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In one embodiment, a method includes transmitting a signal from a wireless transmitter to a radio frequency (RF) device of a plurality of RF devices within a communication range of the transmitter. The signal is to select a group of the RF devices. A reply signal is received from each RF device if t

In one embodiment, a method includes transmitting a signal from a wireless transmitter to a radio frequency (RF) device of a plurality of RF devices within a communication range of the transmitter. The signal is to select a group of the RF devices. A reply signal is received from each RF device if the respective RF device determines that it is a member of the group.

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We claim: 1. A method, comprising: controlling an interrogator using an application program on a host computer to receive data from the interrogator; transmitting, from the interrogator, a forward link signal to implement an arbitration scheme to determine an identification code of a radio frequenc

We claim: 1. A method, comprising: controlling an interrogator using an application program on a host computer to receive data from the interrogator; transmitting, from the interrogator, a forward link signal to implement an arbitration scheme to determine an identification code of a radio frequency identification (RFID) tag from among a plurality of RFID tags contained within an RF field of the interrogator, the forward link signal comprising: a parameter to select a group of RFID tags from the plurality of RFID tags, and return link configuration information; processing, via the RFID tag attached to an item of inventory and storing the identification code to track the item via the host computer, at least a portion of the forward link signal to compare the parameter to a value stored in the RFID tag to determine if the RFID tag is a member of the group; and transmitting, from the tag, a return link signal modulated in accordance with a modulation scheme selected by the return link configuration information, wherein each bit of the return link signal is multiplied by a selectable one of at least three subcarrier sequences selected by the return link configuration information. 2. The method of claim 1, wherein the forward link signal comprises a CRC. 3. The method of claim 1, wherein the modulation scheme selected by the return link configuration information is one of: Binary Phase Shift Keying (BPSK), Direct Sequence Spread Spectrum (DSSS), On-Off Keying (OOK), and Modulated Backscatter (MBS). 4. The method of claim 1, wherein the value stored in the RFID tag is at least a portion of a random number generated by the RFID tag. 5. The method of claim 1, wherein the forward link signal is in accordance with frequency hopping spread spectrum in a frequency range that includes 915 MHz. 6. A method, comprising: transmitting an interrogation signal from an interrogator to a radio frequency identification (RFID) tag of a plurality of RFID tags within a communication range of the interrogator, the interrogation signal comprising: a parameter to select a group of RFID tags from the plurality of RFID tags, and return link configuration information; and receiving a reply signal from the RFID tag if the RFID tag determines that the RFID tag is a member of the group based on comparing the parameter to a value stored in the RFID tag, the reply signal being in accordance with one of a plurality of modulation types selected using the return link configuration information, wherein in accordance with one of the plurality of modulation types the return link configuration information is used to select one of at least three different pulse waveforms to multiply with a baseband waveform. 7. The method of claim 6, wherein the interrogation signal further comprises a preamble comprising at least one data bit-0 and excluding any data bit-1's, and wherein the reply signal comprises a preamble comprising a plurality of data bit-0's and a plurality of data bit-1's. 8. The method of claim 6, further comprising: communicating a kill command from the interrogator to the RFID tag to disable a transmitter of the RFID tag while leaving the receiver functional. 9. The method of claim 6, wherein the reply signal further includes at least a portion of an identification code of the tag. 10. The method of claim 6, wherein a length of a first of the pulse waveforms is at least twice as long as a length of a second of the pulse waveforms; and the length of the second of the pulse waveforms is at least twice as long as a length of a third of the pulse waveforms. 11. The method of claim 6, wherein the reply signal includes a random number generated by the RFID tag. 12. A method, comprising: receiving an interrogation signal from an interrogator, the interrogation signal comprising: a parameter to select a group of radio frequency identification (RFID) tags from a plurality of RFID tags within a communication range of the interrogator, and return link configuration information; comparing the parameter to a value stored in an RFID tag to determine if the RFID tag is a member of the group; and transmitting a reply signal from the RFID tag in accordance with one of a plurality of modulation types selected using the return link configuration information, wherein in accordance with one of the plurality of modulation types the return link configuration information is used to select one of at least three different pulse waveforms to multiply with a baseband waveform. 13. The method of claim 12, further comprising: storing an identification code in a first memory, wherein the tag comprises a second memory dedicated for read/write data storage, and wherein the reply signal includes at least a portion of the identification code; storing a tag identifier to indicate tag manufacture information; and storing a tag revision number in a third memory. 14. The method of claim 13, further comprising: generating a random number, wherein the value stored in the RFID tag is at least a portion of the random number. 