针对现有基于最小均方误差准则的全双工射频域自干扰对消算法存在收敛速度与干扰对消比相互制约的矛盾,提出一种改进时变步长归一化最小均方算法。该算法通过建立最小均方误差步长因子与改进时变sigmod函数的非线性关系,利用实时误差信...针对现有基于最小均方误差准则的全双工射频域自干扰对消算法存在收敛速度与干扰对消比相互制约的矛盾,提出一种改进时变步长归一化最小均方算法。该算法通过建立最小均方误差步长因子与改进时变sigmod函数的非线性关系,利用实时误差信号自相关和时间参量t协同控制步长因子μ(t),较好的兼顾了收敛速度与干扰对消比。分析与仿真表明:在干信比为80 d B、步进间隔Δt=1/32 ms、信噪比Eb/N0=10 d B的2FSK全双工系统模型下,该算法能够实现88 d B的自干扰消除高出同类算法至少1.5 d B且收敛速度和抗突发干扰能力提升显著。展开更多
Ⅰ. INTROOUCTIONLet X be a nonempty finite set called an alphabet, and X~* the free monoid generated by X and X^+=X~*—{1}, where 1 is the identity of X~* called the empty word over X. Elements and subsets of X~* are ...Ⅰ. INTROOUCTIONLet X be a nonempty finite set called an alphabet, and X~* the free monoid generated by X and X^+=X~*—{1}, where 1 is the identity of X~* called the empty word over X. Elements and subsets of X~* are called words and languages over X respectively. The length of a word x which is the number of the letters occurring in x will be denoted by lg(x).展开更多
文摘针对现有基于最小均方误差准则的全双工射频域自干扰对消算法存在收敛速度与干扰对消比相互制约的矛盾,提出一种改进时变步长归一化最小均方算法。该算法通过建立最小均方误差步长因子与改进时变sigmod函数的非线性关系,利用实时误差信号自相关和时间参量t协同控制步长因子μ(t),较好的兼顾了收敛速度与干扰对消比。分析与仿真表明:在干信比为80 d B、步进间隔Δt=1/32 ms、信噪比Eb/N0=10 d B的2FSK全双工系统模型下,该算法能够实现88 d B的自干扰消除高出同类算法至少1.5 d B且收敛速度和抗突发干扰能力提升显著。
文摘近年来,多通道线圈阵列被广泛应用于磁共振成像,以提高图像的质量。针对局部感兴趣区域内的射频场优化,提出一种由不同尺寸单元构成的六通道线圈阵列,可优化盆腔组织中局部感兴趣区域内的射频场。使用宽度为10和20 cm的两种不同尺寸的线圈单元来构建六通道线圈阵列模型,并对其采用几何重叠法和电容网络法进行去耦,以及运用时域有限差分(FDTD)方法进行仿真和计算,分析和评估其在感兴趣区域内产生的射频场。仿真结果表明,在加载盆腔组织椭圆柱电磁模型情况下,提出的线圈阵列的去耦效果S12和S13分别为-27.19和-33.46 d B,在感兴趣区域内产生的射频场B+1强度平均值,比由宽度为15 cm的相同单元构成的常规线圈阵列高出约5.21%。由不同尺寸单元构成的六通道线圈阵列能够优化感兴趣区域内的射频场,为磁共振线圈设计提供新的思路和方法。
基金This research has been supported by the National Research Council of Canada under Grants A7877 and A7350, respectively. The Project is supported by the National Natural Science Foundation of China.
文摘Ⅰ. INTROOUCTIONLet X be a nonempty finite set called an alphabet, and X~* the free monoid generated by X and X^+=X~*—{1}, where 1 is the identity of X~* called the empty word over X. Elements and subsets of X~* are called words and languages over X respectively. The length of a word x which is the number of the letters occurring in x will be denoted by lg(x).