Cooperative Localization for Asynchronous AUVs Using Time Difference of Communication in Underwater Anchor-Free Environments
针对自主水下航行器时钟异步导致协同定位精度下降的问题，提出一种基于通信时间差的相对测量方法，建立时空联合定位模型，并通过迭代优化和误差补偿提升定位精度，仿真和实验验证了方法在长期任务中的优势。
The asynchronization among autonomous underwater vehicles (AUVs) is inevitable due to the inherent offsets and drifts in clocks, which critically degrades the accuracy of AUV cooperative localization (CL), especially in underwater anchor-free environments. This article designs a novel relative measurement representation called time difference of communication (TDOC) to eliminate the impact of asynchronization, which only requires one-way inter-AUV communications at different time steps even in the presence of large asynchronization. By exploiting TDOC, a joint spatial-temporal CL model is established with specially constructed measurement vectors, and a CL method, termed TDOC-CL, is proposed. It transforms the nonlinear observations into a weighted least-square (WLS) formation and is solved via iterative optimization, where various coupled uncertainties (i.e., measurement biases, measurement noises, and position errors) are involved and analyzed. Moreover, to compensate the accuracy degradation caused by the uncertainties, the TDOC-CL with bias reduction and error compensation, named iTDOC-CL-BREC, is further designed. In addition, the hybrid Cramér-Rao lower bound (HCRLB) is derived as the performance benchmark to evaluate the localization behaviors. Simulations and field experiments show that iTDOC-CL-BREC can provide higher localization accuracy compared with state-of-the-art methods, especially for long-duration tasks.