Method of addressing messages and communications systems

Abstract

A method of and apparatus for establishing wireless communications between an interrogator and individual ones of multiple wireless identification devices, the method comprising utilizing a tree search method to establish 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 levels respectively representing subgroups of the multiple wireless identification devices, the method further comprising starting the tree search at a selectable level of the search tree. A communications system comprising an interrogator, and a plurality of wireless identification devices configured to communicate with the interrogator in a wireless fashion, the respective wireless identification devices having a unique identification number, the interrogator being configured to employ a tree search technique to determine the unique identification numbers of the different wireless identification devices so as to be able to establish communications between the interrogator and individual ones of the multiple wireless identification devices without collision by multiple wireless identification devices attempting to respond to the interrogator at the same time, wherein the interrogator is configured to start the tree search at a selectable level of the search tree. The interrogator transmits a first request indicating a subgroup of random numbers out of a total number of possible random numbers. The wireless identification devices each determine if the random number generated by each wireless identification device falls within the subgroup, and if so, the wireless identification device responds to the interrogator. If a collision between wireless identification device responses is detected by the interrogator, the interrogator transmits a second request indicating a subset of the subgroup of random numbers.

What is claimed is: 
     
       1. A method of establishing wireless communications between an interrogator and individual ones of multiple wireless identification devices, the wireless identification devices having respective identification numbers and being addressable by specifying identification numbers with any one of multiple possible degrees of precision, the method comprising utilizing a tree search in an arbitration scheme to determine a degree of precision necessary to establish one-on-one communications 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 selectable levels respectively representing subgroups of the multiple wireless identification devices, the level at which a tree search starts being variable the method further comprising starting the tree search at any selectable level of the search tree. 
     
     
       2. A method in accordance with  claim 1  and further comprising determining the maximum possible number of wireless identification devices that could communicate with the interrogator, and selecting a level of the search tree based on the determined maximum possible number of wireless identification devices that could communicate with the interrogator. 
     
     
       3. A method in accordance with  claim 2  and further comprising starting the tree search at a level determined by taking the base two logarithm of the determined maximum possible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively. 
     
     
       4. A method in accordance with  claim 2  and further comprising starting the tree search at a level determined by taking the base two logarithm of the determined maximum possible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively, and wherein the maximum number of devices in a subgroup in one level is half of the maximum number of devices in the next higher level. 
     
     
       5. A method in accordance with  claim 2  and further comprising starting the tree search at a level determined by taking the base two logarithm of the power of two nearest the determined maximum possible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively, and wherein the maximum number of devices in a subgroup in one level is half of the maximum number of devices in the next higher level. 
     
     
       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 respectively having a first predetermined number of bits;   establishing a second predetermined number of bits to be used for random values;   causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;   determining the maximum number of devices potentially capable of responding to the interrogator;   transmitting a command from the interrogator requesting devices having random values within a specified group of random values to respond, by using a subset of the second predetermined number of bits, the specified group being chosen in response to the determined maximum number;   receiving the command at multiple devices, devices receiving the command respectively determining if the random value chosen by the device falls within the 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 new, smaller, specified group.   
     
     
       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 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 random value of the device sending the reply. 
     
     
       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 sending a reply to the interrogator comprises transmitting both the random value of the device sending the reply and the unique identification number of the device sending the reply. 
     
     
       11. 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 command individually addressed to that device. 
     
     
       12. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices, the method comprising:
 causing the devices to select random values for use as arbitration numbers, wherein respective devices choose random values independently of random values selected by the other devices, the devices being addressable by specifying arbitration numbers with any one of multiple possible degrees of precision;   transmitting a command from 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 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, wherein the size of groups of random values decrease in size by half with each node descended, wherein the specified group is below a node on the tree selected based on the maximum number of devices capable of communicating with the interrogator;   receiving the command at multiple devices, devices receiving the command respectively determining if the random value chosen by the device falls within the specified group and, if so, sending a reply to the interrogator; and, if not, not sending a reply; and   determining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group by descending in the tree.   
     
     
       13. A method of addressing messages from an interrogator 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 communications devices in accordance with  claim 13  wherein the predetermined number of bits to be used for the random values comprises an integer multiple of eight. 
     
     
       15. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices in accordance with  claim 13  wherein devices sending a reply to the interrogator do so within a randomly selected time slot of a number of slots. 
     
     
       16. 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 a predetermined number of bits to be used for random values, the predetermined number being a multiple of sixteen;   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 from 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, wherein the maximum size of groups of random values decrease in size by half with each node descended, wherein the specified group is below a node on a level of the tree selected based on the maximum number of devices known to be capable of communicating with the interrogator;   receiving the command at multiple devices, devices receiving the command respectively determining if the random value chosen by the device falls within the specified group and, only if so, sending a reply to the interrogator, wherein sending a reply to the interrogator comprises transmitting both the random value of the device sending the reply and the unique identification number of the device sending the reply;   using the interrogator to determine if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group using a level of the tree different from the level used in the interrogator transmitting, the interrogator transmitting a command requesting devices having random values within the new 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.   
     
