A 900 MHz short-distance ranging system

摘要

In a wireless radio frequency (RF) ranging system, an accurate distance can be determined by measuring the carrier's phase. In recent years, the industrial, scientific and medical (ISM) radio band has been used for license-free communications applications. Thus, a license-free RF ranging system is possible. By investigating some ranging systems and their techniques, this thesis proposes an ISM 900 MHz land-based short range ranging system.;This thesis will first explain a frequency hopping phase ranging algorithm for the proposed ranging system. It is developed from the classic multi-tone ranging method with its inherited advantages in solving the ambiguity problem. By using up to 431 frequencies in the ISM 900 MHz band, the proposed ranging algorithm has the ability to withstand errors caused by noise, interference and multipath effects, and it could achieve a ranging error of less than three centimeters in a range of 2.5 km.;To build a working platform for the proposed ranging algorithm, a practical system design to accomplish the phase reflection function is proposed. The system consists of several components complying with the regulations for 900 MHz. The system core, which is a complex phase locked loop (PLL), will be explained and discussed. Some key circuits such as the low pass filter of the PLL will be emphasized. The PLL's performance, such as its stability, is discussed based on the circuit design.;The proposed complex PLL is evaluated through experiments. Test results show the proposal is feasible and practical.