15. The method of claim 12, further comprising: decrementing a counter in the RFID tag, wherein the tag refrains from transmitting the reply signal if the counter is greater than zero. 16. The method of claim 12, wherein the reply signal includes a random number generated by the RFID tag. 17. A radio frequency identification (RFID) system, comprising: a host computer; an interrogator coupled to the host computer, wherein the interrogator is configured to transmit commands to implement an arbitration scheme to determine an identification code of an RFID tag from among a plurality of RFID tags contained within an RF field of the interrogator, the commands comprising selection information and modulation information; an item of inventory; and the RFID tag attached to the item and storing the identification code to track the item via the host computer, the tag configured to use the selection information to determine if the RFID tag is a member of a group of tags selected by the interrogator, and to communicate a reply modulated using a modulation type selected from a plurality of modulation types by the modulation information, wherein in accordance with one of the plurality of modulation types each bit of the reply is multiplied by a selectable one of at least three subcarrier sequences selected by the modulation information. 18. The system of claim 17, further comprising: a label attached to the item, the label having a front side and a back side, the front side of the label having visual information, and the RFID tag attached to the back side of the label. 19. The system of claim 17, wherein an RF carrier of the commands transmitted from the interrogator operates in a frequency range that includes 915 MHz; and wherein the interrogator and the tag are configured to operate in accordance with frequency hopping spread spectrum. 20. The system of claim 17, wherein the commands include a preamble comprising at least one data bit-0 and excluding any data bit-1's; and the reply comprises a preamble comprising a plurality of data bit-0's and a plurality of data bit-1's. 21. The system of claim 17, wherein the tag stores the identification code in a first region of memory, the tag further comprises a second region of memory dedicated to user memory for read/write data storage, the tag stores a tag revision number in a third region of memory, and the tag further stores a tag identifier to indicate tag manufacture information. 22. The system of claim 17, wherein the tag further comprises a counter configured to prevent the tag from communicating the reply if the counter is greater than zero. 23. The system of claim 17, wherein the commands further comprise a kill command to disable the tag and to prevent the tag from communicating replies. 24. The system of claim 17, wherein the reply includes at least one of: a CRC, a portion of the identification code, a random number generated in the tag, and a parameter that describes how many bytes are included in at least a portion of the reply; and the tag is configured to use the random number and the selection information to determine if the RFID tag is a member of the group of tags selected by the interrogator. 25. The system of claim 17, wherein the commands further provide a parameter that describes a length of at least a portion of the commands; and wherein the commands are modulated using amplitude shift keying. 26. A system, comprising: an interrogator configured to transmit an interrogation signal to implement an arbitration scheme to determine an identification code of a radio frequency identification (RFID) tag of a plurality of RFID tags disposed within an RF field of the interrogator, the interrogation signal comprising selection information and modulation information; an item to be tracked; the RFID tag attached to the item, the tag configured to: determine if the RFID tag is selected using the selection information, and communicate a reply signal having a baseband waveform multiplied by a pulse waveform selected by the modulation information from at least three different pulse waveforms; and a host computer coupled to the interrogator to receive and process the identification code. 27. The system of claim 26, further comprising: a label affixed to the item, the label having a front side and a back side, the front side of the label having visual information, and the RFID tag attached to the back side of the label, wherein the visual information includes text. 28. The system of claim 26, wherein the tag comprises: a plastic sheet; an antenna disposed on the plastic sheet to receive the interrogation signal; and an integrated circuit storing the identification code associated with the item; wherein the tag is configured to compare the selection information to a value stored in the integrated circuit other than the identification code. 29. The system of claim 28, wherein the tag is configured to transmit the reply signal if, at least in part, the selection information matches the value stored in the integrated circuit. 30. The system of claim 28, wherein the reply signal includes a random number generated by the RFID tag; the interrogator is configured to operate in accordance with frequency hopping spread spectrum in a frequency range that includes 915 MHz; the interrogation signal further comprises a preamble comprising at least one data bit-0 and excluding any data bit-1's; and wherein the reply signal comprises a preamble comprising a plurality of data bit-0's and a plurality of data bit-1's. 31. The system of claim 26, wherein the tag further comprises a counter configured to be decremented and to prevent the tag from communicating the reply signal if the counter is greater than zero. 32. The system of claim 26, wherein the interrogation signal further comprises a kill command to disable a transmitter of the tag while leaving the receiver functional. 33. The system of claim 26, wherein the reply signal includes a random number generated by the RFID tag; and the reply signal includes at least a portion of the identification code. 34. A radio frequency identification (RFID) system, comprising: an interrogator configured to transmit an interrogation signal to perform collision arbitration, the interrogation signal comprising selection information and modulation information; a plurality of items; and a plurality of RFID tags affixed respectively to the plurality of items, each of the RFID tags configured to: determine whether being selected by the selection information, and when selected, communicate a reply signal having a bit represented by a waveform sequence length selected by the modulation information from at least three different waveform sequence lengths. 