Beta-Binomial删除信道中的喷泉码文件传输协议

由于命名数据网络(NDN,Named-Data Networking)无环路、逐包、逐跳转发的特点,使得数据包回传成功率降低,而传统的TCP/IP协议中的ARQ和ACK机制对于多播会话不再适用.由于NDN中的传输信道可以等效为二进制删除信道,因此可以通过应用层编码来实现文件的可靠传输.传统的信道编码技术如卷积码、级联码和RS码等复杂度较高,而将NDN与低复杂度的喷泉码的结合可以实现分布式的存储架构,因而可通过喷泉编码在应用层协议中实现可靠的纠删机制,保证整体文件的传输可靠性.以往的研究一般是基于确定的删除概率信道模型,但是由于网络的异构性和信道噪声等因素影响,可能会造成信道丢包概率呈随机性分布.因此,本文在Beta-Binomial分布模型的前提下,根据贝叶斯统计的先验信息和中心极限定理,对随机概率下的纠删信道的文件可靠传输协议进行了数学建模和理论推导.仿真结果显示此模型更具有普适性,此传输协议可在信道状况未知的前提下从理论上求出最小发包数,减少冗余编码包,提高文件整体的投递成功率,在保证传输可靠性的同时有效提升协议传输效率.     

A Bayes Sampling Allocation Scheme for Stratified Finite Populations With Hyperbinomial Prior Distributions

When sampling is carried out independently for the K strata of a finite stratified dichotomous population (defectives vs. standard items), and the number Z_i of defectives per stratum sample is observed, the corresponding probability function for X = (X_i , …, x_K ) is the product of hypergeometric functions which depend on the sample sizes n_i , the stratum sizes N_i , and the number of defectives M_i in the stratum (i = 1, …, K). It is assumed that prior information is available about the M_i 's which can be expressed, by suitable choice of the parameters a_i and b_i , as the product of independent hyperbinomial functions.

In each stratum the cost per observation is a known constant. Using squared error loss function, the prior Bayes risk is found for the linear function of interest,

and the optimum allocation of sample sizes is found, the one for which the prior Bayes risk is minimum when the total sampling budget is fixed.