• Journal of Microbiology and Biotechnology
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• v.13 no.3
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• pp.451-456
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• 2003

An expression vector system was developed for the secretory production of recombinant Bacillus stearothermophilus L1 lipase in Saccharomyces cerevisiae. The mature L1 lipase gene was fused to ${\alpha}-amylase$ signal sequence from Aspergillus oryzae for the effective secretion into the culture broth and the expression was controlled under GAL10 (the gene coding UDP-galactose epimerase of S. cerevisiae) promoter. S. cerevisiae harboring the resulting plasmid successfully secreted L1 lipase into the culture broth. To examine an optimum condition for L1 lipase expression in the fed-batch culture, L1 lipase expression was induced at three different growth phases (early, mid, and late-exponential growth phases). Maximum product on of L1 lipase (1,254,000 U/l, corresponding to 0.65/1) was found when the culture was induced at an early growth phase. Secreted recombinant L1 lipase was purified only through CM-Sepharose chromatography, and the purified enzyme showed 1,963 U/mg of specific activity and thermoalkalophilic properties similar to those reported for the enzyme expressed in Escherichia coli.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.90-98
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• 2002

To increase system capacity in WCDMA receiver, the coherent detection is an essential technology for recovering transmitted symbols correctly. For coherent detection, an accurate and fast channel estimation is required. In next generation mobile communication system, high frequency carriers are used, and high data rate services are provided for subscribers having high mobility. In this communication environment, however, the rapidly-changing doppler frequency degrades the quality of the transmitted signal a lot. In WCDMA system, the channel estimation is conducted using pilot channel and/or pilot symbols which are known to both transmitter and receiver. Some existing channel estimation algorithms utilize these information quite well, but the performance of channel estimation gets very poor in a complicated fading channel distorted by the doppler effect. In this paper, we propose a new channel estimation algorithm combining an early-late doppler compensator so that the doppler effect and the fading characteristics are compensated at the same time. By computer simulation, the proposed algorithm proved to be a much more efficient channel estimation method in the fast fading channel, even at reasonably low Eb/No.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.794-806
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• 2004

This paper deals with correction of frequency offset and analysis of quantization angle noise in the IEEE 802.1la OFDM system. The rotation phase per symbol due to the carrier frequency offset is estimated from auto-correlation of the short Preambles, which are over-sampled for the reduction of noise in OFDM signals. The pilot signals are introduced to estimate the rotation phase per OFDM symbol due to estimation error of the carrier frequency offset and the sampling frequency onset. During the estimation and correction of the frequency onsets, a CORDIC processor and a look-up table are used for the conversion between a rotation phase and its complex number. Being calculated by a limited number of bits in the CORDIC processor and the look-up table, the rotation phase and its complex number have quantization angle errors. The quantization errors are analyzed as SNR (signal to noise ratio) due to the quantization bit numbers. The minimum bit number is suggested to meet the specification of IEEE 802.1la properly. Finally, the quantization errors are evaluated through simulations on number of quantization bits and SNR of received signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.249-253
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• 2006

We propose a new beamforming algorithm, which is based on simplex downhill optimization method in the presence of pilot channels in cdma2000 reverse-link, for the rake structure antenna array in DS/CDMA communication system. Our approach uses the desired signal(pilot) covariance matrix and the interference covariance matrix. The beamforming weights are made according to maximum SINR criteria using simplex downhill optimization procedure. Our proposed scheme provides lower computational load, better convergence speed, better performance than existingadaptive beamforming algorithm. The simplex downhill method is well suited to finding the optimal or sub-optimal weight vector, since they require only the value of the deterministic function to be optimized. The rake beamformer performances are also evaluated under several set of practical parameter values with regard to spatial channel model. We also compare the performance between conventional rake receiver and the proposed one under same receiving power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10A
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• pp.807-815
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• 2003

MultiCode-CDMA (MC-CDMA) system of chip level MPSK incorporating with clipper (MP-CDMA)[l] shows constant envelope signal which can mitigate the performance degradation due to nonlinear transmit amplifier. In this paper, modulation is modified to carry out differential encoded MPSK rather than MPSK. The modified system is called DMP-CDMA. DMP-CDMA using differential detection has advantages on receiver complexity and pilot overhead. However, it is inferior to coherent detection by about 4.0dB due to inherent power inefficiency of noncoherent detection and the error propagation. Multiple symbol differential detection is employed in order to improve DMP-CDMA using differential detection. As the result, the performance of DMP-CDMA system is improved about 3.6dB compared to differential detection.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.1
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• pp.42-47
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• 2020

