• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4A
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• pp.312-317
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• 2011

In this paper, we studied the frequency hopping(FH) performance on the FH radio communication system via M&S of initial synchronization architecture. It is difficult to test the synchronization performance on the real FH communication environment. Thus, we have modeled the synchronization system similar to the real radio communication structure, and simulated the optimum correlation value and the synchronization performance on AWGN channel. As the result, we could obtain the thresholds of correlation synchronization and the FH synchronization performance under the low SNR.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.7
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• pp.209-220
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• 2014

In this paper, we analyze the discriminability of features for the classification of transient signals with an ambient noise in a shallow water. For the classification of the transient signals, robust features for the variance of a noise are required due to a low SNR under a marine environment. In the modelling the ambient noise in shallow water, theoretical noise model, Wenz's observation data from the shallow water, and Yule-walker filter are used. Discrimination of each feature of the transient signals with an additive ambient noise is analyzed by utilizing a Fisher score. As the analysis of a classification accuracy about the transient signals of 24 classes using the selected features with a high discriminability, the features selected in the environment without a noise relatively have a good classification accuracy. From the analyzed results, we finally select a total 16 features out of 28 features. The recognition using the selected features results in the classification accuracy of 92% in SNR 20dB using Multi-class SVM.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.25-28
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• 2001

A new decision-feedback equalization technique for a filter bank-based orthogonal frequency division multiplexing (OFDM) data transmission system operating in a frequency selective multipath fading channel is presented in this paper. At the cost of relatively increased computational complexity in comparison to the conventional OFDM systems, the proposed system achieves a better performance in terms of bit error rates. The simulation results confirm the superiority and robustness of our method, particularly, in the low SNR channel environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.4 s.119
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• pp.440-447
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• 2007

The switched diversity, although its performance is a little inferior to the selection diversity, is widely used due to its advantage that only one RF circuit is required for its operation without respect to the number of antennas in use. In this paper, we propose an application of the antenna switched diversity to a spread spectrum system with adaptive modulation and derived the optimal antenna switching threshold to maximize the average transmission bit rate. We also compared the performances of the proposed system with those of the two cases using a single antenna and the selection diversity with two antennas in terms of the average number of bits per symbol(BPS), the probability of no transmission, and the average BER. The performance analysis shows that, if the number of paths in a multipath channel environment increases, the performance of the proposed scheme becomes closer to that of the selection diversity based system in terms of the average BPS. Furthermore, the proposed scheme produces as almost high the probability of no transmission as the selection diversity based system for the case of low average SNR, although the former yields a little higher probability of no transmission than the latter fer the case of high average SNR.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.6
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• pp.1-5
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• 2011

We present the Multi-band orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) technology for increasing the transmission reach of wireless speaker systems. The proposed scheme adopts the Reed-Solomon coding for preventing the random error perfectly and shows the SNR gain in low bit error rate (BER) especially. So, we can increase the maximum reach of MB-OFDM UWB technology since the receiver sensitivity is improved. The simulation environment includes most effects of realistic channel environments such as Additive White Gaussian Noise (AWGN), CM1 channel model, Sampling frequency offset (SFO), Carrier frequency offset (CFO) to improve the simulation accuracy. The simulation results show that the proposed scheme can give a maximum 2 dB SNR gain and increase the transmission reach up to 12.6m.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.1
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• pp.64-72
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• 1986

The error rate equation fo DS-BPSK(Direct Sequence Binary Phase Shift Keying) signal transmitted through the nonlinear satellite transponder has been derived in the cochannel interference and downlink Gaussian noise environment. The input to the satellite transponder is the superposition of DS-BPSK signal with one interfere which is a cochannel wide-band PN signal. The error rate performance of DS-BPSK system has been evaluated and shown in figures in terms of carrier to interference power ratio(CIR), downlink signal to noise power ratio(downlink SNR) and process gain. In the analysis, it has been shown that the use of a hard limiter in DS-BPSK satellite system leads to the generation of narrow-band intermodulation products which is independent of the process gain. Also it is known that the error rate performance can be improved in the low levels (below 10dB) of CIR as the CIR increase. As the process gain varies from 10 to 100 the curve gives the about 10 dB gain in downlink SNR to maintain a fixed error rate.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.32 no.2
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• pp.155-162
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• 2022

