A method of establishing wireless communications between an interrogator
and individual ones of multiple wireless identification devices.[., the
method comprising utilizing a tree search method to attempt to identify
individual ones of the multiple wireless identification devices so as to
be able to perform communications, without collision, between the
interrogator and individual ones of the multiple wireless identification
devices, a search tree being defined for the tree search method, the tree
having multiple nodes respectively representing subgroups of the multiple
wireless identification devices, wherein the interrogator transmits a
command at a node, requesting that devices within the subgroup
represented by the node respond, wherein the interrogator determines if a
collision occurs in response to the command and, if not, repeats the
command at the same node. An interrogator configured to transmit a
command at a node, requesting that devices within the subgroup
represented by the node respond, the interrogator further being
configured to determine if a collision occurs in response to the command
and, if not, to repeat the command at the same node.]. . .Iadd.In one
aspect, a method implemented in an RFID device includes: receiving a
first command, comprising a first set of bit values, from an interrogator
to select the RFID device based on a comparison between the first set of
bit values and data stored in the RFID device; transmitting a response to
the first command, the response including an identifier of the RFID
device; if the response is received at an interrogator, remaining silent
when the first command is subsequently repeated; and if the response is
not received at the interrogator, re-transmitting the response when the
first command is subsequently repeated..Iaddend.