Methods and apparatus for rfid tag communications

Abstract

The present invention provides backscatter interrogators, communication systems and backscatter communication methods. According to one aspect of the present invention, a backscatter interrogator includes a data path configured to communicate a data signal; a signal generator configured to generate a carrier signal; and a modulator coupled with the data path and the signal generator, the modulator being configured to spread the data signal to define a spread data signal and amplitude modulate the carrier signal using the spread data signal, the modulator being further configured to phase modulate the carrier signal.

1 - 47 . (canceled) 
     
     
         48 . A method of monitoring inventory, comprising:
 transmitting a command signal, the command signal generated by:
 spreading a data signal to define a spread data signal; and 
 amplitude and phase modulating the spread data signal; 
   transmitting an un-modulated signal;   receiving a return signal that identifies a tagged object, the return signal being responsive to the command signal; and   discriminating the tagged object from a potentially large lot of tagged objects using at least the received return signal, thereby allowing for the monitoring of inventory.   
     
     
         49 . The method according to  claim 48 , further comprising selectively inverting the spread data signal. 
     
     
         50 . The method according to  claim 49 , wherein the phase modulating of the carrier signal is responsive to the inverting. 
     
     
         51 . The method according to  claim 49 , further comprising synchronizing the inverting with the spread data signal. 
     
     
         52 . The method according to  claim 48 , further comprising randomly inverting the spread data signal using a pseudo-noise sequence. 
     
     
         53 . The method according to  claim 48 , further comprising band limiting the spread data signal. 
     
     
         54 . The method according to  claim 48 , wherein the spreading comprises encoding a pseudo-noise sequence with the data signal. 
     
     
         55 . The method according to  claim 48 , further comprising mounting a tag to the tagged object. 
     
     
         56 . The method according to  claim 48 , further comprising mounting a tag to each of a large lot of tagged objects. 
     
     
         57 . A method of monitoring inventory, comprising:
 transmitting an interrogation signal, the interrogation signal intended to elicit a response that identifies an object, the interrogation signal generated by:
 spreading a data signal to generate a spread data signal; and 
 modulating a carrier signal using the spread data signal to suppress the carrier signal during communication of the carrier signal; 
   transmitting a continuous radio frequency signal;   receiving a response to the interrogation signal, the response identifying an object; and   discriminating the object from a potentially large lot of tagged objects using at least the received response thereby allowing for the monitoring of inventory.   
     
     
         58 . The method according to  claim 57 , further comprising band limiting the spread data signal. 
     
     
         59 . The method according to  claim 57 , wherein the modulating comprises amplitude modulating and phase modulating using the spread data signal. 
     
     
         60 . The method according to  claim 57 , where the response is generated by:
 spreading a response data signal to define a response spread data signal;   amplitude modulating a response carrier signal using the response spread data signal; and   phase modulating the response carrier signal.   
     
     
         61 . The method according to  claim 60 , further comprising selectively inverting the response spread data signal. 
     
     
         62 . The method according to  claim 61 , wherein the phase modulating is responsive to the inverting. 
     
     
         63 . The method according to  claim 61 , further comprising synchronizing the inverting with the response spread data signal. 
     
     
         64 . The method according to  claim 60 , further comprising randomly inverting the response spread data signal using a pseudo-noise sequence. 
     
     
         65 . The method according to  claim 60 , further comprising band limiting the response spread data signal. 
     
     
         66 . The method according to  claim 60 , wherein the spreading comprises encoding a pseudo-noise sequence with the response data signal. 
     
     
         67 . The method according to  claim 57 , further comprising mounting a tag to the object, the tag being configured to generate the response. 
     
     
         68 . The method according to  claim 57 , further comprising mounting a tag to each of the potentially large lot of tagged objects. 
     
     
         69 . A method of monitoring inventory, comprising:
 spreading a data signal to define a spread data signal;   selectively inverting the spread data signal;   amplitude modulating a carrier signal using the spread data signal;   communicating the modulated carrier signal; and   transmitting a continuous un-modulated radio frequency signal;   wherein the acts of spreading, selectively inverting, amplitude modulating and communicating allow for the discriminating of an object from a potentially large lot of tagged objects, the ability to discriminate among objects allowing for the monitoring of inventory.   
     
     
         70 . The method according to  claim 69 , further comprising phase modulating the carrier signal responsive to the inverting. 
     
     
         71 . The method according to  claim 69 , further comprising phase modulating the carrier signal using a tri-level signal corresponding to the inverted data signal. 
     
     
         72 . The method according to  claim 69 , wherein the inverting comprises random inverting using a pseudo-noise sequence. 
     
     
         73 . The method according to  claim 69 , further comprising band limiting the spread data signal. 
     
     
         74 . A method of tracking inventory, comprising:
 affixing a radio frequency device to an object of inventory;   disposing said object with said affixed device in a warehouse;   transmitting a command signal, the command signal generated by:
 spreading a data signal to define a spread data signal; and 
 amplitude and phase modulating the spread data signal; 
   entering into a continuous wave mode;   receiving a return signal that identifies the object, the return signal being responsive to the command signal; and   discriminating the object from a plurality of other objects using at least the received return signal.   
     
     
         75 . The method of  claim 74 , further comprising transmitting an un-modulated carrier after said command signal is transmitted. 
     
     
         76 . The method of  claim 75 , wherein said return signal is phase shift keyed. 
     
     
         77 . The method of  claim 74 , wherein said return signal is phase modulated. 
     
     
         78 . The method of  claim 77 , wherein said phase modulation of said return signal comprises phase shift keying. 
     
     
         79 . A method of tracking inventory, comprising:
 affixing a radio frequency device to an object of inventory;   disposing said object with said affixed device in a warehouse;   transmitting a command signal, the command signal generated by amplitude modulating, phase modulating, and frequency-hopping a data signal;   entering into a continuous wave mode;   receiving a return signal that identifies the object, the return signal being responsive to the command signal; and   discriminating the object from a plurality of other objects using at least the received return signal.   
     
     
         80 . The method of  claim 79 , further comprising transmitting an un-modulated carrier after said command signal is transmitted. 
     
     
         81 . The method of  claim 80 , wherein said return signal is phase shift keyed. 
     
     
         82 . The method of  claim 79 , wherein said return signal is phase modulated. 
     
     
         83 . The method of  claim 82 , wherein said phase modulation of said return signal comprises phase shift keying.