Collision arbitration method and apparatus for reading multiple radio frequency identification tags

The present invention relates generally to methods and apparatuses for arbitrating collisions due to simultaneously received data transmissions, and more particularly to a method and apparatus for arbitrating collisions due to simultaneously received data transmissions from multiple sensors. A method for simultaneously reading a serial number and/or other information from multiple colliding RF signals from RF identification tags requires minimal additional logic in the tag's processor and provides for a powerful and rapid sorting and identification scheme. This technique employs a primary communication channel and multiple secondary channels. A locator or reader unit interrogates the tags, which respond with an RF signal. Upon receiving multiple signals, the locator or reader unit commands the RFID tags and requires them to transmit another response, which is transmitted in one of the secondary channels based on a portion of their unique serial identification number, thereby forcing the tags to sort in the secondary channels. These secondary channels are assigned using a portion of the unique serial identification numbers for the tags. The reader then detects an acknowledgment in the occupied secondary channels and commands a tag in a particular channel to move to the primary channel. Once the signal is transmitted in the primary channel, the reader reads the identification number. If there is further collision, the collided tags are returned to the secondary channel and sorted again using a different portion of their ID number. This process continues until all the tags are sorted and identified. Once the tags are all sorted, the tags are assigned yet another channel distinct from the secondary channels that are used for sorting.