RFID reader and tag multi-hop communication for port logistics

The RFID technology has attracted much attention these days due to the far better efficiency than the barcode and magnetic card system. As an important usage, the 433 MHz active RFID tag was already adopted to the container ports in the United States and Europe for container loading and unloading automation and equipment location. However, for the complete automation, one problem should be solved before. Current RFID systems support only the direct (single-hop) communication between readers (interrogators) and tags within their RF transmission range. Then besides containers, there are a lot of equipments such as crane, yard tractor, and forklift in ports; and being made of metal, they interfere the RF transmission, resulting in the occurrence of the dead-zone. In the dead-zone, tags cannot receive any signal from readers. Several solutions may be possible to this problem. Among them, this paper suggests the most economical solution where RFID tags in the dead-zone communicate with readers via neighbor tags in the multi-hop manner. The new RFID communication architecture must be carefully designed in order to maintain the compatibility with the previous standard. Our experiment shows that the proposed method works well even in the case where some tags are out of the RF range of reader.