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Cyclic delay transmission for unique word OFDM systems

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Science China(Information Sciences) 2014年第8期57卷 78-86页

作者： LIAO Mang XIA XiangGen zhang youguang School of Electronic Information Engineering Beihang University Department of Electrical and Computer Engineering University of Delaware

In this article,we propose a cyclic delay diversity(CDD)transmission scheme for unique word(UW)OFDM system,which is denoted as *** our proposed CDD-UW-OFDM system,the first transmit antenna transmits a UW-OFDM and then,for every UW-OFDM block,the i-th transmit antenna transmits a cyclically delayed version of the symbols transmitted at the first transmit *** this proposed CDD-OFDM system,each antenna transmission is a ***,at the receiver under a certain condition on the cyclic delay amounts,the received signal is equivalent to that of a single transmit antenna UW-OFDM transmission with a longer multipath *** design the lengths of UW and cyclic delays to achieve the full multipath and spatial diversities for the CDD-UW-OFDM system when the linear MMSE receiver is *** then present some simulation results to illustrate the claimed performance of the proposed system.

关键词： MIMO-OFDM systems frequency-selective fading channels cyclic delay diversity(CDD) unique word(UW) transmit diversity

Measurement analyses and evaluations of sea-level heights using the HY-2A satellite’s radar altimeter

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Acta Oceanologica Sinica 2019年第11期38卷 134-139页

作者： Xingwei Jiang Yongjun Jia youguang zhang National Satellite Ocean Application Service Beijing 100081China Key Laboratory of Space Ocean Remote Sensing and Application(MNR) Beijing 100081China

The HY-2A satellite is China’s first independent oceanic dynamic environmental satellite,and has been operating continuously for more than six *** satellite’s radar altimeter,which is one of the main loads on the satellite,has the ability to realize all-weather and all-day observations of global sea-surface heights,as well as significant wave heights and sea-surface wind *** observed data have been widely used in marine disaster prevention and reduction,along with resource development,maritime security and other *** order to achieve a comprehensive understanding of the multi-year overall observational performances of the HY-2A satellite’s radar altimeter,all of the observational data of the IGDR product from October 26,2012 to August 27,2017 were selected in this study for a comprehensive *** height measurement capability of the HY-2A satellite’s radar altimeter was evaluated using self-crossover and Jason-2 crossover *** height discrepancies at the self-crossover point of the HY-2A satellite’s ascending and descending orbits were also *** was found that for the HY-2A satellite’s radar altimeter in global waters under the restriction conditions of ascending and descending orbits,the height anomaly differences were within a range of less than 30 *** absolute mean error was determined to be 5.81 cm,and the height anomaly standard deviation was 7.76 *** the conditions of the observational areas being limited within a scope of 60°from the Equator,it was determined that the sea-level height anomaly differences were less than 10 cm at the junction of the ascending and descending orbits,the absolute mean error was 3.95 *** addition,the sea-level height anomaly standard deviation was observed to be *** a mutual cross method with the Jason-2 satellite,it was found that under the conditions of the observational area being within the scope of 66°from the equator,the height anomaly differences at the junction

关键词： HY-2A satellite radar altimeter sea level anomalies

The numerical simulation of the Kuroshio frontal eddies in the East China Sea using a hybrid coordinate ocean mode

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Acta Oceanologica Sinica 2013年第5期32卷 31-41页

作者： JIA Yongjun zhang youguang LIN Mingsen National Satellite Ocean Application Service State Oceanic Administion

A hybrid coordinate ocean model （ltYCOM） is used to simulate the Kuroshio frontal eddies in the East China Sea （ECS）. The research area is located （20°-32°N, 120°-132°E）. Using tile simulating data, it is figured out that the Kuroshio frontal eddies occur in summer as well as in the other season in this area. The life cycle of the Kuroshio and its frontal eddies is different with the position. The life-cycle of the Kuroshio frontal eddies of the northwest Diaoyu Islands is about 14 d; and the life cycle of the Kuroshio frontal eddies of southwest Yakushima about 20 d. This result extends the in situ researching results greatly. In addition, the vertical impact depth of the Kuroshio frontal eddies is also changing with the position. On the whole, in the ECS, the maximum impact depth of the Kuroshio frontal eddies of the northwest Taiwan Islands is about 75 m; the maximum impact depth of the Kuroshio frontal eddies of the northwest Diaoyu Islands is more than 125 m, but no more than 200 m; and the maximum impact depth of the Kuroshio frontal eddies of southwest Yakushima is up to 100 m.

