Anti-Collision Protocols for RFID Systems Exploiting Multi-Antenna Readers

摘要

In conventional RFID systems, only one tag can be identified at a time. Tag collisions occur if more than one tag simultaneously occupies the shared RF channel, resulting in low identification efficiency and long delay, particularly when the population of tags is large. In this paper, we propose two RFID anti-collision protocols, both are based on framed slotted ALOHA (FSA), to concurrently identify multiple tags by using a multi-antenna reader. The first one is Blind Identification Protocol, which relies on blind estimation of the channel between the activated tags and the reader and, as such, does not require redesign of the existing RFID tags. The second one is Orthogonal ID-aided Identification Protocol which estimates the channels with the use of temporary orthogonal IDs, which are randomly selected by the tags and are inserted at the head of each tag's reply signal. The use of orthogonal IDs facilitates both the detection of activated tags and the channel estimation. Unlike code division multiple access (CDMA) techniques which rely on the use of excessive bandwidth and require redesign of tags, the proposed protocols use multiple antennas at the reader to support concurrent identification of multiple tags without the requirement of additional bandwidth and no or minimal modifications to the existing tags. As a result, the proposed techniques yield significant improvement of the identification efficiency and reduction of the identification delay. We analyze, in an analytical framework, the identification efficiency of the proposed protocols, and the optimum frame size is derived.