A residual carrier frequency offset （CFO） estimation scheme is proposed for the uplink of orthogonal frequency division multiple access （OFDMA） systems. Multiple access interference caused by CFOs in the uplink is...A residual carrier frequency offset （CFO） estimation scheme is proposed for the uplink of orthogonal frequency division multiple access （OFDMA） systems. Multiple access interference caused by CFOs in the uplink is investigated, as it severely affects the performance of a classical maximum likelihood （ML） frequency estimator. By the use of the estimated CFOs of the active users, the linear maximum mean square error （LMMSE） equalization is performed before the ML frequency estimator for the interference cancellation, which can help to sufficiently improve the estimation accuracy for the residual CFO of the incoming user. Analysis and simulations show that the modified ML estimator provides a tradeoff between estimation accuracy and computational complexity caused by the LMMSE interference cancellation, and the proposed method allows OFDMA systems flexibly allocating subcarriers to users.展开更多
The inverse of expected error variance is utilized to determine weights of individual ensemble members based on the THORPEX （The Observing System Research and Predictability Experiment） Interactive Grand Global Ense...The inverse of expected error variance is utilized to determine weights of individual ensemble members based on the THORPEX （The Observing System Research and Predictability Experiment） Interactive Grand Global Ensemble （TIGGE） forecast datasets. The weights of all ensemble members are thus calculated for summer 2012, with the NCEP final operational global analysis （FNL） data as the truth. Based on the weights of all ensemble members, the variable weighted ensemble mean （VWEM） of temperature of summer 2013 is derived and compared with that from the simple equally weighted ensemble mean. The results show that VWEM has lower root-mean-square error （RMSE） as well as absolute error, and has improved the temperature prediction accuracy. The improvements are quite notable over the Tibetan Plateau and its surrounding areas; specifically, a relative improvement rate of RMSE of more than 24% in 2-m temperature is demonstrated. Moreover, the improvement rates vary slightly with the pre- diction lead-time （24-96 h）. It is suggested that the VWEM approach be employed in operational ensemble predic- tion to provide guidance for weather forecasting and climate prediction.展开更多
基金Supported by the National High Technology Research and Development Programme of China （No. 2009AA011501）, National Basic Research Program of China （No. 2007CB310608）, the Fundamental Research Funds for the Central Universities in China, and China Postdoctoral Science Foundation funded project.
文摘A residual carrier frequency offset （CFO） estimation scheme is proposed for the uplink of orthogonal frequency division multiple access （OFDMA） systems. Multiple access interference caused by CFOs in the uplink is investigated, as it severely affects the performance of a classical maximum likelihood （ML） frequency estimator. By the use of the estimated CFOs of the active users, the linear maximum mean square error （LMMSE） equalization is performed before the ML frequency estimator for the interference cancellation, which can help to sufficiently improve the estimation accuracy for the residual CFO of the incoming user. Analysis and simulations show that the modified ML estimator provides a tradeoff between estimation accuracy and computational complexity caused by the LMMSE interference cancellation, and the proposed method allows OFDMA systems flexibly allocating subcarriers to users.
基金Supported by the National Natural Science Foundation of China(41405006 and 91224004)Meteorological Key Technology Integration and Application Program(CMAGJ2015M85)+2 种基金National Key Technology Research and Development Program(2015BAK10B03)China Meteorological Administration Special Public Welfare Research Fund(GYHY201506002)Basic Research Fund of the Chinese Academy of Meteorological Sciences(2014R016 and 2015Z003)
文摘The inverse of expected error variance is utilized to determine weights of individual ensemble members based on the THORPEX （The Observing System Research and Predictability Experiment） Interactive Grand Global Ensemble （TIGGE） forecast datasets. The weights of all ensemble members are thus calculated for summer 2012, with the NCEP final operational global analysis （FNL） data as the truth. Based on the weights of all ensemble members, the variable weighted ensemble mean （VWEM） of temperature of summer 2013 is derived and compared with that from the simple equally weighted ensemble mean. The results show that VWEM has lower root-mean-square error （RMSE） as well as absolute error, and has improved the temperature prediction accuracy. The improvements are quite notable over the Tibetan Plateau and its surrounding areas; specifically, a relative improvement rate of RMSE of more than 24% in 2-m temperature is demonstrated. Moreover, the improvement rates vary slightly with the pre- diction lead-time （24-96 h）. It is suggested that the VWEM approach be employed in operational ensemble predic- tion to provide guidance for weather forecasting and climate prediction.
