The technical problem of strengthening multi-read functions in RFID systems is the collision of radio waves from undesired RFIDs in the same space, i. e., collision countermeasures.
ISO 18000-3 mode 1 (ISO 15693 system), ISO 18000-3 mode 2 (Maggellan system), Space Division Multiple Access (SDMA), and Time Division Multiple Access (TDMA) ... are proposed.
We developed a 2.45GHz band active RFID system using Spread Spectrum technology, and published it in 2006. The left photo shows a SS(Spread Spectrum)-RFID reader, and the right photo shows an active SS(Spread Spectrum)-RFID tag.
This prototype has a function to measure the distance between a RFID tag and a reader, and a SS-RFID tag can be selected in the depth direction.