• Title/Summary/Keyword: Doppler shift

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Underwater mobile communication scheme based on the direct sequence spread spectrum transmission using Doppler estimation and its sea trial results with the pseudo-moving transmission (도플러 추정을 적용한 직접수열 대역확산 전송 기반 수중 이동통신 방법 및 가상 이동신호를 이용한 해상시험 결과)

  • Kim, Seung-Geun
    • The Journal of the Acoustical Society of Korea
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    • v.41 no.1
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    • pp.16-29
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    • 2022
  • This paper presents a Doppler shift estimation method and signal processing schemes for Direct Sequence Spread Spectrum (DSSS) transmission to overcome the Doppler shift due to the moving of the underwater communication unit. The proposed method estimates a Doppler shift via 2 step procedures using the preamble with the two 64-length Frank sequences which has a good self-correlation characteristic and is insensitive to the Doppler shift. Furthermore, a packet of DSSS underwater mobile communication and a RAKE receiver are designed using the proposed Doppler shift estimation method. Due to the modulation scheme of the designed DSSS underwater mobile communication using Differential-Quadrature Phase Shift Keying (DQPSK) for the data symbol transmission, the RAKE receiver dose not need a phase tracking and easily makes coherent signals among the combining RAKE branches. The designed RAKE receiving scheme including the proposed Doppler shift estimation method successfully decides information data using the DSSS signal transmitted from the pseudo-moving transmitter with velocity upto about 17.5 m/s.

Laser Doppler Velocimetry Using the Photoacoustic Effect of $CO_2$ Laser (광음향 효과를 이용한 $CO_2$ 레이저 도플러 속도 측정기)

  • 최종운;유문종
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.53 no.1
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    • pp.36-40
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    • 2004
  • A new laser Doppler velocimeter employing a $CO_2$ laser has been developed by using its photoacoustic effect. A change in the pressure of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as much as 34 KHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained.

Path Loss Model with Multiple-Antenna and Doppler Shift for High Speed Railroad Communication (다중 안테나와 Doppler Shift를 고려한 고속 철도의 경로 손실 모델)

  • Park, Hae-Gyu;Yoon, Kee-Hoo;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.39A no.8
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    • pp.437-444
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    • 2014
  • In this paper, we propose a path loss model with the multiple antennas and doppler shift for high speed railroad communication. Path loss model is very important in order to design consider diverse characteristic in high-speed train communication. Currently wireless communication systems use the multiple antennas in order to improve the channel capacity or diversity gain. However, until recently, many researches on path loss model only consider geographical environment between the transmitter and the receiver. There is no study about path loss model considering diversity effect and doppler shift. In order to make average residuals considering doppler shift we use tuned free space path loss model which is utilized for measurement results at high speed railroad. The environment of high speed rail is mostly at viaduct and flatland over than 50 percent. And in order to make average residuals considering multiple antenna we use theoretical estimation of diversity gain with MRC scheme. proposed model predict loss of received signal by estimating average residuals between diversity effect and doppler shift.

Estimation of Ocean Current Velocity near Incheon using Radarsat-1 SAR and HF-radar Data

  • Kang, Moon-Kyung;Lee, Hoon-Yol
    • Korean Journal of Remote Sensing
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    • v.23 no.5
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    • pp.421-430
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    • 2007
  • This paper presents the results of the ocean surface current velocity estimation using 6 Radarsat-1 SAR images acquired in west coastal area near Incheon. We extracted the surface velocity from SAR images based on the Doppler shift approach in which the azimuth frequency shift is related to the motion of surface target in the radar direction. The Doppler shift was measured by the difference between the Doppler centroid estimated in the range-compressed, azimuth-frequency domain and the nominal Doppler centroid used during the SAR focusing process. The extracted SAR current velocities were statistically compared with the current velocities from the high frequency(HF) radar in terms of averages, standard deviations, and root mean square errors. The problem of the unreliable nominal Doppler centroid for the estimation of the SAR current velocity was corrected by subtracting the difference of averages between SAR and HF-radar current velocities from the SAR current velocity. The corrected SAR current velocity inherits the average of HF-radar data while maintaining high-resolution nature of the original SAR data.

Ocean Surface Current Retrieval Using Doppler Centroid of ERS-1 Raw SAR Data

  • Kim Ji-Eun;Kim Duk-jin;Moon Wooil M.
    • Proceedings of the KSRS Conference
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    • 2004.10a
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    • pp.590-593
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    • 2004
  • Extraction of ocean surface current velocity offers important physical oceanographic parameters especially on understanding ocean environment. Although Remote Sensing techniques were highly developed, the investigation of ocean surface current using Synthetic Aperture Radar (SAR) is not an easy task. This paper presents the results of ocean surface current observation using Doppler Centroid of ERS-1 SAR data obtained off the coast of Korea peninsula. We employed the concept, in which Doppler frequency shift and the ocean surface current are closely related, to evaluate ocean surface current. Moving targets cause Doppler frequency shift of the back scattered radar waves of SAR, thus the line-of-sight velocity component of the scatters can be evaluated. The Doppler frequency shift can be measured by estimating the difference between Doppler Centroid of raw SAR data and reference Doppler Centroid. Theoretically, the Doppler Centroid is zero; however, squinted antenna which is affected by several physical factors causes Doppler Centroid to be nonzero. The reference Doppler Centroid can be obtained from measurements of sensor trajectory, attitude and Earth model. The estimated Doppler Centroid was compensated by considering the accurate attitude estimation of ERS-1 SAR. We could verify the correspondence between the estimated ocean surface current and observed in-situ data in the error bound.