35. The system of claim 34, wherein each of the RFID tags is configured to transmit the reply signal to the interrogator if, at least in part, the selection information matches a respective value. 36. The system of claim 35, wherein the respective value is a random number generated by a respective one of the plurality of RFID tags; and the reply signal includes the random number. 37. The system of claim 34, further comprising: a plurality of labels affixed to the plurality of items respectively, each of the plurality of labels having a front side and a back side, the front side having visual information, one of the plurality of the RFID tags being affixed to the back side, wherein the visual information includes text. 38. The system of claim 34, wherein the interrogator is configured to operate in accordance with frequency hopping spread spectrum in a frequency range that includes 915 MHz. 39. The system of claim 38, wherein the interrogation signal further comprises a preamble comprising at least one data bit-0 and excluding any data bit-1's, and wherein each respective reply signal comprises a preamble comprising a plurality of data bit-0's and a plurality of data bit-1's. 40. The system of claim 34, wherein each of the plurality of RFID tags is configured to: store a respective identification code in a respective first region of memory, store respective tag revision information in a respective second region of memory, store a respective tag identifier to indicate tag manufacture information, and dedicate a respective region of user memory for read/write data storage. 41. The system of claim 34, wherein each of the plurality of RFID tags further comprises a respective counter configured to be decremented and to prevent a respective tag from communicating a reply signal while the respective counter is greater than zero. 42. The system of claim 34, wherein the interrogation signal further comprises a kill command to disable a tag. 43. A system, comprising: an interrogator configured to transmit an interrogation signal to implement arbitration, the interrogation signal comprising selection information and modulation information; a host computer coupled to the interrogator to track a plurality of items; and a plurality of radio frequency identification (RFID) tags attached to the plurality of items respectively, the plurality of RFID tags including an RFID tag attached to an item of the plurality of items, the tag storing an identification code associated with the item, the tag configured to communicate a reply signal to the interrogation signal if, at least in part, the tag determines that the tag is selected by the selection information, wherein the reply signal includes at least a bit represented by a waveform sequence selected by the modulation information from at least three waveform sequences of different lengths. 44. The system of claim 43, wherein the tag is attached to the item via a label having a front side and a back side, the front side having visual information including text, the tag being attached to the back side. 45. The system of claim 44, wherein the tag comprises: a plastic substrate; an antenna disposed on the plastic substrate; and an integrated circuit storing the identification code; wherein the integrated circuit is further configured to store a value other than the identification code and to generate a random number. 46. The system of claim 45, wherein the tag determines whether the tag is selected by the selection information by comparing the selection information to a random value generated by the tag. 47. The system of claim 43, wherein the interrogator is configured to operate in accordance with frequency hopping spread spectrum in a frequency range that includes 915 MHz. 48. The system of claim 43, wherein the interrogation signal further comprises a preamble comprising at least one data bit-0 and excluding any data bit-1's, and wherein the reply signal comprises a preamble comprising a plurality of data bit-0's and a plurality of data bit-1's. 49. The system of claim 43, wherein the tag stores the identification code in a first region of memory, a tag revision number in a second region of memory, a tag identifier to indicate tag manufacture information, and the tag further comprises a third region of memory dedicated to user memory for read/write data storage. 50. The system of claim 43, wherein the tag further comprises a counter configured to be decremented and to prevent the tag from communicating the reply signal if the counter is greater than zero; and the tag is further configured to be disabled in response to a kill command transmitted by the interrogator. 51. The system of claim 50, wherein the reply signal includes a random number generated by the tag; and the tag is further configured to include at least a portion of the identification code in the reply signal. 52. The system of claim 43, wherein a length of a first of the waveform sequences is at least twice as long as a length of a second of the waveform sequences, and a length of the second of the waveform sequences is at least twice as long as a length of a third of the waveform sequences. 53. A method, comprising: transmitting an interrogation signal from a wireless transmitter to a radio frequency device of a plurality of radio frequency devices within a communication range of the wireless transmitter, the interrogation signal comprising: a parameter to select a group of radio frequency devices from the plurality of radio frequency devices, and return link configuration information; and receiving a reply signal from the radio frequency device if the radio frequency device determines that the radio frequency device is a member of the group based on comparing the parameter to a value stored in the radio frequency device, the reply signal being in accordance with one of a plurality of modulation types utilized based on the return link configuration information, wherein in accordance with one of the plurality of modulation types the return link configuration information is used to select from at least three different pulse waveforms to multiply with a baseband waveform. 