Backscatter phase evaluation based on scatterplot cluster detection

The paper is focused on methods for the evaluation of backscatter RFID channel parameters. It shows how to obtain the channel transfer function (CTF) using a set of measurements on discrete frequencies with common passive EPC Gen2 RFID tags. The main contribution lies in the received signal phase evaluation with low ambiguity, which is achieved with cluster detection in the constellation diagram of backscattered signal. Experimental results for several tags with various measurement setups are presented and discussed. As a final result, the CTF is transformed to the channel impulse response (CIR), which provides an estimation of signal propagation paths in the environment. The presented method provides higher reliability and accuracy for existing phase-based ranging principles, especially in narrowband systems without strong multipath signal propagation.