RoamingHART: A Collaborative Localization System on WirelessHART

Localization in wireless sensor networks is an important functionality that is required for tracking personnel and assets in industrial environments, especially for emergency response. Current commercial localization systems such as GPS suffer from the limitations of either high cost or low availability in many situations (e.g., in-door environments that exclude direct line-of-sight signal reception). The development of industrial wireless sensor networks such as Wireless Hart provides an alternative. In this paper, we present the design and implementation of Roaming Hart: a collaborative localization system on Wireless Hart as an industrially viable solution. This solution is built upon several technological advances. First, Roaming Hart adds the roaming functionality to Wireless Hart and thus provides a means for keeping mobile Wireless Hart devices connected to the network. Second, Roaming Hart employs a collaborative framework to integrate different types of distance measurements into the location estimation algorithm by weighing them according to their precision levels. Roaming Hart adopts several novel techniques to improve distance estimation accuracy and decreases the RSSI pre-survey cost. These techniques include introducing distance error range constraints to the measurements, judiciously selecting the initial point in location estimation and on line updating the signal propagation models in the anchor nodes. Our implementation of Roaming Hart can be applied to any Wireless Hart-conforming network because no modification is needed on the Wireless Hart field devices. We have implemented a complete Roaming Hart system to validate both the design and the effectiveness of our localization algorithm. Our experiments show that the mobile device never drops out of the Wireless Hart network while moving around, with the help of even one dependable anchor, using RSSI can yield at least 75% of distance errors below 5 meters, which is quite acceptable for many typic- l industrial automation applications.