Method of addressing messages and communications system

Abstract

A method of establishing wireless communications between an interrogator and individual ones of multiple wireless identification devices, the method comprising utilizing a tree search method to attempt to identify individual ones of the multiple wireless identification devices so as to be able to perform communications, without collision, between the interrogator and individual ones of the multiple wireless identification devices, a search tree being defined for the tree search method, the tree having multiple nodes respectively representing subgroups of the multiple wireless identification devices, wherein the interrogator transmits a command at a node, requesting that devices within the subgroup represented by the node respond, wherein the interrogator determines if a collision occurs in response to the command and, if not, repeats the command at the same node. An interrogator configured to transmit a command at a node, requesting that devices within the subgroup represented by the node respond, the interrogator further being configured to determine if a collision occurs in response to the command and, if not, to repeat the command at the same node includes: receiving a first signal from an interrogator in accordance with an algorithm to identify a radio frequency identification (RFID) device in a field of the interrogator, the first signal comprising a first set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the first set of bits; responsive to receiving the first signal, determining if the first set of bits is equal to a first portion of an identifier of the RFID device, and, if so, modulating a radio frequency (RF) field, provided by the interrogator, to communicate a reply to the interrogator in accordance with the algorithm and receiving, in accordance with the algorithm, a retransmission of the first signal from the interrogator in response to the interrogator receiving the reply without detecting a collision.

1. A method of establishing wireless communications between an interrogator and wireless identification devices, the method comprising utilizing a tree search technique to establish communications, without collision, between the interrogator and individual ones of the multiple wireless identification devices, the method including using a search tree having multiple nodes respectively representing subgroups of the multiple wireless identification devices, the method further comprising, for a node, transmitting a command, using the interrogator, requesting that devices within the subgroup represented by the node respond, determining with the interrogator if a collision occurred in response to the command and, if not, repeating the command at the same node. 
     
     
       2. A method in accordance with  claim 1  and further comprising, if a collision occurred in response to the first mentioned command, sending a command at a different node, using the interrogator. 
     
     
       3. A method in accordance with  claim 1  wherein when a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, the device that is not within communications range of the interrogator does not respond to the command. 
     
     
       4. A method in accordance with  claim 1  wherein when a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, the device that is within communications range of the interrogator responds to the command. 
     
     
       5. A method in accordance with  claim 1  wherein a device in a subgroup changes between being within communications range of the interrogator and not being within communications range, over time. 
     
     
       6. A method in accordance with  claim 1  wherein the wireless identification device comprises an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       7. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices, the method comprising:
 establishing for respective devices unique identification numbers;   causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;   transmitting a communication, from the interrogator, requesting devices having random values within a first specified group of random values to respond;   receiving the communication at multiple devices, devices receiving the communication respectively determining if the random value chosen by the device falls within the first specified group and, if so, sending a reply to the interrogator; and   determining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a second specified group smaller than the first specified group; and, if not, again transmitting a communication requesting devices having random values within the first specified group of random values to respond.   
     
     
       8. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices in accordance with  claim 7  wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply. 
     
     
       9. A method in accordance with  claim 7  wherein one of the first and second specified groups contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is not within communications range of the interrogator does not respond to the interrogator. 
     
     
       10. A method of addressing messages from an interrogator to a selected one or more of a number of communications devices in accordance with  claim 7  wherein, after receiving a reply without collision from a device, the interrogator sends a communication individually addressed to that device. 
     
     
       11. A method of addressing messages from a transponder to a selected one or more of a number of communications devices, the method comprising:
 establishing unique identification numbers for respective devices;   causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;   transmitting a communication from the transponder requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels, the specified group being defined as being at one of the nodes;   receiving the communication at multiple devices, devices receiving the communication respectively determining if the random value chosen by the device falls within the specified group and, if so, sending a reply to the transponder; and, if not, not sending a reply; and   determining using the transponder if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group by descending in the tree; and, if not, transmitting a communication at the same node.   
     
