Method of Addressing Messages and Communications System

Abstract

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 includes: transmitting by an interrogator a first signal including a first set of bits, the interrogator to identify a first subgroup of a group of possible random numbers; communicating by each of one or more RFID devices a first response if the one or more RFID devices has generated a random number that is included in the first subgroup; receiving by the interrogator one or more received responses from respective ones of the one or more RFID devices; and responsive to receiving one of the one or more received responses without a collision, retransmitting by the interrogator at least the first signal.

1. A method of establishing wireless communications between an interrogator and wireless identification devices, the method comprising utilizing a tree search technique to establish communications, without collision, between the interrogator and individual ones of the multiple wireless identification devices, the method including using a search tree having multiple nodes respectively representing subgroups of the multiple wireless identification devices, the method further comprising, for a node, transmitting a command, using the interrogator, requesting that devices within the subgroup represented by the node respond, determining with the interrogator if a collision occurred in response to the command and, if not, repeating the command at the same node. 
     
     
       2. A method in accordance with  claim 1  and further comprising, if a collision occurred in response to the first mentioned command, sending a command at a different node, using the interrogator. 
     
     
       3. A method in accordance with  claim 1  wherein when a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, the device that is not within communications range of the interrogator does not respond to the command. 
     
     
       4. A method in accordance with  claim 1  wherein when a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, the device that is within communications range of the interrogator responds to the command. 
     
     
       5. A method in accordance with  claim 1  wherein a device in a subgroup changes between being within communications range of the interrogator and not being within interrogators range, over time. 
     
     
       6. A method in accordance with  claim 1  wherein the wireless identification device comprises an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       7. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices, the method comprising:
 establishing for respective devices unique identification numbers;    causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;    transmitting a communication, from the interrogator, requesting devices having random values within a first specified group of random values to respond;    receiving the communication at multiple devices, devices receiving the communication respectively determining if the random value chosen by the device falls within the first specified group and, if so, sending a reply to the interrogator; and    determining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a second specified group smaller than the first specified group; and, if not, again transmitting a communication requesting devices having random values within the first specified group of random values to respond.    
     
     
       8. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices in accordance with  claim 7  wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply. 
     
     
       9. A method in accordance with  claim 7  wherein one of the first and second specified groups contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is not within communications range of the interrogator does not respond to the interrogator. 
     
     
       10. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices in accordance with  claim 7  wherein, after receiving a reply without collision from a device, the interrogator sends a communication individually addressed to that device. 
     
     
       11. A method of addressing messages from a transponder to a selected one or more of a number of communications devices, the method comprising:
 establishing unique identification numbers for respective devices;    causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;    transmitting a communication from the transponder requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels, the specified group being defined as being at one of the nodes;    receiving the communication at multiple devices, devices receiving the communication respectively determining if the random value chosen by the device falls within the specified group and, if so, sending a reply to the transponder; and, if not, not sending a reply; and    determining using the transponder if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group by descending in the tree; and, if not, transmitting a communication at the same node.    
     
     
       12. A method of addressing messages from a transponder to a selected one or more of a number of communications devices in accordance with  claim 11  wherein establishing unique identification numbers for respective devices comprises establishing a predetermined number of bits to be used for the unique identification numbers. 
     
     
       13. A method of addressing messages from a transponder to a selected one or more of a number of communications devices in accordance with  claim 12  and further including establishing a predetermined number of bits to be used for the random values. 
     
     
       14. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices, the method comprising:
 establishing for respective devices unique identification numbers;    causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;    transmitting a command using the interrogator requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the specified group being equal to or less than the entire set of random values, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels;    receiving the command at multiple RFID devices, RFID devices receiving the command respectively determining if their chosen random values fall within the specified group and, only if so, sending a reply to the interrogator, wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply;    determining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group using a different level of the tree, the interrogator transmitting a command requesting devices having random values within the new specified group of random values to respond; and, if not, the interrogator re-transmitting a command requesting devices having random values within the first mentioned specified group of random values to respond; and    if a reply without collision is received from a device, the interrogator subsequently sending a command individually addressed to that device.    
     
     
       15. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein the first mentioned specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is not within communications range of the interrogator does not respond to the transmitting of the command or the re-transmitting of the command. 
     
     
       16. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein the first mentioned specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is within communications range of the interrogator responds to the transmitting of the command and the re-transmitting of the command. 
     
     
       17. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein a device in the first mentioned specified group is capable of changing between being within communications range of the interrogator and not being within communications range of the interrogator over time. 
     
