A Proposal of Synchronization Beacon Systems over Power-line for Indoor Fine-Grained Localization

One of the problems in power-line communications (PLC) is an unnecessary radiation due to the electrical unbalance of power-lines. However, it means that power-lines can work as antennas. In this paper, a beacon signal radiation system by the power-line antenna for time synchronization among wireless and wired nodes is proposed. The considered application of the radiation system is an indoor fine-grained localization, which is determining where a given node is physically located in a room. A preliminary implementation of the localization by an acoustic rangefinder is described. Unlike other published work in this area, our rangefinder uses Direct-Sequence Code Division Multiplexed (DS-CDM) audible sound signals to detect the distance between the receiver node (i.e. microphone) and the reference point (i.e. speaker) inferred from the time of flight of the sound wave. This technique significantly improves performance in obstructed and noisy environments. The obtained localization accuracy was about 1cm in a 4m²plane. As a merit of using the power-line antenna, its wideness of the coverage area is also described experimentally by comparing with that of a conventional loop antenna system.