     
       12. A method of addressing messages from a transponder to a selected one or more of a number of communications devices in accordance with  claim 11  wherein establishing unique identification numbers for respective devices comprises establishing a predetermined number of bits to be used for the unique identification numbers. 
     
     
       13. A method of addressing messages from a transponder to a selected one or more of a number of communications devices in accordance with  claim 12  and further including establishing a predetermined number of bits to be used for the random values. 
     
     
       14. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices, the method comprising:
 establishing for respective devices unique identification numbers;   causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;   transmitting a command using the interrogator requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the specified group being equal to or less than the entire set of random values, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels;   receiving the command at multiple RFID devices, RFID devices receiving the command respectively determining if their chosen random values fall within the specified group and, only if so, sending a reply to the interrogator, wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply;   determining using the interrogator if a collision occurred between devices that sent a reply and, if so, creating a new, smaller, specified group using a different level of the tree, the interrogator transmitting a command requesting devices having random values within the new specified group of random values to respond; and, if not, the interrogator re-transmitting a command requesting devices having random values within the first mentioned specified group of random values to respond; and   if a reply without collision is received from a device, the interrogator subsequently sending a command individually addressed to that device.   
     
     
       15. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein the first mentioned specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is not within communications range of the interrogator does not respond to the transmitting of the command or the re-transmitting of the command. 
     
     
       16. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein the first mentioned specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is within communications range of the interrogator responds to the transmitting of the command and the re-transmitting of the command. 
     
     
       17. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein a device in the first mentioned specified group is capable of changing between being within communications range of the interrogator and not being within communications range of the interrogator over time. 
     
     
       18. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  wherein the devices respectively comprise an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       19. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 14  and further comprising, after the interrogator transmits a command requesting devices having random values within the new specified group of random values to respond;
 devices receiving the command respectively determining if their chosen random values fall within the new smaller specified group and, if so, sending a reply to the interrogator. 
 
     
     
       20. A method of addressing messages from an interrogator to a selected one or more of a number of RFID devices in accordance with  claim 19  and further comprising, after the interrogator transmits a command requesting devices having random values within the new specified group of random values to respond;
 determining if a collision occurred between devices that sent a reply and, if so, creating a new specified group and repeating the transmitting of the command requesting devices having random values within a specified group of random values to respond using different specified groups until all of the devices capable of communicating with the interrogator are identified. 
 
     
     
       21. A communications system comprising an interrogator, and a plurality of wireless identification devices configured to communicate with the interrogator using RF, the interrogator being configured to employ tree searching to attempt to identify individual ones of the multiple wireless identification devices, so as to be able to perform communications without collision between the interrogator and individual ones of the multiple wireless identification devices, the interrogator being configured to follow a search tree, the tree having multiple nodes respectively representing subgroups of the multiple wireless identification devices, the interrogator being configured to transmit a command at a node, requesting that devices within the subgroup represented by the node respond, the interrogator further being configured to determine if a collision occurs in response to the command and, if not, to repeat the command at the same node. 
     
     
       22. A communications system in accordance with  claim 21  wherein the interrogator is configured to send a command at a different node if a collision occurs in response to the first mentioned command. 
     
     
       23. A communications system in accordance with  claim 21  wherein a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator. 
     
     
       24. A communications system in accordance with  claim 21  wherein a subgroup contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator, and wherein the device that is within communications range of the interrogator responds to the command. 
     
     
       25. A communications system in accordance with  claim 21  wherein a device in a subgroup is movable relative to the interrogator so as to be capable of changing between being within communications range of the interrogator and not being within communications range. 
     
     
       26. A communications system in accordance with  claim 21  wherein the wireless identification device comprises an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       27. A system comprising:
 an interrogator;   a number of communications devices capable of wireless communications with the interrogator;   means for establishing for respective devices unique identification numbers respectively having the first predetermined number of bits;   means for causing the devices to select random values, wherein respective devices choose random values independently of random values selected by the other devices;   means for causing the interrogator to transmit a command requesting devices having random values within a specified group of random values to respond;   means for causing devices receiving the command to determine if their chosen random values fall within the specified group and, if so, to send a reply to the interrogator; and   means for causing the interrogator to determine if a collision occurred between devices that sent a reply and, if so, to create a new, smaller, specified group; and, if not, transmit a command requesting devices having random values within the same specified group of random values to respond.   
     