     
       18. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein the devices respectively comprise an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       19. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  and further comprising, after the interrogator transmits a command requesting devices having random values within the new specified group of random values to respond;
 devices receiving the command respectively determining if their chosen random values fall within the new smaller specified group and, if so, sending a reply to the interrogator.    
     
     
       20. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 19  and further comprising, after the interrogator transmits a command requesting devices having random values within the new specified group of random values to respond;
 determining if a collision occurred between devices that sent a reply and, if so, creating a new specified group and repeating the transmitting of the command requesting devices having random values within a specified group of random values to respond using different specified groups until all of the devices capable of communicating with the interrogator are identified.    
     
     
       21. A communications system comprising an interrogator, and a plurality of wireless identification devices configured to communicate with the interrogator using RF, the interrogator being configured to employ tree searching 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, the interrogator being configured to follow a search tree, the tree having multiple nodes respectively representing subgroups of the multiple wireless identification devices, the interrogator being 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. 
     
     
       22. A communications system in accordance with  claim 21  wherein the interrogator is configured to send a command at a different node if a collision occurs in response to the first mentioned command. 
     
     
       23. A communications system in accordance with  claim 21  wherein a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator. 
     
     
       24. A communications system in accordance with  claim 21  wherein a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is within communications range of the interrogator responds to the command. 
     
     
       25. A communications system in accordance with  claim 21  wherein a device in a subgroup is movable relative to the interrogator so as to be capable of changing between being within communications range of the interrogator and not being within communications range. 
     
     
       26. A communications system in accordance with  claim 21  wherein the wireless identification device comprises an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       27. A system comprising:
 an interrogator;    a number of communications devices capable of wireless communications with the interrogator;    means for establishing for respective devices unique identification numbers respectively having the first predetermined number of bits;    means for causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;    means for causing the interrogator to transmit a command requesting devices having random values within a specified group of random values to respond;    means for causing devices receiving the command to determine if their chosen random values fall within the specified group and, if so, to send a reply to the interrogator; and    means for causing the interrogator to determine if a collision occurred between devices that sent a reply and, if so, to create a new, smaller, specified group; and, if not, transmit a command requesting devices having random values within the same specified group of random values to respond.    
     
     
       28. A system in accordance with  claim 27  wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply. 
     
     
       29. A system in accordance with  claim 27  wherein a specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator. 
     
     
       30. A system in accordance with  claim 27  wherein the interrogator further includes means for, after receiving a reply without collision from a device, sending a command individually addressed to that device. 
     
     
       31. A system comprising:
 an interrogator configured to communicate to a selected one or more of a number of communications devices; and    a plurality of communications devices; the devices being configured to select random values, wherein respective devices choose random values independently of random values selected by the other devices; the interrogator being configured to transmit a command requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the specified group being less than the entire set of random values, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels, the specified group being defined as being at one of the nodes; devices receiving the command being configured to respectively determine if their chosen random values fall within the specified group and, only if so, send a reply to the interrogator, wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply; the interrogator being configured to determine if a collision occurred between devices that sent a reply and, if so, create a new, smaller, specified group using a different level of the tree, the interrogator being configured to transmit a command requesting devices having random values within the new specified group of random values to respond; and, if not, the interrogator being configured to re-transmit a command requesting devices having random values within the first mentioned specified group of random values to respond.    
     
     
       32. A system in accordance with  claim 31  wherein the first mentioned specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator. 
     
     
       33. A system in accordance with  claim 31  wherein a device in the first mentioned specified group is capable of changing between being within communications range of the interrogator and not being within communications range of the interrogator over time. 
     
     
       34. A system in accordance with  claim 31  wherein the respective devices comprise an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       35. A system comprising:
 an interrogator configured to communicate to a selected one or more of a number of RFID devices;    a plurality of RFID devices, respective devices being configured to store a unique identification number, respective devices being further configured to store a random value;    the interrogator being configured to transmit a command requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels, the specified group being defined as being at one of the nodes;    devices receiving the command respectively being configured to determine if their chosen random values fall within the specified group and, if so, send a reply to the interrogator; and, if not, not send a reply; and    the interrogator being configured to determine if a collision occurred between devices that sent a reply and, if so, to create a new, smaller, specified group by descending in the tree; and, if not, to transmit a command at the same node.    
     
     
       36. A system in accordance with  claim 35  wherein the unique identification numbers for respective devices are stored in digital form and respectively comprise a predetermined number of bits. 
     
     
       37. A system in accordance with  claim 35  wherein the random values for respective devices are stored in digital form and respectively comprise a predetermined number of bits. 
     
