Design an asynchronous radio interferometric positioning system using dual-tone signaling

Radio interferometric positioning systems (RIPS) are recently proposed for low-complexity and high-accuracy localization. However, the original RIPS involves four nodes (two transmitters and two receivers) for a ranging session, and requires stringent time synchronization upon two receivers. In this paper, an asynchronous radio interferometric positioning system (ARIPS) is developed with larger positioning ranges. In ARIPS, two anchors (nodes with known positions) transmit two slightly different dual-tone signals. The differences of the two dual-tone signals create two low-frequency differential signals at the target receiver. The phase differences of the differential signals bear the time-difference-of-arrival (TDOA) information, i.e., the distance information. We develop two new methods to estimate the TDOA with and without accurate knowledge of the frequencies of the differential signals, respectively. By switching the pairs of the anchor nodes, several TDOAs can be obtained and thus the location of the target node can be estimated. The proposed ARIPS is robust to carrier frequency offsets (CFOs) and random phases due to asynchronous oscillators, and increases the resolving range limit due to the well-known integer ambiguity issue. Simulation results illustrate the performance of the proposed ARIPS.