Design of spread spectrum based UHF RFID tag for location system

Radio frequency identification (RFID) applications with large tag populations often require the fast identification of the tags present. This paper applies a spread-spectrum technique and adds some new functions based on 18000-6C protocol, so that a RFID tag can transmit the unique spreading code which can be configured by reader for code division multiple access (CDMA). Therefore, an UHF-RFID reader can receive the spreading codes from numbers of tags at the same time and gets the position of each tag by means of time difference of arrival (TDOA) simultaneously.