     
       38. A system in accordance with  claim 35  wherein the interrogator is configured to determine if a collision occurred between devices that sent a reply in response to respective Identify commands and, if so, to create further new specified groups and repeat the transmitting of the command requesting devices having random values within a specified group of random values to respond using different specified groups until all responding devices capable of responding are identified. 
     
     
       39. A method for performing radio frequency communications, the method comprising:
   transmitting by an interrogator a first signal, the first signal including a first set of bits to identify a first subgroup of a group of possible random numbers;        receiving by one or more RFID devices the first signal;        communicating by each of the one or more RFID devices a first response if the one or more RFID devices has generated a random number that is included in the first subgroup;        receiving by the interrogator one or more received responses, the one or more received responses being received from respective ones of the one or more RFID devices; and        responsive to receiving one of the one or more received responses without a collision, retransmitting by the interrogator at least the first signal.     
     
     
       40. The method of  claim 39 , wherein the first signal includes a selection indicator, the selection indicator identifying one or more RFID devices, the communicating by each of the one or more RFID devices only being performed if the selection indicator corresponds to one or more selection bits stored on each respective RFID device. 
     
     
       41. The method of  claim 39 , further comprising setting, by the one or more RFID devices communicating the first response, an inventoried flag to a first state to indicate that each respective RFID device has responded to the interrogator. 
     
     
       42. The method of  claim 39 , further comprising transmitting by the interrogator a wake- up signal, the wake - up signal causing an RFID device to transition out of a sleep state.   
     
     
       43. The method of  claim 39 , wherein the one of the one or more received responses without a collision is received from a first RFID device, and further comprising the interrogator transmitting a command to silence the first RFID device. 
     
     
       44. The method of  claim 39 , wherein the one of the one or more received responses without a collision is received from a first RFID device and includes at least one random number generated by the first RFID device, and further comprising transmitting by the interrogator at least one additional command to the first RFID device, the first RFID device being identified in the at least one additional command by an identifier including the at least one random number. 
     
     
       45. The method of  claim 39 , further comprising transmitting by the interrogator a wake up signal. 
     
     
       46. The method of  claim 39 , further comprising responsive to a collision occurring in the receiving by the interrogator one or more received responses, transmitting by the interrogator a second signal, the second signal including a second set of bits to identify a second subgroup of the group of possible random numbers, wherein the second subgroup is a subgroup of the first subgroup, the second set of bits includes the first set of bits plus one or more additional bits, and the second signal includes the first signal. 
     
     
       47. The method of  claim 46 , wherein the second subgroup is determined at least in part by skipping one or more levels of a search tree. 
     
     
       48. The method of  claim 46 , wherein the second set of bits includes the first set of bits plus two or more of the additional bits. 
     
     
       49. The method of  claim 39 , wherein the first subgroup is based at least in part on a maximum number of possible random numbers. 
     
     
       50. A system for performing radio frequency communications, the system comprising:
   a first radio frequency identification  ( RFID )  device configured to generate a random number and to communicate a response, including at least a portion of the random number, upon receiving a request that includes an indication of a subset of possible random numbers if the first RFID device determines that the subset includes the random number generated by the first RFID device;        an antenna positioned in a first region; and        an interrogator coupled to the antenna, the interrogator configured to transmit a signal comprising a portion of an identifier and to receive a reply to the signal from a target RFID device that has generated a random number having a portion equal to the portion of the identifier, the interrogator further configured to re - transmit the signal, including at least the portion of the identifier, if the reply is received without a collision.     
     
     
       51. The system of  claim 50 , wherein the request includes a selection indicator, the selection indicator identifying one or more RFID devices, the first RFID device being configured to communicate the response only if the selection indicator corresponds to one or more selection bits stored on the first RFID tag. 
     
     
       52. The system of  claim 50 , wherein the first RFID device is further configured to set an inventoried flag to a first state to indicate that the first RFID device has responded to the at least one interrogator. 
     
     
       53. The system of  claim 50 , wherein the first RFID device is further configured to communicate the response after receiving a wake- up signal.   
     
     
       54. The system of  claim 50 , wherein the first RFID device is further configured to communicate a response at a time slot corresponding to a random number generated by the first RFID device. 
     
     
       55. The system of  claim 50 , wherein the interrogator is further configured to transmit a sleep command upon receiving the reply without a collision. 
     
     
       56. The system of  claim 50 , wherein the interrogator is further configured to transmit a larger portion of the identifier if the reply is received with a collision. 
     
     
       57. The system of  claim 56 , wherein a difference between the portion of the identifier and the larger portion of the identifier is two or more bits. 
     
