Patent ID: 8872632

Claim:
A method comprising controlling communications between known tags and unknown tags using a frame structure, wherein the known tags comprise radio frequency identification tags that a radio frequency identification reader has previously identified as being within an interrogation zone and the unknown tags comprise radio frequency identification tags that the radio frequency identification reader has not identified as being within the interrogation zone, comprising: broadcasting, by the radio frequency identification reader, an identification start message indicating a beginning of an identification portion of the frame structure, wherein only the unknown tags communicate with the radio frequency identification reader during the identification portion, wherein the identification start message includes a reader frame identifier that is initialized to zero and increments by one for each successive identification start message, wherein the known tags and the unknown tags compare a tag frame count maintained by the each one of the known tags and the unknown tags to the reader frame identifier to determine whether a tag is a known tag or an unknown tag; allowing, by the radio frequency identification reader, collisions between signals transmitted by ones of the unknown tags during the identification portion of the frame structure in which the unknown tags communicate with the radio frequency identification reader; broadcasting, by the radio frequency identification reader, an access start message indicating a beginning of an access portion of the frame structure, wherein only known tags communicate with the radio frequency identification reader during the access portion; and avoiding collisions between signals transmitted by any of the known tags and signals transmitted by any of the unknown tags and avoiding collisions between signals transmitted by any of the known tags and any other of the known tags by assigning by the radio frequency identification reader during the identification portion of the frame structure each one of the known tags a time slot of the access portion of the frame structure to communicate with the radio frequency identification reader during a respective time slot of the access portion of the frame, wherein the identification portion and the access portion of the frame structure do not have fixed durations.