• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1044-1053
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• 2010

Transmitting correct train control information is important in a train control system which demands safety. The train control information includes the maximum speed of trains, position of preceding trains, incline of tracks and curve sections etc. A radio frequency-communication based train control system is influenced by the noise and interference because the train control information is transmitted by wireless between a on-board system and wayside system. The radio frequency-communication based train control system is a mobile communication system due to moving trains. The inter symbol interference(ISI) occurs by the multipath fading in the mobile ommunication system. As signal-to-noise ratio(SNR) is decreased by the ISI, the train control information is not received correctly. In case of tunnel section, numerous reflected waves exist. Therefore, the power density of receiver is decreased by difference among the received times, magnitudes, phases through the multipath. So, the train suddenly is stopped by the fail-safe operation in the train control system on account of decreasing the power density of receiver. In this paper, a line of sight model-(Additive White Gaussian noise(AWGN) channel), rayleigh and rician fading model are presented. Probability density functions which are related to the SNR are derived from the models. The fading phenomenon severely occurs as a result of analyzing the probability density functions. So, the space diversity method is used in order to reduce the fading effect and it is demonstrated by using Matlab program.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.1
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• pp.103-119
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• 2010

In this paper, we propose a subpixel shift estimation method using phase correlation with a local region for the registration of noisy images. Phase correlation is commonly used to estimate the subpixel shift between images, which is derived from analyzing shifted and downsampled images. However, when the images are affected by additive white Gaussian noise and aliasing artifacts, the estimation error is increased. Thus, instead of using the whole image, the proposed method uses a specific local region that is less affect by noises. In addition, to improve the estimation accuracy, iterative phase correlation is applied between selected local regions rather than using a fitting function. the restricted range is determined by analyzing the maximum peak and the two adjacent values of the inverse Fourier transform of the normalized cross power spectrum. In the experiments, the proposed method shows higher accuracy in registering noisy images than the other methods. Thus, the edge-sharpness and clearness in the super-resolved image is also improved.

• Journal of Korea Multimedia Society
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• v.3 no.4
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• pp.347-355
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• 2000

This paper presents an adaptive AEC(acoustic echo canceller) based on the wavelet transform using M-channel subband QMF filter banks. The proposed algorithm improves the performance of AEC with a realtime process by a low complexity of wavelet transform filter banks, a subband processing and a orthogonality of wavelet subband filter. Adaptive filter coefficients of each subband are updated using LMS algorithm with a low complexity and a easy realization for a realtime processing and a reduction of hardware cost. For a input signal, a white Gaussian noise and a real speech signal with a environment noises are used for a performance estimation of the proposed algorithm. As a result of computer simulation, the proposed AEC has a low asymptotic error, a low computation complexity and a robust performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.19-25
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• 2008

When there are numerous wireless communication systems co-existing in the limited available frequency resource, an unexpected time delay can be caused during the system switching. So, in order to reduce this time delay, a mode selection method is required. In this paper, we propose a mode selection method to minimize the time delay for multi-system wireless communication systems. For the sake of efficiency, the mode selection method is designed by analyzing the preamble characteristics of different standards. Instead of performing a full search, we propose the preamble partial search to reduce the time delay to a minimum. Simulated with Matlab in an additive white Gaussian noise(AWGN) environment with a signal to noise ratio(SNR) of 10dB and bit error rate(BER) of $10^{-6}$, we evaluated and showed the performance improvement gained by using our proposed mode selection method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.9
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• pp.939-950
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• 1992

The performance of common spreading code scheme employing multiple-capture receiver is compared to that of transmitter-oriented (T/O) code division multiple access (CDMA) scheme in view of the possibility of collision-free transmissions and the effect of secondary multiple-access interference. For performance comparisons, secondary multiple-access interference is characterized for the common code scheme and the T/O CDMA scheme that assures perfectly collision-free transmissions. Throughput performance is then evaluated for these two schemes with direct-sequence spread-spectrum/differential-phase-shift-keying (DS-SS/DPSK) data modulation and forward-error-control coding (BCH codes) in the presence of an additive white Gaussian noise (AWGN). It is shown that when the number of radios is relatively large, the maximum normalized throughput is greater for the common code scheme than for the T/O CDMA scheme at a moderate signal-to-noise ration(SNR).

