High-Precision Asynchronous Decawave Ultrawideband Ranging

Asynchronous ranging is commonly used for time of flight (TOF) and time difference of flight (TDOF) estimation in low-cost wireless networks, where ranging bias is a major problem. Although some methods can perform unbiased ranging, their expressions are complex, increasing energy consumption in large-scale scenarios. In addition, the measurement noise of cheap hardware limits the ranging performance, making the precision typically in the order of decimeters. In order to solve these problems, this article first proposes an asynchronous ranging method based on local clock conversion (LCC). This method calculates the LCC factor using clock skew ratio (CSR). It can concisely implement TOF or TDOF estimation and eliminate the ranging bias caused by the variable response delay, that is, unbiased at the protocol level. Second, the noise terms of the proposed protocol-level unbiased ranging method are derived, which provides theoretical support for analyzing the ranging performance. The analysis demonstrates that the noise level of CSR-based unbiased TOF/TDOF estimation is almost unaffected by response delay variations. Then, a high-precision protocol-level unbiased asynchronous ranging method based on the Kalman filter (KF) is proposed, in which carrier frequency offset (CFO) is introduced. CFO can be used to construct carrier frequency ratio (CFR) through Taylor approximation. The CFR is then related to the LCC factor. The proposed method fuses CFR and CSR to estimate the LCC factor. Therefore, it can concisely achieve high-precision unbiased ranging. Finally, the effectiveness of the proposed ranging schemes is verified in the line-of-sight (LOS) and LOS ground-bounce multipath environments.