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In this paper, we propose an innovative motion-capture system using ultrasonic communications. Compared with existing commercial motion-capture systems that use optical or magnetic sensing, the proposed system can provide a cost-effective solution for industrial and entertainment applications. To design and implement the system, a distance-estimation method called the Extended Phase Accordance Method (EPAM), which can measure the distance to a moving object with a standard deviation of less than 1 mm, was devised. To improve the capture rate of the proposed system, the EPAM algorithm was implemented in a field-programmable gate array (FPGA). The current version of the system conducts motion capture using five markers attached to a user. It can work at around 10 frames per second (fps), with an error of less than 55 mm and a standard deviation of 42 mm. This demonstrates a moderate level of accuracy, which will be useful for several applications.