     
       28. A system in accordance with  claim 27  wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply. 
     
     
       29. A system in accordance with  claim 27  wherein a specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator. 
     
     
       30. A system in accordance with  claim 27  wherein the interrogator further includes means for, after receiving a reply without collision from a device, sending a command individually addressed to that device. 
     
     
       31. A system comprising:
 an interrogator configured to communicate to a selected one or more of a number of communications devices; and   a plurality of communications devices; the devices being configured to select random values, wherein respective devices choose random values independently of random values selected by the other devices; the interrogator being configured to transmit a command requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the specified group being less than the entire set of random values, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels, the specified group being defined as being at one of the nodes; devices receiving the command being configured to respectively determine if their chosen random values fall within the specified group and, only if so, send a reply to the interrogator, wherein sending a reply to the interrogator comprises transmitting the unique identification number of the device sending the reply; the interrogator being configured to determine if a collision occurred between devices that sent a reply and, if so, create a new, smaller, specified group using a different level of the tree, the interrogator being configured to transmit a command requesting devices having random values within the new specified group of random values to respond; and, if not, the interrogator being configured to re-transmit a command requesting devices having random values within the first mentioned specified group of random values to respond.   
     
     
       32. A system in accordance with  claim 31  wherein the first mentioned specified group contains both a device that is within communications range of the interrogator, and a device that is not within communications range of the interrogator. 
     
     
       33. A system in accordance with  claim 31  wherein a device in the first mentioned specified group is capable of changing between being within communications range of the interrogator and not being within communications range of the interrogator over time. 
     
     
       34. A system in accordance with  claim 31  wherein the respective devices comprise an integrated circuit including a receiver, a modulator, and a microprocessor in communication with the receiver and modulator. 
     
     
       35. A system comprising:
 an interrogator configured to communicate to a selected one or more of a number of RFID devices;   a plurality of RFID devices, respective devices being configured to store a unique identification number, respective devices being further configured to store a random value;   the interrogator being configured to transmit a command requesting devices having random values within a specified group of a plurality of possible groups of random values to respond, the plurality of possible groups being organized in a binary tree defined by a plurality of nodes at respective levels, the specified group being defined as being at one of the nodes;   devices receiving the command respectively being configured to determine if their chosen random values fall within the specified group and, if so, send a reply to the interrogator; and, if not, not send a reply; and   the interrogator being configured to determine if a collision occurred between devices that sent a reply and, if so, to create a new, smaller, specified group by descending in the tree; and, if not, to transmit a command at the same node.   
     
     
       36. A system in accordance with  claim 35  wherein the unique identification numbers for respective devices are stored in digital form and respectively comprise a predetermined number of bits. 
     
     
       37. A system in accordance with  claim 35  wherein the random values for respective devices are stored in digital form and respectively comprise a predetermined number of bits. 
     
     
       38. A system in accordance with  claim 35  wherein the interrogator is configured to determine if a collision occurred between devices that sent a reply in response to respective Identify commands and, if so, to create further new specified groups and repeat the transmitting of the command requesting devices having random values within a specified group of random values to respond using different specified groups until all responding devices capable of responding are identified. 
     
     
       39. A method, comprising:
 receiving a first signal from an interrogator in accordance with an algorithm to identify a radio frequency identification (RFID) device in a field of the interrogator, the first signal having associated therewith a first set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the first set of bits;   responsive to receiving the first signal, determining if the first set of bits matches a first portion of an identifier of the RFID device, and, if so, modulating a radio frequency (RF) field, provided by the interrogator, to communicate a reply to the interrogator in accordance with the algorithm; and   receiving, in accordance with the algorithm, another transmission of the first signal from the interrogator in response to the interrogator receiving the reply without detecting a collision.   
     
