检索结果-南通市图书馆

Reconstruction of sub cross-correlation cancellation technique for unambiguous acquisition of BOC(kn, n) signals

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2019年第5期30卷 852-860页

作者： JI Yuanfa CHEN Xiaoqian FU Qiang SUN Xiyan zhen weimin Guangxi Key Laboratory of Precision Navigation Technology and Application Guilin University of Electronic TechnologyGuilin 541004China National&Local Joint Engineering Research Center of Satellite Navigation Positioning and Location Service Guilin 541004China Key Laboratory of Radio Wave Environment and Modeling Technology Qingdao 266000China

In order to solve the problem of ambiguous acquisition of BOC signals caused by its property of multiple peaks,an unambiguous acquisition algorithm named reconstruction of sub cross-correlation cancellation technique(RSCCT)for BOC(kn,n)signals is *** this paper,the principle of signal decomposition is combined with the traditional acquisition algorithm structure,and then based on the method of reconstructing the correlation *** method firstly gets the sub-pseudorandom noise(PRN)code by decomposing the local PRN code,then uses BOC(kn,n)and the sub-PRN code cross-correlation to get the sub cross-correlation ***,the correlation peak with a single peak is obtained by reconstructing the sub cross-correlation function so that the ambiguities of BOC acquisition are *** simulation shows that RSCCT can completely eliminate the side peaks of BOC(kn,n)group signals while maintaining the narrow correlation of BOC,and its computational complexity is equivalent to sub carrier phase cancellation(SCPC)and autocorrelation side-peak cancellation technique(ASPeCT),and it reduces the computational complexity relative to *** BOC(n,n),the acquisition sensitivity of RSCCT is 3.25 dB,0.81 dB and 0.25 dB higher than binary phase shift keying(BPSK)-like,SCPC and ASPeCT at the acquisition probability of 90%,*** peak to average power ratio is 1.91,3.0 and 3.7 times higher than ASPeCT,SCPC and BPSK-like at SNR=–20 dB,*** BOC(2n,n),the acquisition sensitivity of RSCCT is 5.5 dB,1.25 dB and 2.69 dB higher than BPSK-like,SCPC and ASPeCT at the acquisition probability of 90%,*** peak to average power ratio is 1.02,1.68 and 2.12 times higher than ASPeCT,SCPC and BPSK-like at SNR=–20 dB,respectively.

关键词： signal decomposition sub cross-correlation reconstructingcorrelation function acquisition performance

Rheological Behavior of Semi-Solid AZ91D Alloy

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2004年第5期20卷 580-582页

作者： weimin MAO, Zisheng zhen, Shijian YAN and Xueyou ZHONGSchool of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China Sch. of Mat. Sci. and Eng. Univ. of Sci. and Technol. Beijing Beijing 100083 China

The rheological behavior and microstructure of semi-solid AZ91D was studied using a Couette type viscometer. The results show that the apparent viscosity of semi-solid AZ91D increases with the cooling rate increasing when it is continuously cooled and mechanically stirred and the empiric relation of the apparent viscosity with the cooling rate and solid fraction at shearing rate 93.7 s-1 is expressed as η=[0.66-0.63e(-ε/3.01)]e(fa/0.14), and with the shearing rate and solid fraction at cooling rate 4℃/min is shown as η=0.55e(fa/0.11-γ/87.59), as well as the cooling rate and shearing rate have an important effect on the microstructure of the semi-solid AZ91D alloy slurry, and decreasing the cooling rate and increasing the shearing rate are favorable to the nondendritic evolution of the primary grains.

关键词： Rheological behavior Magnesium alloys Semi-solid

Microstructure Characteristics and Apparent Viscosity of Hypereutectic Al-24%Si Alloy Melt During Semi-solid State Stirring

在线全文

学校读者我要写书评

暂无评论

Journal of University of Science and Technology Beijing 2001年第2期8卷 126-128页

作者： Yanjun Li, weimin Mao, Zisheng zhen, Xueyou Zhong (Material Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China) Material Sci. and Engineering School University of Science and Technology Beijing 100083 China

The microstructural evolution and apparent viscosity of hypereutectic Al-24%Si alloy during semi-solid state shearing were studied with a Searte type viscometer. When the alloy melt was continuously stirred from 720 degreesC to eutectic temperature, the primary Si crystals were gradually changed from elongated platelets to near-spherical shapes. It was found that some nondendritic a-phase formed when the melt was stirred below 585 degreesC. The experiment showed that the semi-solid stirring had strong effect on inhibiting the anisotropic growth of Si crystals during solidification. The apparent viscosity of the alloy melt increased slowly with the decreasing of temperature before the formation of nondendritic alpha -phase, which caused the dramatic increase of apparent viscosity.

关键词： hypereutectic Al-Si alloy solidification structures apparent viscosity

Ionospheric Spatial Correlation Analysis for China Area

在线全文

学校读者我要写书评

暂无评论

Ionospheric Spatial Correlation Analysis for China Area

Analysis on Characteristics of Delay Errors under Ionospheric Anomaly in China area

第四届中国卫星导航学术年会

作者： Liu Dun Chen Liang zhen weimin China Research Institute of Radiowave Propagation

Ionospheric correlation models are needed for ionospheric grid-based augmentation system development and its rigorous integrity performance requirement. 0th and 1st order ionospheric correlation function was established for China area, and analyzed for various ionospheric conditions. It is shown that the ionospheric delay difference does not vary linearly with the distance, and the residual ionospheric error after the planar fitting of grid model is not a constant as well. These models are different from that of WAAS or EGNOS, which covers the middle latitude area. These China area ionosphere specific characteristics should be taken into account for the regional augmentation system development.

