Position and Velocity Estimation of a Non-cooperative Source From Asynchronous Packet Arrival Time Measurements

We tackle the problem of identifying the trajectory of a moving radio source from Time-of-Arrival (TOA) measurements collected by a set of cooperating receivers. The considered system is completely asynchronous: nodes clocks are affected by unknown time and frequency offsets, and no control is exerted over packet transmission times. In the proposed solution, the receiver clock offset terms are estimated from TOA measurements on packets originated by non-cooperative reference transmitters, possibly but not necessarily coincidental with reference receivers. Transmission time ambiguity is resolved by exploiting the redundancy associated to the reception of the same packet at multiple receivers. A distinguishing feature of the proposed solution is that it seeks to identify the parameters of the trajectory as a whole, rather than the individual points of transmission as done in traditional point-based approaches. This allows the effective exploitation of TOA measurements collected in lossy scenarios, where the generic packet is received by a smaller subset of the available receivers (at least two). For the problem at hand we provide distinct estimators based on TOA and Time-Difference-of-Arrival (TDOA) and prove their equivalence. Numerical results from simulations and from a real WiFi testbed are provided to validate the effectiveness of the proposed method.