     
       58. An interrogator comprising:
   one or more antennas;        a receiver communicatively coupled to at least one of the one or more antennas to receive one or more messages from one or more radio frequency identification  ( RFID )  devices;        a transmitter communicatively coupled to at least one of the one or more antennas to transmit one or more messages; and        a control unit communicatively coupled to the transmitter and the receiver, the control unit configured to implement an algorithm to detect at least a single RFID device in a field of the interrogator, including re - transmitting a first signal responsive to receipt of a first response from the one or more RFID devices without a collision, the first signal including a first set of bits of at least a first portion of possible random numbers that may be generated by the one or more RFID devices, and the first response including at least a second portion of a random number generated by the one or more RFID devices.     
     
     
       59. The interrogator of  claim 58 , wherein the first signal includes a selection indicator, the selection indicator corresponding to one or more selection bits stored on the one or more RFID devices. 
     
     
       60. The interrogator of  claim 58 , wherein the control unit is further configured to transmit a command to silence the one or more RFID devices from which the first response was received without a collision, and the control unit is further configured to indicate a number of time slots from which at least a first RFID device is to randomly select a time slot in which to communicate a random value generated by the first RFID device. 
     
     
       61. The interrogator of  claim 58 , wherein the control unit is further configured to define a second set of bits of at least a second portion, greater than the first portion, of possible random numbers responsive to a collision detected in the receipt of the first response from the one or more RFID devices. 
     
     
       62. The interrogator of  claim 61 , wherein the control unit is further configured to define the second set of bits to be at least two bits greater than the first portion. 
     
     
       63. The interrogator of  claim 58 , wherein the possible random numbers define a binary search tree, the first set of bits define a level in the search tree, and the control unit is further configured to skip one or more intermediate levels in the binary search tree to implement the algorithm. 
     
     
       64. The interrogator of  claim 58 , wherein the control unit is further configured to transmit a wake- up signal, indicate a number of time slots, and receive a random value from a first RFID device in a time slot randomly determined by the first RFID device from among the number of time slots.   
     
     
       65. A method comprising:
   providing an interrogator to generate an RF field and to initiate the implementation of an algorithm to detect at least a single target RFID device out of potentially multiple target RFID devices in the RF field, the algorithm including:      defining a first subgroup of possible random numbers that may be generated by the target device, the first subgroup being defined by a first set of bits common to the first subgroup;        transmitting a signal comprising at least the first set of bits to identify the first subgroup of possible random numbers and requesting the target device to respond if the target device has generated a random number included in the subgroup;        receiving a response from the target device if the target device has generated the random number included in the subgroup;        if no collision is detected in the receiving of the response from the target device, determining, from the response, the random number generated by the target device and retransmitting the signal; and        if a collision is detected in the receiving of the response from the target device, defining a second subgroup of possible random numbers that may be generated by the target device, the second subgroup being a subset of the first subgroup and being defined by a second set of bits common to the second subgroup, and retransmitting the signal.       
     
     
       66. The method of  claim 65 , wherein the signal includes a selection indicator that identifies a class of one or more of a plurality of RFID devices from which a response is being requested. 
     
     
       67. The method of  claim 65 , wherein the algorithm further includes transmitting a command to silence the target device after the determining of the random number generated by the target device. 
     
     
       68. The method of  claim 65 , wherein the algorithm further includes transmitting a number of time slots from which at least a first RFID device is to randomly select a time slot in which to communicate a random value generated by the first RFID device. 
     
     
       69. The method of  claim 65 , wherein the algorithm further comprises transmitting a number of time slots, and receiving a random value from a first RFID device in a time slot randomly determined by the first RFID device from among the number of time slots. 
     
     
       70. The method of  claim 65 , wherein the second set of bits includes the first set of bits and the algorithm further comprises transmitting the second set of bits if the collision is detected in the receiving of the response from the target device. 
     
     
       71. The method of  claim 70 , wherein the algorithm accommodates the second set of bits being two or more bits longer than the first set of bits. 
     
     
       72. A method, comprising:
   receiving a first signal from an interrogator in accordance with an algorithm to identify a radio frequency identification  ( RFID )  device in a field of the interrogator, the first signal comprising a first set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the first set of bits;        responsive to receiving the first signal, determining if the first set of bits is equal to a first portion of a random number generated by the RFID device, and, if so, modulating an RF field, provided by the interrogator, to communicate a reply to the interrogator in accordance with the algorithm; and        receiving, in accordance with the algorithm, a retransmission of the first signal from the interrogator in response to the interrogator receiving the reply without detecting a collision.     
     
     
       73. The method of  claim 72 , further comprising communicating with the interrogator in one of a first communication mode and a second communication mode determined by the interrogator, wherein in accordance with the first communication mode the RFID device modulates an RF field generated by the RFID device and in accordance with the second communication mode the RFID device modulates an RF field generated by the interrogator. 
     
