Asymmetric Multi-way Ranging for Resource-Limited Nodes

Cooperative localization in WSN is used in applications where individual nodes cannot determine their location based on external contact, like e.g. GPS. The applications we focus on are the exploration and mapping of flooded cavities that are otherwise inaccessible or difficult-to-access, e.g. underground (oil-) reservoirs or industrial tanks for e. g. mixing. High levels of miniaturization are required for the nodes to traverse these cavities; nodes will have to be stripped down to a bare minimum. Ultrasound time-of-flight is used as radio communication is infeasible. Network topology is highly unpredictable and fast changing. We present an asymmetric multi-way ranging protocol for these highly resource-limited, miniaturized, autonomous nodes. The specific set of constraints imposed by these applications, like the use of ultrasound, high latency, low data-rates, and non-static network topology is far-reaching and has not been studied before. Simulations of the protocol show trade-off's that can be made between ranging latency, signal overlap and overall energy budget.