Integer-valued data are frequently encountered in time series studies.A pth-order mixed dependence-driven random coefficient integervalued autoregressive time series model(Po-MDDRCINAR(p))in view of binomial and negat...Integer-valued data are frequently encountered in time series studies.A pth-order mixed dependence-driven random coefficient integervalued autoregressive time series model(Po-MDDRCINAR(p))in view of binomial and negative binomial operators,where the innovation sequence follows a Poisson distribution,is investigated to provide meaningful theoretical explanations.Strict stationary and ergodicity of the model are demonstrated.Furthermore,the conditional leastsquares and conditional maximum-likelihood methods are adopted to estimate the parameters,where the asymptotic characterization of the estimators is derived.Finite-sample properties of the conditional maximum-likelihood estimator are examined in relation to the widely used conditional least-squares estimator.The conclusion is that,if the Poisson assumption of the innovation sequence can be justified,conditional maximum-likelihood method performs better in terms of MADE and MSE.Finally,the practical performance of the model is illustrated by a set of COVID-19 data of suspected cases in China with a comparison with relevant models that exist so far in the literature.展开更多
Channel estimation and synchronization are crucial problems in coherent ultra wideband （UWB） receiver designs. A joint maximum-likelihood （ML） and minimum-mean-square-error （MMSE） channel esti- mation scheme was...Channel estimation and synchronization are crucial problems in coherent ultra wideband （UWB） receiver designs. A joint maximum-likelihood （ML） and minimum-mean-square-error （MMSE） channel esti- mation scheme was developed for more precise channel estimates based on the assumption of exponential multipath decay. The performance improvement was analyzed theoretically with a computer simulation using IEEE 802.15.3a ultra-wideband channel models. Theoretical and simulation results show that the scheme further improves the estimation performance of channel gains and multipath delays compared with the traditional ML channel estimator.展开更多
X-ray pulsar navigation(XPNAV) is an attractive method for autonomous navigation of deep space in the future. Currently, techniques for estimating the phase of X-ray pulsar radiation involve the maximization of the ge...X-ray pulsar navigation(XPNAV) is an attractive method for autonomous navigation of deep space in the future. Currently, techniques for estimating the phase of X-ray pulsar radiation involve the maximization of the general non-convex object functions based on the average profile from the epoch folding method. This results in the suppression of useful information and highly complex computation. In this paper, a new maximum likelihood(ML) phase estimation method that directly utilizes the measured time of arrivals(TOAs) is presented. The X-ray pulsar radiation will be treated as a cyclo-stationary process and the TOAs of the photons in a period will be redefined as a new process, whose probability distribution function is the normalized standard profile of the pulsar. We demonstrate that the new process is equivalent to the generally used Poisson model. Then, the phase estimation problem is recast as a cyclic shift parameter estimation under the ML estimation, and we also put forward a parallel ML estimation method to improve the ML solution. Numerical simulation results show that the estimator described here presents a higher precision and reduces the computational complexity compared with currently used estimators.展开更多