     
       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 16  and further comprising determining the maximum possible number of wireless identification devices that could communicate with the interrogator. 
     
     
       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 16  wherein selecting the level of the tree comprises taking the base two logarithm of the determined maximum possible number, wherein a level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively. 
     
     
       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 16  wherein selecting the level of the tree comprises taking the base two logarithm of the determined maximum possible number, wherein a level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively, and wherein the maximum number of devices in a subgroup in one level is half of the maximum number of devices in the next higher level. 
     
     
       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 16  wherein selecting the level of the tree comprises taking the base two logarithm of the power of two nearest the determined maximum possible number, wherein the level of the tree containing all subgroups is considered level zero, and lower levels are numbered consecutively, and wherein the maximum number of devices in a subgroup in one level is half of the maximum number of devices in the next higher level. 
     
     
       21. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 16  wherein the wireless identification device comprises an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       22. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 16  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, using devices receiving the command, if their chosen random values fall within the new smaller specified group and, if so, sending a reply to the interrogator. 
     
     
       23. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 22  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 within communications range are identified. 
     
     
       24. A communications system comprising an interrogator, and a plurality of wireless identification devices configured to communicate with the interrogator in a wireless fashion, the wireless identification devices having respective identification numbers, the interrogator being configured to employ a tree search in a search tree having multiple selectable levels, to determine the identification numbers of the different wireless identification devices with sufficient precision so as to be able to establish one-on-one communications between the interrogator and individual ones of the multiple wireless identification devices, wherein the interrogator is configured to start the tree search at any selectable level of the search tree. 
     
     
       25. A communications system in accordance with  claim 24  wherein the tree search is a binary tree search. 
     
     
       26. A communications system in accordance with  claim 24  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 a predetermined number of bits to be used as random numbers, and for causing respective devices to select random numbers respectively having the predetermined number of bits;   means for inputting a predetermined number indicative of the maximum number of devices possibly capable of communicating with the receiver;   means for causing the interrogator to transmit a command requesting devices having random values within a specified group of random values to respond, the specified group being chosen in response to the inputted predetermined number;   means for causing devices receiving the command to determine if their chosen random values fall within the specified group and, if so, 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, create a new, smaller, specified group.   
     
     
       28. A system in accordance with  claim 27  wherein sending a reply to the interrogator comprises transmitting the random value of the device sending the reply. 
     
     
       29. 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. 
     
     
       30. A system comprising:
 an interrogator configured to communicate to a selected one or more of a number of communications devices;   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, different sized groups of devices being addressable by specifying random values with differing levels of precision;   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, wherein the size of groups of random values decrease in size by half with each node descended, wherein the specified group is below a node on the tree selected based on a predetermined maximum number of devices capable of communicating with the interrogator;   devices receiving the command being configured to respectively 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, create a new, smaller, specified group by descending in the tree.   
     
     
       31. A system in accordance with  claim 30  wherein the random values respectively have a predetermined number of bits. 
     
     
       32. A system in accordance with  claim 30  wherein respective devices are configured to store unique identification numbers of a predetermined number of bits. 
     
     
       33. A system in accordance with  claim 30  wherein respective devices are configured to store unique identification numbers of sixteen bits. 
     
     
       34. 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 unique identification numbers respectively having a first predetermined number of bits, respective devices being further configured to store a second predetermined number of bits to be used for random values, respective devices being configured to select random values independently of random values selected by the other devices;   the interrogator being configured to transmit an identify command requesting a response from devices having random values within a specified group of a plurality of possible groups or random values, the specified group being less than or equal to 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, wherein the maximum size of groups of random values decrease in size by half with each node descended, wherein the specified group is below a node on a level of the tree selected based on the maximum number of devices known to be capable of communicating with the interrogator;   devices receiving the command respectively being configured to 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 both the random value of the device sending the reply and 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 level of the tree different from the level used in previously transmitting an identify command, the interrogator transmitting an identify command requesting devices having random values within the new specified group of random values to respond; and   the interrogator being configured to send a command individually addressed to a device after communicating with a device without a collision.   
     
     
       35. A system in accordance with  claim 34  wherein the interrogator is configured to input and store the predetermined number. 
     
     
       36. A system in accordance with  claim 34  wherein the devices are configured to respectively determine if their chosen random values fall within a specified group and, if so, send a reply, upon receiving respective identify commands. 
     
