Two-Way Ranging Algorithms Using Estimated Frequency Offsets in WPAN and WBAN

Asynchronous two-way ranging methods such as TWR and SDS-TWR have been considered for many ranging systems because these methods are useful in the absence of synchronization. To estimate the location of a mobile node, accurate ranging is essential between an anchor node and the mobile node. Ranging errors calculated with timestamps and reference frequency are derived from the difference of frequency offsets and unequal processing latency of ranging frame. In this paper, we propose to estimate frequency offsets of local nodes. The TWR and SDS-TWR based on measured timestamps and clock frequency offsets give exact relation and guarantee constant accuracy with coarse oscillators. The performance applied to low-rate UWB and high-rate UWB is evaluated according to the distribution of ranging errors.