随着以太网数据传输技术的广泛应用,数据传输速率不断地提升,传统的对时技术难以满足现代通信系统中实时传输的精度需求,网络业界提出了精密时钟同步协议标准(IEEE Standard for a Precision Clock Synchronization Protocol,IEEE1588)...随着以太网数据传输技术的广泛应用,数据传输速率不断地提升,传统的对时技术难以满足现代通信系统中实时传输的精度需求,网络业界提出了精密时钟同步协议标准(IEEE Standard for a Precision Clock Synchronization Protocol,IEEE1588),该标准采用精密时钟同步协议(Precision Time Protocol,PTP),精度可达微秒级。针对网络传输实时性的需求,阐述了PTP协议原理,通过搭建试验平台测试了在不同网络包长度和不同传输数据率下的PTP性能,分析了非PTP设备对传输精度的影响并进行了修正,将PTP协议在实际网络传输系统中的精度提高到了亚微秒级,为采用PTP协议的对时机制研究提供了参考。展开更多
Delay considerttion has been a major issue in design and test of high performance digital circuits . The assumption of input signal change occurring only when all internal nodes are stable restricts the increase of cl...Delay considerttion has been a major issue in design and test of high performance digital circuits . The assumption of input signal change occurring only when all internal nodes are stable restricts the increase of clock frequency. It is no longer true for wave pipelining circuits. However, previous logical delay models are based on the assumption. In addition, the stable time of a robust delay test generally depends on the longest sensitizable path delay. Thus , a new delay model is desirable. This paper explores the necessity first. Then, Boolean process to analytically describe the logical and timing behavior of a digital circuit is reviewed . The concept of sensitization is redefined precisely in this paper. Based on the new concept of sensitization, an analytical delay model is introduced . As a result , many untestable delay faults under the logical delay model can be tested if the output waveforms can be sampled at more time points. The longest sensitiaable path length is computed for circuit design and delay test .展开更多
In underground mines, visible light communication(VLC) system is a promising method to realize effective communication,which supports communication and illumination at the same time. Therefore, adequate research of un...In underground mines, visible light communication(VLC) system is a promising method to realize effective communication,which supports communication and illumination at the same time. Therefore, adequate research of underlying physical propagation phenomenon should be carried out to realize VLC system in underground mines. To design VLC system and evaluate its performance, accurate and efficient channel models, including large-scale fading and scattering characteristics, are needed to be established. However,the characteristics of the underlying VLC channels about fading and scattering have not been sufficiently investigated yet. In this paper, a path loss channel model, based on the recursive model, is proposed precisely. Its path loss exponent is determined by three different trajectories, which is studied in the mining roadway and working face environment. Besides, the shadowing effect for VLC has been modelled by a Bimodal Gaussian distribution in underground mines. Considering the number of transmitters in line-of-sight(Lo S) as well as non-line-of-sight(NLo S) scenarios,our simulation illustrates the fact that, as the curve fitting technique is employed, the path loss displays a linear behavior in log-domain.The path loss expression is derived, it is related to the distance. Finally, root mean square(RMS) delay spread and Mie scattering in underground mines are analyzed.展开更多
To meet the demands for the data combination with multiple space geodetic techniques at the observation level,we developed a new software platform with high extensibility and computation efficiency,named space Geodeti...To meet the demands for the data combination with multiple space geodetic techniques at the observation level,we developed a new software platform with high extensibility and computation efficiency,named space Geodetic SpatioTemporal data Analysis and Research software(GSTAR).Most of the modules in the GSTAR are coded in C++with object-oriented programming.The layered modular theory is adopted for the design of the software,and the antenna-based data architecture is proposed for users to construct personalized geodetic application scenarios easily.The initial performance of the GSTAR software is evaluated by processing the Global Navigation Satellite System(GNSS)data collected from 315 globally distributed stations over two and a half years.The accuracy of GNSS-based geodetic products is evaluated by comparing them with those released by International GNSS Service(IGS)Analysis Centers(AC).Taking the products released by European Space Agency(ESA)as reference,the Three-Dimension(3D)Root-Mean-Squares(RMS)of the orbit differences are 2.7/6.7/3.3/7.7/21.0 cm and the STandard Deviations(STD)of the clock differences are 19/48/16/32/25 ps for Global Positioning System(GPS),GLObal NAvigation Satellite System(GLONASS),Galileo navigation satellite system(Galileo),BeiDou Navigation Satellite System(BDS),Medium Earth Orbit(MEO),and BDS Inclined Geo-Synchronous Orbit(IGSO)satellites,respectively.The mean values of the X and Y components of the polar coordinate and the Length of Day(LOD)with respect to the International Earth Rotation and Reference Systems Service(IERS)14 C04 products are-17.6 microarc-second(μas),9.2μas,and 14.0μs/d.Compared to the IGS daily solution,the RMSs of the site position differences in the north/east/up direction are 1.6/1.5/3.9,3.8/2.4/7.6,2.5/2.4/7.9 and 2.7/2.3/7.4 mm for GPS-only,GLONASS-only,Galileo-only,and BDS-only solution,respectively.The RMSs of the differences of the tropospheric Zenith Path Delay(ZPD),the north gradients,and the east gradients are 5.8,0.9,and 0.9 mm with respect to the展开更多