     
       37. A system in accordance with  claim 36  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, create further new specified groups and repeat the transmitting of the identify command requesting devices having random values within a specified group of random values to respond using different specified groups until all responding devices are identified. 
     
     
       38. A method implemented in a system having an interrogator and a plurality of radio frequency identification (RFID) devices, the interrogator having one or more antennas, a transmitter, a receiver and a controller, each respective device of RFID devices having a receiver, a transmitter and memory to store a respective identification code, the method comprising:
 transmitting, through the one or more antennas using the transmitter of the interrogator, an initial command to select one or more radio frequency identification (RFID) devices from the plurality of RFID devices that are within wireless communications range of the interrogator, the initial command specifying a bit string having multiple bits;   receiving the initial command from the interrogator by the receiver of the respective device of the plurality of RFID devices;   comparing, by the respective device of the plurality of RFID devices, the bit string specified in the initial command against corresponding bits stored in the memory of the respective device to determine whether the respective device is a member of a population of RFID devices selected according to the initial command; and   if the respective device is a member of the population, picking a respective random value by the respective device from a range of values to determine a respective slot and providing by the transmitter of the respective device a respective reply to the interrogator in accordance with the respective slot, the reply including at least a portion of an identifier of the respective device.   
     
     
       39. The method of claim 38, further comprising:
 transmitting, through the one or more antennas using the transmitter of the interrogator, an acknowledge command in response to the interrogator receiving the respective reply from the respective device and in response to the interrogator determining the respective reply to be collision-free, wherein the respective reply includes the bit string.   
     
     
       40. The method of claim 38, further comprising:
 communicating, from the respective device to the interrogator, the respective identification code to identify a person with whom the respective device is associated.   
     
     
       41. The method of claim 38, further comprising:
 accessing, by the interrogator, the respective device individually by sending the identifier to the respective device, after receiving the identifier from the respective device.   
     
     
       42. The method of claim 38, further comprising:
 indicating the range of values by the interrogator.   
     
     
       43. The method of claim 38, wherein the identifier comprises a random number generated by the respective device, and the random number is sixteen bits in length. 
     
     
       44. A method implemented in a system having an interrogator and at least one radio frequency identification (RFID) device, the method comprising:
 sending an initial command from a transmitter of the interrogator via an antenna, the initial command to select one or more radio frequency identification (RFID) devices, the initial command specifying a bit string having multiple bits;   receiving in the RFID device the initial command using a receiver of the RFID device over an antenna;   in response to the initial command, determining by the RFID device whether the RFID device is selected via a comparison between the bit string and a plurality of bits stored in a memory of the RFID device;   if the RFID device is determined to be selected, communicating a response from the RFID device to the interrogator in accordance with a slotted anticollision algorithm, wherein the response is to communicate one or more identifiers of the RFID device to the interrogator in accordance with the slotted anticollision algorithm, and wherein in accordance with the slotted anticollision algorithm the one or more identifiers is to be communicated in a time slot with a certain probability.   
     
     
       45. The method of claim 44, wherein the one or more identifiers comprise a sixteen bit random number; and the method further comprises:
 send an acknowledge command from the interrogator to the RFID device if the interrogator receives the random number without a collision error.   
     
     
       46. The method of claim 44, further comprising:
 communicating an identification code from the RFID device to the interrogator to identify a person with whom the RFID device is associated.   
     
     
       47. The method of claim 44, further comprising:
 individually addressing the RFID device by the interrogator using an access command, wherein the one or more identifiers communicated in the response comprises a random number and the access command includes the random number.   
     
     
       48. The method of claim 44, wherein the one or more identifiers comprise both a random number dynamically generated by the RFID device and a static number programmed into the RFID device. 
     
     
       49. The method of claim 44, wherein the response is to further communicate the plurality of bits, along with the one or more identifiers, to the interrogator in accordance with the slotted anticollision algorithm. 
     
     
       50. A method implemented in a radio frequency identification (RFID) device having a receiver and a transmitter, the method comprising:
 receiving a first command in the receiver of the RFID device from an interrogator after the RFID device is disposed in a wireless communication field of the interrogator and before the interrogator transmits any other command, the first command specifying a bit string comprising two or more bits;   in response to the first command, determining by the RFID device, using the bit string, whether the RFID device is selected for participation in a slotted anticollision algorithm; and   communicating one or more responses from the transmitter of the RFID device to the interrogator in accordance with the slotted anticollision algorithm, if the RFID device is determined to be selected for participation in the slotted anticollision algorithm, wherein the one or more responses include at least a portion of a first identifier and at least a portion of a second identifier stored in the RFID device.   
     
     
       51. The method of claim 50, wherein the first identifier comprises a random number dynamically generated by the RFID device for the interrogator to use to individually address the RFID device, and the second identifier is a static number stored in the RFID device. 
     
