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The authors present the angle diversity technique implemented on a real-time location system designed for tracking applications according to the angle-of-arrival estimation, operating in the 2.4 GHz band. Some problems inherent to the classical interferometers are theoretically analysed relative to the noise-level variation and influence of radiofrequency interferences, due to sharing an unlicensed frequency band, as well as propagation impairments as multipath. From theoretical conclusions, a signal processing algorithm has been derived to solve these impairments, mostly by means of short-term averaging resulting in a good angle-of-arrival estimator technique for the purpose of the system herein described. A full operational bench-top system has been implemented and tested in actual indoor scenarios. Instead of resolving the interferometer equations for multiple baseline receivers, the diversity selection method is applied in reception resulting in an anchor-free system. One of the most important features of the proposed system is the low coast and accuracy besides the fact of working in an unlicensed frequency band. The system provides a precision in the location/direction estimation better than 28 that means 87 cm at a distance of 50 m. This sub-metric precision improves the one achieved by location systems based on received signal strength measurements.
Date of Publication: January 24 2012