• The KIPS Transactions:PartB
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• v.18B no.3
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• pp.147-156
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• 2011

This paper proposes a 3-stage (preprocessing, feature extraction, and classification) fault detection and classification algorithm for induction motors. In the first stage, a low-pass filter is used to remove noise components in the fault signal. In the second stage, a discrete cosine transform (DCT) and a statistical method are used to extract features of the fault signal. Finally, a back propagation neural network (BPNN) method is applied to classify the fault signal. To evaluate the performance of the proposed algorithm, we used one second long normal/abnormal vibration signals of an induction motor sampled at 8kHz. Experimental results showed that the proposed algorithm achieves about 100% accuracy in fault classification, and it provides 50% improved accuracy when compared to the existing fault detection algorithm using a cross-covariance method. In a real-world data acquisition environment, unnecessary noise components are usually included to the real signal. Thus, we conducted an additional simulation to evaluate how well the proposed algorithm classifies the fault signals in a circumstance where a white Gaussian noise is inserted into the fault signals. The simulation results showed that the proposed algorithm achieves over 98% accuracy in fault classification. Moreover, we developed a testbed system including a TI's DSP (digital signal processor) to implement and verify the functionality of the proposed algorithm.

• 전자공학회논문지 IE
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• v.45 no.1
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• pp.44-49
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• 2008

In this paper, the performance for the non-linear satellite channel including the characteristics of group delay and gain ripple of transponder is analyzed with multi-level QAM-OFDM schemes. Comparing the BER performances between general OFDM and CI(Carrier Interferometry)-OFDM for various QAM schemes, the degree of performance improvement is presented in AWGN environments for specified nonlinear characteristics. The simulations are performed with the 36MHz bandwidth of transponder channel and 120Mbps transmission rate for QPSK, 8QAM, 16QAM, 32QAM, 64QAM schemes between normal and worst case condition. It is shown that the improvement measure by the CI-OFDM for the group delay of channel and nonlinear characteristic of HPA outperforms that for the gain ripple in the case of higher level QAM scheme in normal condition. And the simulation results show that the additional techniques like the channel coding and compensation scheme against the nonlinear characteristic are required for 32QAM and higher level QAM in worst case condition.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.5 s.347
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• pp.121-127
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• 2006

It is well known the fact that turbo codes has better performance as the number of iteration and the interleaver size increases in the AWGN channel environment. However, as the number of iteration and the interleaver size are increased, it is required much delay and computation for iterative decoding. Therefore, it is important to devise an efficient criterion to stop the iteration process and prevent unnecessary computations and decoding delay. In this paper, it proposes the efficient stop criterion algorithm for turbo codes using the maximum sign change of LLR. It is verifying that the proposal variable iterative decoding controller can be reduced the average iterative decoding number compared to conventional schemes with a negligible degradation of the error performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.5 s.335
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• pp.39-46
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• 2005

It is well known the fact that turbo codes has better performance as the number of iteration and the interleaver size increases in the AWGN channel environment. However, as the number of iteration and the interleaver size are increased, it is required much delay and computation for iterative decoding. Therefore, it is important to devise an efficient criterion to stop the iteration process and prevent unnecessary computations and decoding delay. In this paper, it proposes the efficient iterative decoding stop criterion using the absolute mean value of LLR difference. It is verifying that the proposal iterative decoding stop criterion can be reduced the average iterative decoding number compared to conventional schemes with a negligible degradation of the error performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.484-492
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• 2006

A multi-code biorthogonal code keying(MBCK) system consists of multiple waveform coding block, and the sum of output codewords is transmitted. Drawback of MBCK is that it requires amplifier with high linearity because its output symbol is multi-level. MBCK with constant amplitude preceding blcok(CA-MBCK) has been proposed, which guarantees sum of orthogonal codes to have constant amplitude. Redundant bits of CA-MBCK for constant amplitude coding are not only used to make constant amplitude signal but also used to improve the bit error rate(BER) performance at receiver. In this paper, we proposed a transmission scheme which combine CA-MBCK with $Q^{2}PSK$ to improve bandwidth efficiency of CA-MBCK. The BER performance of the scheme is same that of CA-MBCK in additive white gaussian noise(AWGN). And we showed that BER performance of the proposed system can be improved using redundant bits of constant amplitude preceding.