Low Earth Orbit(LEO)multibeam satellites will be widely used in the next generation of satellite communication systems,whose inter-beam interference will inevitably limit the performance of the whole system.Nonlinear ...Low Earth Orbit(LEO)multibeam satellites will be widely used in the next generation of satellite communication systems,whose inter-beam interference will inevitably limit the performance of the whole system.Nonlinear precoding such as Tomlinson-Harashima precoding(THP)algorithm has been proved to be a promising technology to solve this problem,which has smaller noise amplification effect compared with linear precoding.However,the similarity of different user channels(defined as channel correlation)will degrade the performance of THP algorithm.In this paper,we qualitatively analyze the inter-beam interference in the whole process of LEO satellite over a specific coverage area,and the impact of channel correlation on Signal-to-Noise Ratio(SNR)of receivers when THP is applied.One user grouping algorithm is proposed based on the analysis of channel correlation,which could decrease the number of users with high channel correlation in each precoding group,thus improve the performance of THP.Furthermore,our algorithm is designed under the premise of co-frequency deployment and orthogonal frequency division multiplexing(OFDM),which leads to more users under severe inter-beam interference compared to the existing research on geostationary orbit satellites broadcasting systems.Simulation results show that the proposed user grouping algorithm possesses higher channel capacity and better bit error rate(BER)performance in high SNR conditions relative to existing works.展开更多
The ability to quantify optical properties(i.e.,absorption and scattering)of strongly turbid media has major implications on the characterization of biological tissues,fluid fields,and many others.However,there are fe...The ability to quantify optical properties(i.e.,absorption and scattering)of strongly turbid media has major implications on the characterization of biological tissues,fluid fields,and many others.However,there are few methods that can provide wide-field quantification of optical properties,and none is able to perform quantitative optical property imaging with high-speed(e.g.,kilohertz)capabilities.Here we develop a new imaging modality termed halftone spatial frequency domain imaging(halftone-SFDI),which is approximately two orders of magnitude faster than the state-of-the-art,and provides kilohertz high-speed,label-free,non-contact,wide-field quantification for the optical properties of strongly turbid media.This method utilizes halftone binary patterned illumination to target the spatial frequency response of turbid media,which is then mapped to optical properties using model-based analysis.We validate the halftone-SFDI on an array of phantoms with a wide range of optical properties as well as in vivo human tissue.We demonstrate with an in vivo rat brain cortex imaging study,and show that halftone-SFDI can longitudinally monitor the absolute concentration as well as spatial distribution of functional chromophores in tissue.We also show that halftone-SFDI can spatially map dual-wavelength optical properties of a highly dynamic flow field at kilohertz speed.Together,these results highlight the potential of halftone-SFDI to enable new capabilities in fundamental research and translational studies including brain science and fluid dynamics.展开更多
基金supported by the Key R&D Project of the Ministry of Science and Technology of China(2020YFB1808005)。
文摘Low Earth Orbit(LEO)multibeam satellites will be widely used in the next generation of satellite communication systems,whose inter-beam interference will inevitably limit the performance of the whole system.Nonlinear precoding such as Tomlinson-Harashima precoding(THP)algorithm has been proved to be a promising technology to solve this problem,which has smaller noise amplification effect compared with linear precoding.However,the similarity of different user channels(defined as channel correlation)will degrade the performance of THP algorithm.In this paper,we qualitatively analyze the inter-beam interference in the whole process of LEO satellite over a specific coverage area,and the impact of channel correlation on Signal-to-Noise Ratio(SNR)of receivers when THP is applied.One user grouping algorithm is proposed based on the analysis of channel correlation,which could decrease the number of users with high channel correlation in each precoding group,thus improve the performance of THP.Furthermore,our algorithm is designed under the premise of co-frequency deployment and orthogonal frequency division multiplexing(OFDM),which leads to more users under severe inter-beam interference compared to the existing research on geostationary orbit satellites broadcasting systems.Simulation results show that the proposed user grouping algorithm possesses higher channel capacity and better bit error rate(BER)performance in high SNR conditions relative to existing works.
基金The authors gratefully acknowledge funding from the National Natural Science Foundation of China(NSFC,No.62005007,11827803,and U20A20390)the Fundamental Research Funds for the Central Universities(Beihang University).
文摘The ability to quantify optical properties(i.e.,absorption and scattering)of strongly turbid media has major implications on the characterization of biological tissues,fluid fields,and many others.However,there are few methods that can provide wide-field quantification of optical properties,and none is able to perform quantitative optical property imaging with high-speed(e.g.,kilohertz)capabilities.Here we develop a new imaging modality termed halftone spatial frequency domain imaging(halftone-SFDI),which is approximately two orders of magnitude faster than the state-of-the-art,and provides kilohertz high-speed,label-free,non-contact,wide-field quantification for the optical properties of strongly turbid media.This method utilizes halftone binary patterned illumination to target the spatial frequency response of turbid media,which is then mapped to optical properties using model-based analysis.We validate the halftone-SFDI on an array of phantoms with a wide range of optical properties as well as in vivo human tissue.We demonstrate with an in vivo rat brain cortex imaging study,and show that halftone-SFDI can longitudinally monitor the absolute concentration as well as spatial distribution of functional chromophores in tissue.We also show that halftone-SFDI can spatially map dual-wavelength optical properties of a highly dynamic flow field at kilohertz speed.Together,these results highlight the potential of halftone-SFDI to enable new capabilities in fundamental research and translational studies including brain science and fluid dynamics.