The SITM (See-In-The-Middle) attack proposed in CHES 2020 is a type of analysis technique that combines differential cryptanalysis and side-channel analysis, and can be applied even in a harsh environment with a low SNR (Signal-to-Noise Ratio). This attack targets partial 1^st or higher order masked block cipher, and uses unmasked middle round weakness. PRESENT is a lightweight blockcipher proposed in CHES 2007, designed to be implemented efficiently in a low-power environment. In this paper, we propose SITM attacks on 14-round masked implementation of PRESENT while the previous attacks were applicable to 4-round masked implementation of PRESENT. This indicates that PRESENT has to be implemented with more than 16-round masking to be resistant to our attacks.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.1183-1186
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• 1998

Adaptive nois canceller can extract the noiseremoved spech in noisy speech signal by adapting the filter-coefficients to the background noise environment. A kind of LMS algorithm is one of the most popular adaptive algorithm for noise cancellation due to low complexity, good numerical property and the merit of easy implementation. However there is the matter of increasing misadjustment at voiced speech signal. Therefore the demanded speech signal may be extracted. In this paper, we propose a fast and noise robust wavelet packet adaptive noise canceller with NLMS-SUM method LMS combined algorithm. That is, we decompose the frequency of noisy speech signal at the base of the proposed analysis tree structure. NLMS algorithm in low frequency band can efficiently dliminate the effect of the low frequency noise and SUM method LMS algorithm at each high frequency band can remove the high frequency nosie. The proposed wavelet packet adaptive noise canceller is enhanced the more in SNR and according to Itakura-Satio(IS) distance, it is closer to the clean speech signal than any other previous adaptive noise canceller.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7A
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• pp.1028-1035
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• 1999

To increase the throughput of data transmission in burst-mode TDMA communication systems and also to get a good BER performance at the same time, it is essential to rapidly acquire the carrier while keeping the desirable tracking performance. To achieve this goal, in this paper, a new decision-directed carrier recovery algorithm is presented. The proposed scheme does not incorporate the PLL and suppress the Gaussian random process of input noise by the pre-stage low pass filter so as to get both the fast acquisition and a good performance. Through computer simulations, the performance of the scheme is analyzed with respect to the acquisition time and bit error rate. The cycle slip in the proposed scheme is seldom observed at very low SNR environment in contrast to the previous proposed one. Because of this merit, it is not required to do the differential encoding and decoding in the proposed scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.7
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• pp.3095-3111
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• 2018

Spectrum sensing (SS) is one of the fundamental tasks for cognitive radio. In SS, decisions can be made via comparing the test statistics with a threshold. Conventional adaptive algorithms for SS usually adjust their thresholds according to the radio environment. This paper concentrates on the issue of adaptive SS whose threshold is adjusted based on the Markovian behavior of primary user (PU). Moreover, Bayesian cost is adopted as the performance metric to achieve a trade-off between false alarm and missed detection probabilities. Two novel adaptive algorithms, including Markov Bayesian energy detection (MBED) algorithm and IMBED (improved MBED) algorithm, are proposed. Both algorithms model the behavior of PU as a two-state Markov process, with which their thresholds are adaptively adjusted according to the detection results at previous slots. Compared with the existing Bayesian energy detection (BED) algorithm, MBED algorithm can achieve lower Bayesian cost, especially in high signal-to-noise ratio (SNR) regime. Furthermore, it has the advantage of low computational complexity. IMBED algorithm is proposed to alleviate the side effects of detection errors at previous slots. It can reduce Bayesian cost more significantly and in a wider SNR region. Simulation results are provided to illustrate the effectiveness and efficiencies of both algorithms.