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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 establish communications without collision between the interrogator and individual ones of the multiple wi

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 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 representing subgroups of the multiple wireless identification devices, the number of devices in a subgroup in one level being half of the number of devices in the next higher level, the tree search method employing level skipping wherein at least one level of the tree is skipped. 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 levels of the tree are occasionally skipped. In one aspect, a method includes: transmitting by an interrogator a first wireless signal, specifying a first set of bit values, to request first replies from radio frequency identification (RFID) devices that have the first set of bit values; and responsive to a collision in the first replies, transmitting by the interrogator a second wireless signal, specifying a second set of bit values having at least two more bits than the first set, to request second replies from RFID devices that have the second set of bit values.

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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

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 binary search tree having multiple levels representing subgroups of the multiple wireless identification devices, the number of devices in a subgroup in one level being less than the number of devices in the next level, the tree search technique employing level skipping wherein every second level of the tree is skipped. 2. 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. 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 communications range, over time. 6. 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 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 specified group and, if so, sending a reply to the interrogator; anddetermining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group, using a search tree, that is one quarter of the first mentioned specified group, wherein at least one level of a search tree is skipped. 7. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices in accordance with claim 6 wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply. 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 6 wherein sending a reply to the interrogator comprises transmitting the random value 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 6 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. 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 6 wherein, after receiving a reply without collision from a device, the interrogator sends a command 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: 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 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 having a plurality of levels, wherein groups of random values decrease in size with each level descended;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; anddetermining using the transponder if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group by descending at least two levels in the tree. 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 and further comprising establishing unique identification numbers for respective devices. 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 a transponder 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 sixteen bits. 15. A method of addressing messages from a transponder to a selected one or more of a number of communications devices in accordance with claim 13 wherein devices sending a reply to the transponder 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 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 from the interrogator 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 or equal to the entire set of random values, the plurality of possible groups being organized in a binary tree having a plurality of levels, wherein groups of random values decrease in size with each level;receiving the command at multiple of the devices, the 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;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 level of the tree different from the level used in the interrogator transmitting, wherein at least one level of the tree is skipped, the interrogator transmitting a command requesting devices having random values within the new specified group of random values to respond; andif 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 wherein every second level is skipped. 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 the unique identification numbers are respectively defined by a predetermined number of bits. 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 the unique identification numbers are respectively defined by a predetermined number of bits and wherein the random values are respectively defined by a predetermined number of bits. 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 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. 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 20 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. 22. 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; andmeans 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 that is one quarter of the first mentioned specified group, wherein at least one level of the tree is skipped. 23. A system in accordance with claim 22 wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply. 24. A system in accordance with claim 22 wherein sending a reply to the interrogator comprises transmitting the random value of the device sending the reply. 25. A system in accordance with claim 22 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. 26. A system in accordance with claim 22 wherein the interrogator further includes means for, after receiving a reply without collision from a device, sending a command individually addressed to that device. 27. A method for initiating wireless communication with radio frequency identification (RFID) devices, comprising: transmitting a first command specifying a first bit sequence;receiving a first response to the first command from an RFID device having a first portion of a random number identifier generated by the RFID device equal to the first bit sequence, the first response including at least a second portion of the random number identifier generated by the RFID device;detecting a collision in the first response;responsive to detecting the collision, transmitting a second command following the first command in succession and absent any intervening commands, the second command specifying a second bit sequence that includes the first bit sequence and is at least two bits longer than the first bit sequence; andreceiving a second response to the second command from the RFID device indicating that the random number identifier generated by the RFID device includes the second bit sequence. 