     
       52. The method of claim 51, further comprising:
 receiving in the receiver from the interrogator an indication of a number of slots from which the RFID device is to randomly select a slot in which to communicate the one or more responses in accordance with the slotted anticollision algorithm.   
     
     
       53. The method of claim 51, further comprising:
 receiving in the receiver from the interrogator an indication of a change in a number of slots in accordance with the slotted anticollision algorithm.   
     
     
       54. The method of claim 51, wherein the RFID device is configured for use in a wireless payment application and the RFID device comprises a memory to store an identification code to identify a person to be charged for payment. 
     
     
       55. The method of claim 51, wherein the random number is sixteen bits long and the method further comprises:
 communicating the bit string from the transmitter back to the interrogator with the one or more responses.   
     
     
       56. The method of claim 51, further comprising:
 picking a random value by the RFID device from a range of values to communicate the one or more responses with a probability corresponding to the random value in accordance with the slotted anticollision algorithm, wherein the first command is to indicate the range of values.   
     
     
       57. The method of claim 56, further comprising:
 receiving in the receiver a second command comprising an indication of a change in the range of values.   
     
     
       58. The method of claim 51, further comprising: communicating the bit string from the transmitter back to the interrogator with the one or more responses. 
     
     
       59. The method of claim 50, further comprising:
 receiving a signal in the receiver of the RFID device from the interrogator, after the interrogator sends the first command and before the transmitter of the RFID device communicates the one or more responses to the interrogator, wherein the signal indicates to the RFID device when to communicate the one or more responses to the interrogator.   
     
     
       60. The method of claim 50, wherein the one or more responses is communicated via the transmitter modulating an radio frequency (RF) field provided by the interrogator. 
     
     
       61. The method of claim 50, wherein the one or more responses includes the bit string. 
     
     
       62. The method of claim 50, wherein the RFID device is configured for use in a wireless payment system; and the method further comprises:
 storing in a memory of the RFID device an identification code to identify a person to be charged for payment.   
     
     
       63. The method of claim 50, further comprising: randomly picking an integer by the RFID device from a number of integers to communicate the one or more responses in a first slot with a probability corresponding to the randomly picked integer in accordance with the slotted anticollision algorithm, wherein the first command is to indicate the number of integers. 
     
     
       64. The method of claim 63, further comprising:
 receiving in the receiver of the RFID device from the interrogator a second command, the second command to indicate a different number of integers for the RFID device to use in accordance with the slotted anticollision algorithm.   
     
     
       65. A method implemented in a system having an interrogator and at least a first radio frequency identification (RFID) device and a second RFID device, the method comprising:
 providing a radio frequency (RF) field using at least one antenna of the interrogator, wherein a plurality of RFID devices are to modulate the RF field to transmit responses to the interrogator;   sending from a transmitter of the interrogator a first signal after the plurality of RFID devices are disposed in the field and before any of the plurality of RFID devices transmit responses to the interrogator, the first signal including a bit string comprising multiple bits;   storing in the first RFID device a first set of bits;   receiving in the first RFID device the first signal;   comparing the bit string received in the first signal with the first set of bits by the first RFID device to determine whether the first RFID device is selected by the interrogator;   if the first RFID device is selected by the interrogator, picking a first random integer by the first RFID device from a variable range of random integers to associate the first random integer with a first time slot in accordance with a slotted anticollision algorithm and modulating the RF field to communicate a first identification code of the first RFID device during the first time slot;   storing in the second RFID device a second set of bits;   receiving in the second RFID device the first signal;   comparing the bit string received in the first signal with the second set of bits by the second RFID device to determine whether the second RFID device is selected by the interrogator;   if the second RFID device is selected by the interrogator, picking a second random integer by the second RFID device from a variable range of random integers to associate the second random integer with a second time slot in accordance with the slotted anticollision algorithm and modulating the RF field to communicate a second identification code of the second RFID device during the second time slot; and   receiving in a receiver of the interrogator responses to the first signal in accordance with the slotted anticollision algorithm.   
     
     
       66. The method of claim 65, wherein the first identification code includes a first random number generated by the first RFID device; and
 the second identification code includes a second random number generated by the second RFID device.   
     
     
       67. The method of claim 66, wherein the receiving comprises receiving in the receiver of the interrogator the first random number from the first RFID device during a period of time associated with the first time slot; and
 receiving in the receiver of the interrogator the second random number from the second RFID device during a period of time associated with the second time slot; and   wherein the method further comprises:
 sending a first acknowledge signal to acknowledge the first RFID device in response to the receiving of the first random number; and 
 sending a second acknowledge signal to acknowledge the second RFID device in response to the receiving of the second random number. 
   
