How to obtain accurate channel state information(CSI)at the transmitter with less pilot overhead for frequency division duplexing(FDD) massive multiple-input multiple-output(MIMO)system is a challenging issue due to t...How to obtain accurate channel state information(CSI)at the transmitter with less pilot overhead for frequency division duplexing(FDD) massive multiple-input multiple-output(MIMO)system is a challenging issue due to the large number of antennas. To reduce the overwhelming pilot overhead, a hybrid orthogonal and non-orthogonal pilot distribution at the base station(BS),which is a generalization of the existing pilot distribution scheme,is proposed by exploiting the common sparsity of channel due to the compact antenna arrangement. Then the block sparsity for antennas with hybrid pilot distribution is derived respectively and can be used to obtain channel impulse response. By employing the theoretical analysis of block sparse recovery, the total coherence criterion is proposed to optimize the sensing matrix composed by orthogonal pilots. Due to the huge complexity of optimal pilot acquisition, a genetic algorithm based pilot allocation(GAPA) algorithm is proposed to acquire optimal pilot distribution locations with fast convergence. Furthermore, the Cramer Rao lower bound is derived for non-orthogonal pilot-based channel estimation and can be asymptotically approached by the prior support set, especially when the optimized pilot is employed.展开更多
A hybrid pilots assisted channel estimation algorithm for multiple input multiple output（MIMO） orthogonal frequency division multiplexing（OFDM） systems under low signal-to-noise ratio（SNR） and arbitrary Doppler ...A hybrid pilots assisted channel estimation algorithm for multiple input multiple output（MIMO） orthogonal frequency division multiplexing（OFDM） systems under low signal-to-noise ratio（SNR） and arbitrary Doppler spread scenarios is proposed.Motivated by the dissatisfactory performance of the optimal pilots（OPs） designed under static channels over multiple OFDM symbols imposed by fast fading channels,the proposed scheme first assumes that the virtual pilot tones superimposed at data locations over specific subcarriers are transmitted from all antennas,then the virtual received pilot signals at the corresponding locations can be obtained by making full use of the time and frequency domain correlations of the frequency responses of the time varying dispersive fading channels and the received signals at pilot subcarriers,finally the channel parameters are derived from the combination of the real and virtual received pilot signals over one OFDM symbol based on least square（LS） criterion.Simulation results illustrate that the proposed method is insensitive to Doppler spread and can effectively ameliorate the mean square error（MSE） floor inherent to the previous method,meanwhile its performance outmatches that of OPs at low SNR region under static channels.展开更多
The phenomenological theory of sedimentation-thickening processes predicts the settling behavior of a flocculated suspension in dependence of two functions, the batch flux density function and the effective solid stre...The phenomenological theory of sedimentation-thickening processes predicts the settling behavior of a flocculated suspension in dependence of two functions, the batch flux density function and the effective solid stress. These functions were determined using batch settling tests. The governing equations for sedimentation were then solved numerically for these functions and the predictions were compared to the experimental results from pilot scale thickener tests. Firstly, the continuous tests were performed in the plexiglass pilot thickener at different feed flow rates and discharge rates and the solid volume fraction of discharge, the bed height and the time were recorded for each condition. These tests were also simulated and it was observed that there is a good agreement between the results of continuous tests and the results of dynamic simulation. Secondly, the discontinuous tests were performed in the plexiglass pilot thickener at different feed flow rates with a discharge rate of zero. The bed formation rate was determined for each condition. These tests were also simulated and it was observed that there is a good agreement between the results of discontinuous tests and the results of simulation.展开更多