关键词： Integrity Ionosphere Anomaly Storm Spatial correlation model

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

Analysis on Characteristics of Delay Errors under Ionospheri...

Analysis of ionospheric grid model performance for China area

第九届中国卫星导航学术年会

作者： Dun LIU Liang Chen Xiao Yu weimin zhen No.22nd Research Institute CETC

Ionospheric anomaly in south of China will degrade the performance of SBAS grid models *** of ionospheric delay errors are analyzed with observations from the mid and low latitudes area in China for various solar activities and ionospheric *** show the error distribution is symmetric,unimodal,and overbounded by a biased normal error *** biased distributions would reduce the overbounding capability of the estimated *** anomaly contribute to the complicated spatial and temporal variations of the delay errors as storms,and even is the main influencing factors under certain condition.

关键词： Ionosphere Grid model Space-based augmentation system(SBAS) Integrity Error overbounding

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

Analysis of ionospheric grid model performance for China are...

Modeling of BDS Positioning Errors Due to Ionospheric Scintillation and its Application

第十一届中国卫星导航年会

作者： Dun LIU Xiao YU Liang CHEN weimin zhen No.22nd Research Institute CETC

Special characteristics of regional ionosphere generally impact the grid model of SBAS most seriously. Performance of grid model is analyzed for stormy ionosphere conditions with GNSS data in the year

关键词： ionosphere Equatorial Ionization Anomaly(EIA) ionospheric storm SBAS ionospheric grid model integrity

来源： cnki会议 cnki会议 cnki会议评论

在线全文

学校读者我要写书评

暂无评论

Modeling of BDS Positioning Errors Due to Ionospheric Scinti...

Intelligent Recognition Technology of GNSS Interference Source Based on Electromagnetic Fingerprint

第十一届中国卫星导航年会

作者： Dun Liu Xiao Yu Jian Feng weimin zhen No.22nd Research Institute CETC

In this work, efforts are made to develop models of BDS positioning errors due to ionospheric scintillation. Two aspects are specially considered in the modeling work, namely the lose-of-lock on signa

关键词： ionospheric scintillation possibility of loss-of-lock ranging error scintillation index

来源： cnki会议 cnki会议 cnki会议评论

在线全文

学校读者我要写书评

暂无评论

Intelligent Recognition Technology of GNSS Interference Sour...

Preliminary observation results of the Coherent Beacon Systemonboard the China Seismo-Electromagnetic Satellite-1

第十一届中国卫星导航年会

作者： Xinyu Yan Xin Chen Weihua Xie weimin zhen Shanghai Key Laboratory of Navigation and Location Based Services School of Electronic Information and Electrical Engineering Shanghai Jiaotong University Beijing satellite navigation center China Research Institute of Radiowave Propagation

Due to the influence of transmission path attenuation, Received Global Navigation Satellite System(GNSS) signal is weak, and extremely susceptible to suppression interference, resulting in degradation

关键词： suppression interference interference detection and identification electromagnetic fingerprint feature GoogLeNet model

来源： cnki会议 cnki会议 cnki会议评论

在线全文

学校读者我要写书评

暂无评论

Earth and Planetary Physics 2018年第6期2卷 505-514页

作者： Liang Chen Ming Ou YaPing Yuan Fang Sun Xiao Yu weimin zhen China Research Institute of Radiowave Propagation Qingdao 266107 China

This paper reports, for the first time, observation results of the Coherent Beacon System(CBS) onboard the China SeismoElectromagnetic Satellite-1(CSES-1). We describe the CBS, and the Computerized Ionospheric Tomography(CIT) algorithm program is validated by numerical experiment. Two examples are shown, for daytime and nighttime respectively. The Equatorial Ionization Anomaly(EIA) can be seen, and the northern crest core is located at ～20°N in the reconstruction image at 07:28 UTC on 20 July 2018(daytime).Disturbances are shown in the reconstruction image at 18:40 UTC on 13 July 2018(nighttime). We find that beacon measurements are more consistent with ionosonde measurements than model results, by comparing Nm F2 at three sites at Lanzhou, Chongqing, and Kunming; consistency with ionosonde measurements validates beacon measurements. Finally, we have studied Vertical Total Electron Content(VTEC) variations from ground to ～500 km(the height of CSES-1 orbit) and ratios of VTEC between beacon measurements and CODE(Center for Orbit Determination in Europe) data. VTEC variation from ground to ～500 km has a range of 7.2–16.5 TECU for the daytime case and a range of 1.1–1.7 TECU for the nighttime case. The Beacon/CODE ratio of VTEC varies with latitude and time. The mean Beacon/CODE ratio is 0.69 for the daytime case and 0.26 for the nighttime case. The fact that the nighttime case yields lower ratios indicates the higher altitude of the ionosphere during nighttime when the ionosphere is assumed to be a thin layer.

关键词： Coherent Beacon System(CBS) China Seismo-Electromagnetic Satellite-1(CSES-1) Computerized Ionospheric Tomography(CIT) Total Electron Content(TEC)