Anti-collision methods for global SAW RFID tag systems

The global SAW tag (Hartmann (2002)) is projected to be a large-volume SAW device application. The modulation method and overall tag data structure are reviewed for a family of proposed radio frequency identification (RFID) devices. The global SAW tag is implemented using a basic group structure that encodes 16 information bits using 4 reflectors chosen from 75 reflector slots. Several groups are placed in-line on a single acoustic track to achieve ID tag devices with capacities up to 256 bits. Many RFID systems require robust operation even when numerous tagged items are located in close proximity. Hence, multiple ID tags often occupy the field of a tag reader at the same time. These tags produce simultaneous reply signals which "collide" when they arrive back at the tag reader. This paper presents "anti-collision" methods that deal with this issue.