Title: Routing and Time Synchronization Protocols for Low Duty Cycle Operation of a Sensor Network Based Bridge Monitoring System
Abstract:
Railways form a crucial part of transport infrastructure in many parts of the world. A large fraction of bridges used by railways may be considerably old and may be in use for decades. For instance, Indian Railways has about 127,000 bridges of which 51,000 are about 100 years old. For smooth functioning of the system, safety of travel over these bridges must be assured. For this, a structural health monitoring system is required, that is capable of indicating any deterioration of physical condition of the bridges, thereby calling for maintenance. Existing techniques are mostly wired solutions, requiring technical personnel to be present at the bridge site during the inspections.
In this work, we present BriMon, a Wireless Sensor Network based structural health monitoring system that has the essential features like ease of deployability, long life with minimum maintenance, and remote monitoring. It also satisfies the constraints imposed by structural engineers on data collection and analysis. The solution is based on wireless sensor motes and MEMS accelerometers. We have designed various mechanisms and protocols required for providing the afore-said features in an application specific manner. The implemented solution shows how the design choices dictated solely by the application are different from the general solutions that exist in the sensor network domain. We implemented the solution on Moteivs Tmote-sky and used TinyOS and nesC for programming the motes.
In this work, we discuss the routing and time synchronization protocols that we have designed, implemented and evaluated. These are very simple, light-weight and efficient in our application setting, when compared to existing protocols in literature. We also describe a signal strength based event detection mechanism in order to detect the oncoming train. This subsequently triggers either data collection or mobile data transfer to a node on the train depending on the context. The event detection mechanism allows us to detect the oncoming train at a distance of about 1Km, which allows the nodes to sleep-wakeup with a very low duty cycle of 1-2%. The moving train itself is used as a carrier of the vibration data collected at the bridge, which is one of the novel aspects of this design. We also discuss about the careful integration of the above components of routing, sleep-wakeup and time synchronization with the other aspects of BriMon namely high fidelity data acquisition, reliable data transfer onto moving train.