Pilot contamination can spoil the accuracy of channel estimation and then has become one of the key problems influencing the performance of massive multiple input multiple output(MIMO)systems.This paper proposes a met...Pilot contamination can spoil the accuracy of channel estimation and then has become one of the key problems influencing the performance of massive multiple input multiple output(MIMO)systems.This paper proposes a method based on cell classification and users grouping to mitigate the pilot contamination in multi-cell massive MIMO systems and improve the spectral efficiency.The pilots of the terminals are allocated onebit orthogonal identifier to diminish the cell categories by the operation of exclusive OR(XOR).At the same time,the users are divided into edge user groups and central user groups according to the large-scale fading coefficients by the clustering algorithm,and different pilot sequences are assigned to different groups.The simulation results show that the proposed method can effectively improve the spectral efficiency of multi-cell massive MIMO systems.展开更多
Background: The Occupational Safety and Health Council(OSHC) is committed to improve the safety performance of the high risk construction industry.In the past three years,about 40% of the fatal accidents in the constr...Background: The Occupational Safety and Health Council(OSHC) is committed to improve the safety performance of the high risk construction industry.In the past three years,about 40% of the fatal accidents in the construction industry were related to Renovation,Maintenance,Alteration and Addition(RMAA).Due to the poor safety record,some of the RMAA contractors have difficulty in obtaining the Employees' Compensation Insurance(ECI) cover in the market,or if they could obtain the ECI,the premium rate would be exceedingly high.In view of this,the OSHC,the Labour Department jointly launched"OSH Star Enterprise-Pilot Scheme on Safety Accreditation for the RMAA Industry",which prompts the industry to take practicable safety measures to improve the safety of working environment and reduce occupational injuries.The program also helps the stakeholders and insurers to identify safety-conscious contractors and thereby provide them with a favourable premium rate under the Employees' Compensation Insurance Residual Scheme(ECIRS).Objectives: The OSHC launches the Pilot Scheme to improve the safety performance of the RMAA industry through providing safety training,subsidizing enterprise to purchase safety equipment and providing safety audit.We also use financial incentive to encourage RMAA enterprises to join the Pilot Scheme-for those who are accredited as "OSH Star Enterprise"could receive a premium discount from the ERIRS when obtaining the ECI.The scheme also differentiates those safety-conscious and law-abiding enterprises from the poor performers,which helps the industry and public identifying the RMAA contractors who pay attention to work safety.Methods: The Pilot Scheme targets RMAA enterprises that employ less than 50 employees in Hong Kong.A three-pronged approach is used to improve the safety performance of the RMAA industry: the Pilot Scheme provides(1) financial support for the RMAA contractors to buy a transportable temporary anchor device and full body safety harness and its anchor system;(2) safety training on RMAA work safety and safety & health supervisor course;and(3) safety audit.Results: Enterprises that successfully pass the safety audit and satisfied the Scheme requirements will be accredited as"OSH Star Enterprise",which will be valid for two years.These enterprises can also be upgraded to"OSH Gold Star Enterprise"based on their continuous improvement in safety performance.OSHC will set up a register of OSH-accredited enterprises in RMAA works for reference of the public to facilitate their choosing of accredited contractors.The Employees' Compensation Insurance Residual Scheme Bureau will provide privileged premium rate for enterprises with OSH accreditation."OSH Star Enterprise"could enjoy 40% discounts when joining their insurance scheme.For example,a skilled worker's annual premium can be reduced by about HK $ 36,000.While,the "OSH Gold Star Enterprise"could enjoy 50% discounts when joining their insurance scheme,which means a skilled worker's annual premium can be reduced up to HK $ 45,000.Achievements: This Pilot Scheme offers practical assistance as well as attractive financial incentives for the RMAA industry to improve their safety performance.The Employees'Compensation Insurance Residual Scheme provides premium discounts for enterprises that have a good safety record.It provides incentive for RMAA contractors to actively participate in the Pilot Scheme.The Scheme demonstrates that by providing a safe working environment and appropriate personal protective equipment to workers,the enterprise not only helps to reduce the accident rate of the industry but also receive an economic return.The Pilot Scheme bridges stakeholders of RMAA industry,the government and the insurance industry creating an "all-win"situation.This partnership approach to prevent injuries and accidents in the construction industry could be an effective model for other industries.展开更多
