幅度与相位联合调制(Amplitude and Phase Shift Keying,APSK)对于映射到星座图上同一个符号点的不同比特具有不均等的差错保护,其中受保护程度较低的比特限制了编码调制系统的整体误码性能。为消除这一限制,提出了一种非均衡编码方案,...幅度与相位联合调制(Amplitude and Phase Shift Keying,APSK)对于映射到星座图上同一个符号点的不同比特具有不均等的差错保护,其中受保护程度较低的比特限制了编码调制系统的整体误码性能。为消除这一限制,提出了一种非均衡编码方案,即对不同保护程度的数据进行分组,通过比特交织的方式匹配不同纠错能力的低密度奇偶校验码(Low Density Parity Check Code,LDPC)进行编码。在64-APSK调制方式下进行计算机仿真,仿真结果表明:均衡编码方案相比传统编码调制方案具有0.3 dB以上的性能增益。展开更多
We apply in this study an area preserving level set method to simulate gas/water interface flow.For the sake of accuracy,the spatial derivative terms in the equations of motion for an incompressible fluid flow are app...We apply in this study an area preserving level set method to simulate gas/water interface flow.For the sake of accuracy,the spatial derivative terms in the equations of motion for an incompressible fluid flow are approximated by the fifthorder accurate upwinding combined compact difference(UCCD)scheme.This scheme development employs two coupled equations to calculate the first-and second-order derivative terms in the momentum equations.For accurately predicting the level set value,the interface tracking scheme is also developed to minimize phase error of the first-order derivative term shown in the pure advection equation.For the purpose of retaining the long-term accurate Hamiltonian in the advection equation for the level set function,the time derivative term is discretized by the sixth-order accurate symplectic Runge-Kutta scheme.Also,to keep as a distance function for ensuring the front having a finite thickness for all time,the re-initialization equation is used.For the verification of the optimized UCCD scheme for the pure advection equation,two benchmark problems have been chosen to investigate in this study.The level set method with excellent area conservation property proposed for capturing the interface in incompressible fluid flows is also verified by solving the dam-break,Rayleigh-Taylor instability,two-bubble rising in water,and droplet falling problems.展开更多
文摘幅度与相位联合调制(Amplitude and Phase Shift Keying,APSK)对于映射到星座图上同一个符号点的不同比特具有不均等的差错保护,其中受保护程度较低的比特限制了编码调制系统的整体误码性能。为消除这一限制,提出了一种非均衡编码方案,即对不同保护程度的数据进行分组,通过比特交织的方式匹配不同纠错能力的低密度奇偶校验码(Low Density Parity Check Code,LDPC)进行编码。在64-APSK调制方式下进行计算机仿真,仿真结果表明:均衡编码方案相比传统编码调制方案具有0.3 dB以上的性能增益。
基金This work was supported by the National Science Council of Republic of China under the Grants NSC-94-2611-E-002-021,NSC-94-2745-P-002-002 and CQSE project 97R0066-69.
文摘We apply in this study an area preserving level set method to simulate gas/water interface flow.For the sake of accuracy,the spatial derivative terms in the equations of motion for an incompressible fluid flow are approximated by the fifthorder accurate upwinding combined compact difference(UCCD)scheme.This scheme development employs two coupled equations to calculate the first-and second-order derivative terms in the momentum equations.For accurately predicting the level set value,the interface tracking scheme is also developed to minimize phase error of the first-order derivative term shown in the pure advection equation.For the purpose of retaining the long-term accurate Hamiltonian in the advection equation for the level set function,the time derivative term is discretized by the sixth-order accurate symplectic Runge-Kutta scheme.Also,to keep as a distance function for ensuring the front having a finite thickness for all time,the re-initialization equation is used.For the verification of the optimized UCCD scheme for the pure advection equation,two benchmark problems have been chosen to investigate in this study.The level set method with excellent area conservation property proposed for capturing the interface in incompressible fluid flows is also verified by solving the dam-break,Rayleigh-Taylor instability,two-bubble rising in water,and droplet falling problems.
