It is related to the paper Z. Situ, I. W.-H. Ho, H. C. B. Chan, D. P. K. Lun, "The Impact of Node Reliability on Indoor Cooperative Positioning," IEEE International Conference on Digital Signal Processing (DSP), Oct 2016. And the patent C. M. Lau, D. P.-K. Lun, I.-W.H. Ho, "An Effective Location Tracking System in Exhibition Environment," U.S. Patent Application No. 62/912,674, filed Oct 9, 2019.