提出一种分析模型,基于信号流图和母函数方法分析了无线局域网中EDCA(enhanced distribution channel access)机制的MAC(medium access control)接入延时.得到了MAC接入延时的概率分布和相关的数字特征,包括接入延时的均值、方差、标准...提出一种分析模型,基于信号流图和母函数方法分析了无线局域网中EDCA(enhanced distribution channel access)机制的MAC(medium access control)接入延时.得到了MAC接入延时的概率分布和相关的数字特征,包括接入延时的均值、方差、标准差和变异系数.仿真结果与模型的分析结果吻合良好,验证了模型和计算方法的正确性.进一步分析了各类AC(access category)的发送概率、碰撞概率、挂起概率和延时均值随终端数目变化的规律;分析了MAC接入延时的成因;指出了AIFS(arbitration inter frame spacing)值对MAC接入延时的影响;指出接入延时的变异系数大于1,因此,采用负指数分布作为MAC接入延时的近似分布,会错误地估计系统的服务能力.展开更多
A new three-dimensional coordination polymer {[Co（BPTC）0.5（bix）]′（H2O）}n （1, H4BPTC = 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid, bix = 1,3-bis（imidazol-l-ylmethyl）-benzene） has been synthesized by the...A new three-dimensional coordination polymer {[Co（BPTC）0.5（bix）]′（H2O）}n （1, H4BPTC = 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid, bix = 1,3-bis（imidazol-l-ylmethyl）-benzene） has been synthesized by the hydrothermal method and characterized by IR, elemental analysis, and single-crystal X-ray analysis. The crystal is of orthorhombic, space group Pbcn with a = 13.2975（10）, b = 13.8424（12）, c = 22.6367（17） A, CoC22H19N4Os, Mr = 478.34, V = 4166.7（6） A3, Dc = 1.525 g/cm^3, F（000） = 1968,μ = 0.867 mm^-1, S = 1.023 and Z = 8. The final R = 0.0683 and wR = 0.1529 for 3655 observed reflections with I 〉 20（I）. In the title complex, the 2D Co-BPTC layer is formed through self-assembly of Co（II） ions and bridging BPTC4-ligands in a molar ratio of 2：1. The metal-organic lattice layers are further united together through the second bridging ligand bix to form a 3D metal-organic framework. The thermal stability of the title complex was studied by thermal gravimetric （TG） and differential thermal analysis （DTA）.展开更多
文摘提出一种分析模型,基于信号流图和母函数方法分析了无线局域网中EDCA(enhanced distribution channel access)机制的MAC(medium access control)接入延时.得到了MAC接入延时的概率分布和相关的数字特征,包括接入延时的均值、方差、标准差和变异系数.仿真结果与模型的分析结果吻合良好,验证了模型和计算方法的正确性.进一步分析了各类AC(access category)的发送概率、碰撞概率、挂起概率和延时均值随终端数目变化的规律;分析了MAC接入延时的成因;指出了AIFS(arbitration inter frame spacing)值对MAC接入延时的影响;指出接入延时的变异系数大于1,因此,采用负指数分布作为MAC接入延时的近似分布,会错误地估计系统的服务能力.
基金supported by the International Technology Cooperation Project of Science and Technology Department of Henan Province (No. 124300510050)
文摘A new three-dimensional coordination polymer {[Co（BPTC）0.5（bix）]′（H2O）}n （1, H4BPTC = 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid, bix = 1,3-bis（imidazol-l-ylmethyl）-benzene） has been synthesized by the hydrothermal method and characterized by IR, elemental analysis, and single-crystal X-ray analysis. The crystal is of orthorhombic, space group Pbcn with a = 13.2975（10）, b = 13.8424（12）, c = 22.6367（17） A, CoC22H19N4Os, Mr = 478.34, V = 4166.7（6） A3, Dc = 1.525 g/cm^3, F（000） = 1968,μ = 0.867 mm^-1, S = 1.023 and Z = 8. The final R = 0.0683 and wR = 0.1529 for 3655 observed reflections with I 〉 20（I）. In the title complex, the 2D Co-BPTC layer is formed through self-assembly of Co（II） ions and bridging BPTC4-ligands in a molar ratio of 2：1. The metal-organic lattice layers are further united together through the second bridging ligand bix to form a 3D metal-organic framework. The thermal stability of the title complex was studied by thermal gravimetric （TG） and differential thermal analysis （DTA）.
