Method and apparatus for improving the efficiency and accuracy of rfid systems

Abstract

The present invention relates to a method and apparatus for transmitting a narrow signal beam that allows the precise location of RFID tags to be determined and reduces tag collisions. The present invention further relates to a method and apparatus for combing an RFID reader with an optical source to visualize the interrogation zone of the reader. The present invention also relates to a method and apparatus for improving the efficiency of RFID systems.

1 . A method for interrogating RFID tags comprising: 
 transmitting a data signal that causes said RFID tags to respond,    transmitting one or more scramble signals that do not cause said RFID tags to respond, and    adjusting said data signal and said one or more scramble signals such that said one or more scramble signals overshadow said data signal in all but selected regions.    
   
   
       2 . The method of  claim 1 , wherein at least one of said one or more scramble signals contains a separate intelligible data stream.  
   
   
       3 . The method of  claim 1 , wherein at least one of said one or more scramble signals charges said RFID tags when said RFID tags are not being interrogated.  
   
   
       4 . The method of  claim 1 , wherein at least one of said one or more scramble signals broadcasts a sine wave.  
   
   
       5 . The method of  claim 1 , wherein said selected regions are varied during the transmission of said data signal.  
   
   
       6 . The method of  claim 1 , wherein said data signal comprises a plurality of bits, and said plurality of bits is divided into a first part and a second part.  
   
   
       7 . The method of  claim 6 , wherein for each of said first part and said second part, a corresponding scramble-signal null direction is defined that is slightly away from the peak direction of said data signal.  
   
   
       8 . The method of  claim 6 , wherein each of said first part and said second part is transmitted while at least one of said one or more scramble signals has its central null steered in the direction of a corresponding scramble-signal null direction.  
   
   
       9 . The method of  claim 1 , wherein said one or more scramble signals have approximately constant amplitudes away from a central null for each scramble signal, and the total radiated power is approximately omni-directional.  
   
   
       10 . The method of  claim 9 , wherein constant-amplitude scramble signals are achieved by moving zeros off the Schelkunoff unit circle.  
   
   
       11 . The method of  claim 9 , wherein constant-amplitude scramble signals are achieved by iterative methods.  
   
   
       12 . The method of  claim 1 , further comprising the steps of: 
 employing two or more array readers that scan an area with data and scramble signals to determine the angular positions of each tag within range, and    determining the absolute position of said RFID tags through triangulation using the angular positions obtained with said two or more array readers.    
   
   
       13 . The method of  claim 12 , further comprising the step of: 
 employing anti-collision methods when more than one of said RFID tags responds at any given scan angle.    
   
   
       14 . The method of  claim 1 , wherein said reader and said RFID tags are inductively coupled and said reader employs two or more loops to transmit said data signal and said one or more scramble signals.  
   
   
       15 . The method of  claim 14 , wherein the configuration of said loops of said reader is optimized with iterative techniques to ensure that the magnetic field of said data signal is overshadowed by the magnetic fields of said one or more scramble signal except in selected regions.  
   
   
       16 . The method of  claim 1 , further comprising the step of employing one or more security measures.  
   
   
       17 . The method of  claim 16 , wherein said one or more security measures comprises placing of nulls in receiving patterns.  
   
   
       18 . The method of  claim 16 , wherein said one or more security measures comprises using highly directive antennas.  
   
   
       19 . The method of  claim 16 , wherein said one or more security measures comprises transmitting scramble signals.  
   
   
       20 . A method for optically displaying the interrogation zone of an RFID reader, comprising the steps of: 
 attaching an optical source to an RFID reader, and,    transmitting one or more light beams with said optical source to visualize said interrogation zone.    
   
   
       21 . The method of  claim 20 , wherein at least one of said one or more light beams is pointed in the direction of the center of said interrogation zone.  
   
   
       22 . The method of  claim 20 , further comprising the step of transmitting two or more light beams such that each light beam coincides with a boundary of said interrogation zone.  
   
   
       23 . The method of  claim 20 , further comprising the step of scanning a light beam back and forth between boundaries of said interrogation zone.  
   
   
       24 . The method of  claim 22 , wherein said light beams are transmitted with lasers.  
   
   
       25 . The method of  claim 20 , wherein said optical source is built into the housing of said RFID reader.  
   
   
       26 . The method of  claim 20 , wherein said optical source is attached to the housing of said RFID reader.  
   
   
       27 . A method for improving the efficiency of RFID systems having RFID readers and RFID tags, comprising the steps of: 
 employing an antenna array by an RFID reader,    broadcasting a data signal using said antenna array, and,    broadcasting a scramble signal using said antenna array.    
   
   
       28 . The method of  claim 27 , wherein said antenna array employs patch antennas.  
   
   
       29 . The method of  claim 27 , further comprising the step of employing three antenna elements by said RFID reader, wherein two antenna elements transmit said scramble signal and one antenna element interrogates RFID tags.  
   
   
       30 . The method of  claim 27 , further comprising the step of adjusting the array excitation coefficients for said data signal and said scramble signal to create an interrogation beam that fits an opening in a container.  
   
   
       31 . The method of  claim 27 , further comprising the step of employing an antenna, wherein said antenna transmits two or more interrogation beams and wherein any of said RFID tags in said interrogation zone receive sufficient power to operate from at least one of said two or more interrogation beams.  
   
   
       32 . The method of  claim 27 , further comprising the step of employing two or more scramble signals, wherein said two or more scramble signals prevent leakage of said data signal.  
   
   
       33 . The method of  claim 32 , wherein two or more scramble signals employ coefficients that are mirror images.  
   
   
       34 . The method of  claim 27 , further comprising the step of transmitting said data signal and said scramble signal adjusted to create closely spaced disjoint interrogation zones.  
   
   
       35 . The method of  claim 27 , wherein the position of said RFID reader is determined from the solution of an inverse source problem.  
   
   
       36 . The method of  claim 35 , wherein the inverse source problem is solved with an iterative optimization scheme.  
   
   
       37 . The method of  claim 27 , wherein the position of said RFID reader is determined from measurements.  
   
   
       38 . The method of  claim 27 , wherein the array excitation coefficients are determined from the solution to an inverse source problem.  
   
   
       39 . The method of  claim 38 , wherein the inverse source problem is solved with an iterative optimization scheme.  
   
   
       40 . The method of  claim 27 , wherein the array excitation coefficients are determined from measurements.  
   
   
       41 . A method for interrogating RFID tags comprising the steps of: 
 providing a tag antenna to interrogate said RFID tags, and,    placing said RFID tags at locations where said tag antenna creates maximum disruption of a field distribution.    
   
   
       42 . The method of  claim 41 , wherein the field distribution on an object is computed with a numerical method.  
   
   
       43 . The method of  claim 41 , wherein the field distribution on an object is obtained from measurements.  
   
   
       44 . The method of  claim 41  further comprising the step of transmitting and receiving signals in a bistatic mode of operation.  
   
   
       45 . The method of  claim 41  further comprising the step of transmitting and receiving signals in a multistatic mode of operation.  
   
   
       46 . The method of  claim 45  further comprising the step of determining the location of said receivers by solving a scattering problem.