     
       74. The method of  claim 73 , further comprising communicating with the interrogator at one of a plurality of bit rates determined by the interrogator. 
     
     
       75. The method of  claim 72 , further comprising receiving a wake up command from the interrogator and, in response, transitioning from a sleep state. 
     
     
       76. The method of  claim 75 , further comprising receiving a sleep command from the interrogator. 
     
     
       77. The method of  claim 76 , wherein the sleep command is received in response to the interrogator receiving the reply without detecting a collision, in accordance with the algorithm, before the receiving of the retransmission of the first signal. 
     
     
       78. The method of  claim 72 , wherein the reply comprises a random value generated by the RFID device. 
     
     
       79. The method of  claim 78 , wherein the random number comprises the random value. 
     
     
       80. The method of  claim 79 , wherein the random value is the random number. 
     
     
       81. The method of  claim 72 , further comprising
   receiving, in accordance with the algorithm, a second signal from the interrogator in response to the interrogator detecting a collision in the reply, the second signal comprising a second set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the second set of bits; and        responsive to receiving the second signal, determining if the second set of bits is equal to a second portion of the random number generated by the RFID device, and, if so, modulating the RF field to communicate a second reply to the interrogator in accordance with the algorithm, wherein the second signal comprises the first signal, the second set of bits comprises the first set of bits plus at least two additional bits, and the second portion of the random number comprises the first portion of the random number.     
     
     
       82. The method of  claim 81 , wherein the second reply comprises at least a portion of the random number. 
     
     
       83. The method of  claim 82 , further comprising communicating a random value to the interrogator during a time slot randomly selected from a number of time slots. 
     
     
       84. The method of  claim 72 , further comprising communicating a random value to the interrogator during a time slot randomly selected from a number of time slots. 
     
     
       85. A system, comprising:
   a radio frequency identification  ( RFID )  device comprising a receiver to receive a first command including a portion of an identification number, a random number generator to generate a random number to identify the device, and a transmitter to communicate a reply to the first command if the portion of the identification number is equal to a first portion of the random number; and        an interrogator configured to implement an algorithm to identify one or more RFID devices in a field of the interrogator, the algorithm comprising transmitting a first signal with a first set of bits to request a response from a selected one or more devices, receiving a first response thereto from the selected one or more devices, detecting if a collision occurred in the first response, and retransmitting the first signal with at least the first set of bits to request a second response from at least one of the selected one or more devices in response to detecting no collision in the first response.     
     
     
       86. The system of  claim 85 , further comprising memory storing a unique identification code to be transmitted by the system. 
     
     
       87. The system of  claim 85 , wherein the transmitter is configured to communicate by modulating an RF field provided by a remote device. 
     
     
       88. The system of  claim 87 , wherein the algorithm further comprises transmitting an indication of the number of bits of the first set of bits. 
     
     
       89. The system of  claim 85 , wherein retransmitting the first signal with at least the first set of bits comprises retransmitting the first signal with no more than the first set of bits. 
     
     
       90. The system of  claim 85 , wherein the system is configured to communicate at one of a plurality of bit rates determined by a remote device. 
     
     
       91. The system of  claim 90 , wherein the system is configured to operate in a first communication mode during a first period of time and in a second communication mode during a second period of time, wherein in accordance with the first communication mode the system is configured to modulate an RF field generated by the remote device and in accordance with the second communication mode the system is configured to generate and modulate an RF field. 
     
     
       92. The system of  claim 85 , wherein the RFID device is configured to receive a signal to silence the RFID device. 
     
     
       93. The system of  claim 92 , wherein the RFID device is configured to receive a wake up command and, in response, to transition from a sleep state. 
     
     
       94. The system of  claim 85 , wherein the algorithm further comprises transmitting a signal to silence at least one of the one or more RFID devices in response to the detecting no collision and before the retransmitting of the first signal. 
     
     
       95. The system of  claim 85 , wherein the replay comprises at least a second portion of the random number that is not part of the first portion of the random number. 
     
     
       96. The system of  claim 95 , wherein the interrogator is further configured to use the first response to determine a random value generated by the selected one or more devices in accordance with the algorithm. 
     
     
       97. The system of  claim 85 , wherein the algorithm further comprises transmitting a second signal from the interrogator in response to detecting a collision in the first response, the second signal comprising a second set of bits and requesting a response from at least one of the one or more RFID devices in the field selected in accordance with at least the second set of bits, wherein the second set of bits includes the first set of bits plus at least one additional bit. 
     