     
       40. The method of claim 39, further comprising communicating with the interrogator in one of a first communication mode and a second communication mode determined by the interrogator, wherein in accordance with the first communication mode the RFID device modulates a radio frequency (RF) field generated by the RFID device and in accordance with the second communication mode the RFID device modulates a radio frequency (RF field generated by the interrogator. 
     
     
       41. The method of claim 40, further comprising communicating with the interrogator at one of a plurality of bit rates determined by the interrogator. 
     
     
       42. The method of claim 39, further comprising receiving a wake up command from the interrogator and, in response, transitioning from a sleep state. 
     
     
       43. The method of claim 42, further comprising receiving a sleep command from the interrogator. 
     
     
       44. The method of claim 43, wherein the sleep command is received in response to the interrogator receiving the reply without detecting a collision, in accordance with the algorithm, before the receiving of the retransmission of the first signal. 
     
     
       45. The method of claim 39, wherein the reply comprises a random value generated by the RFID device. 
     
     
       46. The method of claim 45, wherein the identifier comprises the random value. 
     
     
       47. The method of claim 46, wherein the random value is the identifier. 
     
     
       48. The method of claim 39, further comprising:
 receiving, in accordance with the algorithm, a second signal from the interrogator in response to the interrogator detecting a collision in the reply, the second signal comprising a second set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the second set of bits; and   responsive to receiving the second signal, determining if the second set of bits matches a second portion of the identifier of the RFID device, and, if so, modulating the radio frequency (RF) field to communicate a second reply to the interrogator in accordance with the algorithm, wherein the second signal comprises the first signal, the second set of bits comprises the first set of bits plus at least two additional bits, and the second portion of the identifier comprises the first portion of the identifier.   
     
     
       49. The method of claim 48, wherein the second reply comprises at least a portion of the identifier. 
     
     
       50. The method of claim 49, further comprising communicating a random value to the interrogator during a time slot randomly selected from a number of time slots. 
     
     
       51. The method of claim 39, further comprising communicating a random value to the interrogator during a time slot randomly selected from a number of time slots. 
     
     
       52. A system, comprising:
 a radio frequency identification (RFID) device comprising a receiver to receive a first command including a portion of an identification number, memory to store an identifier of the device, and a transmitter to communicate a reply to the first command if the portion of the identification number matches a first portion of the identifier; and   an interrogator configured to implement an algorithm to identify one or more RFID devices in a field of the interrogator, the algorithm comprising transmitting a first signal with a first set of bits to request a response from a selected one or more devices, receiving a first response thereto from the selected one or more devices, detecting if a collision occurred in the first response, and retransmitting the first signal with at least the first set of bits to request a second response from at least one of the selected one or more devices in response to detecting no collision in the first response.   
     
     
       53. The system of claim 52, further comprising memory storing a unique identification code to be transmitted by the system. 
     
     
       54. The system of claim 52, wherein the transmitter is configured to communicate by modulating a radio frequency (RF) field provided by a remote device. 
     
     
       55. The system of claim 54, wherein the algorithm further comprises transmitting an indication of the number of bits of the first set of bits. 
     
     
       56. The system of claim 52, wherein retransmitting the first signal with at least the first set of bits comprises retransmitting the first signal with no more than the first set of bits. 
     
     
       57. The system of claim 52, wherein the system is configured to communicate at one of a plurality of bit rates determined by a remote device. 
     
     
       58. The system of claim 57, wherein the system is configured to operate in a first communication mode during a first period of time and in a second communication mode during a second period of time, wherein in accordance with the first communication mode the system is configured to modulate a radio frequency (RF) field generated by the remote device and in accordance with the second communication mode the system is configured to generate and modulate a radio frequency (RF) field. 
     
     
       59. The system of claim 52, wherein the RFID device is configured to receive a signal to silence the RFID device. 
     
     
       60. The system of claim 59, wherein the RFID device is configured to receive a wake up command and, in response, to transition from a sleep state. 
     