In OFDM-based very high-speed communication systems, FFT/IFFT processor should have several properties of low-area and low-power consumption as well as high throughput and low processing latency. Thus, radix-2k MDF (multipath delay feedback) architectures by adopting pipeline and parallel processing are suitable. In MDF architecture, the feedback memory which increases in proportion to the input signal word-length has a large area and power consumption. This paper presents a feedback memory size reduction method of radix-22 MDF IFFT processor for OFDM applications. The proposed method focuses on reducing the feedback memory size in the first two stages of MDF architectures since the first two stages occupy about 75% of the total feedback memory. In OFDM transmissions, IFFT input signals are composed of modulated data and pilot, null signals. In order to reduce the IFFT input word-length, the integer mapping which generates mapped data composed of two signed integer corresponding to modulated data and pilot/null signals is proposed. By simulation, it is shown that the proposed method has achieved a feedback memory reduction up to 39% compared to conventional approach.

• Journal of Advanced Navigation Technology
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• v.17 no.3
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• pp.298-305
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• 2013

In this paper, we propose simple combining schemes for sensing ATSC digital television signals with spectral correlation density (SCD). The detection algorithms exploiting the cyclostationarity exhibited by the pilot of ATSC digital television signals usually use the SCD value at a given particular frequency. However, we found that non-zero SCDs are found to be distributed over a certain range of frequencies in multipath fading environment. To utilize a set of non-zero SCD values computed in the vicinity of the pilot location, we formulate a class of combining methods in analogy with the maximal ratio combining, the square law combining and the equal gain combining. We show that the proposed simple combining schemes improve the detection performance by 0.5~1.0dB under multipath fading environments.

• Journal of the Korea Society of Computer and Information
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• v.11 no.4 s.42
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• pp.35-45
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• 2006

RIn this paper. we describe real-time parallel processing simulator developed for the use of performance analysis of rolling missiles. The real-time parallel processing simulator developed here consists of seeker emulator generating infrared image signal on aircraft, real-time computer, host computer, system unit, and actual equipments such as auto-pilot processor and seeker processor. Software is developed according to the design requirements of mathematic model, 6 degree-of-freedom module, aerodynamic module which are resided in real-time computer. and graphic user interface program resided in host computer. The real-time computer consists of six TI C-40 processors connected in parallel. The seeker emulator is designed by using analog circuits coupled with mechanical equipments. The system unit provides interface function to match impedance between the components and processes very small electrical signals. Also real launch unit of missiles is interfaced to simulator through system unit. In order to use the real-time parallel processing simulator developed here as a performance analysis equipment for rolling missiles, we perform verification test through experimental results in the field.

• Journal of Biomedical Engineering Research
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• v.44 no.1
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• pp.80-84
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• 2023

Electrodes are one of the types of biosensors capable of measuring bio signals, such as electrocardiogram (ECG) and electromyogram (EMG) signals. These electrodes are used in various fields and offer the advantage of being able to measure ECG signals without the need for skin attachment, compared to Ag/AgCl electrodes. The purpose of this study was to evaluate the efficacy of conductive textile electrodes in collecting ECG signals in a bed-like environment. Three adult participants were involved, and a total of 30 minutes of ECG signals were collected for each participant. The collected ECG signals were analyzed to determine the heart rate, normLF and a comparison was made between the conductive textile electrodes and Ag/AgCl electrodes. As a result, the change in heart rate and normLF could be observed, and in particular, the difference between the two electrodes decreased. This study confirmed that conductive textile electrodes can effectively collect ECG signals in a bed-like environment. It is hoped that this research will lead to the development of a system that can detect various sleep-related diseases through the use of these electrodes.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.8
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• pp.26-33
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• 2017

Vehicle communication can facilitate efficient coordination among vehicles on the road and enable future vehicular applications such as vehicle safety enhancement, infotainment, or even autonomous driving. In the $3^{rd}$ Generation Partnership Project (3GPP), many studies focus on long term evolution (LTE)-based vehicle communication. Because vehicle speed is high enough to cause severe channel distortion in vehicle-to-vehicle (V2V) environments. We can utilize channel estimation methods to approach a reliable vehicle communication systems. Conventional channel estimation schemes can be categorized as least-squares (LS), decision-directed channel estimation (DDCE), spectral temporal averaging (STA), and smoothing methods. In this study, we propose a smart channel estimation scheme in LTE-based V2V environments. The channel estimation scheme, based on an LTE uplink system, uses a demodulation reference signal (DMRS) as the pilot symbol. Unlike conventional channel estimation schemes, we propose an adaptive smoothing channel estimation scheme (ASCE) using quadratic smoothing (QS) of the pilot symbols, which estimates a channel with greater accuracy and adaptively estimates channels in data symbols. In simulation results, the proposed ASCE scheme shows improved overall performance in terms of the normalized mean square error (NMSE) and bit error rate (BER) relative to conventional schemes.