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Analysis of the Signal Degradations and Its Compensation Techniques in the LEO Mobile Satellite Communication (저궤도 이동위성통신에 있어서의 신호열화 해석 및 이의 보상기술)

  • ;S. Sampei;N. Morinaga
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.8 no.1
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    • pp.22-34
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    • 1997
  • In LEO system, the signal degradation is mainly due to fading and Doppler shift, so that the analysis of the signal degradation and compensation techniques are very important. As the Doppler shift compensator, the block demodulator has been known to be useful in compensating for the time-varing Doppler shift, but its compensating ability is about several hundreds Hz in 32 ksymbols / s QAM (QPSK) signal transmission. Therefore, in this paper, to compensate for severe fading and Doppler shift more than several kHz, we use a conventional pilot symbol-aided fading compensator, and propose the Doppler shift compensator. It is shown that the proposed compensator is able to compensate for Doppler shift more than several kHz. And a pilot symbol-aided fading compensator is shown to be a suitable scheme for severe Rician fading ($K{\leq}10 dB$) as well as Rayleigh fading. Also, it is shown that the equal gain combiner improves greatly the QAM performance even if the fading or Doppler shift becomes deeper or larger.

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Audio Processing Algorithm Using Base Line Shift Method in Pulsed Doppler Systems (PW 도플러 시스템에서 Base Line 이동 기법을 이용한 오디오 신호 처리 방법)

  • 김기덕;송태경
    • Journal of Biomedical Engineering Research
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    • v.20 no.3
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    • pp.275-281
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    • 1999
  • Conventional PW Doppler systems suffer from the ambiguity of measured blood velocities due to the spectrum aliasing when the corresponding Doppler frequencies are greater than the Nyquist frequency. Base-line shift is a customary method for dealiasing the Doppler spectrums. I lowever, Doppler audio signals still remain unchanged even when the base-line shift method is applied. This paper de scribes an method for dealiasing both the Doppler spectra and audio signals by using sampling rate expansion, frequency shifting, and filtering poerations. For undirectional flows, the method can increase the maximum detectable Doppler frequency from the Nyquist limit of one-half of the Pulse Repetition Frequency(PRF) to the PRF. Experiments with real data have been performed to verify the proposed method.

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Laser doppler velocimetry using the optogalvanic effect of $Co_2$ laser (광전류 효과를 이용한 $Co_2$ 레이저 도플러 속도 측정기)

  • 최종운;김용평;김윤명
    • Korean Journal of Optics and Photonics
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    • v.8 no.6
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    • pp.482-485
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    • 1997
  • A new laser Doppler velocimeter employing a $CO_2$laser has been developed by using its optogalvanic effect. A change in the electric impedance of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, was employed to detect the Doppler frequency shift. A Doppler frequency shift as much as 60 KHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained.

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Photoacoustic Laser Doppler Velocimetrv Using the Self - mixing Effect of RF - excited CO2 Laser

  • Choi, Jong-Woon;You, Moon-Jong;Choi, Sung-Woong;Woo, Sam-Young
    • Journal of the Optical Society of Korea
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    • v.8 no.4
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    • pp.188-191
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    • 2004
  • A new laser Doppler velocimeter employing a $CO_2$ laser has been developed by using its photoacoustic effect. A change in the pressure of a discharge, induced by mixing of a returned wave with an originally existing wave inside the cavity, is employed to detect the Doppler frequency shift. We found that a Doppler frequency shift as small as 50 kHz was detected, and also a good linear relationship between the velocity and the Doppler frequency shift was obtained.

Technical Survey and Analysis of DSSS (직접대역확산방식 기술조사 및 분석)

  • Lim, You-Chol;Ma, Keun-Soo;Kim, Myung-Hwan;Lee, Jae-Deuk
    • Aerospace Engineering and Technology
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    • v.10 no.1
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    • pp.45-53
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    • 2011
  • This paper is technical review about Direct Sequence Spread Spectrum(DSSS) to apply in launch vehicle system. First, we introduce communication protocol(carrier frequency, code length, process gain, data rate, chip rate etc) about several application system using DSSS. And then, we survey and summarize the effect of doppler shift to the DSSS. The doppler shift is important error factor for PN code tracking in the fast moving system like launch vehicle. So, spread spectrum code acquisition technique for a direct sequence system in the presence of doppler effect must be investigated.