• Journal of Integrative Natural Science
• /
• v.8 no.2
• /
• pp.141-144
• /
• 2015

As the visual quality of X-ray images is a critical reference for the accuracy of the clinical diagnosis, the methods to improve the quality of X-ray images have been investigated. Among many existing methods, using frequency domain filter is a very powerful method to improve the visual quality of images. In this paper, the inherent noises of the input images are suppressed by adding the Laplacian image to the subjected image. The medical X-ray images using the optimal high pass filter has shown improved edges. Further, the optimal high frequency emphasis filter has shown the improved contrast of flat areas by using the result image from the optimal high pass filter. Also the resulting images of the global contrast have improved by the histogram equalization. As a result, the proposed methods have shown enhanced contrast and edges of the images with noise canceling effect.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.63 no.1
• /
• pp.29-33
• /
• 2014

This paper proposes an alternate time-switched space-frequency block coding transmission technique for single-carrier modulation with frequency domain equalization. There are two antennas in the transmitter but it still has only a baseband and RF and a switch that alternates between the antennas at every symbol timing. Alternating transmit symbols result in zeros which make maximal ratio receive combining possible in the receiver. Simulation results show that it has better performance than the traditional algorithm at the expense of one additional antenna.

• Proceedings of the IEEK Conference
• /
• 2000.09a
• /
• pp.479-482
• /
• 2000

다중경로 채널의 시변 특성은 OFDM(orthogonal frequency division multiplexing) 신호의 직교성을 파괴시키며 이는 인접 채널간 간섭(ICI: interchannel interference)을 발생시켜 도플러 주파수에 비례하는 오류를 발생시킨다. 본 논문에서는 채널 시변의 원인을 주파수 옵셋과 도플러효과로 규정하고, 주파수 옵셋을 보정하기 위해 기존의 선형보간법(LI: linear interpolation method)대신 선형위상보간법(LPI: linear phase interpolation)과 도플러효과에 의한 ICI 를 제거하기 위해 기존의 주파수영역 등화기법보다 효과적인 시간영역 등화기법을 제안한다. 제안된 기법이 주파수 옵셋이 있는 시변 다중경로 페이딩 환경에서 OFDM 시스템에 적합함을 컴퓨터 모의실험을 통해 확인한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 1999.11b
• /
• pp.161-165
• /
• 1999

다중경로 채널의 시변 특성은 OFDM(orthogonal frequency division multiplexing) 신호의 직교성을 파괴시키며 이는 인접 채널간 간섭(ICI: inter channel interference)을 발생시켜 도플러 주파수에 비례하는 오류를 발생시킨다. 본 논문에서는 채널 시변의 원인을 주파수 옵셋과 도플러효과로 규정하고, 주파수 옵셋을 보정하기 위해 기존의 선형보간법(LI: linear interpolation method)대신 선형위상보간법(LPI: linear phase interpolation)과 도플러효과에 의한 ICI를 제거하기 위해 기존의 주파수영역 둥화기법보다 효과적인 시간영역 등화기법을 제안한다. 제안된 기법이 주파수 옵셋이 있는 시변다중경로 페이딩 환경에서 OFDM 시스템에 적합함을 컴퓨터 모의실험을 통해 확인한다.

• Journal of information and communication convergence engineering
• /
• v.8 no.6
• /
• pp.687-689
• /
• 2010

In this paper, the equalization for frequency slope of path loss in Multi-Band(MB) OFDM UWB is proposed. The path loss of a signal is proportionate to the square of the signal's frequency. So, the received signal amplitudes of OFDM subcarrier can be different up to 3dB when MB-OFDM occupies bandwidth over 1.5GHz. The differences of subcarrier-amplitudes make an effective of 0.3 bit reduction of soft decision bits of viterbi decoder, and when the effective of 0.3 bit reduction can cause 0.5dB SNR degradation. This paper proposes two modem architectures which compensate for the degraded subcarrier by multiplying the reciprocal of degraded values in analog or digital domain. It is shown that, for the proposed architecture applied to MB-OFDM UWB, the performance improvements up to 0.5dB can be obtained over the conventional uncompensated receiver architecture.

