Request efficient channel estimation method for MIMO passive RFID systems

In this paper, we propose a new channel estimation method for multiple-input multiple-output (MIMO) passive radio frequency identification (RFID) systems. The basic idea consists in applying, at the reader side, a regularized least squares algorithm on the preamble of the tag response in which the information data is superimposed to pilot symbols. We derive a solution for the regularized optimization problem and a closed-form expression of the mean square error (MSE) for the proposed method. The performance of our approach is compared with the conventional framed slotted aloha (FSA) and an existing pilot estimation approach for different numbers of tags and receive antennas. The results show that the proposed method exhibits reduced total number of requests needed for successful identification in a dense tag population scenario and provides robustness against pilot contamination effect as well as good channel estimation performance.