     
       61. The system of claim 52, wherein the algorithm further comprises transmitting a signal to silence at least one of the one or more RFID devices in response to the detecting no collision and before the retransmitting of the first signal. 
     
     
       62. The system of claim 52, wherein the reply comprises at least a second portion of the identifier that is not part of the first portion of the identifier. 
     
     
       63. The system of claim 62, wherein the interrogator is further configured to use the first response to determine a random value generated by the selected one or more devices in accordance with the algorithm. 
     
     
       64. The system of claim 52, wherein the algorithm further comprises transmitting a second signal from the interrogator in response to detecting a collision in the first response, the second signal comprising a second set of bits and requesting a response from at least one of the one or more RFID devices in the field selected in accordance with at least the second set of bits, wherein the second set of bits includes the first set of bits plus at least one additional bit. 
     
     
       65. The system of claim 64, wherein the interrogator is configured to generate, as part of the algorithm, the second set of bits including the first set of bits plus at least two additional bits. 
     
     
       66. The system of claim 52, wherein the RFID device is configured to communicate a random value during a first time slot randomly selected from a first number of timeslots. 
     
     
       67. The system of claim 66, wherein the transmitter is configured to communicate by modulating a radio frequency (RF) field provided by a remote device. 
     
     
       68. The system of claim 67, wherein the random value identifies the device to the remote device. 
     
     
       69. The system of claim 68, wherein the RFID device is further configured to communicate the random value to the remote device during a second time slot randomly selected from a second number of time slots, wherein the first number of time slots is different from the second number of time slots and is indicated by the remote device. 
     
     
       70. The system of claim 69, wherein the algorithm further comprises transmitting a second signal from the interrogator in response to detecting a collision in the first response, the second signal comprising a second set of bits and requesting a response from at least one of the one or more RFID devices in the field selected in accordance with at least the second set of bits, wherein, in accordance with the algorithm, the second set of bits include at least two bits in addition to the first set of bits. 
     
     
       71. An apparatus for wirelessly reading at least one radio frequency identification (RFID) device, comprising:
 a transmitter to transmit a command along with a first portion of a set of identifiers to request a response from at least one RFID device that has an identifier in the set;   an antenna to provide a radio frequency (RF) field to be modulated by the device;   a receiver to receive the response; and   processing circuitry to perform collision detection, to determine the identifier using the response, and to cause the transmitter to retransmit the command along with at least the first portion of the set of identifiers responsive to detecting no collision in the response.   
     
     
       72. The apparatus of claim 71, wherein the transmitter is configured to transmit the command along with an indication of the number of bits of the first portion. 
     
     
       73. The apparatus of claim 72, wherein the transmitter is configured to communicate with the least one RFID device at one of a plurality of bit rates determined by the apparatus. 
     
     
       74. The apparatus of claim 71, wherein the processing circuitry is configured to cause the transmitter to retransmit the command along with no more than the first portion of the set of identifiers responsive to the detecting. 
     
     
       75. The apparatus of claim 71, wherein the processing circuitry is configured to cause the transmitter to transmit a signal addressed to the least one RFID device responsive to receiving the response without collision. 
     
     
       76. The apparatus of claim 75, wherein the signal is configured to place the least one RFID device in a listen-only mode. 
     
     
       77. The apparatus of claim 76, wherein the processing circuitry is configured to cause the transmitter to transmit the signal to place the least one RFID device into a listen-only state before causing the transmitter to retransmit the command. 
     
     
       78. The apparatus of claim 71, wherein the transmitter is configured to transmit a wake up command to transition the least one RFID device from a sleep state. 
     
     
       79. The apparatus of claim 71, wherein the response comprises at least a second portion of the identifier that is not part of the first portion. 
     
     
       80. The apparatus of claim 79, wherein the processing circuitry is configured to determine a unique identification code stored in the least one RFID device in addition to the identifier. 
     