关键词： Kuroshio frontal eddies hybrid coordinate ocean model East China Sea

Shenzhou-4 spaceborne altimeter waveform processing and significant wave height retrieval

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Acta Oceanologica Sinica 2006年第3期25卷 40-47页

作者： JI Yonggang zhang Jie zhang youguang MENG Junmin Institute of Oceanology Chinese Academy of Sciences Qingdao 266071 China Graduate School of Chinese Academy of Sciences Beijing 100039 China First Institute of Oceanography State Oceanic Administration Qingdao 266061 China National Satellite Ocean Application Service Beijing 100081 China

The Shenzhou -4 spaceborne （SZ -4） altimeter waveforms were processed, and then the significant wave heights （SWH） was retrieved on the basis of waveform fitting and waveform retracking. Waveforms processing includes the waveform ls averaging, the elimination of thermal noise and the waveforms normalization. Double peaks were found on each SZ - 4 waveform, and it was pointed out that the region of waveforms with the second peak is abnormal and its effects on the whole waveform in the waveform fit should be taken into consideration. To obtain the width of the waveform leading-edge, a method was proposed to find the starting point of waveform, and the half-power point of waveform was found by retracking the waveform. The normalized wavefornis were fitted with the Haynes model by using the weighting least square fit method. Then the selections of the weighting coefficients and their effects on significant wave hight retrieving were discussed, and the optimal five-region weighting method was proposed. At last, the SWH data of SZ -4 altimeter retrieved by using the proposed method were compared with those of ERS -2 and Jason - 1 altimeter, and it was concluded that the SZ -4 altimeter can detect significant wave height.

关键词： SZ-4 spaeeborne altimeter significant wave height double peaks waveform retraeking waveform fit

Wind speed inversion and in-orbit assessment of the imaging altimeter on Tiangong-2 space station

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Acta Oceanologica Sinica 2020年第12期39卷 114-120页

作者： youguang zhang Qingliu Bao Mingsen Lin Shuyan Lang Key Laboratory of Space Ocean Remote Sensing and Application National Satellite Ocean Application ServiceBeijing 100081China Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) Guangzhou 511458China Beijing Piesat Information Technology Co. Ltd.Beijing 100195China

Imaging altimeter(IALT)is a new type of radar altimeter *** contrast to the conventional nadir-looking altimeters,such as HY-2 A altimeter,Jason-1/2,and TOPEX/Poseidon,IALT observes the earth surface at low incident angles(2.5°–8°),so its swath is much wider and its spatial resolution is much higher than the previous *** paper presents a wind speed inversion method for the recently launched IALT onboard Tiangong-2 space *** the current calibration results of IALT do not agree well with the well-known wind geophysical model function at low incidence angles,a neural network is used to retrieve the ocean surface wind speed in this *** wind speed inversion accuracy is evaluated by comparing with the ECMWF reanalysis wind speed,buoy wind speed,and in-situ ship *** results show that the retrieved wind speed bias is about–0.21 m/s,and the root-mean-square(RMS)error is about 1.85 m/*** wind speed accuracy of IALT meets the performance requirement.

关键词： imaging altimeter ocean surface wind speed inversion accuracy analysis in-orbit assessment

An ocean current inversion accuracy analysis based on a Doppler spectrum model

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Acta Oceanologica Sinica 2017年第9期36卷 101-107页

作者： BAO Qingliu zhang youguang LIN Mingsen GONG Peng Key Laboratory of State Oceanic Administration for Space Ocean Remote Sensing and Application National Satellite Ocean Application ServiceState Oceanic Administration Key Laboratory of Ministry of Education for Earth System Modeling Department of Earth System Science Tsinghua University

Microwave remote sensing is one of the most useful methods for observing the ocean parameters. The Doppler frequency or interferometric phase of the radar echoes can be used for an ocean surface current speed retrieval,which is widely used in spaceborne and airborne radars. While the effect of the ocean currents and waves is interactional. It is impossible to retrieve the ocean surface current speed from Doppler frequency shift directly. In order to study the relationship between the ocean surface current speed and the Doppler frequency shift, a numerical ocean surface Doppler spectrum model is established and validated with a reference. The input parameters of ocean Doppler spectrum include an ocean wave elevation model, a directional distribution function, and wind speed and direction. The suitable ocean wave elevation spectrum and the directional distribution function are selected by comparing the ocean Doppler spectrum in C band with an empirical geophysical model function（CDOP）. What is more, the error sensitivities of ocean surface current speed to the wind speed and direction are analyzed. All these simulations are in Ku band. The simulation results show that the ocean surface current speed error is sensitive to the wind speed and direction errors. With VV polarization, the ocean surface current speed error is about 0.15 m/s when the wind speed error is 2 m/s, and the ocean surface current speed error is smaller than 0.3 m/s when the wind direction error is within 20° in the cross wind direction.

