We study the coverage problem for sensor networks from the fault tolerance and reliability point of view. Fault tolerance is a critical issue for sensors deployed in places where they are not easily replaceable, repairable and rechargeable. Failure of one node should not incapacitate the entire network. We propose three 1-fault tolerant topologies, namely square, hexagonal and improved 8-node. We show how to extend these to k-fault tolerant schemes and calculate reliabilities using Markov models. The proposed models are compared to one another, as well as with the minimal coverage model of Zhang and Hou. The minimum coverage model is the most unreliable among the models, whereas the improved 8-node model is the most reliable except at the very beginning of the system, where the square model is more reliable. To our knowledge, this is the first paper which studies a pattern from the perspective of reliability.

We study the coverage problem from the fault tolerance point of view for sensor networks. Fault tolerance is a critical issue for sensors deployed in places where are not easily replaceable, repairable and rechargeable. The failure of one node should not incapacitate the entire network. We propose three 1 fault tolerant models, and we compare them among themselves, and with the minimal coverage model [8].

Abstract. Developing a collaborative application running on a collection of heterogeneous, possibly mobile, devices, each potentially hosting data stores, using existing middleware technologies such as JXTA, BREW, compact .NET and J2ME requires too many ad-hoc techniques as well as cumbersome and time-consuming programming. Our System on Mobile Devices (SyD) middleware, on the other hand, has a modular architecture that makes such application development very systematic and streamlined. The architecture supports transactions over mobile data stores, with a range of remote group invocation options and embedded interdependencies among such data store objects. The architecture further provides a persistent uniform object view, group transaction with Quality of Service (QoS) specifications, and XML vocabulary for interdevice communication. This paper presents the basic SyD concepts and introduces the architecture and the design of the SyD middleware and its components. We also provide guidelines for SyD application development and deployment process. We include the basic performance figures of SyD components and a few SyD applications on Personal Digital Assistant (PDA) platforms. We believe that SyD is the first comprehensive working prototype of its kind, with a small code footprint of 112 KB with 76 KB being device-resident, and has a good potential for incorporating many ideas for performance extensions, scalability, QoS, workflows and security.

Abstract

Future web applications will be more collaborative and will use the standard and ubiquitous Internet protocols. We have previously developed System on Mobile Devices (SyD) middleware to rapidly develop and deploy collaborative applications over heterogeneous and possibly mobile devices hosting web objects. In this paper, we present the software engineering methodology for developing SyD-enabled web applications and illustrate it through a case study on a System of Calendar application, with implementation on iPAQs and its performance metrics study. SyD-enabled web objects allow us to create a collaborative application rapidly with limited coding. In this case study, the modular software architecture allowed us to hide the inherent heterogeneity among devices, data stores, and networks by presenting a uniform and persistent object view of mobile calendar objects interacting through XML/SOAP requests and responses. The performance results we obtained show that the application scales well as we increase the group size and adapts well within the constraints of mobile devices.