文摘随着以太网数据传输技术的广泛应用,数据传输速率不断地提升,传统的对时技术难以满足现代通信系统中实时传输的精度需求,网络业界提出了精密时钟同步协议标准(IEEE Standard for a Precision Clock Synchronization Protocol,IEEE1588),该标准采用精密时钟同步协议(Precision Time Protocol,PTP),精度可达微秒级。针对网络传输实时性的需求,阐述了PTP协议原理,通过搭建试验平台测试了在不同网络包长度和不同传输数据率下的PTP性能,分析了非PTP设备对传输精度的影响并进行了修正,将PTP协议在实际网络传输系统中的精度提高到了亚微秒级,为采用PTP协议的对时机制研究提供了参考。
文摘Delay considerttion has been a major issue in design and test of high performance digital circuits . The assumption of input signal change occurring only when all internal nodes are stable restricts the increase of clock frequency. It is no longer true for wave pipelining circuits. However, previous logical delay models are based on the assumption. In addition, the stable time of a robust delay test generally depends on the longest sensitizable path delay. Thus , a new delay model is desirable. This paper explores the necessity first. Then, Boolean process to analytically describe the logical and timing behavior of a digital circuit is reviewed . The concept of sensitization is redefined precisely in this paper. Based on the new concept of sensitization, an analytical delay model is introduced . As a result , many untestable delay faults under the logical delay model can be tested if the output waveforms can be sampled at more time points. The longest sensitiaable path length is computed for circuit design and delay test .
基金support from the National Natural Science Foundation of China (Grant No. 61371110)Key R&D Program of Shandong Province (Grant No. 2016GGX101014)+1 种基金EU H2020 RISE TESTBED project (Grant No. 734325)the Fundamental Research Funds of Shandong University (No. 2017JC029)
文摘In underground mines, visible light communication(VLC) system is a promising method to realize effective communication,which supports communication and illumination at the same time. Therefore, adequate research of underlying physical propagation phenomenon should be carried out to realize VLC system in underground mines. To design VLC system and evaluate its performance, accurate and efficient channel models, including large-scale fading and scattering characteristics, are needed to be established. However,the characteristics of the underlying VLC channels about fading and scattering have not been sufficiently investigated yet. In this paper, a path loss channel model, based on the recursive model, is proposed precisely. Its path loss exponent is determined by three different trajectories, which is studied in the mining roadway and working face environment. Besides, the shadowing effect for VLC has been modelled by a Bimodal Gaussian distribution in underground mines. Considering the number of transmitters in line-of-sight(Lo S) as well as non-line-of-sight(NLo S) scenarios,our simulation illustrates the fact that, as the curve fitting technique is employed, the path loss displays a linear behavior in log-domain.The path loss expression is derived, it is related to the distance. Finally, root mean square(RMS) delay spread and Mie scattering in underground mines are analyzed.
基金This work was sponsored by National Natural Science Foundation of China(Grant No.41931075,42274041).
文摘To meet the demands for the data combination with multiple space geodetic techniques at the observation level,we developed a new software platform with high extensibility and computation efficiency,named space Geodetic SpatioTemporal data Analysis and Research software(GSTAR).Most of the modules in the GSTAR are coded in C++with object-oriented programming.The layered modular theory is adopted for the design of the software,and the antenna-based data architecture is proposed for users to construct personalized geodetic application scenarios easily.The initial performance of the GSTAR software is evaluated by processing the Global Navigation Satellite System(GNSS)data collected from 315 globally distributed stations over two and a half years.The accuracy of GNSS-based geodetic products is evaluated by comparing them with those released by International GNSS Service(IGS)Analysis Centers(AC).Taking the products released by European Space Agency(ESA)as reference,the Three-Dimension(3D)Root-Mean-Squares(RMS)of the orbit differences are 2.7/6.7/3.3/7.7/21.0 cm and the STandard Deviations(STD)of the clock differences are 19/48/16/32/25 ps for Global Positioning System(GPS),GLObal NAvigation Satellite System(GLONASS),Galileo navigation satellite system(Galileo),BeiDou Navigation Satellite System(BDS),Medium Earth Orbit(MEO),and BDS Inclined Geo-Synchronous Orbit(IGSO)satellites,respectively.The mean values of the X and Y components of the polar coordinate and the Length of Day(LOD)with respect to the International Earth Rotation and Reference Systems Service(IERS)14 C04 products are-17.6 microarc-second(μas),9.2μas,and 14.0μs/d.Compared to the IGS daily solution,the RMSs of the site position differences in the north/east/up direction are 1.6/1.5/3.9,3.8/2.4/7.6,2.5/2.4/7.9 and 2.7/2.3/7.4 mm for GPS-only,GLONASS-only,Galileo-only,and BDS-only solution,respectively.The RMSs of the differences of the tropospheric Zenith Path Delay(ZPD),the north gradients,and the east gradients are 5.8,0.9,and 0.9 mm with respect to the