     
       98. The system of  claim 97 , wherein the interrogator is configured to generate, as part of the algorithm, the second set of bits including the first set of bits plus at least two additional bits. 
     
     
       99. The system of  claim 85 , wherein the RFID device is configured to communicate a random value during a first time slot randomly selected from a first number of time slots. 
     
     
       100. The system of  claim 99 , wherein the transmitter is configured to communicate by modulating an RF field provided by a remote device. 
     
     
       101. The system of  claim 100 , wherein the random value identifies the device to the remote device. 
     
     
       102. The system of  claim 101 , wherein the RFID device is further configured to communicate the random value to the remote device during a second time slot randomly selected from a second number of time slots, wherein the first number of time slots is different from the second number of time slots and is indicated by the remote device. 
     
     
       103. The system of  claim 102 , wherein the algorithm further comprises transmitting a second signal from the interrogator in response to detecting a collision in the first response, the second signal comprising a second set of bits and requesting a response from at least one of the one or more RFID devices in the field selected in accordance with at least the second set of bits, wherein, in accordance with the algorithm, the second set of bits include at least two bits in addition to the first set of bits. 
     
     
       104. An apparatus for wirelessly reading radio frequency identification ( RFID )  devices, comprising:      a transmitter to transmit a command along with a first portion of a set of random numbers to request a response from at least one RFID device that has generated a random number in the set;        an antenna to provide an RF field to be modulated by the device;        a receiver to receive the response; and        processing circuitry to perform collision detection, to determine the random number using the response, and to cause the transmitter to retransmit the command along with at least the first portion of the set of random numbers responsive to detecting no collision in the response.     
     
     
       105. The apparatus of  claim 104 , wherein the transmitter is configured to transmit the command along with an indication of the number of bits on the first portion. 
     
     
       106. The apparatus of  claim 105 , wherein the transmitter is configured to communicate with the RFID device at one of a plurality of bit rates determined by the apparatus. 
     
     
       107. The apparatus of  claim 104 , wherein the processing circuitry is configured to cause the transmitter to retransmit the command along with no more than the first portion of the set of random numbers responsive to the detecting. 
     
     
       108. The apparatus of  claim 104 , wherein the processing circuitry is configured to cause the transmitter to transmit a signal addressed to the RFID device responsive to receiving the response without collision. 
     
     
       109. The apparatus of  claim 108 , wherein the signal is configured to silence the RFID device. 
     
     
       110. The apparatus of  claim 109 , wherein the processing circuitry is configured to cause the transmitter to transmit the signal to silence the RFID device before causing the transmitter to retransmit the command. 
     
     
       111. The apparatus of  claim 104 , wherein the transmitter is configured to transmit a wake up command to transition the RFID device from a sleep state. 
     
     
       112. The apparatus of  claim 104 , wherein the response comprises at least a second portion of the random number that is not part of the first portion. 
     
     
       113. The apparatus of  claim 112 , wherein the processing circuitry is configured to determine a unique identification code stored in the RFID device in addition to the random number. 
     
     
       114. The apparatus of  claim 104 , wherein the processing circuitry is configured to specify a second portion of the set of random numbers in response to detecting a collision in the response, the second portion being a subset of the first portion. 
     
     
       115. The apparatus of  claim 114 , wherein the processing circuitry is further configured to enable the second portion to be less than half of the first portion. 
     
     
       116. The apparatus of  claim 115 , wherein the receiver is to receive a reply from one or more RFID devices in one of a number of time slots indicated by the apparatus to the one or more RFID devices. 
     
     
       117. The apparatus of  claim 116 , wherein the reply comprises a random value generated by the one or more RFID devices. 
     
     
       118. The apparatus of  claim 104 , wherein the processing circuitry if further configured to cause the transmitter to transmit a signal to indicate a number of time slots in which one or more RFID devices responds to the apparatus with a reply. 
     
     
       119. The apparatus of  claim 118 , wherein the reply comprises a random value generated by the one or more RFID devices. 
     
     
       120. The apparatus of  claim 119 , wherein the one or more RFID devices comprises the RFID device and the random value is equal to the random number. 
     
     
       121. The apparatus of  claim 104 , wherein the random number identifies the device to the apparatus. 
     
     
       122. A radio frequency identification ( RFID )  reader, comprising:      a transmitter to transmit at least a first portion of an identifier along with an indication of a first number of bits in the first portion, and to request a first response from an RFID device that has generated a first portion of a random number equal to the first portion of the identifier;        a receiver to receive the first response from the device; and        a processing circuit coupled to the transmitter and receiver to implement an algorithm to detect at least one from among potentially multiple RFID devices, wherein in accordance with the algorithm the processing circuit is to perform collision detection on the first response and, in response to detecting no collision, to retransmit, via the transmitter, the at least first portion of the identifier and to request a second response thereto.     
     