     
       81. The apparatus of claim 71, wherein the processing circuitry is configured to specify a second portion of the set of identifiers in response to detecting a collision, the second portion being a subset of the first portion. 
     
     
       82. The apparatus of claim 81, wherein the processing circuitry is further configured to enable the second portion to be less than half of the first portion. 
     
     
       83. The apparatus of claim 82, wherein the receiver is to receive a reply from one or more RFID devices in one of a number of time slots indicated by the apparatus to the one or more RFID devices. 
     
     
       84. The apparatus of claim 83, wherein the reply comprises a random value generated by the one or more RFID devices. 
     
     
       85. The apparatus of claim 71, wherein the processing circuitry is further configured to cause the transmitter to transmit a signal to indicate a number of time slots in which one or more RFID devices responds to the apparatus with a reply. 
     
     
       86. The apparatus of claim 85, wherein the reply comprises a random value generated by the one or more RFID devices. 
     
     
       87. The apparatus of claim 86, wherein the one or more RFID devices comprises the RFID device and the random value matches the identifier value. 
     
     
       88. The apparatus of claim 71, wherein the identifier identifies the device to the apparatus. 
     
     
       89. The wireless apparatus of claim 71, wherein the wireless apparatus is at least partially disposed within a card. 
     
     
       90. The wireless apparatus of claim 89, wherein the card is at least partially plastic. 
     
     
       91. The wireless apparatus of claim 89, wherein the card comprises a card useful for paying for goods or services. 
     
     
       92. The wireless apparatus of claim 71, the wireless apparatus is substantially disposed in a form factor suitable for use within a vehicle, and is capable of interfacing with a toll booth. 
     
     
       93. The wireless apparatus of claim 92, wherein the form factor comprises a means for affixing the form factor to an object. 
     
     
       94. The method of claim 39, wherein the act communicating a reply to the interrogator is performed as a part of a payment for goods or services. 
     
     
       95. The method of claim 39, further comprising disposing the RFID device at least partially within a card. 
     
     
       96. The method of claim 95, wherein the card comprises a card useful for paying for goods or services. 
     
     
       97. The method of claim 95, further comprising disposing visual identification information on a front side of the card, said visual identification information identifying a financial entity. 
     
     
       98. The method of claim 39, further comprising disposing RFID device in a form factor suitable for use within a vehicle. 
     
     
       99. The method of claim 39, wherein the form factor comprises a means for affixing the form factor to an object. 
     
     
       100. The method of claim 39, wherein the communication of a reply to the interrogator is performed as a part of a payment for a toll for use of a roadway. 
     
     
       101. The method of claim 39, further comprising effecting an interface between the RFID device and a toll booth. 
     
     
       102. Wireless apparatus, comprising:
 first apparatus configured to receive a command signal from an interrogator in accordance with an algorithm to identify a radio frequency identification (RFID) device in a field of the interrogator, the first command comprising a first set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the first set of bits; and   logic configured to, responsive to receiving the first command, determine whether the first set of bits matches a first portion of an identifier of the RFID device; and   a second apparatus configured to modulate a radio frequency (RF) field provided by the interrogator in order to communicate a reply to the interrogator in accordance with the algorithm;   wherein said first apparatus is further configured to receive a second transmission of the first command from the interrogator in response to the interrogator receiving the reply without detecting a collision; and   wherein said communication of the reply is performed based at least in part on said determination of whether the first set of bits matches a first portion of an identifier of the RFID device.   
     
     
       103. The wireless apparatus of claim 102, wherein the wireless apparatus is at least partially disposed within a card. 
     
     
       104. The wireless apparatus of claim 103, wherein the card is at least partially plastic. 
     
     
       105. The wireless apparatus of claim 103, wherein the card comprises a payment card comprising visual identification information disposed on a front side of the card. 
     
     
       106. The wireless apparatus of claim 102, wherein the wireless apparatus is substantially disposed in a form factor suitable for use within a vehicle, and is capable of interfacing with a toll booth. 
     
     
       107. The wireless apparatus of claim 106, wherein the form factor comprises a means for affixing the form factor to an object. 
     
