Synch-free RF time-of-flight measurement system for wireless sensor networks based on vernier effect

This paper proposes a synch-free RF Time-of-Flight (ToF) measurement system as an epoch-making protocol of RF ToF ranging for wireless sensor networks (WSNs). This system is based on vernier effect due to two heterogeneous clocks, which are basically adopted in order to generate new virtual time resolution much smaller than the intrinsic time resolution of two clocks of which the ratio is n:(n-1). On the basis of the virtual time resolution, the consecutive (n-1)-transmission of RF signal generates the unique sensing patterns, which consists of n-sensing value, depending on the size of RF ToF; consequently, it is possible to estimate RF ToF using the particular sensing patterns. The synch-free RF ToF measurement system suggests efficient and promising methodology of RF ToF ranging by applying this RF ToF measurement principle.