     
       123. The reader of  claim 122 , wherein the processing circuit is configured to determine the random number using the first response. 
     
     
       124. The reader of  claim 123 , wherein the transmitter is configured to provide an RF field to be modulated by the RFID device to communicate the first response. 
     
     
       125. The reader of  claim 122 , wherein in accordance with the algorithm the processing circuit is to retransmit no more than the first portion of the identifier. 
     
     
       126. The reader of  claim 122 , wherein the transmitter is configured to communicate at a first bit rate during a first period of time, and at a second bit rate during a second period of time. 
     
     
       127. The reader of  claim 122 , wherein the reader is configured to operate in a first communication mode during a first period of time and in a second communication mode during a second period of time, wherein in accordance with the first communication mode the receiver is configured to receive a remotely generated and remotely modulated RF field and in accordance with the second communication mode the receiver is configured to receive an RF field locally generated by the transmitter and remotely modulated. 
     
     
       128. The reader of  claim 122 , wherein the transmitter is configured to transmit a signal to silence the RFID device and to transmit a wake up command to transition the RFID device from a sleep state. 
     
     
       129. The reader of  claim 122 , wherein in accordance with the algorithm the processing circuit is to transmit, via the transmitter, a signal to silence the RFID device in response to the detecting no collision and before retransmitting the first portion. 
     
     
       130. The reader of  claim 122 , wherein in accordance with the algorithm the processing circuit is to transmit a second portion of the identifier along with an indication of a second number of bits in the second portion in response to detecting a collision on the first response, wherein the second portion includes the first portion. 
     
     
       131. The reader of  claim 130 , wherein in accordance with the algorithm the second number of bits is greater than the first number of bits by at least two bits. 
     
     
       132. The reader of  claim 131 , wherein the receiver is to receive the first response comprising at least a second portion of the random number that is not part of the first portion of the random number. 
     
     
       133. The reader of  claim 122 , wherein the transmitter is configured to transmit an indication of a first number of time slots from which one or more RFID devices are to randomly select a first time slot in which to communicate a random value identifier to the reader. 
     
     
       134. The reader of  claim 133 , wherein the transmitter is further configured to transmit an indication of a second number of time slots, different from the first number of time slots, responsive to collision detection by the processing circuit. 
     
     
       135. The reader of  claim 134 , wherein the processing circuit is to transmit a second portion of the identifier along with an indication of a second number of bits in the second portion in response to detecting a collision on the first response, wherein the second portion includes the first portion and the processing circuit supports the second number of bits being greater than the first number of bits by at least two bits. 
     
     
       136. A system, comprising:
   an RFID target device to receive a portion of an identifier, to compare the portion of the identifier to a portion of a random value generated by the target device, and to communicate a reply value if the portion of the identifier is equal to the portion of the random value; and        an RFID initiating device to initiate communication with one or more RFID target devices, the initiating device to transmit a first request including a first command and first information, to receive a first response to the first request from each of one or more RFID target devices that has generated a respective random number that is included in a first subgroup of one or more of a group of possible random numbers indicated by the first information, to perform collision detection on the first response, and to transmit a second request including a retransmission of at least the first command and the first information responsive to detecting no collision.     
     
     
       137. The system of  claim 136 , wherein the target and initiating devices are to implement a time slot method in accordance with a protocol with which the target and initiating devices are compliant. 
     
     
       138. The system of  claim 137 , wherein the target device is to modulate an RF field provided by a remote device to communicate the reply. 
     
     
       139. The system of  claim 138 , wherein the system is to operate in a selectable one of a first communication mode and a second communication mode in accordance with the protocol, wherein in accordance with the first communication mode the target device is to communicate by modulating a remotely generated RF field and in accordance with the second communication mode the target device is to generate an RF field. 
     
     
       140. The system of  claim 139 , wherein the target and initiating devices are to communicate at a selectable one of a plurality of bit rates in accordance with the protocol. 
     
     
       141. The system of  claim 140 , wherein the target device is to transition from a sleep state upon receiving a wake up command. 
     
     
       142. The system of  claim 136 , further comprising memory storing a unique identification code, separate from the random value and random number, to be transmitted by the system. 
     
     
       143. The system of  claim 136 , wherein the target device is to modulate an RF field provided by a remote device to communicate the reply. 
     
     
       144. The system of  claim 136 , wherein the initiating device is to transmit a signal to silence the one or more target devices. 
     