随着风电渗透率的持续上升,电力系统的惯量水平显著下降,对系统频率稳定性构成了新的挑战。为有效评估风电并网情况下电力系统节点惯量的变化,提出了一种基于受控自回归滑动平均(autoregressive moving average with exogenous variable...随着风电渗透率的持续上升,电力系统的惯量水平显著下降,对系统频率稳定性构成了新的挑战。为有效评估风电并网情况下电力系统节点惯量的变化,提出了一种基于受控自回归滑动平均(autoregressive moving average with exogenous variable,ARMAX)模型的改进最大似然估计(maximum likelihood estimation,MLE)参数辨识方法对系统机组直接相连节点进行惯量评估。首先,构建ARMAX模型对发电机组直接相连节点的动态特性进行建模,并利用改进MLE对模型参数进行辨识,以评估与机组直接相连的节点惯量。然后,基于k-means聚类算法对发电机组节点惯量进行分区,计算得到系统区域惯量和中心频率,并进一步对非发电机组节点频率进行自适应多项式拟合计算,得到其系统节点惯量。最后,搭建IEEE39含风力发电机组节点系统,绘制热力图直观展示电力系统节点和区域的惯量分布,验证了所提改进方法的有效性。该方法有助于精准识别系统中不同节点的动态响应特性,为风电并网系统的分析和规划提供了有力支持。展开更多
【目的】设计一种基于FIML和DAE的填充缺失值的方法,即聚类全信息选择性过滤编码器数据填补算法(clustering-based comprehensive information selective filtering encoder data imputation algorithm,CFSM-DAE),为水稻种质资源缺失数...【目的】设计一种基于FIML和DAE的填充缺失值的方法,即聚类全信息选择性过滤编码器数据填补算法(clustering-based comprehensive information selective filtering encoder data imputation algorithm,CFSM-DAE),为水稻种质资源缺失数据进行填充。【方法】利用聚类辅助避免数据异常值对算法的影响,采用选择性过滤层用于识别高质量估算、减少低质量估算的影响。传统的DAE框架通常没有选择性过滤层,所有的估算值都被视为同等重要,无法区分高质量和低质量的估算值。为了进一步提高估算精度,研究采用集成框架将全信息最大似然性(FIML)与多对抗性自编码器(DAE)结合的方法(CFSM-DAE),在选择性过滤层基础上,自适应填充,即当估算值不符合设定阈值时,采用FIML填充策略以确保填充结果的稳定性和精确度,从而进一步来提高整体估算精度。在3种缺失数据机制(随机缺失(MAR)、完全随机缺失(MCAR)和非随机缺失(MNAR))下对模拟数据和实际水稻种质资源数据集进行研究,将CFSM-DAE方法与多种常用填充算法比较(全信息最大似然性(FIML)、对抗自编码器(DAE)、K近邻填充(KNN)、随机森林(RF)、链式方程多重插补(MICE))。【结果】CFSM-DAE在模拟数据上的表现为S_(RME)=0.0676,E_(MA)=0.0093,R^(2)=0.9958;在水稻种质资源数据上的表现为S_(RME)=0.0395,E_(MA)=0.0078,R^(2)=0.8913。相比之下,其他算法如DAE在这两类数据下的SRME表现分别为0.8896和0.7707;KNN算法的EMA表现分别为0.1183和0.1305;FIML算法的R2表现为0.3382和0.7321。因此,CFSM-DAE在多个评价指标上相较于其他算法都表现出了一定的提升,CFSM-DAE在模拟数据和水稻种质资源数据的表现优于其他算法。【结论】CFSM-DAE方法通过结合聚类、选择性过滤和全信息最大似然性等策略,显著提高了水稻种质资源数据中缺失值的填补精度,展示了其在处理复杂缺失值问题上的有效性和潜力。展开更多
基金supported by Fundamental Research Program of Shanxi Province[Grant No.202103021223084]National Natural Science Foundation of China[Grant No.12271231]+1 种基金Natural Science Foundation ofHenan Province[GrantNo.222300420127]2023Graduate Education Innovation Program Various Projects and Special Funds for Innovation and Entrepreneurship[Grant No.RC2300003332].
文摘Integer-valued data are frequently encountered in time series studies.A pth-order mixed dependence-driven random coefficient integervalued autoregressive time series model(Po-MDDRCINAR(p))in view of binomial and negative binomial operators,where the innovation sequence follows a Poisson distribution,is investigated to provide meaningful theoretical explanations.Strict stationary and ergodicity of the model are demonstrated.Furthermore,the conditional leastsquares and conditional maximum-likelihood methods are adopted to estimate the parameters,where the asymptotic characterization of the estimators is derived.Finite-sample properties of the conditional maximum-likelihood estimator are examined in relation to the widely used conditional least-squares estimator.The conclusion is that,if the Poisson assumption of the innovation sequence can be justified,conditional maximum-likelihood method performs better in terms of MADE and MSE.Finally,the practical performance of the model is illustrated by a set of COVID-19 data of suspected cases in China with a comparison with relevant models that exist so far in the literature.
基金Supported by the National Natural Science Foundation of China (No. 90204001)
文摘Channel estimation and synchronization are crucial problems in coherent ultra wideband （UWB） receiver designs. A joint maximum-likelihood （ML） and minimum-mean-square-error （MMSE） channel esti- mation scheme was developed for more precise channel estimates based on the assumption of exponential multipath decay. The performance improvement was analyzed theoretically with a computer simulation using IEEE 802.15.3a ultra-wideband channel models. Theoretical and simulation results show that the scheme further improves the estimation performance of channel gains and multipath delays compared with the traditional ML channel estimator.
