The careers of three Chinese physicists,Hu Ning,Ma Shijun,and Peng Huanwu at the Dublin Institute for Advance Studies in the 1940s,and later,are described.A brief history of the foundation and operations of the instit...The careers of three Chinese physicists,Hu Ning,Ma Shijun,and Peng Huanwu at the Dublin Institute for Advance Studies in the 1940s,and later,are described.A brief history of the foundation and operations of the institute,as well as the roles in it of Erwin Schrodinger,Walter Heitler,Max Born,and others are included.Some details are given of the works carried out there.The three men's post-institute careers are described,Ma eventually in Australia,and Hu and Peng in the People's Republic of China where they became distinguished leaders of theoretical physics research.展开更多
A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training sy...A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset （CFO） estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramer-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error （MMSE）.展开更多
Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of fact...Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of factors, such as errors in the measurement of signal parameters, uncertainties regarding the position of satellites, and errors in the location of calibration sources, are known to degrade the accuracy of target localization in satellite geolocation systems. We systematically analyze the performance of multi-satellite joint geolocation based on time difference of arrival （TDOA） measurements. The theoretical analysis starts with Cramer Rao bound （CRB） derivations for four localization scenarios under an altitude constraint and Gaussian noise assumption. In scenario 1, only the TDOA measurement errors of the emitting source are considered and the satellite positions are assumed to be perfectly estimated. In scenario 2, both the TDOA measurement errors and satellite position uncertainties are taken into account. Scenario 3 assumes that some calibration sources with accurate position information are used to mitigate the influence of satellite position perturbations. In scenario 4, several calibration sources at inaccurate locations are used to alleviate satellite position errors in target localization. Through comparing the CRBs of the four localization scenarios, some valuable＇s insights are gained into the effects of various error sources on the estimation performance. Two kinds of location mean-square errors （MSE） expressions under the altitude constraint are derived through first-order perturbation analysis and the Lagrange method. The first location MSE provides the theoretical prediction when an estimator assumes that the satellite locations are accurate but in fact have errors. The second location MSE provides the localization accuracy if an estimator assumes that the known calibration source locations are precise while in fact erroneous. Simulation results are included to verify the theoretical analysis.展开更多
文摘The careers of three Chinese physicists,Hu Ning,Ma Shijun,and Peng Huanwu at the Dublin Institute for Advance Studies in the 1940s,and later,are described.A brief history of the foundation and operations of the institute,as well as the roles in it of Erwin Schrodinger,Walter Heitler,Max Born,and others are included.Some details are given of the works carried out there.The three men's post-institute careers are described,Ma eventually in Australia,and Hu and Peng in the People's Republic of China where they became distinguished leaders of theoretical physics research.
文摘A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset （CFO） estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramer-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error （MMSE）.
基金Project supported by the National Natural Science Foundation of China （No. 61201381）, the Future Development Foundation of Zhengzhou Information Science and Technology Institute （No. YPI2JJ202057）, China Postdoctoral Science Foundation （No. 2016M592989）, and the Outstanding Youth Foundation of Information Engineering University （No. 2016603201）
文摘Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of factors, such as errors in the measurement of signal parameters, uncertainties regarding the position of satellites, and errors in the location of calibration sources, are known to degrade the accuracy of target localization in satellite geolocation systems. We systematically analyze the performance of multi-satellite joint geolocation based on time difference of arrival （TDOA） measurements. The theoretical analysis starts with Cramer Rao bound （CRB） derivations for four localization scenarios under an altitude constraint and Gaussian noise assumption. In scenario 1, only the TDOA measurement errors of the emitting source are considered and the satellite positions are assumed to be perfectly estimated. In scenario 2, both the TDOA measurement errors and satellite position uncertainties are taken into account. Scenario 3 assumes that some calibration sources with accurate position information are used to mitigate the influence of satellite position perturbations. In scenario 4, several calibration sources at inaccurate locations are used to alleviate satellite position errors in target localization. Through comparing the CRBs of the four localization scenarios, some valuable＇s insights are gained into the effects of various error sources on the estimation performance. Two kinds of location mean-square errors （MSE） expressions under the altitude constraint are derived through first-order perturbation analysis and the Lagrange method. The first location MSE provides the theoretical prediction when an estimator assumes that the satellite locations are accurate but in fact have errors. The second location MSE provides the localization accuracy if an estimator assumes that the known calibration source locations are precise while in fact erroneous. Simulation results are included to verify the theoretical analysis.