To solve the flight safety problem caused by nonlinear instabilities（category II pilot induced oscillations, PIOs） of the closed-loop pilot-vehicle system with rate-limiting actuator, the antiwindup（AW） compensati...To solve the flight safety problem caused by nonlinear instabilities（category II pilot induced oscillations, PIOs） of the closed-loop pilot-vehicle system with rate-limiting actuator, the antiwindup（AW） compensation method to avoid category II PIOs is investigated. Firstly, the AW compensation method originally used for controlling input magnitude limited system is introduced, then this method is extended for controlling input rate-limiting system through a circle criterion theorem. Secondly, the establishment of the AW compensator is transformed into the solving of linear matrix inequalities. Finally, an AW compensator establishment algorithm for the closed-loop pilot-vehicle system with the rate-limiting actuator is obtained. The effectiveness of the AW compensation method to avoid category II PIOs is validated by time-domain simulations,and compared with rate-limited feedback（RLF） command rate compensation method. The results show that the AW compensation method can effectively suppress category II PIOs and maintain the nominal performance when the closed-loop pilot-vehicle system is normal. Unlike the command rate compensator which works upon system uninterruptedly, the AW compensation method affects the closed-loop pilot-vehicle system only when the rate-limiting of actuator is activated, so it is a novel PIO avoidance method.展开更多
The influence of cells groupings factor to the performance of the cells groupings time-shift pilot scheme is researched for the multiple cells large scale antennas systems（LSAS）. The former researches have confirmed...The influence of cells groupings factor to the performance of the cells groupings time-shift pilot scheme is researched for the multiple cells large scale antennas systems（LSAS）. The former researches have confirmed that the cells groupings time-shift pilots scheme is effective to reduce inter-cell interference, especially pilot contamination, which results from the pilot reuse in adjacent cells. However, they have not specified reasonable cells groupings factor, which plays a critical role in the general performance of the LSAS. Therefore, this problem is researched in details. The time for reverse-link data transmission will be compressed, when the groupings factor surpasses a certain range. Thus it is not always beneficial to increase the cells groupings factor without limitation. Furthermore,a reasonable cells groupings factor is deduced from the perspective of optimization to enhance the system performance. Simulations verify the proposed cell grouping factor.展开更多
Introduction-The cervical spine is subjected to injury frequently,especially among pilots who are usually on the condition of high acceleration.Injuries of the cervical spine will be potential risk of damage to the sp...Introduction-The cervical spine is subjected to injury frequently,especially among pilots who are usually on the condition of high acceleration.Injuries of the cervical spine will be potential risk of damage to the spinal cord,which could be result in life threatening展开更多
Pilot implementation proposed by the State Council should be taken as an incentive measure not an authorization of the State Council to local authorities.It is the outcome of the exercise of local legislative authorit...Pilot implementation proposed by the State Council should be taken as an incentive measure not an authorization of the State Council to local authorities.It is the outcome of the exercise of local legislative authority.So long as the pilot program does not conflict with the Constitution and other Laws,to enact local regulations about pilot implementation will be more conducive to the independent local development.展开更多
As the penetration of wind power into power grids increases,higher demands are made on the stability and protection of power systems.Unlike traditional synchronous generators,wind turbines are different on the short-c...As the penetration of wind power into power grids increases,higher demands are made on the stability and protection of power systems.Unlike traditional synchronous generators,wind turbines are different on the short-circuit and impedance characteristics,thus some problems exist in pilot protections of transmission lines connecting wind farms.When a single-phase fault occurs on a transmission line,the phase selector based on current-difference sudden-change may mistake the single-phase fault for a phase-to-phase fault.This paper studies the impedance characteristics of an asynchronous wind generator,and analyzes the behavior of a fault phase selector under different conditions.Then,the paper explains that inequality between positive and negative branch coefficients is the cause for the mal-operation of the fault phase selector.Finally,some simulations are done in MATLAB to validate analysis results.展开更多