     
       108. The wireless apparatus of claim 102, wherein:
 the first apparatus is further configured to communicate with the interrogator in one of a first communication mode and a second communication mode determined by the interrogator;   in accordance with the first communication mode, the RFID device modulates a radio frequency (RF) field generated by the RFID device; and   in accordance with the second communication mode, the RFID device modulates a radio frequency (RF) field generated by the interrogator.   
     
     
       109. The wireless apparatus of claim 108, wherein the second apparatus is further configured to communicate with the interrogator at one of a plurality of bit rates determined by the interrogator. 
     
     
       110. The wireless apparatus of claim 102, wherein the first apparatus is further configured to receive a wake up command from the interrogator; and
 in response, to transition from a sleep state.   
     
     
       111. The wireless apparatus of claim 110, wherein the first apparatus is further configured to receive a sleep command from the interrogator. 
     
     
       112. The wireless apparatus of claim 111, wherein the sleep command is received in response to the interrogator receiving the reply without detecting a collision, in accordance with the algorithm, before the receiving of the retransmission of the first command. 
     
     
       113. The wireless apparatus of claim 102, wherein the reply comprises a random value generated by the RFID device. 
     
     
       114. The wireless apparatus of claim 113, wherein the identifier comprises the random value. 
     
     
       115. The wireless apparatus of claim 102, wherein the first apparatus is further configured to:
 receive, in accordance with the algorithm, a second command from the interrogator in response to the interrogator detecting a collision in the reply, the second command comprising a second set of bits and requesting a response from one or more RFID devices in the field selected in accordance with at least the second set of bits; and   responsive to receive the second command, determine if the second set of bits matches a second portion of the identifier of the RFID device, and, if so, modulate the radio frequency (RF) field to communicate a second reply to the interrogator in accordance with the algorithm;   wherein:
 the second command comprises the first command; 
 the second set of bits comprises the first set of bits plus at least two additional bits; and 
 the second portion of the identifier comprises the first portion of the identifier. 
   
     
     
       116. The wireless apparatus of claim 115, wherein the second reply comprises at least a portion of the identifier. 
     
     
       117. The wireless apparatus of claim 102, wherein the second apparatus is further configured to communicate a random value to the interrogator during a time slot randomly selected from a number of time slots. 
     
     
       118. A method for wirelessly reading at least one radio frequency identification (RFID) device, comprising:
 transmitting a command along with a first portion of a set of identifiers to request a response from the at least one RFID device that has an identifier in the set, the command being transmitted via an antenna configured to provide a radio frequency (RF) field to be modulated by the least one RFID device;   receiving the response; and   performing collision detection to determine the identifier using the response, and to cause the transmitter to transmit the command a second time along with at least the first portion of the set of identifiers responsive to detecting no collision.   
     
     
       119. The method of claim 118, wherein the command transmission comprises an indication of the number of bits of the first portion. 
     
     
       120. The method of claim 119, wherein the transmission is performed at one of a plurality of bit rates. 
     
     
       121. The method of claim 118, further comprising transmitting the command said second time along with no more than the first portion of the set of identifiers responsive to the said detection of no collision. 
     
     
       122. The method of claim 118, further comprising transmitting a signal addressed to the at least one RFID device responsive to receiving the response to without detecting a collision. 
     
     
       123. The method of claim 122, wherein the signal is configured to place the least one RFID device into a listen-only state. 
     
     
       124. The method of claim 122, wherein the act of transmitting the signal to place the at least one RFID device into a listen-only state precedes the act of retransmitting of the command. 
     
     
       125. The method of claim 118, wherein the response comprises at least a second portion of the identifier that is not part of the first portion. 
     
     
       126. The method of claim 125, further comprising determining a unique identification code stored in the at least one RFID device in addition to the identifier. 
     
     
       127. The method of claim 118, further comprising specifying a second portion of the set of identifiers in response to detecting a collision, the second portion being a subset of the first portion. 
     