     
     
       68. The method of claim 66, further comprising:
 sending, using at least one antenna of the interrogator, a command that includes the first random number to individually identify the first RFID device, after receiving the first random number and the first identification code from the first RFID device.   
     
     
       69. The method of claim 68, further comprising:
 receiving in the interrogator a first identifier from the first RFID device to identify a person with whom the first RFID device is associated; and   receiving in the interrogator a second identifier from the second RFID device to identify a person with whom the second RFID device is associated.   
     
     
       70. The method of claim 69, further comprising:
 sending a second signal from the interrogator after sending the first signal, wherein the first identification code is communicated in response to receiving the second signal.   
     
     
       71. The method of claim 65, further comprising:
 sending a first acknowledge signal from the interrogator to acknowledge the first RFID device; and   sending a second acknowledge signal from the interrogator to acknowledge the second RFID device.   
     
     
       72. A method implemented in a system having an interrogator and at least one radio frequency identification (RFID) device, the method comprising:
 providing a radio frequency (RF) field to interrogate using an antenna of the interrogator;   sending an initial command from a transmitter of the interrogator to identify RFID devices disposed in the field, the initial command to be sent after the RFID devices are disposed in the field and before any of the RFID devices communicate any responses to the interrogator, the initial command to include a field specifying a plurality of bit values to select one or more of the RFID devices to participate in a slotted anticollision algorithm;   wirelessly receive the initial command in a receiver of the RFID device, after the RFID device is disposed in the RF field of the interrogator;   randomly selecting an integer value by the RFID device from a range of integer values in accordance with the slotted anticollision algorithm, the range to be adjustable and to be indicated to the RFID device by the interrogator;   modulating the RF field using a transmitter of the RFID device to communicate one or more responses to the interrogator based at least in part on whether the plurality of bit values received from the interrogator identify the RFID device for response, wherein the one or more responses include a first identifier and are communicated in accordance with the randomly selected integer value in accordance with the slotted anticollision algorithm; and   receiving in a receiver of the interrogator responses to the initial command in accordance with the slotted anticollision algorithm.   
     
     
       73. The method of claim 72, wherein the RFID device communicates at least a portion of an identification code to the interrogator, wherein the identification code identifies a person with whom the RFID device is associated. 
     
     
       74. The method of claim 72, wherein the one or more responses further include a second identifier communicated in accordance with the randomly selected integer value in accordance with the slotted anticollision algorithm. 
     
     
       75. The method of claim 74, wherein the first identifier comprises a random number generated by the RFID device; and
 the second identifier comprises a static code programmed into the RFID device.   
     
     
       76. The method of claim 72, further comprising:
 comparing the plurality of bit values by the RFID device to at least a portion of a number stored in the RFID device to determine whether the plurality of bit values received from the interrogator identify the RFID device for response;   wherein the one or more responses to the interrogator include the number as a second identifier from the RFID device; and the method further comprises:   sending a subsequent command specifically addressed to the RFID device using the first identifier.   
     
     
       77. The method of claim 76, wherein the one or more responses is communicated in a first slot in accordance with the slotted anticollision algorithm with a first probability corresponding to the integer value. 
     
     
       78. The method of claim 72, wherein the range is indicated to the RFID device by the initial command, and a different range is indicated to the RFID device by a subsequent command, wherein the subsequent command includes a field re-specifying the plurality of bit values to select one or more of the RFID devices. 
     
     
       79. A system, comprising:
 an interrogator having a communication field, the interrogator comprising:
 at least one antenna; 
 a transmitter coupled to the antenna to send a select command, the select command including a set of parameters, the set of parameters including a bit string and describing a memory range, the memory range comprising multiple bit locations; 
 a receiver to receive replies to the select command; and 
 a circuit to determining whether the replies are collision-free, wherein the transmitter is to send an acknowledge command in response to a collision free reply; and 
   a plurality of radio frequency identification (RFID) tags disposed in the communication field of the interrogator, each respective tag of the plurality of RFID tags comprising:
 respective memory to store a respective identification code that identifies a respective object to which the respective tag is affixed; 
 a receiver to receive the select command that is sent from the interrogator after the plurality of RFID tags are disposed in the field and before any of the plurality of RFID tags communicate to the interrogator; 
 a circuit to compare the bit string against the memory range of the memory to determine whether the respective tag is a member of a population of tags; 
 a random generator to pick a respective random value if the respective tag is a member of at least a portion the population of tags, the random value associated with a respective slot, wherein a sequence in which the population of tags are to reply to the interrogator is determined by each respective slot; and 
 a transmitter to backscatter a respective reply to the interrogator in accordance with the sequence if the respective tag is a member of at least the portion of the population of tags, the respective reply including a respective random number generated by the respective tag. 
   
     
     
       80. The system of claim 79, wherein the transmitter is to backscatter at least a portion of the respective identification code, if the respective tag is a member of at least the portion of the population. 
     
