-jamming performance of chaos communications system using the DCSK and CDSK system. The simulation results show that the Gauss iterated map has better BER performance than the other maps(tent map, logistic map, Henon map). Also, DCSK and CDSK system can get the better anti-jamming performance by applying different chaotic maps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.7A
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• pp.1028-1036
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• 2000

In this paper, an error-resilient image compression technique using wavelet transform is proposed. The zerotree technique that uses properties of statistics, energy and directions of wavelet coefficients in the space-frequency domain shows effective compression results. Since it is highly sensitive to the propagation of channel errors, evena single bit error degrades the whole image quality severely. In the proposed algorithm, the image is encoded by the SPIHT(Set Partitioning in Hierarchical Trees) algorithm using the zerotree coding technique. Encoded bitstreams are partitioned into some blocks using the subband correlations and then fixed-length blocks are made by using the effective bit reorganization algorithm. finally, an effective bit allocation technique is used to limit error propagation in each block. Therefore, in low BER the proposed algorithm shows similar compression performance to the zerotree compression technique and in high BER it shows better performance in terms of PSNR than the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1C
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• pp.82-91
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• 2005

This paper introduces an efficient affine projection algorithm(APA) using iterative hyperplane projection. Among various fast converging adaptation algorithms, APA has been preferred to be employed for various applications due to its inherent effectiveness against the rank deficient problem. However, the amount of complexity of the conventional APA could not be negligible because of the accomplishment of sample matrix inversion(SMI). Moreover, the 'shifting invariance property' usually exploited in single channel case does not hold for the application of space-time decision-directed equalizer(STDE) deployed in single-input-multi-output(SIMO) systems. Thus, it is impossible to utilize the fast adaptation schemes such as fast transversal filter(FlF) having low-complexity. To accomplish such tasks, this paper introduces the low-complexity APA by employing hyperplane projection algorithm, which shows the excellent tracking capability as well as the fast convergence. In order to confirm th validity of the proposed method, its performance is evaluated under wireless SIMO channel in respect to bit error rate(BER) behavior and computational complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.1
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• pp.94-105
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• 1988

In this paper, we deal with to survey a narrow band ISDN transmission capability through the local subscriber line in Korea. First, we disscuss international activity trends of technical references required for a narrow band ISDN services using existing pair cables. Second, we have measured transmission characteristics to send digital signals at 144kbps ratio through the local subscriber line With this result, we have found that 3.6% of measured lines are not availlable for a narow band ISDN channel, obtained a conclusion that the input level of U-transceiver should be more than -31dBm so as to assure the sufficient digital transmission quality. We also know that majority noise cased by transmission error are due to impulsive noise and near end crosstalk. Fianlly. as a result of the BER measruement, it is observed that, within 2.5km, more than 70% of measured cables are satisfied with the reference quality.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11A
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• pp.1820-1826
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• 2001

In this paper, we present a modeling scheme for the already-installed two-wire home phone lines with arbitrary topologies and show that the inter-symbol interference due to the topology can be removed using an adaptive equalizer. The transmission characteristics of the arbitrary-configured two-wire home phone lines can be analyzed through the ABCD matrices. The simulation result shows that the impedance mismatch due to the branch lines renders nulls in the frequency response or delayed pulses in the impulse response. These nulls or delayed pulses cause inter-symbol interference that inhibits correct signal detection. An adaptive equalizer is shown to be effective in eliminating the interference. Also, the simulation result shows that the equalizer converges in 1.5 ms at a data rate of 1 Msps at signal-to-noise ratios greater than 15 dB. In addition, from the result of relation between E$\_$b//N$\_$and BER(Bit Error Rate), we can see that E$\_$b//N$\_$o/ more than 19 dB is required for the data communication with a BER less than 10$\^$-5/.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1860-1865
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• 2008

40Gbps WDMSystems have been studied by numerical simulation to optimize their performance. Standard single mode fiber is assumed, and the most popular modulation format, NRZ, is used for the study. These assumptions are valid when existing WDM systems are required to upgrade their performance to 40Gbps. It is shown that the standard single mode fiber can transmit optical signals over 4800 (BER < 10-15) by optimizing optical and electrical filter characteristics at the receiver and by compensation of dispersion. In addition, when the system performance is mainly limited by ASE noise of EDFAs, it is found that flattop-shaped optical filter at the receiver gives a better result than Gaussian-shaped filter unless the insertion loss of the optical filter is larger than 5dB.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.444-448
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• 2016

Hollow silicon/carbon (H-Si/C) composites as anode materials for lithium ion batteries were investigated to overcome the large volume expansion. H-Si/C composites were prepared as follows; hollow $SiO_2\;(H-SiO_2)$ was prepared by adding $NaBH_4$ to $SiO_2$ synthesized using $st{\ddot{o}}ber$ method followed by magnesiothermic reduction and carbonization of phenolic resin. The H-Si/C composites were analyzed by XRD, SEM, BET and EDX. To improve the capacity and cycle performance, the electrochemical characteristics of H-Si/C composites synthesized with various $NaBH_4$ contents were investigated by charge/discharge, cycle, cyclic voltammetry and impedance tests. The coin cell using H-Si/C composite ($SiO_2:NaBH_4=1:1$ in weight) in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC : DMC : EMC = 1 : 1 : 1 vol%) has better capacity (1459 mAh/g) than those of other composition coin cells. It is found that the coin cell ($SiO_2:NaBH_4=1:1$ in weight) has an excellent capacity retention from 2nd cycle to 40th cycle.

• 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.