     
       145. The system of  claim 144 , wherein the initiating device is to transmit the signal in response to the detecting no collision before transmitting the second request. 
     
     
       146. The system of  claim 136 , wherein the random value comprises the reply value. 
     
     
       147. The system of  claim 146 , wherein the random number comprises the first response. 
     
     
       148. The system of  claim 136 , wherein the target device is to implement a slotted aloha algorithm in which the target device is to communicate an identifier, randomly generated by the target device, in a randomly selected time slot of a number of time slots indicated to the target device. 
     
     
       149. The system of  claim 148 , further comprising memory storing a unique identification code, separate from the random value, to be transmitted by the target device. 
     
     
       150. The system of  claim 149 , wherein the target device is to modulate a remotely generated RF field to communicate the reply. 
     
     
       151. The system of  claim 136 , wherein the initiating device is to transmit a third request, including a retransmission of at least the first command and the first information responsive to detecting a collision in the first response, wherein the third request indicates a second subgroup that is a subset of the first subgroup. 
     
     
       152. The system of  claim 151 , wherein the second subgroup is less than half of the first subgroup in accordance with a protocol with which the target and initiating devices are compliant. 
     
     
       153. The system of  claim 152 , wherein the target device is to implement a slotted aloha algorithm in which the target device is to communicate an identifier, randomly generated by the target device, in a randomly selected time slot of a number of time slots. 
     
     
       154. The system of  claim 153 , wherein the initiating device is to transmit a signal to indicate a number of time slots in which the initiating device is to receive a response. 
     
     
       155. The system of  claim 136 , wherein the one or more target devices comprises the target device. 
     
     
       156. The system of  claim 136 , wherein the first request includes a mask to identify a common portion of random numbers included in the first subgroup. 
     
     
       157. A radio frequency identification ( RFID )  device, comprising:      a random number generator to generate a first random number identifier;        a receiver coupled to an antenna to receive a transmission of a first set of bits from a reader in accordance with an algorithm to enable the reader to determine the first identifier;        processing circuitry to compare the first set of bits to a first portion of the first identifier; and        a modulating circuit to modulate an RF field produced by the reader to communicate a second set of bits to the reader if the first set of bits is equal to the first portion of the first identifier, wherein the first identifier comprises the second set of bits, and wherein in accordance with the algorithm the receiver is to further receive a retransmission of at least the first set of bits from the reader if the reader receives the second set of bits without collision.     
     
     
       158. The device of  claim 157 , wherein the second set of bits comprises the first set of bits. 
     
     
       159. The device of  claim 157 , wherein the random number generator is to generate a second random number identifier and a random value, wherein the random value is to be used to select a slot in which to communicate the second identifier in accordance with a time slot method. 
     
     
       160. The device of  claim 157 , wherein the modulating circuit is to operate in an alternate communication mode in which the modulating circuit is to modulate an RF field produced by the device itself. 
     
     
       161. The device of  claim 157 , wherein the modulating circuit is to communicate at one of a plurality of selectable bit rates. 
     
     
       162. The device of  claim 161 , wherein the receiver is receive a wake up command from the reader to transition the device from a sleep state. 
     
     
       163. The device of  claim 157 , wherein the processing circuitry is to implement a slotted aloha algorithm. 
     
     
       164. The device of  claim 163 , further comprising memory storing a unique identification code, separate from the first identifier, to be wirelessly communicated. 
     
     
       165. The device of  claim 157 , further comprising memory storing a unique identification code, separate from the first identifier, to be wirelessly communicated to a reader. 
     
     
       166. The device of  claim 157 , wherein in accordance with the algorithm the receiver is to receive a signal from the reader addressed to the device responsive to the reader receiving the second set of bits without collision. 
     
     
       167. The device of  claim 166 , wherein the signal is to silence the device. 
     
     
       168. The device of  claim 167 , wherein in accordance with the algorithm the signal is to be received by the receiver before the retransmission of the at least first set of bits. 
     
     
       169. The device of  claim 157 , wherein the receiver is to receive a retransmission of the first set of bits along with additional bits from the reader for comparison to at least a second portion of the first identifier in accordance with the algorithm if the reader detects a collision upon receiving the second set of bits, wherein in accordance with the algorithm, the additional bits are at least two bits. 
     
     
       170. The device of  claim 169 , wherein the modulating circuit is to communicate a second random number identifier in a randomly selected time slot of a number of time slots. 
     
     
       171. The device of  claim 157 , wherein the receiver is to receive an indication of a first number of time slots from which the device is to randomly select a first time slot in which to communicate a second random number identifier and to receive an indication of a second number of time slots, different from the first number of time slots.