Prototype wireless sensor network node for novel asynchronous RF Time-of-flight ranging

Short distance measurement based on RF Time-of-flight (TOF) is difficult because of high sampling clock resolution and wireless synchronization needs. For precise estimation, previous researchers have developed heterogeneous clock systems (HCSs) using Vernier effect of two clocks with different frequencies to measure TOF precisely. Besides, they have performed easier synchronization inside a main node and used a mirror node to return RF signal to the main. Therefore, each node, in general, must be able to change between main and mirror roles. However, role changing is troublesome, thus we propose a new prototype based on a novel asynchronous estimation method with almost similar roles for both ranging nodes. This is made by calculating TOF from the difference of the round trip time and reply time between nodes.