针对现有信道估计方案导致正交时频空间(Orthogonal Time Frequency Space,OTFS)调制系统峰均功率比(Peak-to-Average Power Ratio,PAPR)高或频谱效率(Spectral Efficiency,SE)低的问题,提出一种多叠加导频的低PAPR、高SE信道估计方法...针对现有信道估计方案导致正交时频空间(Orthogonal Time Frequency Space,OTFS)调制系统峰均功率比(Peak-to-Average Power Ratio,PAPR)高或频谱效率(Spectral Efficiency,SE)低的问题,提出一种多叠加导频的低PAPR、高SE信道估计方法。发送端利用时域正交性和离散傅里叶域相位的随机性,在时延多普勒域中嵌入与数据相叠加的5导频符号的导频图案实现低PAPR,提高SE。接收端以数据符号与噪声之和的能量均值为基准,实现导频信号检测,同时根据每个导频的不同位置信息恢复出存在相位旋转的数据信号。基于能量准则,利用多个独立的接收信号进行联合信道估计,以降低数据符号的干扰,并采用消息传递算法进行数据恢复。仿真结果表明,该方法比单叠加导频信道估计的PAPR低,同时较嵌入式导频信道估计的SE提高约14.4%。展开更多
基金supported by the National Natural Science Foundation of China(61671176 61671173)the Fundamental Research Funds for the Center Universities(HIT.MKSTISP.2016 13)
文摘How to obtain accurate channel state information(CSI)at the transmitter with less pilot overhead for frequency division duplexing(FDD) massive multiple-input multiple-output(MIMO)system is a challenging issue due to the large number of antennas. To reduce the overwhelming pilot overhead, a hybrid orthogonal and non-orthogonal pilot distribution at the base station(BS),which is a generalization of the existing pilot distribution scheme,is proposed by exploiting the common sparsity of channel due to the compact antenna arrangement. Then the block sparsity for antennas with hybrid pilot distribution is derived respectively and can be used to obtain channel impulse response. By employing the theoretical analysis of block sparse recovery, the total coherence criterion is proposed to optimize the sensing matrix composed by orthogonal pilots. Due to the huge complexity of optimal pilot acquisition, a genetic algorithm based pilot allocation(GAPA) algorithm is proposed to acquire optimal pilot distribution locations with fast convergence. Furthermore, the Cramer Rao lower bound is derived for non-orthogonal pilot-based channel estimation and can be asymptotically approached by the prior support set, especially when the optimized pilot is employed.
基金supported by the National High Technology Research and Development Program of China (863 Program) (2007AA01Z288)the National Natural Science Foundation of China (60702057)+2 种基金the National Science Fund for Distinguished Young Scholars (60725105)the Program for Changjiang Scholars and Innovative Research Team in University (IRT0852)the Fundamental Research Projects,Xidian University (JY10000901030)
文摘A hybrid pilots assisted channel estimation algorithm for multiple input multiple output（MIMO） orthogonal frequency division multiplexing（OFDM） systems under low signal-to-noise ratio（SNR） and arbitrary Doppler spread scenarios is proposed.Motivated by the dissatisfactory performance of the optimal pilots（OPs） designed under static channels over multiple OFDM symbols imposed by fast fading channels,the proposed scheme first assumes that the virtual pilot tones superimposed at data locations over specific subcarriers are transmitted from all antennas,then the virtual received pilot signals at the corresponding locations can be obtained by making full use of the time and frequency domain correlations of the frequency responses of the time varying dispersive fading channels and the received signals at pilot subcarriers,finally the channel parameters are derived from the combination of the real and virtual received pilot signals over one OFDM symbol based on least square（LS） criterion.Simulation results illustrate that the proposed method is insensitive to Doppler spread and can effectively ameliorate the mean square error（MSE） floor inherent to the previous method,meanwhile its performance outmatches that of OPs at low SNR region under static channels.
文摘The phenomenological theory of sedimentation-thickening processes predicts the settling behavior of a flocculated suspension in dependence of two functions, the batch flux density function and the effective solid stress. These functions were determined using batch settling tests. The governing equations for sedimentation were then solved numerically for these functions and the predictions were compared to the experimental results from pilot scale thickener tests. Firstly, the continuous tests were performed in the plexiglass pilot thickener at different feed flow rates and discharge rates and the solid volume fraction of discharge, the bed height and the time were recorded for each condition. These tests were also simulated and it was observed that there is a good agreement between the results of continuous tests and the results of dynamic simulation. Secondly, the discontinuous tests were performed in the plexiglass pilot thickener at different feed flow rates with a discharge rate of zero. The bed formation rate was determined for each condition. These tests were also simulated and it was observed that there is a good agreement between the results of discontinuous tests and the results of simulation.
基金supported by the Scientific and Technological Innovation Foundation of Shunde Graduate School,USTB(BK19CF002).
