Extending Reading Range of Commercial RFID Readers

In this paper, multisine excitation signals are used to extend the reading range of commercial RF identification readers. To do so, a commercial reader is equipped with an external multisine front-end that implements previous mathematical proposals. A mathematical description is presented in order to show the ability of multisine signals to communicate data, with minimal changes in the downlink path, while no changes are required in the conventional tag architecture. Moreover, and most important, if a proper multisine design is performed, a conventional reader receiver is still able to demodulate and decode the backscattered multisine signal from the tag, without any hardware change. Thus, guidelines are presented for multisine design, including multisine nature, central tone positioning, tone separation, and bandwidth requirements. In order to evaluate the reading range improvement, when compared with the conventional single carrier approach with the same average power, two experiments are conducted: in the first one, an oscilloscope is used to measure the tag response and to decide whether the tag does or does not respond. In the second measurement scenario, the downlink path is implemented by the reader combined with the front-end and the uplink is implemented solely by the reader. In this case, the decision on successful tag response is taken when the reader reads the tag identification. The first measurement scenario has pointed out for a maximum reading range improvement of near 43% for an eight-tone multisine signal with 2-MHz tone separation. In the second scenario, a more realistic one, a reading range improvement of almost 25% has been obtained for a 8 + 1 tones multisine.