     
       81. The system of claim 80, wherein after receiving the respective random number from the respective tag, the interrogator is to access the respective tag individually by sending the respective random number to the respective tag. 
     
     
       82. The system of claim 81, wherein the memory range of the memory of the tag includes at least a portion of the random number. 
     
     
       83. The system of claim 79, wherein each respective random number generated by each respective tag is sixteen bits in length. 
     
     
       84. A system, comprising:
 an interrogator, comprising:
 an antenna having a communication field; 
 a transmitter coupled with the antenna to transmit a first signal and subsequently a second signal, the first signal including parameters that describe a memory range and a bit string; and 
 a receiver to receive responses; 
   an object; and   a radio frequency identification (RFID) tag affixed to the object disposed in the communication field of the interrogator, the tag comprising:
 tag memory; 
 a receiver to receive the first signal that is transmitted from the interrogator to the tag after the tag is disposed in the communication field and before the tag communicates to the interrogator; 
 a circuit to compare the bit string against the memory range of the tag memory to determine whether the tag is selected, the memory range of the tag memory storing a plurality of bits; 
 a random number generator to pick a random value and associate the random value with a slot in accordance with an arbitration scheme for an inventory operation, if the tag is determined to be selected; 
 a transmitter to provide a random number generated by the tag to the interrogator in accordance with the slot in response to receiving the second signal, if the tag is determined to be selected; 
   wherein the interrogator is to send an acknowledge command to the tag in response to the interrogator receiving the random number.   
     
     
       85. The system of claim 84, wherein the transmitter of the tag is to further provide at least a portion of an identification code from the tag to the interrogator, wherein the identification code is stored in tag memory and identifies the object. 
     
     
       86. The system of claim 85, wherein the interrogator is to send an access command to the tag to individually access the tag, after the interrogator sends the acknowledge command and receives the at least a portion of the identification code, wherein the access command includes the random number. 
     
     
       87. The system of claim 86, wherein the random number is sixteen bits long. 
     
     
       88. The system of claim 84, wherein the plurality of bits includes at least a portion of the random number. 
     
     
       89. An interrogator, comprising:
 an antenna having a communication field;   a transmitter coupled with the antenna to send a select command after a radio frequency identification (RFID) tag is disposed in the communication field and before the tag communicates to the interrogator, the select command including parameters that describe a memory range and a bit string, wherein the tag having tag memory and configured to receive the select command, and in response thereto, compare the bit string against the memory range of the tag memory to determine whether the tag is selected to respond, the memory range of the tag memory storing at least two bits; and   a receiver coupled with the antenna to receive a random number generated by the tag from the tag in accordance with an arbitration scheme, if the tag is determined to be selected to respond with the random number.   
     
     
       90. The interrogator of claim 89, wherein the random number is stored in the tag memory. 
     
     
       91. The interrogator of claim 89, wherein the at least two bits include at least a portion of the random number. 
     
     
       92. The interrogator of claim 89, wherein the receiver is to further receive at least a portion of an identification code from the tag in accordance with the arbitration scheme, wherein the identification code identifies an object to which the tag is affixed. 
     
     
       93. The interrogator of claim 92, wherein the identification code is stored in the tag memory. 
     
     
       94. The interrogator of claim 89, wherein the random number is sixteen bits long. 
     
     
       95. The interrogator of claim 89, wherein the tag is to pick a random value and communicate the random number in a slot of time associated with the random number in accordance with the arbitration scheme. 
     
     
       96. The interrogator of claim 95, wherein the transmitter is to send an acknowledge command from the interrogator to the tag in response to the interrogator receiving the random number. 
     
     
       97. The interrogator of claim 96, wherein the transmitter is to further send a signal from the interrogator to the tag, after sending the select command from the interrogator to the tag and before the random number is received in the receiver from the tag, wherein the signal indicates to the tag the time to communicate the random number. 
     
     
       98. The interrogator of claim 89, wherein the transmitter is to further send a signal from the interrogator to the tag, after sending the select command from the interrogator to the tag and before the random number is received in the receiver from the tag, wherein the signal indicates to the tag when to communicate the random number to the interrogator. 
     
     
       99. The interrogator of claim 89, wherein the random number is backscattered from the tag to the interrogator. 
     
     
       100. The interrogator of claim 89, wherein the transmitter is to further send an acknowledge command from the interrogator to the tag in response to the interrogator receiving the random number. 
     
     
       101. The interrogator of claim 100, wherein the receiver is to further receiving at least a portion of an identification code from the tag in accordance with the arbitration scheme, wherein the identification code identifies an object to which the tag is affixed. 
     
     
       102. The interrogator of claim 101, wherein the transmitter is to send an access command to the tag to individually access the tag after the receiver receives the random number, wherein the access command includes a sixteen bit random number. 
     
