Multi-tone carrier technique for signal recovery from collisions in UHF RFID with multiple acknowledgments in a slot

In passive Radio Frequency IDentification (RFID) systems, tags do not have their own power source and they receive their operating energy from continuous modulated RF carrier transmitted by the reader. The tag while receiving this carrier randomly selects a slot and sends back its RN16 using backscatter modulation for purpose of its identification. The efficiency of the existing UHF RFID systems is limited, as only response from a single tag in a slot can be decoded successfully. If multiple tags select the same slot collision happens, information of physical layer is discarded and retransmission is executed. In this work, a multi-tone carrier wave is exploited to make the collided tag signals decodable. In addition, a novel method to acknowledge the multiple tag signals in a single slot is proposed. The system performance in terms of expected throughput is significantly improved with the use of both multi-tone carrier and the multiple acknowledgements technique at the same time.