This article addresses the multicast resource allocation problem with min-rate requirement constraints in orthogonal frequency division multiplexing （OFDM） systems. Due to the prohibitively high complexity for nonli...This article addresses the multicast resource allocation problem with min-rate requirement constraints in orthogonal frequency division multiplexing （OFDM） systems. Due to the prohibitively high complexity for nonlinear and combinatorial optimization, the original problem is relaxed and reformulated to form a standard optimization problem. By theoretical derivation according to the Karush-Kuhn-Tucker （KKT） conditions, two propositions are presented as the necessary criteria for optimality. Furthermore, a two-step resource allocation scheme, including subcarrier assignment and power allocation, is proposed on a basis of the propositions for practical implementation. With the rain-rate based multicast group order, subcarriers are assigned in a greedy fashion to maximize the capacity. When subcarrier assignment is determined, the proposed power allocation can achieve the optimal performance for the rain-rate constrained capacity maximization with an acceptable complexity. Simulation results indicate that the proposed scheme approximates to optimal resource allocation obtained by exhaustive search with a negligible capacity gap, and considerably outperforms equal power distribution. Meanwhile, multicast is remarkably beneficial to resource utilization in OFDM systems.展开更多
目的:比较乙型肝炎表面抗原(hepatitis B surface antigen,HBsAg)、胆碱酯酶(cholinesterase,CHE)和吲哚氰绿15min滞留率(indocyanine green retention rate at 15min,ICGR15)在慢性乙型肝炎组、肝硬化代偿组、肝硬化失代偿组的水平,并...目的:比较乙型肝炎表面抗原(hepatitis B surface antigen,HBsAg)、胆碱酯酶(cholinesterase,CHE)和吲哚氰绿15min滞留率(indocyanine green retention rate at 15min,ICGR15)在慢性乙型肝炎组、肝硬化代偿组、肝硬化失代偿组的水平,并研究3者之间的相关性.方法:观察95例慢性乙型肝炎病毒感染患者,按病情分为慢性乙型肝炎组、肝硬化失代偿组和肝硬化代偿组3组.分别检测血清HBsAg、CHE、ICGR15,评价3组间观察指标的差异及相关性.结果:3组间HBsAg水平3.44lgIU/mL±0.55lgIU/mL、3.14lgIU/mL±0.39lgIU/mL、2.76lgIU/mL±0.55lgIU/mL有显著差异(P<0.05);慢性乙型肝炎组与肝硬化失代偿组CHE(6631.37U/L±1907.18U/Lvs4838.51U/L±2134.35U/L,P<0.05)、ICGR15(9.77%±5.57%vs27.69%±13.30%,P<0.05)有显著性差异.相关分析显示各组间CHE和ICGR15均呈负相关,r分别为-0.401、-0.625、-0.444,P<0.05;肝硬化代偿组和失代偿组HBsAg与CHE呈正相关,r分别为0.449、0.407,P<0.05;肝硬化代偿组和失代偿组HBsAg与ICGR15呈负相关,r分别为-0.498、-0.757,P<0.05.结论:随着乙型肝炎向肝硬化进展,HBsAg、CHE水平逐渐降低,ICGR15水平逐渐升高.肝硬化阶段HBsAg与ICGR15呈负相关,与CHE呈正相关,提示HBsAg可能与肝脏残余有效肝细胞量呈正比.且肝硬化阶段CHE和ICGR15呈负相关,因此一定程度上可通过HBsAg、CHE来反映肝硬化患者ICGR15水平.展开更多
为了提高低密度奇偶校验(LDPC)码的单最小值最小和(single-minimum Min-Sum,sm MS)算法的误码性能,提出了一种基于变量节点LLR(Log Likelihood Ratio)消息加权的改进最小和(Improved Min Sum algorithm based on weighted message LLR o...为了提高低密度奇偶校验(LDPC)码的单最小值最小和(single-minimum Min-Sum,sm MS)算法的误码性能,提出了一种基于变量节点LLR(Log Likelihood Ratio)消息加权的改进最小和(Improved Min Sum algorithm based on weighted message LLR of variable nodes,IMS-WVN)算法。首先,将迭代次数所确定的次小值的估值参数与最小值相加后取代次小值,以增强sm MS算法校验节点的可靠度。然后,将变量节点输出LLR消息与迭代前LLR消息进行加权处理,降低变量节点的振荡幅度,降低平均译码迭代次数。仿真结果表明,在信噪比为3.2 d B时,IMS-WVN算法的误码性能比VWMS算法提升0.53 d B,当误码率为10-5时,IMS-WVN算法平均译码迭代次数较MS算法减少58%。展开更多