28. The method of claim 27, further comprising receiving an identification number from the RFID device, separate from the random number identifier, to identify a person with whom the RFID device is associated. 29. The method of claim 27, further comprising transmitting signals in accordance with a slotted anti-collision algorithm. 30. The method of claim 27, wherein the first command is to further specify a first value that provides an indication of a number of valid bits contained in the first bit sequence, and the second command is to further specify a second value that provides an indication of a number of valid bits contained in the second bit sequence. 31. The method of claim 27, further comprising transmitting a wake up signal to cause the RFID device to transition from a non-responsive state to a responsive state. 32. The method of claim 31, wherein the non-responsive state is a sleep state. 33. The method of claim 27, further comprising communicating at one of the bit rates supported by the RFID device. 34. The method of claim 27, further comprising generating a radio frequency (RF) field and modulating the RF field to transmit signals in an active mode, and modulating an RF field provided by a remote wireless device to transmit signals in a passive mode. 35. A radio frequency identification (RFID) system, comprising: an RFID device to generate a random number identifier and to store an identification number, separate from the random number identifier, for use in identifying a person with whom the RFID device is associated; andan interrogator to transmit a command comprising a first bit string to cause the RFID device to transmit at least a portion of the random number generated by the RFID device if the RFID device determines that the random number includes the first bit string, and to transmit a successive command, comprising a second bit string, absent any intervening commands, to cause the RFID device to transmit a response if the RFID device determines that the random number includes the second bit string, wherein the second bit string includes the first bit string plus at least two additional bits. 36. The system of claim 35, wherein the interrogator is to detect a collision upon receiving the at least portion of the random number generated by the RFID device, and wherein the successive command is to be transmitted responsive to detecting the collision. 37. The system of claim 35, wherein the interrogator is to transmit a signal to indicate a number of time slots available for response from a plurality of RFID devices in a field of the interrogator in accordance with a single device detection algorithm. 38. The system of claim 35, wherein the response comprises at least a second portion of the random number generated by the RFID device. 39. The system of claim 35, wherein the command further comprises a first value to indicate a number of valid bits contained in the command. 40. The system of claim 35, wherein the RFID device and the interrogator are configured to communicate at one of a plurality of bit rates identified by the interrogator. 41. The system of claim 35, wherein the RFID device is to transmit in a first mode in which the RFID device is to generate and modulate its own radio frequency (RF) field, and to transmit in a second mode in which the RFID device is to modulate an RF field provided by the interrogator. 42. A wireless payment method, comprising: transmitting by an interrogator a first wireless command, specifying a first set of bit values, to request one or more first replies from one or more radio frequency identification (RFID) devices that have randomly generated the first set of bit values;responsive to detecting a collision in the first replies, transmitting by the interrogator a second wireless command successively following the first wireless command, absent any intervening commands, and specifying a second set of bit values that include the first set of bit values and have at least two more bits than the first set, to request one or more second replies from one or more RFID devices that have randomly generated the second set of bit values;responsive to receiving a reply, without collision, from an RFID device of the one or more RFID devices, transmitting by the interrogator a third wireless command comprising an identifier randomly generated by the RFID device to select the RFID device, the identifier including the second set of bit values; andreceiving by the interrogator an identification code, separate from the identifier, from the RFID device to identify a person to be charged for payment. 43. The method of claim 42, wherein the first replies comprise random numbers generated by the RFID devices. 44. The method of claim 42, further comprising transmitting a plurality of signals from the interrogator to indicate time slots in accordance with an adaptive slotted collision avoidance algorithm. 45. The method of claim 42, further comprising: generating by the interrogator a radio frequency (RF) field;modulating, by the interrogator, the RF field to transmit commands from the interrogator to the RFID devices; andmodulating, by the one or more RFID devices, the RF field generated by the interrogator to communicate responses from the one or more RFID devices to the interrogator. 46. The method of claim 45, further comprising the RFID device, wherein the RFID device is to further generate and modulate an RF field to wirelessly transmit signals to one or more remote devices. 47. The method of claim 45, wherein the first command is to further specify a first value that provides an indication of a number of valid bits contained in the first set of bit values, and the second command is to further specify a second value that provides an indication of a number of valid bits contained in the second set of bit values. 48. The method of claim 47, further comprising communicating between the interrogator and the one or more RFID devices at one of a plurality of bit rates selected by the interrogator. 49. The method of claim 42, further comprising transmitting by the interrogator a wake up signal to cause an RFID device to transition from a non-responsive state to a responsive state. 50. The method of claim 49, wherein the non-responsive state is a sleep state. 51. The method of claim 42, further comprising communicating between the interrogator and the one or more RFID devices at one of a plurality of bit rates selected by the interrogator. 