• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.11
• /
• pp.1264-1271
• /
• 2012

Fast tracking is important for high-speed data transmission in high-speed mobile environment such as high speed rail and vehicular. Digital retrodirective array antenna is possible to do automatically beam tracking because it can control the phase information of the output signal toward opposite direction to input signal without no a priori knowledge of the arrival direction. Also, Digital retrodirective array antennas has merit that it is easy to upgrade and modify compare with analogue retrodirective array antennas. In this paper, we analyze the BER performance of digital retrodirective array antenna under AWGN environment and multipath signal. Simulation results show correct phase estimation and conjugation of retrodirective array antenna by using phase detector block. Also, phase conjugation technique has better BER performance about 1 dB at source than that of without phase conjugation when phase lag is $15^{\circ}$ in AWGN environment. This paper also discusses effect of the presence of multipath signal. Phase and amplitude error about direction of direct signal occurs when retrodirective array system is affected by interference and multipath signal in the presence of multipath signal.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.5 no.2
• /
• pp.289-296
• /
• 2001

We propose a method to add phase-modulation to binary amplitude data pages using a twisted-nematic liquid crystal display as a dynamic phase mask. For this, the phase modulation characteristics of the display were examined both theoretically and experimentally, and an unexpected abnormal phenomenon was found experimentally in which the modulation property changed as the incident beam intensity increased. To investigate the characteristics of holographically storing the binary data images, eight pages of holograms were stored at one spot of in un-thick Dupont's photopolymer with angle multiplexing. When phase-modulation-added pages were stored at the Fourier plane, the uniformity of the signal beam at the plane was improved, and thus more holograms can be recorded with our method, compared with the conventional case of using only binary amplitude modulation under the same condition.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.10
• /
• pp.51-60
• /
• 1999

For an effective phase-multiplexing in holographic memory system, four types of phase code used as reference beam are generated. In case of $32 {\times} 32$ address beam, a phase error with 0%, 5%, 10% 15%, 20%, and 25% error rate, is purposely added to the real phase values in order to consider the practical SLM's nonlinear characteristics of phase modulation in computer simulation, cross talks and SNRs are comparatively analysed for these phase-codes by the auto and cross-correlation. Pseudo-Random(PSR) Phase Code has the lowest cross-correlation mean value of 0.067 among four types of Phase Code, which means the SNR of the PSR is higher than other Phase Codes. Also, the standard deviation of the PSR phase code indicating the degree of recalled data degradation is the lowest value of 0.0113.

• Proceedings of the IEEK Conference
• /
• 2003.07a
• /
• pp.545-548
• /
• 2003

본 논문은 UWB 통신 시스템에서 DPSK를 적용한 다중비트 변조 알고리즘을 제안한다. UWB 통신 시스템은 매우 낮은 파워의 신호를 사용하므로, 한 펄스를 이용한 다중비트를 보낼 수 있는 변조 알고리즘이 중요한 부분으로 작용한다. 이 논문에서는 UWB 시스템에서Gaussian 펄스에 정현파 가 곱해진 두 개 펄스의 조합을 이용하여 FCC Mask 에 저촉되지 않으면서 한 펄스에 다중 비트를 전송을 실현한 M-ary 전송 방식을 사용한다. 또한 채널상에서 펄스의 원치 않는 위상변화에 민감하지 않도록 하기 위해 DPSK 방식을 적용한 UWB 제안한다. 제안된 알고리즘의 성능 평가를 위해 시뮬레이션 하였고 그 결과와 구조를 본 논문에 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.26 no.8B
• /
• pp.1085-1091
• /
• 2001

이 논문에서는 주기적인 특성을 가진 펄스 열들이 서로 다른 초기 위상을 가지고 수신기에 입력되었을 때 도래시간 차이를 이용하여 펄스 열을 분리하는 방법을 제시하고자 한다. 주기적인 펄스 열을 주파수 관점에서 고찰해 보면 하나의 펄스 열 주파수 값으로 특성 지울 수 있으며 이러한 성질은 다중의 펄스 열이 포함된 신호 환경 하에서도 동일하게 나타난다. 제안된 기법은 기존의 스펙트럼 영역에서 사용된 신호 도래 시간의 지수함수로의 매핑을 대신하여 신호 도래 시간 차이를 이용하였으며 실제 다중 환경에서 나타날 수 있는 신호 성분들의 펄스 열 주파수 추정을 위하여 기존의 방법과 비교함으로써 제시한 방법의 타당성을 검증하였다.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.6 no.4
• /
• pp.535-543
• /
• 2002

In this paper, we propose $\pi$/8 shift 8PSK and trellis-coded $\pi$/8 shift 8PSK-OFDM techniques by applying $\pi$/4 shift QPSK to trellis-coded modulation (TCM), and performing signal set expansion and set partition correspondingly based on phase difference. In our Viterbi decoding algorithm, up to L phase differences from successively received symbols are employed in the new branch metrics. Such sliding multiple symbol detection (SMSD) method provides improved bit-error-rate (BER) performance in the differential detection of the trellis-coded $\pi$/8 shift 8PSK-OFDM signals. The performance improvements are achieved for different communication channels without sacrificing bandwidth and power efficiency. It thus makes the proposed modulation and sliding detection scheme more attractive for power and band-limited systems.

