In our experiment, we use a PC, equipped with Duo Core 1.6GHz Pentium(R) CPU and 1.0GB of RAM, to emulate a RFID reader. Each PC is attached with a TI TelosB mote as a gateway, communicating with a user’s smart tag, which is also emulated by TI TelosB mote 12, supported by UC Berkeley’s 22.x TinyOS[16] operating system and the NesC programming language.