基金Project supported by the National Natural Science Foundation of China(No.61172138)the Fundamental Research Funds for the Central Universities(Nos.K5051302015 and K5051302040)+1 种基金the Natural Science Basic Research Plan in Shaanxi Province of China(No.2013JQ8040)the Research Fund for the Doctoral Program of Higher Education of China(No.20130203120004)
文摘X-ray pulsar navigation(XPNAV) is an attractive method for autonomous navigation of deep space in the future. Currently, techniques for estimating the phase of X-ray pulsar radiation involve the maximization of the general non-convex object functions based on the average profile from the epoch folding method. This results in the suppression of useful information and highly complex computation. In this paper, a new maximum likelihood(ML) phase estimation method that directly utilizes the measured time of arrivals(TOAs) is presented. The X-ray pulsar radiation will be treated as a cyclo-stationary process and the TOAs of the photons in a period will be redefined as a new process, whose probability distribution function is the normalized standard profile of the pulsar. We demonstrate that the new process is equivalent to the generally used Poisson model. Then, the phase estimation problem is recast as a cyclic shift parameter estimation under the ML estimation, and we also put forward a parallel ML estimation method to improve the ML solution. Numerical simulation results show that the estimator described here presents a higher precision and reduces the computational complexity compared with currently used estimators.
文摘随着风电渗透率的持续上升,电力系统的惯量水平显著下降,对系统频率稳定性构成了新的挑战。为有效评估风电并网情况下电力系统节点惯量的变化,提出了一种基于受控自回归滑动平均(autoregressive moving average with exogenous variable,ARMAX)模型的改进最大似然估计(maximum likelihood estimation,MLE)参数辨识方法对系统机组直接相连节点进行惯量评估。首先,构建ARMAX模型对发电机组直接相连节点的动态特性进行建模,并利用改进MLE对模型参数进行辨识,以评估与机组直接相连的节点惯量。然后,基于k-means聚类算法对发电机组节点惯量进行分区,计算得到系统区域惯量和中心频率,并进一步对非发电机组节点频率进行自适应多项式拟合计算,得到其系统节点惯量。最后,搭建IEEE39含风力发电机组节点系统,绘制热力图直观展示电力系统节点和区域的惯量分布,验证了所提改进方法的有效性。该方法有助于精准识别系统中不同节点的动态响应特性,为风电并网系统的分析和规划提供了有力支持。
文摘【目的】设计一种基于FIML和DAE的填充缺失值的方法,即聚类全信息选择性过滤编码器数据填补算法(clustering-based comprehensive information selective filtering encoder data imputation algorithm,CFSM-DAE),为水稻种质资源缺失数据进行填充。【方法】利用聚类辅助避免数据异常值对算法的影响,采用选择性过滤层用于识别高质量估算、减少低质量估算的影响。传统的DAE框架通常没有选择性过滤层,所有的估算值都被视为同等重要,无法区分高质量和低质量的估算值。为了进一步提高估算精度,研究采用集成框架将全信息最大似然性(FIML)与多对抗性自编码器(DAE)结合的方法(CFSM-DAE),在选择性过滤层基础上,自适应填充,即当估算值不符合设定阈值时,采用FIML填充策略以确保填充结果的稳定性和精确度,从而进一步来提高整体估算精度。在3种缺失数据机制(随机缺失(MAR)、完全随机缺失(MCAR)和非随机缺失(MNAR))下对模拟数据和实际水稻种质资源数据集进行研究,将CFSM-DAE方法与多种常用填充算法比较(全信息最大似然性(FIML)、对抗自编码器(DAE)、K近邻填充(KNN)、随机森林(RF)、链式方程多重插补(MICE))。【结果】CFSM-DAE在模拟数据上的表现为S_(RME)=0.0676,E_(MA)=0.0093,R^(2)=0.9958;在水稻种质资源数据上的表现为S_(RME)=0.0395,E_(MA)=0.0078,R^(2)=0.8913。相比之下,其他算法如DAE在这两类数据下的SRME表现分别为0.8896和0.7707;KNN算法的EMA表现分别为0.1183和0.1305;FIML算法的R2表现为0.3382和0.7321。因此,CFSM-DAE在多个评价指标上相较于其他算法都表现出了一定的提升,CFSM-DAE在模拟数据和水稻种质资源数据的表现优于其他算法。【结论】CFSM-DAE方法通过结合聚类、选择性过滤和全信息最大似然性等策略,显著提高了水稻种质资源数据中缺失值的填补精度,展示了其在处理复杂缺失值问题上的有效性和潜力。