• Journal of the Korea Society of Computer and Information
• /
• v.16 no.8
• /
• pp.129-135
• /
• 2011

In this paper, we propose a multi target's elevation angle estimation method using multi beam forming technique. This method make a stacked beam to digital processing a received signal in array element. There can be desired receiving beam to application weight value at antenna element in beam forming. Currently, we are to make multi stacked beam using fast fourier transform in stead of phase shifter to be a computer performance much improvement. Also, we improve multi beam directivity using beam steering error correction technique in order to beam steering to desired direction in receiver. Through simulation, we show that the proposed elevation estimation method based on fast fourier transform and beam steering error correction technique, improves th performance of target estimation compared to previous method.

• Geophysics and Geophysical Exploration
• /
• v.8 no.1
• /
• pp.26-33
• /
• 2005

Inversion of multi-mode surface-wave phase velocity for shallow engineering site investigation has received much attention in recent years. A sensitivity analysis and inversion of both synthetic and field data demonstrates the greater effectiveness of this method over employing the fundamental mode alone. Perturbation of thickness and shear-wave velocity parameters in multi-modal Rayleigh wave phase velocities revealed that the sensitivities of higher modes: (a) concentrate in different frequency bands, and (b) are greater than the fundamental mode for deeper parameters. These observations suggest that multi-mode phase velocity inversion can provide better parameter discrimination and imaging of deep structure, especially with a velocity reversal, than can inversion of fundamental mode data alone. An inversion of the theoretical phase velocities in a model with a low velocity layer at 20 m depth can only image the soft layer when the first higher mode is incorporated. This is especially important when the lowest measurable frequency is only 6 Hz. Field tests were conducted at sites surveyed by borehole and PS logging. At the first site, an array microtremor survey, often used for deep geological surveying in Japan, was used to survey the soil down to 35 m depth. At the second site, linear multichannel spreads with a sledgehammer source were recorded, for an investigation down to 12 m depth. The f-k power spectrum method was applied for dispersion analysis, and velocities up to the second higher mode were observed in each test. The multi-mode inversion results agree well with PS logs, but models estimated from the fundamental mode alone show f large underestimation of the depth to shallow soft layers below artificial fill.

• Korean Journal of Optics and Photonics
• /
• v.19 no.4
• /
• pp.262-269
• /
• 2008

In this paper, we propose an image watermark method using multiple decoding keys. The advantages of this method are that the multiple original images are reconstructed by using multiple decoding keys in the same watermark image, and that the quality of reconstructed images is clearly enhanced based on the idea of Walsh code without any side lobe components in the decoding process. The zero-padded original images, multiplied with random-phase pattern to each other, are Fourier transformed. Encoded images are then obtained by taking the real-valued data from these Fourier transformed images. The embedding images are obtained by the product of independent Walsh codes, and these spreaded phase-encoded images which are multiplied with new random-phase images. Also we obtain the decoding keys by multiplying these random-phase images with the same Walsh code images used in the embedding images. A watermark image is then made from the linear superposition of the weighted embedding images and a cover image, which is multiplied with a new independent Walsh code. The original image is simply reconstructed by the inverse-Fourier transform of the despreaded image of the multiplication between the watermark image and the decoding key. Computer simulations demonstrate the efficiency of the proposed watermark method with multiple decoding keys and a good robustness to the external attacks such as cropping and compression.

• Journal of KSNVE
• /
• v.5 no.4
• /
• pp.453-460
• /
• 1995

본 논문에서는 정현파 소음을 제어하기 위한 filtered-x LMS에 바탕을 둔 새로운 적응 알고리듬을 제안하였다. 이러한 알고리듬은 두개의 연속적인 계수조정 식으로, 제어기의 계수를 조정한다. 서로 독립인 각 주파수별로 처리하기 때문에 빠른 수렴을 얻을 수 있다. 두번째식은 이차경로로 인한 위상지연을 추정한다. 정현 파 신호 주파수보다 4배 이상 빠른 표본화 주파수를 선택하여 추정된 위상지연 추정 값은 $2{\pi}f_0$만큼 오차를 나타내며, 이 값은 $\pi$2보다 작다. 정현파 신호의 주파수를 알면 이러한 오차는 $2{\pi}f_0$를 더함으로써 제거할 수 있다. 이러한 방법은 위상지연이 $\pi$2보다 큰 경우 수렴속도를 증가시킨다는 사실을 실험을 통하 여 알 수 있다. 추정된 위상지연은 제어기 계수값을 조정하는데 필요한 필터링된 참조신호를 발생시키믄데 사용된다. 참조신호의 위상지연이 각 주파수 성분별로 수행 되기 때문에, 콘볼루션 연산이 생략되어 계산량을 줄일 수 있다. 또한 연속적으로 위상지연을 추정하기 때문에 시변 상황에 적용이 가능하다. 조정식의 수렴조건을 유도하였다. 제안된 알고리듬은 제어기 계수를 추정하는데 바이어스가 없으며, 위상 지연추정을 위한 수렴상수의 최대허용치는 제어기계수에 대한 수렴상수에 반비례함을 이론적으로 분석을 통해 알 수 있다. 모의실험을 통하여 제안된 알고리듬이 filtered-x LMS 알고리듬에 바탕을 둔 다른 알고리듬보다 환경변화에 우수한 성능을 보임을 알 수 있다.