Chinese Journal of Computers   Full Text
Title	Partial Connection Availability Modeling for Wireless Networks
Authors	ZHANG Tian-Le1) LI Zhong-Cheng2) LIU Min2)
Address	1)(Beijing Key Laboratory of Intelligent Telecommunications Software and Multimedia, Beijing University of Posts and Telecommunications, Beijing 100876) 2)(Institute of Computing Technology, Chinese Academy of Sciences, Beijing 100080)
Year	2007
Issue	No.4(505—513)
Abstract &   Background	Abstract In energy-constrained wireless networks, alternately sleeping is an effective way to reduce power consumption. However，this method may destroy the connectivity of network. Such a network is called the partially connected network. The numerical evaluation for the availability of partial connection is essential for wireless network running in periodically sleeping mode. In this paper, a computing model of partial connection availability based on alternate activity model is introduced. A node with packet to be send can hold the packet for certain period and resume packet forwarding when the sleeping next-hop node wakes up. Based on the Poisson process model and complete probability method, the formula of the partial connection availability is deduced. The formula can be very close to the actual capacity of the partially connected network in alternately sleeping mode. It is proved that compared with the full connection availability, within tolerable delay the partial connection availability is much higher. The theoretical criterion is provided in the process of deployment of energy-constrained wireless networks. Numerical analysis is conducted on the relationship among relevant network parameters and performance of networks such as packet delivery ratio and delay. Methods for setting the parameters are introduced. Simulation validates the methods and results. keywords partial connection; full connection; connection availability; alternate activity; energy background The research of this paper is supported by the National Natural Science Foundation of China under grant No.90604016, "Research on Key Technologies of Mobile Instant Messaging", and partially supported by Microsoft embedded research project. Mobile instant messaging is an emerging communication tool in the Internet. It provides messaging service and presence service to facilitate contact and communication with others. Mobile wireless devices are gaining a growing interest due to their flexibility and low price. The extension of instant messaging (IM) to mobile Ad Hoc networks offers considerable potential. However, due to mobile devices’ strong dependency on batteries, this kind of Ad Hoc network is energy-constrained. The users of this system would enter or leave the system unfriendly and arbitrarily only because of the sleeping of devices, the battery depletion and the willingness of users to communication. Then the nodes may be active alternately. Difficulties exist in providing available IM service in the absence of continuously connection to the destination. It is released in project that is in energy-constrained Ad Hoc network where the nodes are switched to active state alternately, the connectivity of network may be destroyed. The network then becomes partially connected network. The most of current Ad Hoc routing protocols hold the promise of full connection to destination. In partially connected network running those protocols, performance degrades greatly. Routing protocols for partially connected network offer advanced features that facilitate instant communications between mobile and Internet users within tolerable delay, where a fully connected end-to-end path may never exist. These protocols are important for instant messaging technologies to be adopted over a wide range of application classes. Connection availability is key factor to measure the capacity of communication. However, to the best of our knowledge, most previous research of availability is for fully connected network, and that of partially connected network is lacking. In this paper, the authors propose a computing model of partial connection availability. The formulas of mean packet delivery ratio in tolerable delay are deduced. Methods for setting of the parameters are introduced. As an independent toolkit, this analytical model can be applied to research on optimization of routing protocol and deployment of networks. The theoretical criterion is provided in the process of adoption of instant messaging technologies in energy-constrained Ad Hoc network. The major research interests of this group include instant messaging, routing protocols and energy efficiency and handoff. Some evaluation models and new protocols have been proposed. Most of them have been published. The work in this paper mainly investigates the numerical relationship between partial connection availability and tolerable delay of users in instant messaging systems.