     
       128. The method of claim 127, further comprising enabling the second portion to be less than half of the first portion. 
     
     
       129. The method of claim 128, wherein the reply comprises a random value generated by the one or more RFID devices. 
     
     
       130. The method of claim 118, further comprising:
 providing to the at least one RFID devices a number of time slots;   causing the response from the at least one RFID device within at least one of the number if time slots; and   receiving the response in the at least one of the number of time slots.   
     
     
       131. The method of claim 130, wherein the random value matches the identifier value. 
     
     
       132. The method of claim 118, wherein the act wirelessly reading the at least one RFID device is performed as part of a payment for goods or services. 
     
     
       133. The method of claim 118, further comprising disposing the at least one RFID device at least partly within a card. 
     
     
       134. The method of claim 133, wherein the card comprises a payment card useful for paying for goods or services. 
     
     
       135. The method of claim 134, further comprising disposing visual identification information on a front side of the card, said visual identification information identifying a financial entity. 
     
     
       136. The method of claim 118, further comprising disposing the at least one RFID device in a form factor suitable for use within a vehicle. 
     
     
       137. The method of claim 136, wherein the form factor comprises a means for affixing the form factor to an object. 
     
     
       138. The method of claim 136, further comprising effecting an interface between the at least one RFID device and a toll booth. 
     
     
       139. The method of claim 118, wherein the act of wirelessly reading the at least one RFID device is performed as a part of a payment for a toll for use of a roadway. 
     
     
       140. A method of wireless communication of data, comprising:
 receiving a first signal from an interrogator in accordance with an algorithm to identify a radio frequency identification (RFID) device in a field of the interrogator, the first signal comprising a first set of bits and requesting a response from the RFID device in the field selected in accordance with at least the first set of bits;   responsive to receiving the first signal:
 determining if the first set of bits matches a predefined value related to the RFID device; and 
 if so, modulating a radio frequency (RF) field, provided by the interrogator, to communicate a first reply to the interrogator in accordance with the algorithm; and 
   receiving, in accordance with the algorithm, a retransmission from the interrogator of at least a portion of the first reply, in response to the interrogator receiving the first reply without detecting a collision;   wherein the first signal further comprises slot information useful for issuing said first reply by said RFID device.   
     
     
       141. The method of claim 140, wherein the act of wireless communication of data is performed as a part of a payment for goods or services. 
     
     
       142. The method of claim 140, further comprising disposing the RFID device at least partly within a card. 
     
     
       143. The method of claim 142, wherein the card comprises a payment card useful for paying for goods or services. 
     
     
       144. The method of claim 138, further comprising disposing visual identification information on a front side of the card, said visual identification information identifying a financial entity. 
     
     
       145. The method of claim 140, further comprising disposing the one or more RFID devices in a form factor suitable for use within a vehicle. 
     
     
       146. The apparatus of claim 145, wherein the form factor comprises a means for affixing the form factor to an object. 
     
     
       147. The method of claim 146, further comprising effecting an interface between the RFID device and a toll booth. 
     
     
       148. The method of claim 140, wherein the act of wireless communication of data is performed as a part of a payment for a toll for use of a roadway. 
     
     
       149. The method of claim 140, further comprising communicating with the interrogator in one of a first communication mode and a second communication mode determined by the interrogator;
 wherein in accordance with the first communication mode, the RFID device modulates a radio frequency (RF) field generated by the RFID device; and   wherein in accordance with the second communication mode, the RFID device modulates a radio frequency (RF) field generated by the interrogator.   
     
     
       150. The method of claim 140, further comprising:
 receiving a wake up command from the interrogator; and   in response, transitioning from a sleep state.   
     
     
       151. The method of claim 150, further comprising receiving a third signal from the interrogator, the third signal configured to place the RFID device into a listen-only state. 
     
     
       152. The method of claim 151, wherein the third signal is received in response to the interrogator receiving the reply without detecting a collision, before the receiving of the retransmission of the first signal. 
     
     
       153. The method of claim 140, wherein the reply comprises a random value generated by the RFID device.