Orthogonal frequency division multiplexing (OFDM) is a strong candidate for the next generation wireless communica-tion. But the frequency offset between the local oscillators at the transmitter and receiver causes a ...Orthogonal frequency division multiplexing (OFDM) is a strong candidate for the next generation wireless communica-tion. But the frequency offset between the local oscillators at the transmitter and receiver causes a single frequency offset in the signal, while a time-varying channel can cause a spread of frequency offsets known as the Doppler spread. Frequency offsets ruin the orthogonal of OFDM sub-carriers and cause inter-carrier interference (ICI), therefore, quickly diminishing the performance of the system. A novel all phase OFDM (AP-OFDM) system is established. APFFT is introduced for the first time to overcome ICI aroused by carrier frequency offset (CFO) in OFDM systems. This scheme makes use of APFFT in time domain and zero inserting in frequency domain to reduce the amount of ICI gener-ated as a result of frequency offset, with little additional computational complexity. At the same time, the proposed sys-tem has zero phase error. It is proved to be correct and effective in mathematics. The simulation results indicate that AP-OFDM system has a better performance than conventional OFDM system.展开更多
In forest ecosystem studies,tree stem structure variables(SSVs)proved to be an essential kind of parameters,and now simultaneously deriving SSVs of as many kinds as possible at large scales is preferred for enhancing ...In forest ecosystem studies,tree stem structure variables(SSVs)proved to be an essential kind of parameters,and now simultaneously deriving SSVs of as many kinds as possible at large scales is preferred for enhancing the frontier studies on marcoecosystem ecology and global carbon cycle.For this newly emerging task,satellite imagery such as WorldView-2 panchromatic images(WPIs)is used as a potential solution for co-prediction of tree-level multifarious SSVs,with static terrestrial laser scanning(TLS)assumed as a‘bridge’.The specific operation is to pursue the allometric relationships between TLS-derived SSVs and WPI-derived feature parameters,and regression analyses with one or multiple explanatory variables are applied to deduce the prediction models(termed as Model1s and Model2s).In the case of Picea abies,Pinus sylvestris,Populus tremul and Quercus robur in a boreal forest,tests showed that Model1s and Model2s for different tree species can be derived(e.g.the maximum R^(2)=0.574 for Q.robur).Overall,this study basically validated the algorithm proposed for co-prediction of multifarious SSVs,and the contribution is equivalent to developing a viable solution for SSV-estimation upscaling,which is useful for large-scale investigations of forest understory,macroecosystem ecology,global vegetation dynamics and global carbon cycle.展开更多
文摘Orthogonal frequency division multiplexing (OFDM) is a strong candidate for the next generation wireless communica-tion. But the frequency offset between the local oscillators at the transmitter and receiver causes a single frequency offset in the signal, while a time-varying channel can cause a spread of frequency offsets known as the Doppler spread. Frequency offsets ruin the orthogonal of OFDM sub-carriers and cause inter-carrier interference (ICI), therefore, quickly diminishing the performance of the system. A novel all phase OFDM (AP-OFDM) system is established. APFFT is introduced for the first time to overcome ICI aroused by carrier frequency offset (CFO) in OFDM systems. This scheme makes use of APFFT in time domain and zero inserting in frequency domain to reduce the amount of ICI gener-ated as a result of frequency offset, with little additional computational complexity. At the same time, the proposed sys-tem has zero phase error. It is proved to be correct and effective in mathematics. The simulation results indicate that AP-OFDM system has a better performance than conventional OFDM system.
基金This work was financially supported in part by the National Natural Science Foundation of China[grant numbers 41471281 and 31670718]in part by the SRF for ROCS,SEM,China.
文摘In forest ecosystem studies,tree stem structure variables(SSVs)proved to be an essential kind of parameters,and now simultaneously deriving SSVs of as many kinds as possible at large scales is preferred for enhancing the frontier studies on marcoecosystem ecology and global carbon cycle.For this newly emerging task,satellite imagery such as WorldView-2 panchromatic images(WPIs)is used as a potential solution for co-prediction of tree-level multifarious SSVs,with static terrestrial laser scanning(TLS)assumed as a‘bridge’.The specific operation is to pursue the allometric relationships between TLS-derived SSVs and WPI-derived feature parameters,and regression analyses with one or multiple explanatory variables are applied to deduce the prediction models(termed as Model1s and Model2s).In the case of Picea abies,Pinus sylvestris,Populus tremul and Quercus robur in a boreal forest,tests showed that Model1s and Model2s for different tree species can be derived(e.g.the maximum R^(2)=0.574 for Q.robur).Overall,this study basically validated the algorithm proposed for co-prediction of multifarious SSVs,and the contribution is equivalent to developing a viable solution for SSV-estimation upscaling,which is useful for large-scale investigations of forest understory,macroecosystem ecology,global vegetation dynamics and global carbon cycle.
