Main objective of this contribution is to introduce a novel collision avoidance protocol for the chipless Radio Frequency Identification (RFID) systems. The chipless RFID tags are dummy, memoryless, with limited number of bits, very low backscattered power and short reading range. Therefore, the existing RFID standards and protocols designed for the chipped RFID systems are not applicable for the chipless systems. In this work, a new Notch Position Modulation (NPM) scheme is presented as the first Medium Access Control (MAC) algorithm for handling the multi-tag identification scenario of the frequency signature based chipless RFID tags. This intelligent NPM algorithm reduces the sensing and identification time and accordingly the overall system latency. The proposed protocol enables fetching the frequency signatures of the chipless RFID tags through the whole Ultra Wideband (UWB) range effectively. Furthermore, an advanced UWB signaling scheme based on frequency sweeping criteria is designed for the RFID reader in order to make the best use of the Federal Communications Commission (FCC) UWB regulations for increasing the maximum transmitted power and the corresponding reading range. This protocol provides MAC identity for each chipless RFID tag, enables determining the number of the existing tags, orthogonal modulated signatures for each tag and the corresponding modulation parameters. Moreover, the mitigation of the interference between the several chipless RFID tags and the undesired environmental reflections is a straightforward result of this new protocol. Based on this technique, the MAC layer and protocol stack designers can apply their concepts on the physical layer of the dummy chipless RFID tags. In the meanwhile, the new concept offers the guidelines for the RF and antenna designers to meet the new protocol requirements. Finally, it could be the ground base in drafting the chipless RFID standards. |
