Construction of Local Anchor Map for Indoor Position Measurement System

A prerequisite for a position measurement system is knowledge of anchor positions. In this paper, a local anchor-positioning method based on rotational time-difference-of-arrival (TDOA) measurement and ordinal multidimensional scaling (MDS) is proposed. The calibrated anchor positions serve as basis points to construct the local coordinate system for subsequent target localization. During the calibration phase, each anchor acts as a transmitter in turn, and the TDOA of the signal at rest of the anchors is measured. Although the true interanchor ranges are unknown, we can infer their relative rank from their range differences. Ordinal MDS allows us to find a configuration of anchor positions that preserves the order of interanchor range measurement without involving the exact value of the true range. As the number of anchors increases, the solution space of ordinal MDS rapidly shrinks; hence, an accurate local map of anchors can be constructed. Our simulation shows that, when the number of anchors exceeds ten, ordinal-based MDS outperforms classical metric MDS, as it is more robust to range offset errors.