关键词： Doppler spectrum model ocean surface current speed parameter sensitivity analysis measurement error

SER analysis and power allocation for hybrid cooperative transmission system

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Journal of Systems Engineering and Electronics 2012年第5期23卷 661-670页

作者： Guoyan Li youguang zhang Wang Kang School of Electronics and Information Engineering Beihang UniversityBeijing 100191E R.China

The symbol-error-rate（SER） and power allocation for hybrid cooperative（HC） transmission system are ***-form SER expression is derived by using the moment generating function（MGF）-based ***,the resultant SER contains an MGF of the harmonic mean of two independent random variables（RVs）,which is not tractable in SER *** present a simple MGF expression of the harmonic mean of two independent RVs which avoids the hypergeometric functions used commonly in previous *** the simple MGF,closed-form SER for HC system with M-ary phase shift keying（M-PSK） signals is ***,an approximation as well as an upper bound of the SER is *** is shown that the SER approximation is asymptotically *** on the tight SER approximation,the power allocation of the HC system is *** is shown that the optimal power allocation does not depend on the fading parameters of the source-destination（SD） channel and it only depends on the source-relay（SR） and relay-destination（RD） ***,the performance gain of the power allocation depends on the ratio of the channel quality between RD and *** the increase of this ratio,more performance gain can be acquired.

关键词： cooperative transmission relaying protocols hybrid cooperation symbol-error-rate(SER) power allocation

Evaluation of wave retrieval for Chinese Gaofen-3 synthetic aperture radar

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Geo-Spatial Information Science 2022年第2期25卷 229-243页

作者： Weizeng Shao Xingwei Jiang Zhanfeng Sun Yuyi Hu Armando Marino youguang zhang College of Marine Sciences Shanghai Ocean UniversityShanghaiChina National Satellite Ocean Application Service Ministry of Natural ResourcesBeijingChina Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) GuangzhouChina dNatural Sciences University of StirlingStirlingUK

The goal of this study was to investigate the performance of a spectral-transformation wave retrieval algorithm and confirm the accuracy of wave retrieval from C-band Chinese Gaofen-3(GF-3)Synthetic Aperture Radar(SAR)*** than 200 GF-3 SAR images of the coastal China Sea and the Japan Sea for dates from January to July 2020 were acquired in the Quad-Polarization Strip(QPS)*** images had a swath of 30 km and a spatial resolution of 8 m pixel *** were processed to retrieve Significant Wave Height(SWH),which is simulated from a numerical wave model called Simulating WAves Nearshore(SWAN).The first-guess spectrum is essential to the accuracy of Synthetic Aperture Radar(SAR)wave spectrum ***,we proposed a wave retrieval scheme combining the theocratic-based Max Planck Institute Algorithm(MPI),a Semi-Parametric Retrieval Algorithm(SPRA),and the Parameterized First-guess Spectrum Method(PFSM),in which a full wave-number spectrum and a non-empirical ocean spectrum proposed by Elfouhaily are *** PFSM can be driven using the wind speed without calculating the dominant wave phase *** speeds were retrieved using a Vertical-Vertical(VV)polarized geophysical model function *** proposed algorithm was implemented for all collected SAR images.A comparison of SAR-derived wind speeds with European Center for Medium-Range Weather Forecasts(ECMWF)ERA-5 data showed a 1.95 m/s Root-Mean-Squared Error(RMSE).The comparison of retrieved SWH with SWAN-simulated results demonstrated a 0.47 m RMSE,which is less than the 0.68 m RMSE of SWH when using the PFSM algorithm.

关键词： Wave retrieval Gaofen-3(GF-3) Synthetic Aperture Radar(SAR)

Assimilation of Ocean Surface Wind Data by the HY-2B Satellite in GRAPES: Impacts on Analyses and Forecasts

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Advances in Atmospheric Sciences 2023年第1期40卷 44-61页

作者： Jincheng WANG Xingwei JIANG Xueshun SHEN youguang zhang Xiaomin WAN Wei HAN Dan WANG CMA Earth System Modeling and Prediction Center China Meteorological AdministrationBeijing 100081China National Meteorology Center China Meteorological AdministrationBeijing 100081China Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) Guangzhou 511458China National Satellite Ocean Application Service Beijing 100081China

The ocean surface wind(OSW)data retrieved from microwave scatterometers have high spatial accuracy and represent the only wind data assimilated by global numerical models on the ocean surface,thus playing an important role in improving the forecast skills of global medium-range weather prediction *** improve the forecast skills of the Global/Regional Assimilation and Prediction System Global Forecast System(GRAPES_GFS),the HY-2B OSW data is assimilated into the GRAPES_GFS four-dimensional variational assimilation(4DVAR)***,the impacts of the HY-2B OSW data assimilation on the analyses and forecasts of GRAPES_GFS are analyzed based on one-month assimilation cycle *** results show that after assimilating the HY-2B OSW data,the analysis errors of the wind fields in the lower-middle troposphere(1000-600 hPa)of the tropics and the southern hemisphere(SH)are significantly reduced by an average rate of about 5%.The impacts of the HY-2B OSW data assimilation on the analysis fields of wind,geopotential height,and temperature are not solely limited to the boundary layer but also extend throughout the entire troposphere after about two days of cycling ***,assimilating the HY-2B OSW data can significantly improve the forecast skill of wind,geopotential height,and temperature in the troposphere of the tropics and SH.

关键词： HY-2B ocean surface wind 4DVAR GRAPES-GFS medium-range weather forecast