Channel estimation for recovery of UHF RFID tag collision on physical layer

In a passive ultra-high frequency (UHF) radio-frequency identification (RFID) system, tag collision is generally resolved on medium access control (MAC) layer. However, some of collided tag signals could be recovered on physical (PHY) layer and thus enhance the identification efficiency of the RFID system. For the recovery on the PHY layer, channel estimation is a critical issue. Good channel estimation will help to correctly recover the collided signals. Existing channel estimates work well under the environment of two collided tags. When the number of collided tags is beyond two, however, the existing estimates have higher estimation errors. In this work, we propose a novel channel estimate for the UHF RFID system. The proposed estimate uses the information of preambles which is a-priori known for a reader and applies a least-square (LS) criterion. From numerical results, the proposed estimate has lower estimation errors than the existing estimates under the environment of more than two collided tags.