Bin ZHEN †a) , Mamoru KOBAYASHI †b) , Nonmembers, and Masashi SHIMIZU †c) , Member SUMMARY Radio frequency identification (RFID) enables everyday objects to be identified, tracked, and recorded. The RFID tags are must be extremely simple and of low cost to be suitable for large scale application. An efficient RFID anti-collision mechanism must have low access latency and low power consumption. This paper investigates how to recognize multiple RFID tags within the reader's interrogation ranges without knowing the number of tags in advance by using framed ALOHA. To optimize power consumption and overall tag read time, a combinatory model was proposed to analyze both passive and active tags with consideration on capture effect over wireless fading channels. By using the model, the parameters on tag set estimation and frame size update were presented. Simulations were conducted to verify the analysis. In addition, we come up with a proposal to combat capture effect in deterministic anti-collision algorithms.

IEEE 802.15 established a new working group, wireless body area networks (WBAN), to develop short range wireless technology in and around human body recently. This paper investigates networking issues in implant communications of WBAN. The object is better understanding of medical implant sensor networks and how to start WBAN's work. We applied IEEE 802.15.4b and 802.15.4a-chirp spread spectrum (CSS) for implant communications. We found two issues: clear channel assessment of implant devices and adjacent-channel interference from free space signals. Both of them can be attributed to the rapid attenuation of electromagnetic wave through tissues. Therefore the carrier sense multiple access mechanism and transmit mask of 802.15.4b cannot be directly adopted. The modulation of 802.15.4a-CSS is a good reference to WBAN. Besides, a simple two-hop protocol which uses a body surface forwarder was presented for long distance wireless implant communications.

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