基金supported by the National Basic Research Program of China (2007CB310604, 2009CB320401)the National Natural Science Foundation of China (60772108, 60702048)the Fundamental Research Funds for the Central Universities (BUPT2009RC0111)
文摘This article addresses the multicast resource allocation problem with min-rate requirement constraints in orthogonal frequency division multiplexing （OFDM） systems. Due to the prohibitively high complexity for nonlinear and combinatorial optimization, the original problem is relaxed and reformulated to form a standard optimization problem. By theoretical derivation according to the Karush-Kuhn-Tucker （KKT） conditions, two propositions are presented as the necessary criteria for optimality. Furthermore, a two-step resource allocation scheme, including subcarrier assignment and power allocation, is proposed on a basis of the propositions for practical implementation. With the rain-rate based multicast group order, subcarriers are assigned in a greedy fashion to maximize the capacity. When subcarrier assignment is determined, the proposed power allocation can achieve the optimal performance for the rain-rate constrained capacity maximization with an acceptable complexity. Simulation results indicate that the proposed scheme approximates to optimal resource allocation obtained by exhaustive search with a negligible capacity gap, and considerably outperforms equal power distribution. Meanwhile, multicast is remarkably beneficial to resource utilization in OFDM systems.
文摘目的:比较乙型肝炎表面抗原(hepatitis B surface antigen,HBsAg)、胆碱酯酶(cholinesterase,CHE)和吲哚氰绿15min滞留率(indocyanine green retention rate at 15min,ICGR15)在慢性乙型肝炎组、肝硬化代偿组、肝硬化失代偿组的水平,并研究3者之间的相关性.方法:观察95例慢性乙型肝炎病毒感染患者,按病情分为慢性乙型肝炎组、肝硬化失代偿组和肝硬化代偿组3组.分别检测血清HBsAg、CHE、ICGR15,评价3组间观察指标的差异及相关性.结果:3组间HBsAg水平3.44lgIU/mL±0.55lgIU/mL、3.14lgIU/mL±0.39lgIU/mL、2.76lgIU/mL±0.55lgIU/mL有显著差异(P<0.05);慢性乙型肝炎组与肝硬化失代偿组CHE(6631.37U/L±1907.18U/Lvs4838.51U/L±2134.35U/L,P<0.05)、ICGR15(9.77%±5.57%vs27.69%±13.30%,P<0.05)有显著性差异.相关分析显示各组间CHE和ICGR15均呈负相关,r分别为-0.401、-0.625、-0.444,P<0.05;肝硬化代偿组和失代偿组HBsAg与CHE呈正相关,r分别为0.449、0.407,P<0.05;肝硬化代偿组和失代偿组HBsAg与ICGR15呈负相关,r分别为-0.498、-0.757,P<0.05.结论:随着乙型肝炎向肝硬化进展,HBsAg、CHE水平逐渐降低,ICGR15水平逐渐升高.肝硬化阶段HBsAg与ICGR15呈负相关,与CHE呈正相关,提示HBsAg可能与肝脏残余有效肝细胞量呈正比.且肝硬化阶段CHE和ICGR15呈负相关,因此一定程度上可通过HBsAg、CHE来反映肝硬化患者ICGR15水平.
文摘为了提高低密度奇偶校验(LDPC)码的单最小值最小和(single-minimum Min-Sum,sm MS)算法的误码性能,提出了一种基于变量节点LLR(Log Likelihood Ratio)消息加权的改进最小和(Improved Min Sum algorithm based on weighted message LLR of variable nodes,IMS-WVN)算法。首先,将迭代次数所确定的次小值的估值参数与最小值相加后取代次小值,以增强sm MS算法校验节点的可靠度。然后,将变量节点输出LLR消息与迭代前LLR消息进行加权处理,降低变量节点的振荡幅度,降低平均译码迭代次数。仿真结果表明,在信噪比为3.2 d B时,IMS-WVN算法的误码性能比VWMS算法提升0.53 d B,当误码率为10-5时,IMS-WVN算法平均译码迭代次数较MS算法减少58%。
