Communication Scheme for a Highly Collision-Resistive RFID System

Yohei FUKUMIZU  Shuji OHNO  Makoto NAGATA  Kazuo TAKI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E89-A   No.2   pp.408-415
Publication Date: 2006/02/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e89-a.2.408
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics)
RFID,  anti-collision,  TD-CDMA,  low-power,  impulse modulation,  inductive coupling,  hardware emulation,  

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A highly collision-resistive RFID system multiplexes communications between thousands of tags and a single reader in combination with time-domain multiplexing code division multiple access (TD-CDMA), CRC error detection, and re-transmission for error recovery. The collision probability due to a random selection of CDMA codes and TDMA channels bounds the number of IDs successfully transmitted to a reader during a limited time frame. However, theoretical analysis showed that the re-transmission greatly reduced the collision probability and that an ID error rate of 2.510-9 could be achieved when 1,000 ID tags responded within a time frame of 400 msec in ideal communication channels. The proposed collision-resistive communication scheme for a thousand multiplexed channels was modeled on a discrete-time digital expression and an FPGA-based emulator was built to evaluate a practical ID error rate under the presence of background noise in communication channels. To achieve simple anti-noise communication in a multiple-response RFID system, as well as unurged re-transmission of ID data, adjusting of correlator thresholds provides a significant improvement to the error rate. Thus, the proposed scheme does not require a reader to request ID transmission to erroneously responding tags. A reader also can lower noise influence by using correlator thresholds, since the scheme multiplexes IDs by CDMA-based communication. The effectiveness of the re-transmission was confirmed experimentally even in noisy channels, and the ID error rate derived from the emulation was 1.910-5. The emulation was useful for deriving an optimum set of RFID system parameters to be used in the design of mixed analog and digital integrated circuits for RFID communication.