Using CDMA as Anti-Collision Method for RFID - Research & Applications

The increasing number of deployed RFID systems and the resulting need for fast recognition of a given amount of RFID tags puts great demand on future RFID readers. Applications requesting for a fast capture of RFID tags are mainly found in logistic and manufacturing processes. Imagine trucks driving through large RFID gates, where each RFID tagged package or even item has to be identified. Also, fast production with tagged units approaching in quick succession would need a fast recognition of RFID tags. Therefore, if several tags are located within the range of a reader, signals from some of these tags will clash. For this very reason anti-collision procedures are widely deployed to prevent tags from broadcasting their information simultaneously. Existing RFID multiple access solutions for the uplink channel are based on Time Division Multiple Access (TDMA). Fig. 1 shows the TDMA method, pointing out that the tags in the reader’s field transmit their data at different moments in time (slots) (Finkenzeller, 2003). As may be imagined, the application of TDMA in RFID systems ensures that each RFID tag in range will be detected on condition that the amount of time available is sufficient. If this condition is false, the system comes to hard decisions, so that, finally, not every tag in range has been recognized successfully. Therefore, the usage of TDMA methods pushes the