52. An initiating radio frequency identification (RFID) device, comprising: a transmitter to send a first signal, including a first portion of a first set of random numbers, to request a first set of one or more target RFID devices that have generated the first portion to respond with one or more first random values, and to send a second signal, including a second portion of a second set of one or more random numbers, to request a second set of one or more target RFID devices that have generated the second portion to respond, wherein the first set of random numbers includes the second set of random numbers;an antenna to provide a radio frequency (RF) field to be modulated by the first and second sets of one or more target RFID devices to respond to the first and second signals;a receiver to receive responses to the first and second signals; andprocessing circuitry to detect a collision in the responses, wherein the second signal is to be sent successively after the first signal in response to a collision detected by the processing circuitry after the first signal is sent, and the second set of one or more random numbers is less than half of the first set of random numbers. 53. The initiating RFID device of claim 52, wherein the transmitter is to transmit signals in accordance with a slotted anti-collision algorithm. 54. The initiating RFID device of claim 52, wherein the transmitter is configured to send a wake up signal to cause target RFID devices to transition from a non-responsive state to a responsive state. 55. The initiating device of claim 52, wherein the receiver is to further receive one or more identification numbers from the RFID device, separate from the random number identifier, to identify a person with whom the RFID device is associated. 56. The initiating RFID device of claim 52, wherein the transmitter is configured to communicate with RFID devices at one of a plurality of bit rates determined by the initiating RFID device. 57. A target radio frequency identification (RFID) device, comprising: memory storing information for use in determining an identity of a person with whom the RFID device is associated;a receiver to receive, in succession, a first wireless command from an initiating RFID device and a second wireless command from the initiating RFID device, absent reception of any intervening wireless commands from the initiating RFID device, the first wireless command to provide a first set of bits and the second wireless command to provide a second set of bits, wherein the second set of bits includes the first set of bits and is longer than the first set of bits by at least two bits;a random number generator to generate a random number identifier of the RFID device;processing circuitry to compare the first set of bits with a first portion of the random number identifier to determine if they are equal, and to compare the second set of bits with a second portion of the random number identifier to determine if they are equal; anda transmitter to transmit at least a third portion of the random number identifier in response to the first wireless command, before the second wireless command is received, if the first set of bits are determined to be equal to the first portion of the random number identifier, to transmit a response to the second wireless command if the second set of bits are determined to be equal to the second portion of the random number identifier, and to transmit the information. 58. The target RFID device of claim 57, wherein the third portion includes bits of the random number identifier not in the first portion. 59. The target RFID device of claim 57, wherein the receiver is configured to receive a wake up signal to transition from a non-responsive state to a responsive state. 60. The target RFID device of claim 57, wherein the target RFID device is to receive an indication of a change from a first number of slots to a second number of slots, and to randomly select a slot from the second number of slots in which to transmit a signal in accordance with a slotted anti-collision algorithm. 61. The target RFID device of claim 57, wherein the transmitter is configured to communicate at one of a plurality of bit rates specified by the initiating device. 62. The target RFID device of claim 57, wherein the transmitter is configured to provide a first reply at a first bit rate and a second reply at a second bit rate. 63. The target RFID device of claim 57, wherein the transmitter is to transmit the third portion of the random number identifier by modulating an RF field provided by the initiating device. 64. The target RFID device of claim 63, wherein the transmitter is to transmit the third portion of the random number in accordance with a first mode of operation during a first period of time, and, during a second period of time, the transmitter is to transmit signals in accordance with a second mode of operation in which the RFID device is to generate and modulate its own radio frequency (RF) field. 65. A wireless payment method, comprising: transmitting a first command specifying a first bit sequence;receiving a first response to the first command from an RFID device having a first portion of a unique number identifier equal to the first bit sequence, the first response including at least a second portion of the unique number identifier;detecting that a collision has occurred with respect to the first response;responsive to detecting that the collision has occurred, transmitting a second command following the first command in succession and absent any intervening commands, the second command specifying a second bit sequence that includes the first bit sequence and is at least two bits longer than the first bit sequence;receiving a second response to the second command from the RFID device indicating that the unique number identifier includes the second bit sequence;determining an owner of the RFID device based at least in part on said unique number identifier of said RFID device; andcausing debiting of an account held by said owner. 66. The method of claim 65, wherein the causing of the debiting of the account held by the owner is associated with the payment of a toll. 67. The method of claim 66, wherein a master wireless device is disposed within a toll both, and said method further comprises operating said master wireless device disposed within said toll both at least when said RFID device issuing said response to said first command is in proximity thereto. 68. The method of claim 66, wherein the causing the debiting of the account comprises receiving a credit card number against which the toll can be charged. 69. The method of claim 66, wherein the causing the debiting of the account comprises receiving a credit card number that can be charged. 70. The method of claim 66, wherein the causing the debiting of the account held by the owner is for payment for goods or services. 71. The method of claim 70, wherein the response comprises further information about the RFID device. 72. The method of claim 70, wherein the unique number identifier comprises a random number generated by the RFID device. 73. The method of claim 65, further comprising receiving an identification number from the RFID device, separate from the random number identifier, to identify a person with whom the RFID device is associated. 