Communication system for communicating with tags

A communication system for efficiently communicating with a large number of tags in a communication region formed by a plurality of cells where the location of the tags in the region may not be known and where tags may be removed from or introduced into the region comprising,

• a plurality of interrogators, one for each cell, for communicating with said tags in said plurality of cells, each cell having a corresponding interrogator, said tags and said corresponding interrogator communicating over a common communication channel with a sequence including a plurality of collection periods, said collection periods including interrogator communication periods for said interrogator to send commands over said communication channel to said tags and including tag communication periods for said tags to send responses over said communication channel to said corresponding interrogator, where said responses from different tags collide if tag communication periods for said different tags coincide and where said responses from said different tags do not collide if the tag communication periods for said different tags do not coincide, each of said interrogators including,
• interrogator memory for storing interrogator code including a broadcast command and a directed command and including bandwidth code for controlling the bandwidth of said collection periods,
• interrogator processor means connected for accessing said interrogator memory and for processing said interrogator code to send said broadcast command and to send said directed command,
• interrogator transceiver means connected to said interrogator processor means for sending said commands and receiving said responses tags within the interrogator cell over said common communication channel, said communications including sending said broadcast command and said directed command a plurality of times,
• each of said tags located in one or more of said cells within said communication region, each of said plurality of tags including,
• a tag transceiver for sending and receiving communications to and from said interrogator transceiver means over said common communication channel,
• a tag memory for storing information including tag code,
• a tag processor, connected to said tag transceiver, for processing said tag code to receive said broadcast command and said directed command said plurality of times, and to send a response to said interrogator for one or more of said plurality of times,
• a computer connecting to each of said interrogators for controlling the operation of said interrogators.

Apparatus for identifying items through transmission and reception of signals comprising:

• a plurality of tags, one for each of said items;
• an interrogator for communicating with said tags,
• said tags and said interrogator communicating over a common communication channel with a communication protocol including a sequence, common to all tags, said sequence including a plurality of collection periods, each collection period having,
• interrogator communication periods for said interrogator to send commands over said communication channel to said tags,
• a listen period having time slots during which one or more of said plurality of tags can communicate a tag identifying signal to said interrogator, where tag identifying signals from different tags collide if the time slots for said tag identifying signals for said different tags coincide and where tag identifying signals from different tags do not collide if the time slots for said tag identifying signals for said different tags do not coincide,
• an acknowledge period during which said interrogator can communicate acknowledge signals to said tags,
• said interrogator including,
• bandwidth control means for controlling the bandwidth of the collection periods by controlling the duration of the listen periods,
• signal sending means, operable for each of said collection periods, for sending a signal to the tags to signal the commencement of the listen period,
• receiver means, operable for each of said collection periods, for receiving tag identifying signals during said listen period from a subset of said tags,
• acknowledge sending means, operable for each of said collection periods, for sending acknowledge signals during said acknowledge period to said subset of said tags,
• each of said tags including,
• signal receiving means, operable for one or more of said collection periods, for receiving the signal from the signal sending means so as to identify the start of the listen period,
• identification sending means, operable for one or more of said collection periods, for sending a tag identifying signal during the listen period,
• acknowledge receiving means, operable for one or more of said collection periods, for receiving an acknowledge signal from said interrogator during the acknowledge period.

In a communication system for communicating in a communication region over a common communication channel between an interrogator and a plurality of tags, where the interrogator includes,

• interrogator memory for storing interrogator code including a broadcast command and a directed command, interrogator processor means connected for accessing said interrogator memory, interrogator transceiver means connected to said interrogator processor means,
• and where each of said tags includes,
• a tag transceiver for sending and receiving communications to and from said interrogator transceiver means over said common communication channel, a tag memory for storing information including tag code, a tag processor, connected to said tag transceiver,
• the method comprising,
• processing, in said interrogator processor, said interrogator code to sequence said broadcast command and said directed command a plurality of times,
• sending and receiving communications in said communication region over said common communication channel by said interrogator transceiver, including sending said broadcast command and said directed command said plurality of times, said communications having a sequence including a plurality of collection periods, said collection periods including interrogator communication periods for said interrogator to send commands over said communication channel to said tags and including tag communication periods for said tags to send responses over said communication channel to said interrogator, where said responses from different tags collide if tag communication periods for said different tags coincide and where said responses from said different tags do not collide if the tag communication periods for said different tags do not coincide,
• in each of said tags,
• receiving said broadcast command and said directed command said plurality of times by said tag transceiver,
• processing said tag code to send a response to said interrogator through said tag transceiver for one or more of said plurality of times,
• for each of two or more of said plurality of tags, sending a response over said common communication channel such that at some times, a collision of responses occurs during one of said plurality of times and such that at another one of said plurality of times, no collision of responses occurs.

Apparatus for identifying items through transmission and reception of signals comprising:

• a plurality of tags, one for each of said items;
• an interrogator for communicating with said tags,
• said tags and said interrogator communicating over a common communication channel with a communication protocol, said communication protocol including a sequence common to all tags, said sequence including a plurality of collection periods, each collection period having,
• a synchronization period during which said interrogator can communicate with said plurality of tags,
• a listen period having time slots during which one or more of said plurality of tags can communicate a tag identifying signal to said interrogator over said communication channel, where tag identifying signals from different tags collide if the time slots for said tag identifying signals for said different tags coincide and where tag identifying signals from different tags do not collide if the time slots for said tag identifying signals for said different tags do not coincide, and
• an acknowledge period during which said interrogator can communicate acknowledge signals to said tags over said communication channel,
• said interrogator including,
• interrogator memory for storing interrogator code including one or more broadcast commands and one or more directed commands and including bandwidth code for controlling the bandwidth of said tag communication periods,
• interrogator processor means connected for accessing said interrogator memory and for processing said interrogator code to sequence said broadcast commands and said directed commands,
• signal sending means, operable for each of said collection periods, for sending during said synchronization period one of said broadcast commands over the common communication channel to the tags to signal the commencement of the listen period,
• receiver means, operable for each of said collection periods, for receiving tag identifying signals over the common communication channel from said tags during said listen period,
• acknowledge sending means, operable for each of said collection periods, for sending acknowledge signals as directed commands over the common communication channel to said tags during said acknowledge period,
• each of said tags including,
• signal receiving means, operable for one or more of said collection periods, for receiving said one of said broadcast commands from said signal sending means during said synchronization period so as to identify the start of the listen period,
• identification sending means, operable for one or more of said collection periods, for sending a tag identifying signal during one of a plurality of time slots during the listen period,
• acknowledge receiving means, operable for one of said collection periods, for receiving an acknowledge signal from said interrogator during the acknowledge period,
• control means, operable for said one or more of said collection periods, for controlling said identification sending means,
• said control means operative, before said acknowledge receiving means receives said acknowledge signal and during each of said one or more of said collection periods, for selecting one of said time slots for sending a tag identifying signal whereby two or more of said plurality of tags may each send a respective tag identifying signal over said common communication channel such that during one time slot of a listen period a collision of tag identifying signals may occur and such that during another time slot of a listen period no collision of tag identifying signals occurs,
• said control means operative, after said acknowledge receiving means receives said acknowledge signal, for inhibiting said identification sending means from sending said tag identifying signal.