Time Synchronization Algorithms for Digital Sensor Networks Used in Structural Health Monitoring Systems
Norihisa Shimoyama, Akira Mita · 2006
Recently, much attention is paid on structural health monitoring technology for maintaining the healthiness of buildings. As for the technique called Sensor Grid which is used for a digital sensor network, related studies are applied in various research organizations. A lot of sensor units consisting of sensors, CPUs and network interfaces are used for the Sensor Grid. In the Sensor Grid, since data are processed and integrated in a network by sensor elements, infrastructure for a network can be reduced significantly. As a basic technology for digital sensor network, in this paper, Time Synchronization is discussed. Two simple techniques on Time Synchronization were examined and related experiments were conducted. At the same kind of nodes, we obtained performances of Time Synchronization as good as 8.50±7.22μsec. However, with different models or different network interfaces, the performance varies. With Broadcast Delivery type for Time Stamps, we obtained stable synchronous performance in all trials. Under the same network topology and using the same network interface, the performance was stable. It was about 20.8±6.37μsec. Broadcast Delivery type for Time Stamps was inferior to Network Delay Measurement Type in performance of the synchronization. However its performance stability was better. And it shows a peculiar performance by environment (a network, topology, hardware and others) of a node. By considering all of these facts, a good and feasible time synchronization system may be established. INTRODUCTION Recently, much attention is paid on structural health monitoring technology for maintaining the healthiness of buildings. For example, it is reported that for the structural health monitoring system of Tsing Ma Bridge completed in 1997 in Hong Kong, each _____________ * Graduate Student, School of Science for Open and Environmental Systems, Keio University, 3-14-1 Hiyoshi Kohoku, Yokohama 223-8522, Japan, [email protected] **Professor, Department of System Design Engineering, Keio University, 3-14-1 Hiyoshi Kohoku, Yokohama 223-8522, Japan