     
       103. The interrogator of claim 102, wherein the sixteen bit random number is the random number generated by the tag and communicated from the tag to the interrogator in accordance with the arbitration scheme. 
     
     
       104. A system, comprising:
 an interrogator having a communication field; and   a plurality of radio frequency identification (RFID) tags disposed in the communication field of the interrogator, the interrogator to send a first signal after the plurality of tags are disposed in the field and before any of the plurality of tags communicate to the interrogator, the first signal including a bit string and indicating a portion of memory, the portion of memory comprising multiple bit storage locations, the plurality of RFID tags comprising:
 a first tag having first memory storing a first set of bits in bit storage locations corresponding to the portion of memory; 
 a first receiver to receive the first signal; 
 a first circuit to compare the bit string against the first set of bits to determine whether the first tag is selected and to pick a first random value associated with a first slot in accordance with an arbitration scheme; and 
 a first transmitter to send a first identification code that identifies a first object to which the first tag is affixed; and 
   a second tag having second memory storing a second set of bits in bit storage locations corresponding to the portion of memory;   a second receiver to receive the first signal;   a second circuit to compare the bit string against the second set of bits to determine whether the second tag is selected and to pick a second random value associated with a second slot in accordance with the arbitration scheme; and   a second transmitter to send a second identification code that identifies a second object to which the second tag is affixed.   
     
     
       105. The system of claim 104, wherein the first transmitter is to send a first random number generated by the first tag; and
 the second transmitter is to send a second random number generated by the second tag.   
     
     
       106. The system of claim 105, wherein the interrogator is to receive the first random number from the first tag during a period of time associated with the first slot, and in response thereto, send a first acknowledge signal to acknowledge the first tag; and
 wherein the interrogator is to receive the second random number from the second tag during a period of time associated with the second slot, and in response thereto, send a second acknowledge signal to acknowledge the second tag.   
     
     
       107. The system of claim 106, wherein after receiving both the first random number and the first identification code from the first tag, the interrogator is to access the first tag individually by sending a command that includes a number randomly generated by the first tag that identifies the first tag. 
     
     
       108. The system of claim 107, wherein the number randomly generated by the first tag that identifies the first tag is the first random number, and the first random number is 16 bits in length. 
     
     
       109. The system of claim 108, wherein after sending the first signal from the interrogator, the interrogator is to send a second signal, in response to which the first tag backscatters the first identification code. 
     
     
       110. The system of claim 104, wherein the interrogator is to send a first acknowledge signal to acknowledge the first tag and send a second acknowledge signal to acknowledge the second tag. 
     
     
       111. A radio frequency identification (RFID) tag, comprising:
 an antenna;   a receiver coupled with the antenna to receive a first command sent from an interrogator after the tag is disposed in a communication field of the interrogator and before the tag communicates to the interrogator, the first command including a first set of fields comprising at least two first bit values, the receiver to further receive a second command from the interrogator, the second command including a second set of fields comprising at least two second bit values;   a circuit to determine whether the two first bit values received from the interrogator match two corresponding bit values stored in the tag and to determine whether the two second bit values received from the interrogator match the two corresponding bit values stored in the tag; and   a backscatter transmitter coupled with the antenna to transmit a first reply based, at least in part, on whether the two first bit values received from the interrogator match two corresponding bit values stored in the tag, the first reply including a random number generated by the tag, the transmitter to further transmit a second reply based, at least in part, on whether the two second bit values received from the interrogator match the two corresponding bit values stored in the tag, the second reply including a random number generated by the tag.   
     
     
       112. The RFID tag of claim 111, wherein the transmitter is to backscatter at least a portion of an identification code from the tag to the interrogator, wherein the identification code identifies an object to which the tag is affixed. 
     
     
       113. The RFID tag of claim 111, wherein the circuit is to pick a random value for a slot in accordance with an arbitration scheme, and the transmitter is to backscatter a signal to the interrogator at a time associated with the slot. 
     
     
       114. The RFID tag of claim 113, wherein the receiver is to receive an acknowledge command from the interrogator. 
     
     
       115. The RFID tag of claim 111, wherein the receiver is to receive an access command individually accessing the tag using a sixteen bit random number. 
     
     
       116. The RFID tag of claim 115, wherein the transmitter is to backscatter at least a portion of an identification code from the tag to the interrogator, wherein the identification code identifies an object to which the tag is affixed. 
     
