Study of Irregular Constellations of RFID Tags for Indoor Distance Estimation

This paper presents an improved multi-antenna (MISO-like) system for indoor distance estimation taking advantage of spatial diversity. We call irregular constellation a four active tags irregular array. As real environments do not have a symmetric shape nor a homogeneous electromagnetic behaviour, we assume that a regular constellation is not the best suited to such environments. The main purpose of this work is to compare regular constellations (four equidistant tags with diamond shape) to irregular ones considering the mean error of the distance estimation. Constellations are characterized by their area and the sum of their distances from the four constellation tags to their barycentre. It is shown that most of the small area constellations (less than 0.25 square meters) outperforms the best regular constellation.