부산대학교 도서관

Developing positioning systems for the underground environment is challenging, particularly if radio-frequency-based techniques are used. Low-frequency magnetic-induction (MI)-based positioning systems are accurate both in indoor and underground environments as the relative magnetic permeability of most of the materials in such environments is close to unity. However, the positioning range of the MI-based systems is limited because of the attenuation of the artificially generated quasi-static field with distance. An incrementally deployed network using transmitters can be used to increase the positioning range. However, the complexity of the system increases as the number of transmitters increases. Moreover, identifying the contribution of each particular transmitter to the received signal becomes challenging. In this letter, we present an MI positioning system using a dual-multiplexing technique. The proposed system combines both time-division multiplexing and frequency-division multiplexing for efficient positioning. We developed a proof-of-concept prototype to validate the proposed system. The experimental results show that the proposed system is able to estimate the 3-D position with an error of less than $\pm$ 0.05 m within a measurement field of size 1 m × 1 m × 0.45 m in $X$, $Y\!$, and $Z$ (width × length × depth). The proposed dual-multiplexing approach allows for increasing the positioning range by incrementally deploying the transmitters.