     
       117. The RFID tag of claim 111, wherein the interrogator is to detect a collision upon receiving the first reply. 
     
     
       118. A method of conducting a financial transaction, comprising:
 sending an initial command from a transmitter via an antenna, the initial command to select one or more radio frequency devices, the initial command specifying a bit string having multiple bits;   receiving a response from the radio frequency device, the response being in accordance with a slotted anticollision algorithm if the radio frequency device determines it has been selected via a comparison between the bit string and a plurality of bits stored in a memory of the radio frequency device, wherein the response communicates one or more identifiers of the radio frequency device in accordance with the slotted anticollision algorithm, and wherein in accordance with the slotted anticollision algorithm the one or more identifiers is to be communicated in a time slot with a certain probability;   determining an account associated with an owner of the radio frequency device based at least in part on said one or more identifiers; and   debiting the account for payment.   
     
     
       119. The method of claim 118, wherein the debiting of the account is associated with the payment of a toll. 
     
     
       120. The method of claim 119, wherein said transmitter is disposed within a toll booth, and said method further comprises operating said transmitter disposed within said toll booth at least when said radio frequency device issuing said response is in proximity thereto. 
     
     
       121. The method of claim 119, wherein the debiting of the account comprises receiving a credit card number against which the toll can be charged. 
     
     
       122. The method of claim 118, wherein the debiting of the account comprises receiving a credit card number which can be charged. 
     
     
       123. The method of claim 118, wherein the debiting of the account is for the payment of goods or services. 
     
     
       124. The method of claim 118, wherein the method further comprises:
 sending an acknowledge command from the transmitter to the radio frequency device if the transmitter receives the response without a collision error.   
     
     
       125. The method of claim 118, further comprising:
 individually addressing the radio frequency device by the transmitter using an access command, wherein the one or more identifiers communicated in the response comprises a random number and the access command includes the random number.   
     
     
       126. The method of claim 118, wherein the one or more identifiers comprises a number dynamically generated by the radio frequency device. 
     
     
       127. A method of conducting a financial transaction, the method comprising:
 transmitting, through one or more antennas using a transmitter of an interrogation apparatus, an initial command to select a respective device from one or more radio frequency devices that are within wireless communications range of the interrogation apparatus, the initial command specifying a bit string having multiple bits;   receiving the initial command from the interrogation apparatus by the receiver of the respective device of the one or more radio frequency devices;   comparing, by the respective device of the one or more radio frequency devices, the bit string specified in the initial command against corresponding bits stored in the memory of the respective device to deteiuiine whether the respective device is a member of a population of radio frequency devices selected according to the initial command;   if the respective device is a member of the population, picking a respective random value by the respective device from a range of values to determine a respective slot and providing by the transmitter of the respective device a respective reply to the interrogation apparatus in accordance with the respective slot, the reply including at least a portion of an identifier of the respective device:   determining an account associated with an owner of the respective device based at least in part on said at least a portion of said identifier of the respective device; and   debiting said account so as to conduct said financial transaction.   
     
     
       128. The method of claim 127, wherein the debiting of the account is associated with the payment of a toll. 
     
     
       129. The method of claim 128, wherein said interrogation apparatus is disposed within a toll booth, and said method further comprises operating said interrogation apparatus disposed within said toll booth at least when said respective device issuing said response is in proximity thereto. 
     
     
       130. The method of claim 128, wherein the debiting of the account comprises receiving a credit card number against which the toll can be charged. 
     
     
       131. The method of claim 127, wherein the debiting of the account comprises receiving a credit card number which can be charged. 
     
     
       132. The method of claim 127, wherein the debiting of the account is for the payment of goods or services. 
     
     
       133. A method of conducting a financial transaction, comprising:
 sending an initial command from a transmitter via an antenna, the initial command to select one or more radio frequency devices, the initial command specifying a bit string having multiple bits;   receiving a response from the radio frequency device, the response being in accordance with a slotted anticollision algorithm if the radio frequency device determines it has been selected via a comparison between the bit string and a plurality of bits stored in a memory of the radio frequency device, wherein the response communicates one or more identifiers of the radio frequency device in accordance with the slotted anticollision algorithm, and wherein in accordance with the slotted anticollision algorithm the one or more identifiers is to be communicated in a time slot with a certain probability; and   receiving funds for the payment of goods or services based at least on part on the received response from the radio frequency device.   
     
     
       134. The method of claim 133, wherein said transmitter is disposed within a toll booth, and said method further comprises operating said transmitter disposed within said toll booth at least when said radio frequency device issuing said response is in proximity thereto. 
     
     
       135. The method of claim 133, wherein the method further comprises:
 sending an acknowledge command from the transmitter to the radio frequency device if the transmitter receives the response without a collision error.   
     
     
       136. The method of claim 133, further comprising:
 individually addressing the radio frequency device by the transmitter using an access command, wherein the one or more identifiers communicated in the response comprises a random number and the access command includes the random number.   
     
     
       137. The method of claim 133, wherein the one or more identifiers comprises a number dynamically generated by the radio frequency device.