74. The method of claim 65, wherein the first command is to further specify a first value that provides an indication of a number of valid bits contained in the first bit sequence, and the second command is to further specify a second value that provides an indication of a number of valid bits contained in the second bit sequence. 75. The method of claim 65, further comprising transmitting a wake up signal to cause the RFID device to transition from a non-responsive state to a responsive state. 76. The method of claim 75, wherein the non-responsive state is a sleep state. 77. The method of claim 65, further comprising communicating at one of a plurality of bit rates supported by the RFID device. 78. The method of claim 65, further comprising generating a radio frequency (RF) field and modulating the RF field to transmit signals in an active mode, and modulating an RF field provided by a remote wireless device to transmit signals in a passive mode. 79. A wireless payment method, comprising: transmitting by an interrogator a first wireless command, specifying a first set of bit values to request one or more first replies from one or more radio frequency identification (RFID) devices that have a respective unique identifier containing a portion equal to the first set of bit values;responsive to detecting a collision in the first replies, transmitting by the interrogator a second wireless command successively following the first wireless command, absent any intervening commands, and specifying a second set of bit values that include the first set of bit values and have at least two more bits than the first set of bit values, to request one or more second replies from one or more RFID devices that have a respective unique identifier containing a portion equal to the second set of bit values;responsive to receiving a reply, without collision, from an RFID device of the one or more RFID devices, transmitting by the interrogator a third wireless command comprising a unique identifier of the RFID device to select the RFID device, the unique identifier of the RFID device including the second set of bit values; andreceiving funds for the remote payment of goods or services based at least on part on the reply and the unique identifier of the RFID device. 80. The method of claim 79, further comprising disposing the one or more RFID devices at least partly within a card. 81. The method of claim 80, wherein the card further includes information typically found on a credit card. 82. A wireless payment method, comprising: transmitting by an interrogator a first wireless command, specifying a first set of bit values to request one or more first replies from one or more radio frequency identification (RFID) devices that have a respective unique identifier containing a portion equal to the first set of bit values;responsive to detecting a collision in the first replies, transmitting by the interrogator a second wireless command successively following the first wireless command, absent any intervening commands, and specifying a second set of bit values that include the first set of bit values and have at least two more bits than the first set of bit values, to request one or more second replies from one or more RFID devices that have a respective unique identifier containing a portion equal to the second set of bit values;responsive to receiving a reply, without collision, from an RFID device of the one or more RFID devices, transmitting by the interrogator a third wireless command comprising a unique identifier of the RFID device to select the RFID device, the identifier including the second set of bit values;identifying an account to be charged for payment based at least in part on the reply and the unique identifier of the RFID device; anddebiting funds of the identified account associated with the RFID device. 83. The method of claim 82, further comprising disposing the one or more RFID devices at least partly within a card. 84. The method of claim 82, further comprising disposing the one or more RFID devices within the housing of an object. 85. A wireless payment method, comprising: transmitting a first command specifying a first bit sequence;receiving a first response to the first command from an RFID device having a first portion of a unique identifier equal to the first bit sequence, the first response including at least a second portion of the unique identifier;detecting that a collision has occurred with respect to the first response;responsive to detecting that the collision has occurred, transmitting a second command following the first command in succession and absent any intervening commands, the second command specifying a second bit sequence that includes the first bit sequence and is at least two bits longer than the first bit sequence;receiving a response to the second command from the RFID device indicating that the unique identifier includes the second bit sequence; andreceiving funds for the remote payment of goods or services based at least in part on the response to the second command received from the RFID device. 86. The method of claim of 85, further comprising disposing the one or more RFID devices at least partly within a card. 87. The method of claim of 86, wherein the card includes visual identification features including at least one of graphics and/or text. 88. The method of claim of 87, wherein the card further includes information typically found on a credit card. 89. A wireless payment method, comprising: transmitting a first command specifying a first bit sequence;receiving a first response to the first command from an RFID device having a first portion of a unique identifier equal to the first bit sequence, the first response including at least a second portion of the unique identifier;detecting that a collision has occurred with respect to the first response;responsive to detecting that the collision has occurred, transmitting a second command following the first command in succession and absent any intervening commands, the second command specifying a second bit sequence that includes the first bit sequence and is at least two bits longer than the first bit sequence;receiving a response to the second command from the RFID device indicating that the unique identifier includes the second bit sequence;determining an account of the RFID device based at least in part on the response to the second command received from the RFID device; andcausing the debiting of funds associated with the determined account. 90. The method of claim 89, further comprising disposing the RFID device at least partly within a card. 91. The method of claim 89, further comprising disposing the RFID device within the housing of an object. 92. The method of claim 89, wherein the debiting of funds is for the wireless payment of a toll.