文摘Pilot contamination can spoil the accuracy of channel estimation and then has become one of the key problems influencing the performance of massive multiple input multiple output(MIMO)systems.This paper proposes a method based on cell classification and users grouping to mitigate the pilot contamination in multi-cell massive MIMO systems and improve the spectral efficiency.The pilots of the terminals are allocated onebit orthogonal identifier to diminish the cell categories by the operation of exclusive OR(XOR).At the same time,the users are divided into edge user groups and central user groups according to the large-scale fading coefficients by the clustering algorithm,and different pilot sequences are assigned to different groups.The simulation results show that the proposed method can effectively improve the spectral efficiency of multi-cell massive MIMO systems.
文摘Background: The Occupational Safety and Health Council(OSHC) is committed to improve the safety performance of the high risk construction industry.In the past three years,about 40% of the fatal accidents in the construction industry were related to Renovation,Maintenance,Alteration and Addition(RMAA).Due to the poor safety record,some of the RMAA contractors have difficulty in obtaining the Employees' Compensation Insurance(ECI) cover in the market,or if they could obtain the ECI,the premium rate would be exceedingly high.In view of this,the OSHC,the Labour Department jointly launched"OSH Star Enterprise-Pilot Scheme on Safety Accreditation for the RMAA Industry",which prompts the industry to take practicable safety measures to improve the safety of working environment and reduce occupational injuries.The program also helps the stakeholders and insurers to identify safety-conscious contractors and thereby provide them with a favourable premium rate under the Employees' Compensation Insurance Residual Scheme(ECIRS).Objectives: The OSHC launches the Pilot Scheme to improve the safety performance of the RMAA industry through providing safety training,subsidizing enterprise to purchase safety equipment and providing safety audit.We also use financial incentive to encourage RMAA enterprises to join the Pilot Scheme-for those who are accredited as "OSH Star Enterprise"could receive a premium discount from the ERIRS when obtaining the ECI.The scheme also differentiates those safety-conscious and law-abiding enterprises from the poor performers,which helps the industry and public identifying the RMAA contractors who pay attention to work safety.Methods: The Pilot Scheme targets RMAA enterprises that employ less than 50 employees in Hong Kong.A three-pronged approach is used to improve the safety performance of the RMAA industry: the Pilot Scheme provides(1) financial support for the RMAA contractors to buy a transportable temporary anchor device and full body safety harness and its anchor system;(2) safety training on RMAA work safety and safety & health supervisor course;and(3) safety audit.Results: Enterprises that successfully pass the safety audit and satisfied the Scheme requirements will be accredited as"OSH Star Enterprise",which will be valid for two years.These enterprises can also be upgraded to"OSH Gold Star Enterprise"based on their continuous improvement in safety performance.OSHC will set up a register of OSH-accredited enterprises in RMAA works for reference of the public to facilitate their choosing of accredited contractors.The Employees' Compensation Insurance Residual Scheme Bureau will provide privileged premium rate for enterprises with OSH accreditation."OSH Star Enterprise"could enjoy 40% discounts when joining their insurance scheme.For example,a skilled worker's annual premium can be reduced by about HK $ 36,000.While,the "OSH Gold Star Enterprise"could enjoy 50% discounts when joining their insurance scheme,which means a skilled worker's annual premium can be reduced up to HK $ 45,000.Achievements: This Pilot Scheme offers practical assistance as well as attractive financial incentives for the RMAA industry to improve their safety performance.The Employees'Compensation Insurance Residual Scheme provides premium discounts for enterprises that have a good safety record.It provides incentive for RMAA contractors to actively participate in the Pilot Scheme.The Scheme demonstrates that by providing a safe working environment and appropriate personal protective equipment to workers,the enterprise not only helps to reduce the accident rate of the industry but also receive an economic return.The Pilot Scheme bridges stakeholders of RMAA industry,the government and the insurance industry creating an "all-win"situation.This partnership approach to prevent injuries and accidents in the construction industry could be an effective model for other industries.
