Optimal layout of four anchors to improve accuracy of Ultra-Wide band based indoor positioning

Despite extensive research on three-dimensional (3D) indoor positioning algorithms, there remains room for improvement in the optimal placement strategy for four ultra-wideband (UWB) anchors in line-of-sight (LOS) situations. We conducted 20 observations at five different heights within a 210 m3 experimental area, performing a total of 4845 weighted trilaterations. The experimental results demonstrated that a larger virtual polyhedron volume between the Mobile Terminal (MT) and the anchors resulted in a smaller 3D error. This 3D error-volume relationship was statistically verified. Furthermore, this study revealed that the mask angle can be disregarded in indoor positioning and that anchor placement need not be limited to the Z-axis, unlike Global Navigation Satellite System (GNSS). Thus, all axes should be considered within a cuboid in space. Consequently, the optimal anchor placement to minimize the 3D error is one that maximizes the volume between the anchors and the MT along any direction in the three-dimensional space.