54. The method of claim 53, wherein the interrogation signal comprises a CRC. 55. The method of claim 53, wherein the value stored in the radio frequency device comprises at least a portion of a random number. 56. The method of claim 53, wherein the interrogation signal is in accordance with frequency hopping spread spectrum. 57. The method of claim 53, wherein the reply signal further includes at least a portion of an identification code of the radio frequency device. 58. The method of claim 53, wherein the reply signal includes a random number. 59. Apparatus, comprising: transmitter apparatus configured to transmit a first signal to a first radio frequency device, the first device being one of a plurality of radio frequency devices within a communication range of the transmitter apparatus, the first signal comprising: a parameter to select a subset of radio frequency devices from the plurality of radio frequency devices, and return link configuration information; and receiver apparatus configured to receive a reply signal from the first radio frequency device if the radio frequency device determines that the first radio frequency device is a member of the subset based on comparing the parameter to a value stored in the first radio frequency device, the reply signal having been modulated according to one of a plurality of modulation types utilized based on the return link configuration information, wherein the return link configuration information is used to select from at least three different pulse waveforms to multiply with a baseband waveform. 60. The apparatus of claim 59, wherein the first signal comprises a CRC. 61. The apparatus of claim 59, wherein the first signal is in accordance with frequency hopping spread spectrum. 62. The apparatus of claim 59, wherein the apparatus and the first radio frequency device are configured to operate in accordance with frequency hopping spread spectrum. 63. Apparatus, comprising: transmitter apparatus configured to transmit a first signal to a first radio frequency device, the first device being one of a plurality of radio frequency devices within a communication range of the transmitter apparatus, the first signal comprising: a parameter to select a subset of radio frequency devices from the plurality of radio frequency devices, and return link configuration information; and receiver apparatus configured to receive a reply signal from the first radio frequency device if the first radio frequency device determines that it is a member of the subset based on comparing the parameter to a value stored in the first radio frequency device, the reply signal having been modulated according to one of a plurality of modulation types utilized based on the return link configuration information, wherein the return link configuration information is used to select an operating mode that utilizes at least one of at least three different pulse waveforms to multiply with a baseband waveform. 64. The apparatus of claim 63, wherein the first signal comprises a CRC. 65. The apparatus of claim 63, wherein the first signal is in accordance with frequency hopping spread spectrum. 66. The apparatus of claim 63, wherein the apparatus and the first radio frequency device are configured to operate in accordance with frequency hopping spread spectrum. 67. A radio frequency device, comprising: a storage apparatus; receiver apparatus configured to receive a first signal from a wireless transmitter device, the radio frequency device being one of a plurality of radio frequency devices within a communication range of the wireless transmitter device, the first signal comprising: a parameter to select a subset of radio frequency devices from the plurality of radio frequency devices, and return link configuration information; and transmitter apparatus configured to transmit a reply signal from the radio frequency device if the radio frequency device determines that the first radio frequency device is a member of the subset based on comparing the parameter to a value stored in the storage device, the transmitter apparatus being configured to modulate the reply signal according to one of a plurality of modulation types utilized based on the received return link configuration information, wherein the received return link configuration information is configured to permit selection from at least three different pulse waveforms to multiply with a baseband waveform generated by the radio frequency device. 68. The radio frequency device of claim 67, wherein the value stored in the storage device comprises at least a portion of a random number. 69. The radio frequency device of claim 67, wherein the reply signal further includes at least a portion of an identification code of the radio frequency device. 70. The radio frequency device of claim 67, wherein the reply signal includes a random number. 71. A radio frequency device, comprising: a storage apparatus; receiver apparatus configured to receive a first signal from a wireless transmitter device, the radio frequency device being one of a plurality of radio frequency devices within a communication range of the wireless transmitter device, the first signal comprising: a parameter to select a subset of radio frequency devices from the plurality of radio frequency devices, and return link configuration information; and transmitter apparatus configured to transmit a reply signal from the radio frequency device if the radio frequency device determines that the first radio frequency device is a member of the subset based on comparing the parameter to a value stored in the storage device, the transmitter apparatus being configured to modulate the reply signal according to one of a plurality of modulation types utilized based on the received return link configuration information, wherein the return link configuration information is used to select an operating mode that utilizes at least one of at least three different pulse waveforms to multiply with a baseband waveform. 72. The radio frequency device of claim 71, wherein the value stored in the storage device comprises at least a portion of a random number. 73. The radio frequency device of claim 71, wherein the reply signal further includes at least a portion of an identification code of the radio frequency device. 74. The radio frequency device of claim 71, wherein the reply signal includes a random number.