基金supported by the National Basic Research Program(973Program)(2015CB755805)the National Natural Science Foundation of China(61374145)
文摘To solve the flight safety problem caused by nonlinear instabilities（category II pilot induced oscillations, PIOs） of the closed-loop pilot-vehicle system with rate-limiting actuator, the antiwindup（AW） compensation method to avoid category II PIOs is investigated. Firstly, the AW compensation method originally used for controlling input magnitude limited system is introduced, then this method is extended for controlling input rate-limiting system through a circle criterion theorem. Secondly, the establishment of the AW compensator is transformed into the solving of linear matrix inequalities. Finally, an AW compensator establishment algorithm for the closed-loop pilot-vehicle system with the rate-limiting actuator is obtained. The effectiveness of the AW compensation method to avoid category II PIOs is validated by time-domain simulations,and compared with rate-limited feedback（RLF） command rate compensation method. The results show that the AW compensation method can effectively suppress category II PIOs and maintain the nominal performance when the closed-loop pilot-vehicle system is normal. Unlike the command rate compensator which works upon system uninterruptedly, the AW compensation method affects the closed-loop pilot-vehicle system only when the rate-limiting of actuator is activated, so it is a novel PIO avoidance method.
基金supported by the National Natural Science Foundation of China(6110602261574013)
文摘The influence of cells groupings factor to the performance of the cells groupings time-shift pilot scheme is researched for the multiple cells large scale antennas systems（LSAS）. The former researches have confirmed that the cells groupings time-shift pilots scheme is effective to reduce inter-cell interference, especially pilot contamination, which results from the pilot reuse in adjacent cells. However, they have not specified reasonable cells groupings factor, which plays a critical role in the general performance of the LSAS. Therefore, this problem is researched in details. The time for reverse-link data transmission will be compressed, when the groupings factor surpasses a certain range. Thus it is not always beneficial to increase the cells groupings factor without limitation. Furthermore,a reasonable cells groupings factor is deduced from the perspective of optimization to enhance the system performance. Simulations verify the proposed cell grouping factor.
文摘Introduction-The cervical spine is subjected to injury frequently,especially among pilots who are usually on the condition of high acceleration.Injuries of the cervical spine will be potential risk of damage to the spinal cord,which could be result in life threatening
基金This paper is the initial result of“Research on Legal Issues Concerning Lawmaking and Decision Making about Pilot Implimentation”- A Scientific Research Innovation Program ( No. IO ZS136)Sponsored by key Disciplines of Administrative Jurisprudence of Shanghai Municipal Education Commission of Higher Education in the Construction of key Disciplines of Administrative Jurisprudence
文摘Pilot implementation proposed by the State Council should be taken as an incentive measure not an authorization of the State Council to local authorities.It is the outcome of the exercise of local legislative authority.So long as the pilot program does not conflict with the Constitution and other Laws,to enact local regulations about pilot implementation will be more conducive to the independent local development.
基金supported by National Basic Research Program of China(No.2009CB219704)National Natural Science Foundation of China (No. 50977061)National Natural Science Foundation of Tianjin City (No. 11JCYBJC07600)
文摘As the penetration of wind power into power grids increases,higher demands are made on the stability and protection of power systems.Unlike traditional synchronous generators,wind turbines are different on the short-circuit and impedance characteristics,thus some problems exist in pilot protections of transmission lines connecting wind farms.When a single-phase fault occurs on a transmission line,the phase selector based on current-difference sudden-change may mistake the single-phase fault for a phase-to-phase fault.This paper studies the impedance characteristics of an asynchronous wind generator,and analyzes the behavior of a fault phase selector under different conditions.Then,the paper explains that inequality between positive and negative branch coefficients is the cause for the mal-operation of the fault phase selector.Finally,some simulations are done in MATLAB to validate analysis results.
文摘针对现有信道估计方案导致正交时频空间(Orthogonal Time Frequency Space,OTFS)调制系统峰均功率比(Peak-to-Average Power Ratio,PAPR)高或频谱效率(Spectral Efficiency,SE)低的问题,提出一种多叠加导频的低PAPR、高SE信道估计方法。发送端利用时域正交性和离散傅里叶域相位的随机性,在时延多普勒域中嵌入与数据相叠加的5导频符号的导频图案实现低PAPR,提高SE。接收端以数据符号与噪声之和的能量均值为基准,实现导频信号检测,同时根据每个导频的不同位置信息恢复出存在相位旋转的数据信号。基于能量准则,利用多个独立的接收信号进行联合信道估计,以降低数据符号的干扰,并采用消息传递算法进行数据恢复。仿真结果表明,该方法比单叠加导频信道估计的PAPR低,同时较嵌入式导频信道估计的SE提高约14.4%。