• Journal of Information Processing Systems
• /
• v.15 no.4
• /
• pp.890-903
• /
• 2019

The single carrier frequency domain equalization (SC-FDE) technology is an important part of the broadband wireless access communication system, which can effectively combat the frequency selective fading in the wireless channel. In SC-FDE communication system, the accuracy of timing synchronization directly affects the performance of the SC-FDE system. In this paper, on the basis of Schmidl timing synchronization algorithm a timing synchronization algorithm suitable for FPGA (field programmable gate array) implementation is proposed. In the FPGA implementation of the timing synchronization algorithm, the sliding window accumulation, quantization processing and amplitude reduction techniques are adopted to reduce the complexity in the implementation of FPGA. The simulation results show that the algorithm can effectively realize the timing synchronization function under the condition of reducing computational complexity and hardware overhead.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.6C
• /
• pp.572-579
• /
• 2010

Filtered multi-tone (FMT) is a form of multicarrier modulation utilizing frequency-domain equalization efficient in multi-path fading channels. Doppler frequency information can be employed for channel estimation and link adaptation to improve the performance. However, most previous studies have concentrated on the orthogonal frequency division multiplexing (OFDM) instead of FMT. Moreover, they have not considered the synchronization error that can commonly occur in practical systems. In this paper, we propose Doppler frequency estimation scheme that is effective in FMT systems with residual synchronization error and high noise levels.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.10 no.4
• /
• pp.13-19
• /
• 2000

With the rapid development of the information communication technology, more and more distribution multimedia data and electronic publishing in the web, has created a need for the copyright protection with authentication of digital information. In this paper, we propose a multi-watermarking adding and adaptive spectral watermark algorithm well adaptive frequency domain of each hierarchical using orthogonal forward wavelet transform(FWT. Numerical test results, created watermarking image robustness not only image transform such as low-pass filtering, bluring, sharpen filtering, wavelet compression but also brightness, contrast gamma correction, histogram equalization, cropping.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.12
• /
• pp.77-84
• /
• 2005

The orthogonal frequency division multiplexing (OFDM) technique and the single carrier with cyclic prefix (SC-CP) scheme are very attractive solutions for wireless applications, being computationally efficient since equalization is performed in the frequency domain. The equalizer could not entirely handle significant mean. Doppler shift. This motivates the use of a phase error tracking loop that operates jointly with the frequency equalizer. This paper describes the effect of the mean phase error and the performance of the proportional equalizer coupled with a phase error tracking loop based on decision-directed method. Furthermore, simulation results show that we can reduce the computational toad of the tracking loop with minimal performance degradation.

• ETRI Journal
• /
• v.40 no.4
• /
• pp.537-545
• /
• 2018

In this paper, we present a comprehensive analytical study of the symbol error rate (SER) of single-carrier frequency-division multiple access (SC-FDMA) with zero-forcing frequency domain equalization (ZF-FDE) over a Rayleigh fading channel. SC-FDMA is considered as a potential waveform candidate for fifth-generation (5G) radio access networks (RANs). First, the $N_C$ fold convolution of the noise distribution of an orthogonal frequency-division multiplexing (OFDM) system is computed for each value of the signal-to-noise ratio (SNR) in order to determine the noise distribution of the SC-FDMA system. $N_C$ is the number of subcarriers assigned to a user or the size of the discrete Fourier transform (DFT) precoding. Here, we present a simple alternative method of calculating the SER by simplifying the $N_C$ fold convolution using time and amplitude scaling properties. The effects of the $N_C$ fold convolution and SNR over the computation of the SER of the SC-FDMA system has been separated out. As a result, the proposed approach only requires the computation of the $N_C$ fold convolution once, and it is used for different values of SNR to calculate the SER of SC-FDMA systems.