The Floating Sensor Network system is a fleet of robotic sensor packages with water quality sensors, GPS receivers, and 802.15.4 wireless communication modules. They are deployed in riverine and estuarine environments to observe the water flow and propagation of constituents such as salt, nitrates, and other contaminants. Their observations will be used for real-time estimates and forecasts of the system state. The connectivity is dynamic and unpredictable, making a centralized scheme challenging. Our project will develop networking algorithms and methods to enable reliable decentralized data collection and fleet coordination for long-term, distributed sensing missions. Time Synchronized Channel Hopping (TSCH) is an existing medium access control scheme which enables robust communication through channel hopping and high data rates through synchronization. It is based on a time-slotted architecture, and its correct functioning depends on a schedule which is typically computed by a central node. We are developing a scheduling algorithm for TSCH networks which both is distributed and which copes with mobile nodes. Two scheduling algorithms are presented. Aloha-based scheduling allocates one frequency channel for broadcasting advertisements for new neighbors. Reservation-based scheduling augments Aloha-based scheduling with a dedicated slot for targeted advertisements based on gossip information. We have assessed the performance of the two proposed algorithms against the optimal case by simulating a mobile ad-hoc network with frequent connectivity changes. Reservation-based scheduling performs significantly better than Aloha-based scheduling, suggesting that the improved network reactivity is worth the increased algorithmic complexity and resource consumption. Our next step is to realize these algorithms on the Floating Sensor Network system and validate their performance in real-world deployments.
Project end date: 08/05/11