A fixed-parameter-tractable algorithm for set packing

1. IntroductionIt is a useful and challenging task to find efficient algorithms for many computationalhard problems. Recently, the research on Fixed-Parameter nactable Theory arouses muchinterest. FOr example, different fixed- p ax amet er- t rac t ab le- algori t hms for many well- knowndecisio11 pruble11ls illc1udi11g 3-dimellsio11al IIlatchiIlg: a11d vertex--cover Problen1 have beenPrese11ted in [1 8]. Jia11er Chen, DoIlald K. FYiesen al1d Weijia Jia proPosed a coll1pletelynew appro…     

Analysis of reactive routing protocols for mobile ad hoc networks in Markov models

Mobile ad hoc networks (MANETs) have become a hot issue in the area of wireless networks for their non-infrastructure and mobile features. In this paper, a MANET is modeled so that the length of each link in the network is considered as a birth-death process and the space is reused for n times in the flooding process, which is named as an n-spatial reuse birth-death model (n-SRBDM). We analyze the performance of the network under the dynamic source routing protocol (DSR) which is a famous reactive routing protocol. Some performance parameters of the route discovery are studied such as the probability distribution and the expectation of the flooding distance, the probability that a route is discovered by a query packet with a hop limit, the probability that a request packet finds a r-time-valid route or a symmetric-valid route, and the average time needed to discover a valid route. For the route maintenance, some parameters are introduced and studied such as the average frequency of route recovery and the average time of a route to be valid. We compare the two models with spatial reuse and without spatial reuse by evaluating these parameters. It is shown that the spatial reuse model is much more effective in routing.     

马氏模型下移动自组网随选型路由协议特性分析

移动自组网络(简称MANET)因其移动性及无基础设施支持等特点已经成为无线通信网络中的热门问题.通过将一个MANET网络中每条链边的长度看作一个生灭过程,并且假设在泛洪过程中空间可以复用n次,建立了移动自组网络空间可复用的马氏模型,简记为n-SRBD.M在一个典型的随选型路由协议即动态源路由(DSR)协议的基础上,研究了网络的一些关键性能参数,给出了路由泛洪距离的概率分布和期望,限定泛洪步数时成功寻路的概率、发现τ-时有效路径及对称有效路径的概率,发现一条有效路径的平均时间等,对于路由维护过程,也引入并研究了一些网络性能参数,例如,路由恢复的平均频率,路由有效的平均时间.对于这些网络参数在空间可复用和空间不可复用两种情形下进行了比较.证明了空间可复用模型下的路由选择更为有效.